A discussion ...."Marie Michon" ?

[Larks]

Peter, did you get any copies of your drawings run off when you scanned them? Just wondering whether you'd fancy a half hull of them now that I have another 2 months in Darwin??

[PeterSibley]

G'day Ian ...I'll do 6 foot , lots of spare for me !
Greg , I'm still working on it , subtle changes , a bit fuller in the aft sections and a slightly more shapely transom .The forward sections are fine to my eye .

I have a copy of the first version .

[rufustr]

I think it might be better to shorten Ian than wreck a good boat with too much headroom.

At the next EBS we will shorten you by about 12 inches Ian.

Should solve lots of problems for you.:cool:

[The Bigfella]

Hey, I wasn't talking about the plans... I want a boat....

[The Bigfella]

I think it might be better to shorten Ian than wreck a good boat with too much headroom.

At the next EBS we will shorten you by about 12 inches Ian.

Should solve lots of problems for you.:cool:

But what about my height?

[rufustr]

I never thought of you as a tripod Ian.

I was thinking of the lump above your shoulders.:D

[rufustr]

This is the Cabin and Deck layout I was thinking about Peter.

http://i359.photobucket.com/albums/oo39/rufustr/Heard28.jpg

[Andrew Craig-Bennett]

The nice broad side decks would be a great advantage, and if you keep the cabin top as short as possible the foredeck would be uncluttered.

The great thing about the photo is the open feeling of the interior.

Bulkheads and enclosures clutter up an interior and make spaces feel even smaller than they are.

http://pic40.picturetrail.com/VOL282/9443996/17245530/368304766.jpg

"The inside of a boat should be like a church - open from end to end" - H.W. Tilman

"Marie Michon" was all open, apart of course from the heads compartment. This was quite unusual for the time.

Compare "Mirelle":

http://i535.photobucket.com/albums/ee352/acraigbennett/DSCF0948.jpg?t=1246357230

The difference is mainly that there is no vertical opening for the companion hatch - the aft coachroof coaming goes straight across - a trademark of her designer. But certainly the bulkheads close you in. Note that she is only 5ft draft with harder bilges so she needs the coachroof.

Personally, I would like a boat of Peter's form with the skylight and companion the same width as the cabin sole at its widest point, or slightly wider.

Peter - an idea for the stern sections - take a look at another Warrington-Smyth boat - Nigel Warrington-Smyth's "Providence" (so named as she was built from an unexpected legacy!)l

[Larks]

This is the Cabin and Deck layout I was thinking about Peter.



That Heard 28 isone of my favourite boats Rufus, I went to Falmouth specifically to meet the guy and missed him by a day when he went to France or somewhere for a week.

[rufustr]

Larks,

The boat in the photo has a smaller cabin structure than the standard design, but to my eye looks just right.

[PeterSibley]

Andrew , I've been receiving some very welcome advice from Ed Burnett .He also recommended a look at "Providence".

http://pic40.picturetrail.com/VOL282/9443996/17245530/368400516.jpg

Her hull is lot firmer than mine but I have hardened up my aft sections and put a bit more shape into the transom as a result .I'll have another drawing to show as soon as I can get it scanned .A2 is too big for the scanners in town .

Regarding "Province " I'd say the closest modern design to her (other than Ed's design 119 ) would be the Hess cutters .....not quite the same , but there is a family similarity .

The skylight /hatch arrangement versus a coach house .Either way it would be narrow ....as I mentioned earlier it would be worth roughing it out with ply and sticks to see how it fits .An advantage for a deckhouse , say 4'6' wide is that it makes a secure mount for a dinghy of similar width ,perhaps a bit more secure than one on deck over the skylight with the stern kicked up on top by necessity .

Interior , the more open the better ...structural strength being the prime consideration .Bulkheads are great stiffeners by way of the mast but perhaps semi bulkheads and knees would work as well .I'll seek advice .

[PeterSibley]

http://i359.photobucket.com/albums/oo39/rufustr/Heard28.jpg

Rufus ,that's a pleasing looking house isn't it ? IfIhad one , rather than Andrew's suggestion ,it would be around 9' long ,less and there is nowhere for a dinghy .

[rufustr]

It looks right with it's nice slope forward Peter.

The clear decks, bulwarks just the right height, all go to make a great combination.

[Andrew Craig-Bennett]

Peter - how big a dinghy are you thinking of? You need to slide the hatch back by 2ft to get in through it so the house either has to be
2ft longer than the dinghy or you have to have the bows of the dinghy on deck and the transom on the coachroof.

My solution to carrying a 9ft dinghy on an 8ft coachroof is to have the stem of the dinghy to one side of the mast:

http://i535.photobucket.com/albums/ee352/acraigbennett/MirelleinOrwell2003.jpg?t=1246362179

[PeterSibley]

Really the longest I can carry ! :D
8 foot seems the minimum useful length .I shall have to work something out , my measurement for a the possible coach roof is very loose , no drawings yet ,it might end up at 10 foot , but less is likely .

Actually Andrew , I can't see how I could have a much longer house than you , your LWL is 27 foot ? Mine is 28.8" , quite similar ,even with your counter .

[paladin]

It looks like a very workable interior Peter...however.....I would get rid of the square corners on that engine box...they are good for cracking ribs when falling against the upper edges or corners.....

[Wiley Baggins]

...take a look at another Warrington-Smyth boat - Nigel Warrington-Smyth's "Providence"...

I've seen one or two additional designs of his and the curves are just so. Providence reminds me of Cresset by the Urry brothers, which has been discussed here previously.

[PeterSibley]

http://pic40.picturetrail.com/VOL282/9443996/17245530/364808955.jpg

http://pic40.picturetrail.com/VOL282/9443996/17245530/364808956.jpg

http://pic40.picturetrail.com/VOL282/9443996/17245530/364808957.jpg

Not all of Warrington Smyth's designs were so "curvy" .Marie Michon ,above , was his .A much plainer feast .

[Ed Burnett]

There were I think three Warrington Smyth brothers. My father will be better able to fill in the details but I think the following is the case:

Bevil designed Marie Michon, as well as many other small Westcountry type yachts and work boat types.

Nigel designed Providence, and others of a similar (but smaller) form, which show more influence of the French working boats of the time.

[PeterSibley]

Ed , MM's stern post angle is a French influence isn't it ? It's actually less than Providence's .

[Ed Burnett]

Ed , MM's stern post angle is a French influence isn't it ? It's actually less than Providence's .

Possibly, but her section shape remains very English!

My understanding is that the French fishing boats were taxed on the basis of keel length, so lots of sternpost rake was a bit of a rule cheater in that regard. (It is worth bearing in mind that not all developments in boat design are justified on the basis of performance, and may not necessarily be beneficial if copied!)

It could be argued that local builders (working without the formality of an external designer) will tend to follow a trodden path, making incremental progress in one direction under the influence of things that made a difference in their area. An "independent" designer is more likely to shop around for ideas and influences, blending features that seem appropriate or desirable for the boat under consideration at the time.

The Warrington Smyth brothers made cruises around Brittany (producing wonderful drawings and sketches of the boats at the time) and no doubt finding things they liked in the boats they saw.

[PeterSibley]

Ed ,I notice that the stern post angle on your design # 119 is less than Providence but very similar to MM's .
If I recall correctly you mentioned problems of balance with too much angle .....could you elaborate ?

[Ed Burnett]

Well, it's simply a matter of where the centre of lateral area of the underbody falls.

Generally with this sort of boat you need all the help you can get to balance the helm, so an underbody profile that leads to a CLA well aft is handy. A more upright sternpost makes a difference, but the trade off is more wetted area, and lots of rake does look nice.

[PeterSibley]

I've sent the current drawing off with a friend to scan at his office ,but if I remember correctly my CLB is 1.3% aft Station 6 with the LWL as designed .If I raise the WL 2" as planned the LCB should move a little aft .

How would that be ?

[Ed Burnett]

Hang on a minute.

In relation to stern post angle I am talking about the centre of lateral area, which frequently gets referred to as the centre of lateral resistance.

LCB (longitudinal centre of buoyancy) is something else altogether.

[maxwaterline]

Peter, from an unqualified point of view, I think your second design has a certain "rightness". I suspect that you'll be taking orders for a "Sibley 30" fairly soon.

Cheers

Adrian

[Ed Burnett]

I suspect that you'll be taking orders for a "Sibley 30" fairly soon.

Well if that's the case I had better either send along a bill or stop the advise forthwith!

[PeterSibley]

Hang on a minute.

In relation to stern post angle I am talking about the centre of lateral area, which frequently gets referred to as the centre of lateral resistance.

LCB (longitudinal centre of buoyancy) is something else altogether.

Opps !...amatuer confusion :o.I'll plead a long day , it evening here .:o

[PeterSibley]

Well if that's the case I had better either send along a bill or stop the advise forthwith!

Don't worry , I know where to forward them to .:D

[Ed Burnett]

Don't worry , I know where to forward them to .:D

The bills or the orders??

On the matter of CLA, you might want to sketch up a quick sail plan to see where you are balance wise. That will help you form an opinion on the sternpost angle thing.

[RFNK]

Peter
This site has a brokerage with some nice boats that might give you some ideas for interiors, deck layout, cockpit etc. You might already be familiar with it. Rick

www.woodenships.co.uk (http://www.woodenships.co.uk)

[PeterSibley]

Well the angle is set and reinforced with a wopping big knee ,so it will be the sail plan that gets tweaked :).I have a sail plan drawn up from the last attempt ,lateral areas haven't changed so it might be worth a review .

For a hull like this where would you place centre of effort in relation to centre of lateral plane ?

[marcin]

For a hull like this where would you place centre of effort in relation to centre of lateral plane ?

I second this question. Does the CE have to have a fairly large lead on a boat like this, i.e. in the 10-15% range? Or would a smaller lead serve as well...

[Ed Burnett]

For a hull like this where would you place centre of effort in relation to centre of lateral plane ?

Well, as far forward as possible is probably what you will end up doing. Not sure I wish to divulge the secret numbers here (although you will probably wheedle an opinion out of me eventually)!

[PeterSibley]

:):) Thanks Ed !

[PeterSibley]

Peter
This site has a brokerage with some nice boats that might give you some ideas for interiors, deck layout, cockpit etc. You might already be familiar with it. Rick

www.woodenships.co.uk (http://www.woodenships.co.uk)

Thanks Rick ,I haven't seen it and missed your post yesterday .Some lovely boats !:)

[PeterSibley]

Here's the latest modification , not much to look at but a bit fuller aft on the LWL and a corresponding change to the transom .Hmmmm ,looks like I didn't correct B3 between #13 and the transom.

I think it looks better .The NIGEL Warrington Smyth influence .

http://pic40.picturetrail.com/VOL282/9443996/17245530/368551509.jpg

[rufustr]

Thought I'd enhance it a little Peter.

I can see a tiny difference right near the Transom.

http://i359.photobucket.com/albums/oo39/rufustr/368551509.jpg

[PeterSibley]

http://pic40.picturetrail.com/VOL282/9443996/17245530/368286865.jpg

Yes , it doesn't look much but there is a quite a bit more fullness right aft .It's hard to see at this scale .

Thanks for enhancing that Rufus , I don't know how .What program do you use ?

[WX]

if you open it in the Gimp Peter you can adjust the brightness/contrast. That will bring out the lines a bit more. Look under Tools - Colour Tools.

[Ed Burnett]

Hello Peter,

Thanks for sending along the latest, I will put these comments up here as others may find them of interest.

Firstly, I think this shape is now starting to look pretty nice and this latest version represents a very significant improvement over the last - much better progression in the section shape through the aft body.

The forebody is now very nearly there I would think. There is still just a little flat spot in S2 in the D1 area. Don't forget the link between bow profile and bow section shape (think of the section gradually rolling round into the profile). As it is, the stem is smoothly rounded at WL2a (D1 sits nicely through the points of maximum curve in the sections, so it makes sense for the stem to retain some curvature where this diagonal his the centreline). S2 is just a little out of step so maybe try re-fairling through the points to echo the character of the stem and S3 a bit better.

As I mentioned above, the aft body now looks much better, but I would go round the loop one more time and just be a little more bold. There is something funny with B3 in the S11 - S12 area, this may be the batten reflexing from the tightening curve aft of S12, but I also think it tells us something about S11 and S12. The shape of S13 still looks a little round to my eye (I would be inclined to nudge it up and inboard at B2, and out around D1, the effect will be to smooth the point of maximum curvature up towards D1), but it's your design at the end of the day. Try to look at S13 rather than the transom as the angle of the transom will distort the impression it gives of the form. In effect, the transom shape results from the form rather than being a controlling station as it were. You may find it helpful to drop an intermediate station in at S12.5 to give a bit more control of the buttock as it runs up through that area, and possibly another at 13.5 so you can run the shape beyond the transom cut (think of it as looking at the follow through of a golf swing - I don't play the game but it's easy to imagine why that makes a difference!).

If I am interpreting the marks correctly, it looks like your LCB is at around 52% (as S1 is not actually at the cutwater, S7 isn't perfectly amidships so 1.3% aft of S7 isn't a useful measure). Either way, 52% aft is fine - you wouldn't want it any further forward but it's fine. What is the displacement (cu. ft) and max section area (sq ft)? With those we can work out prismatic which will give us a little more information on what final tweaks are needed aft.

Hope that helps - sorry if it sounds hypercritical! I've got to take the dog for her lunchtime stroll now.....

ED.

[WX]

I love this forum, so much good information and so many skills.

[PeterSibley]

Thanks Ed ,
I think S2 is going to have to wait for the loft floor ! I just can't quite get it .I know I want the plank runs to be quite flat over the last 2 or 3 feet of there run .Getting a curve in there would be no fun .

I'll look at S13 again , not surprisingly , you have a very good eye ! Mine tends to loose these tiny changes , but they do add up .

I'm glad to LCB is OK ,phew !

Displacement at LWL is 312 cft .
2" above at the full loaded position ,340.

Max cross section is down the shed on a drawing .I'll post it tomorrow .It 10.30 at night here and cold !

Very educational !

[Ed Burnett]

You should be able to sort S2 on the loft floor. You can just about see the flat area in B2 as well (at around WL1a), just let your eye float from B1, through B2 to B3 and you can see there is more of a change in character from B1 to B2 as there is from B2 to B3.

I do think you should do a bit more work aft before lofting however. Lofting is great for fairing individual lines, but it's harder for the eye to take in the whole shape of the boat at full scale.

In these final stages we are talking about truly "reading" the lines plan rather than just looking at individual lines (you need to be looking at the spaces between the lines as much as the lines themselves). A good analogy is to an accomplished musician who can scan a score and virtually hear the music, as opposed to someone like me who looks at each individual note, plays it, and in doing so discovers what the tune is.

At some point I would recommend you put this drawing away for a week or so and spend that time browsing through other lines plans to reset your eye. The first thought that comes into your mind after you look at your drawing again will be worth paying attention to.

[rufustr]

Peter,

I edit the photo in Microsoft Picture Manager using the brightness and contrast.

Ed Burnett's comments are fascinating when the drawing is there to look at.

[Peerie Maa]

Well, as far forward as possible is probably what you will end up doing. Not sure I wish to divulge the secret numbers here (although you will probably wheedle an opinion out of me eventually)!

Ed
Do you remember that very good paper published in the RINA Journal a few years ago on sail balance, based on the CE of lifting surfaces?

[PeterSibley]

At some point I would recommend you put this drawing away for a week or so and spend that time browsing through other lines plans to reset your eye. The first thought that comes into your mind after you look at your drawing again will be worth paying attention to.

That sounds like good advice Ed , it is possible to get too involved .It really comes down to a bit of minute variation over the B2 and B3 lines around #12 and #13 .I'll leave it a few days ! :)

I'll look at this advice from last night ,
"Try to look at S13 rather than the transom as the angle of the transom will distort the impression it gives of the form. In effect, the transom shape results from the form rather than being a controlling station as it were. You may find it helpful to drop an intermediate station in at S12.5 to give a bit more control of the buttock as it runs up through that area, and possibly another at 13.5 so you can run the shape beyond the transom cut (think of it as looking at the follow through of a golf swing - I don't play the game but it's easy to imagine why that makes a difference!)."

[PeterSibley]

Peter,

I edit the photo in Microsoft Picture Manager using the brightness and contrast.



Rufus , I can do that in the Gimp (on Luinux ) but don't seem to be able to get the strength of black you can .

[PeterSibley]

Hi Ed
Displacement at LWL is 312 cft .
2" above at the full loaded position ,340.

Area of largest section #7 ......19.7 squ feet .

[Ed Burnett]

Peter,

Well, assuming a section area of 19.7 sq ft relates to the displacment of 312 cu ft, and an LWL of 28.66 ft, prismatic works out at 0.553.

This is actually pretty low for a hull of this type. Skenes gives a range of suitable Cp which relates to boats with substantial lateral plane cut away forward, and this does lead to generally lower prismatic. For the sort of boat we are discussing here, I would generally be looking for Cp in the 0.57 to 0.58 area.

So, what this is suggesting is that your hull is, relatively speaking, a little fine in the ends. Considered at the same time as your 52% LCB (which is quite a long way forward) we can say more specifically that she is a bit on the fine side aft. We know this anyway from looking at the lines, but the numbers help frame the picture.

As an aside, before anyone comes along and starts saying things like, "well, if it looks right it is right" and "they didn't bother with prismatic coefficient in the old days" and so on, I will just say this: You can walk down the street perfectly well with one eye closed - you can see the lamp posts, avoid the other people and so on - but if you open both eyes you get a much better view. It adds another dimension. In the same way, looking at a few ratios and coefficients when considering a set of lines adds a level of precision to ones evaluation of the form. We aren't suddenly ignoring what we can read of the hull shape from just looking at the lines, in the same way that we don't just swap eyes in the analogy above.

Anyway... A low Cp, indicating a fine ended hull, suggests a form that will be relatively efficient at low speeds, but might start to suffer when pushed into higher speed length ratios. We might expect her to pull up more of a quarter wave when she really gets going and to squat down a little harder. Overall, the suggestion is that she will slip along nicely in light airs, but might find a slightly slower and more practicably limiting "hull speed".

It is up to you as to whether you consider this to be an issue. We are talking pretty small differences here - I certainly don't mean to say that your hull is a nightmare all of a sudden. But, if you are doing a bit more work on the aft body anyway, a little more volume back there might not go amiss.

This is where computer modelling hull forms is quite nice. If I were modelling this hull now, I could just ease out a few control points in the quarters to fill her out a bit. Then again, if one were following a more professional approach to drawing the lines by hand, we would have drawn a target curve of areas first and checked the various section areas against this as they are defined. In this way, you end up closer to your target displacement, LCB and Cp rather than only finding out what they area at the end!

If you have had enough of tweaking then fine - there does come a point where you have to say you are done!

[Ed Burnett]

Ed
Do you remember that very good paper published in the RINA Journal a few years ago on sail balance, based on the CE of lifting surfaces?

Yes, I remember it but can't recall the contents in detail.

Helm balance really is a pretty big subject. Particularly in relation to long keeled hulls (as opposed to relatively easily analysed fins), there is just so much going on that any theoretical approach is going to have to be hugely complex in order to be remotely valid.

In practice, and certainly for the sort of boat we are considering in this thread, the geometric lead method does work pretty well. It doesn't really relate to much in the way of theory but it gives us a way of comparing one boat with another so that, by bearing a few other things in mind at the same time, we can be pretty confident in the outcome.

[Andrew Craig-Bennett]

In support of Ed, not that he needs any help from me, remember how Harrison Butler got carried away by the metacentric shelf theory and fined his ends down too much, especially aft - don't say this in earshot of Joan Jardine-Brown but the later boats are slower...

[PeterSibley]

Hi Ed
so a little more displacement aft ? I'm going to be doing a little more work on those stations anyway ,so doing this will be another reason beside the shapes of #13 etc .

But how much ? I can work out my displacement with various slightly increased areas at the aft stations , but how much increase in displacement overall am I looking at ....seeing it will all be aft ? Another 800 pound between 9 ½ and 13 ?

This almost requires a complete reworking aft ....the increased displacement will change things quite a lot .....not to worry ! But some indication of the increase I need would be good .

Edited to add ..I've just been reading through Skenes again and if I work from the other end ...ie .58 . I can derive the increase required .:)

[PeterSibley]

Reading the above , I feel I am presuming on your generousity quite a bit ! Should you feel like walking away from this tutorial Ed ...I would completely understand .

[Ed Burnett]

Hello Peter,

It's a quick sum, no problem....

With the midships section area and LWL fixed as they are, the difference between a prismatic of 0.55, and 0.58 (the extremes of the range) is around 500kg (1100lbs) of displacement. It is a linear relationship between these points, so you can find your compromise anywhere along the line.

800 lbs more than you have now will give you Cp in the region of 0.574 which would be spot on, but a little less will be fine if working in that much more volume compromises the run. You will probably need a little more beam back there to make it work. The DWL does start to come in quite sharply after amidships, so holding on to a bit more waterline beam through S8, S9 and S10 might be the way to go.

One up side to adding volume there will be increased breadth of cabin sole and the ability to nudge the engine a bit further aft.

[PeterSibley]

Required ,another 1150 pound aft .18 cubic feet to achieve a PC of .58 .

[PeterSibley]

A cross post , thanks Ed ! A bit of width aft will be good on the cabin sole .

800 pound sounds easier ...less inside ballast .

[Ed Burnett]

Well at least our sums agree!

[Peerie Maa]

Yes, I remember it but can't recall the contents in detail.

Helm balance really is a pretty big subject. Particularly in relation to long keeled hulls (as opposed to relatively easily analysed fins), there is just so much going on that any theoretical approach is going to have to be hugely complex in order to be remotely valid.

In practice, and certainly for the sort of boat we are considering in this thread, the geometric lead method does work pretty well. It doesn't really relate to much in the way of theory but it gives us a way of comparing one boat with another so that, by bearing a few other things in mind at the same time, we can be pretty confident in the outcome.

You are right about confidence in the "lead" method, the figures quoted in Skene will work for the classic long keeler discussed here, and have been based on decades of experience.

I thought that the RINA paper was excellent though, the author checking his method against existing boats of known performance. His method was no more difficult either, by placing the centre of lift at 1/4 of the chord length, the only clever part is deciding where the canoe body stops and the keel starts. A difficult judgement for Marie Michon, even using the authors advice to use a station line slope of 45 degrees.:confused:

[PeterSibley]

Well, as far forward as possible is probably what you will end up doing. Not sure I wish to divulge the secret numbers here (although you will probably wheedle an opinion out of me eventually)!

Well ,I've just roughed out a sail plan .692 sq feet on the 3 lowers + 108 topsail = 800 sq feet .

Lead is 7% as drawn .

How would that be ? The numbers are managable , how about the lead ,is it sufficient ?

[Larks]

And here is the "Shed of envy" where all this design is being generated from:

http://i260.photobucket.com/albums/ii11/Larks_01/P7040237.jpg



http://i260.photobucket.com/albums/ii11/Larks_01/P7040238.jpg

The design desk:

http://i260.photobucket.com/albums/ii11/Larks_01/P7040242.jpg

[rufustr]

OK.

Now I'm going to have to go for a drive.:o

[Ed Burnett]

Well ,I've just roughed out a sail plan .692 sq feet on the 3 lowers + 108 topsail = 800 sq feet .

Lead is 7% as drawn .

How would that be ? The numbers are managable , how about the lead ,is it sufficient ?

Ok, assuming you end up with a displacement in the region of 10.5 tons (which I think is where you were headed?) 692 sq ft of sail gives a sail area/ displacment ratio of 13.6. Adding the topsail nudges this up to 15.8. Pretty modest, but ok in an area where you get breeze most days, and assuming the topsail is set up for reasonably efficient handling (ie. you can use it as a working sail). She could probably carry a little more, but its up to you to set the tone of this.

7% lead is, I am afraid, going to require you to build a pretty strong tiller.

[WX]

Isn't 13.6-15.8 a bit low?

[PeterSibley]

Ok, assuming you end up with a displacement in the region of 10.5 tons (which I think is where you were headed?) 692 sq ft of sail gives a sail area/ displacment ratio of 13.6. Adding the topsail nudges this up to 15.8. Pretty modest, but ok in an area where you get breeze most days, and assuming the topsail is set up for reasonably efficient handling (ie. you can use it as a working sail). She could probably carry a little more, but its up to you to set the tone of this.

7% lead is, I am afraid, going to require you to build a pretty strong tiller.

More can be found and a longer bowsprit by the sound of it ! 80 square foot per ton was the number I had in my head as a reasonable aim ....I'm a bit short .

I'll be considering a topsail a standard or not having one at all .

A lead of 12% sounds a bit more acceptable if I've understood Skenes .

[PeterSibley]

OK.

Now I'm going to have to go for a drive.:o

Welcome friend ! :):)

[WX]

Another EBS, count me in:D

[PeterSibley]

Yes, it was a very good day ! :):) Thanks all for turning up .

[dhic001]

Man alive, I've just read this thread right through from page 1 to page 7. its now 1:10am, but I've sure enjoyed reading this. A lot of it doesn't make sense to me, but I'm not so good on the technical terms and numbers, so its not suprising.
Great stuff guys, and i'll be following this with interest, thanks to all who have contributed to this.
Daniel

[Ed Burnett]

Isn't 13.6-15.8 a bit low?

Yes, as I say, this is a pretty modest total area. Then again, she is mostly internally ballasted and not hugely powerful in terms of midsection so we don't want to overdo it.

With gaff cutters there is ample scope for additional sail area as it is required. Peter has not yet posted his sail plan, so we don't know yet how much overlap there is in the headsails for example (ie. how much scope remains for light airs stuff). In due course I don't doubt there will be more discussion of all this!

The main reason I am suggesting a look at the rig at this early stage is to check that it will at least be possible to balance the helm to an acceptable degree. Placement of the mast will have a bearing on this, and we are not far off the time where thought will need to go into the structure and which if any frames would benefit from a bit more section to deal with rig loads. It's nice to have at least a rough idea of most aspects of the boat before going too far with actual building.

Peter,

I would take 12% as the bottom end of what will be acceptable.

[PeterSibley]

Ed , I'll do another sail plan ,but freely admit to being poorly informed on sail design and very open to advice !

[PeterSibley]

I've hit an interesting wall that anyone but me would have seen coming !:D

With a hull form like mine , LOTS of forefoot it is very hard to get enough sail area forward to get the required 12%+ lead .The photo below (of a rough I did and redid today :o )has the 3 lowers with an area of 800 suare feet .The jib has ended up unmanagably huge at 260 square feet , the staysail 130 .
Main 410 Topsail 121. Bowsprit 10' 6" .

Reducing the main a bit helps but not much .

The result is an 8% lead ...not good !
Will any passersby please offer advice !

The photo is pretty horrible but the scan shop is closed today .

http://pic40.picturetrail.com/VOL282/9443996/17245530/368763463.jpg

[dhic001]

Whats the idea behind going for a yarded topsail? If it was me building a boat like this, I'd go for a proper topmast, and a three headsail rig. Sure, you have the weight of topmast aloft all the time, but the topsail is easy to set, and you get a flying jib to help with your sail balance. Incase I'm not being clear here, a rig such as shown here http://aquapx.com/site/#/gallery/fresh-uploads/sewell-boats-mg-3463/ on Ripple (obviously without the mizzen). More a workboat rig than a yacht rig.

I also wonder if the cut of your main is correct, maybe reduce the length of the gaff a bit? Your luff looks a bit too vertical to my eye. But I don't claim to be a sail designer, so I may be wrong!
Daniel

[rufustr]

Not a big improvement, but a bit clearer.:D

http://i359.photobucket.com/albums/oo39/rufustr/368763463.jpg

[shamus]

Interesting stuff as always. I just had a quick look at Ronita's figures which are probably not directly relevant. Her IMS certificate from 10 years ago says 8 tons- 17900 pounds in round figures. Working sail is 704 sq ft, in a low aspect rig. I don't know exactly what her external ballast is, but it isn't all that low as she only draws a little over 4 feet. I keep meeting people who have sailed on her and all say "she's got that lovely stumpy rig that you hardly ever reef". This is appreciated by people who sailed on the NSW coast where sometimes you encounter a succession of sudden changes from 15 to 25 or 30knots, and similarly right here in the Derwent where sudden puffs over the mountain, often out of a clear sky, can find you over powered. We usually reef if it is consistently 25, or if it is 20 and we encounter a couple of puffs to 30. This is where I hate the furling headsail, because as you roll it up it becomes horribly less efficient and the CE rises. But always the temptation is to say "she'll be right" and take the easy way instead of changing to the right sail. As I said, probably not particularly relevant, but thanks for making me think about it.

[shamus]

Ah, so I took quite a while typing that last post up while having a wine with Lynne, taking a phone call from one of the kids, and there is a new problem. If the backbone is truely locked in, and you can't cut away the forefoot at all, maybe you need a small centreboard aft of the present CLR, which will allow you to balance the the helm in all states of sail. Just trying to add to the simplicity here! I've always thought those designs with two centreboards looked clever, for such purpose.

[PeterSibley]

Daniel , that's a great gallery ! I've considered a topmast but with Ed nearby I'm not mentioning such things ....he doesn't approve !

Your comment re the luff and gaff length is pretty useful ...thanks .I really have very litle idea of sail design !

[dhic001]

Peter,
Regardless of what Ed thinks, I personally think the topmasts with the workboat rigs are great. Ripple, in the photo, is 42 on deck, so larger than what you are building, but the main is easily handled by one person, and is probably similar in size to what you need. Take a look at photos of working boats, they'll give you an idea of sail proportions that work.
Daniel

[PeterSibley]

Something else ,I'm not quite sure I'm working out the centre of effort of the foretriangle properly either ! The main is OK , but the overlapping sections of the jib and staysail are a problem for me , also the centre of the 2 triangles .:confused:

[shamus]

The CE of the triangular sails is the intesrsection of lines from the apex to the midpoint of the opposite side. Doesn't matter about overlap, you work out the individual CEs of the sails then combine them in proportion to the areas of each sail, I think.

[PeterSibley]

The CE of the triangular sails is the intesrsection of lines from the apex to the midpoint of the opposite side. Doesn't matter about overlap, you work out the individual CEs of the sails then combine them in proportion to the areas of each sail, I think.

OK ....that's what I've been doing .How about the centre of effort of the 2 triangles ? How do you derive that ?
I've been using a ratio of areas as a means of finding the point along the connection line between the 2 centres .

[shamus]

I think (this is from memory!) you can take the combined CE of any two (in proportion as above) and then treat that as if it was one sail of that area, and do the calculation again in proportion to the remaining sail. So you could work out the main and staysail, and then treat that as one sail and combine it with the jib, or you could work out the effective CE of the foresails, then combine it with the main. Someone who actually knows will correct me if I'm wrong!

[shamus]

PS: Then work it out when the sail is not quite sheeted right and has some unattached flow or or the bottom is working and the top is feathered off or when the helmsman was looking at the boat behind... it's a pretty rough number really, I believe.

[RFNK]

Shaun (Sean?)
SWMBO and self are heading to the freezer from 21 to 29 July. Any chance of catching up (all jokes about THAT lake aside please!)? Rick

[shamus]

Excellent Rick. What's your agenda? Meal on Friday night, here or at restaurant? Or a sail around the river on Saturday, weather permitting?
(Shaun!)

[RFNK]

Great! How about both? We'll shout the restaurant (you like instant noodles don't you?) and a sail would be fantastic if that suits you! No agenda. I want to do some diving at Bicheno sometime and off Bruny sometime but otherwise we'll just poke around the Channel etc. looking longingly at homesites and boats! I'll email you with contact details. I'll contact Andrew too - I'd love to see his shop.

Sorry to hijack your thread for a minute Peter!!

Rick

[shamus]

Oh good! I want to visit Andrew as well sometime.
email gcr25082@bigpond.net.au Sounds good.

Other folks- we return you to your normal programming

[Ed Burnett]

With a hull form like mine , LOTS of forefoot it is very hard to get enough sail area forward to get the required 12%+ lead .The photo below (of a rough I did and redid today :o )has the 3 lowers with an area of 800 suare feet .The jib has ended up unmanagably huge at 260 square feet , the staysail 130 .
Main 410 Topsail 121. Bowsprit 10' 6" .

Welcome to dilemma no.1 in the design of this sort of boat. No need to panic though, it should be possible to work it out.

Firstly, it's as well to make sure you are working out these centres correctly. It sounds like you are, but just to check:

1. Find the centre of each triangular sail by drawing a line from one corner to the mid point of the opposite side, and from a second corner to the midpoint of its opposite side. Where these cross is the centre of area of that shape. (I tend to call these centres of area rather than centres of effort - the latter implies that it is a realistic indicator of where the forces act, which it isn't).

2. To combine two sails into one, join the individual centres. The combined centre will be a point on that line, with the ratio of the distances to each end being the same as the ratio of the sail areas. Make sure you get it the right way around (the bigger sail will pull the combined centre in its direction)!

3. Combine the various areas in pairs, and then combine the pairs and so on. Treat the main as two triangles to find its centre. You don't need to bother with the topsail in the early stages as its area is usually more or less above the combined lower sail area so it doesn't make much difference.

Ok, assuming the method is correct, looking at the sail plan it doesn't surprise me you are struggling for lead.

Regarding the configuration, I am not averse to fidded topmasts full stop, but if you do have one you have to do it well. Many are too short, poorly worked out and troublesome as a result. My opinion is that on a boat of this size a fidded topmast is likely to be more trouble than it is worth, but many would dissagree and that's fine. All I will say is that whatever way you go, make sure the reasoning is valid, and then be sure to recognise and take account of the various constraints that the path you choose imposes on the shape of the rig. The danger is to cherry pick features that you like the look of, but that do not work well together as one rig, on the boat in question.

So, as to the nub of the problem, a few observations of your drawing.

1. The gaff is pretty long, as is the luff of the main. Is there 6' clear headroom to the boom from the cockpit sole?

2. The mast is quite well back in the boat, but that's actually quite a nice thing and moving it forwards doesn't always help.

3. The staysail could be a lot bigger.

4. The jib is pretty big, obviously to try to compensate for the other things.

I would start by chopping a bit off the gaff, and dropping the throat a bit to increase the angle. This will also lower the hounds and make it easier to stay the mast. Leave the forestay where it is though.

The staysail is the easiest sail on the boat to handle, and it is conveniently far forward, so pack as much area into it as you can. Draw as much overlap as possible, although this will be limited by the forward lower shroud. This is where having the mast aft is handy, as you have space for a nice powerful staysail.

Now see how the centers are doing and if you still need the big jib. While you are at it, how about tightening up the bobstay a bit?

All these things go by degrees. Try something, see how big a difference it makes, and decide if it's worth a bit more.

Finally (and I may get shot at for saying this), certainly look at old boats for ideas of normal proportion and so on, but absolutely do not assume that these boats balance well. The chances are they don't. If there comes a point where you have to say "well, there is going to be some weather helm, but I really can't tollerate a larger jib" then so be it.

[Larks]

Peter, just to toss my hat in the ring (but having no real idea whether this is relevant or not), the mast looks quite perpendicular to the waterline to my eye. Would it make any useful difference to add a few degrees of rake while leaving the luff roughly where it is? Assuming that would add some sail area up forward and reduce some sail area aft. Is that what you are trying to achieve or have I misunderstood your post?

[ewan]

i noticed you said you use a scan shop... does the photocopier at your local library have a usb port ? i just realized mine did and there all copies/scans to usb are free..no paper or toner, so, free..

[PeterSibley]

Ewan , a good idea but the drawings are 12 to 1 on an A2 sheet and they are too big for most machines around here .

[PeterSibley]

Peter, just to toss my hat in the ring (but having no real idea whether this is relevant or not), the mast looks quite perpendicular to the waterline to my eye. Would it make any useful difference to add a few degrees of rake while leaving the luff roughly where it is? Assuming that would add some sail area up forward and reduce some sail area aft. Is that what you are trying to achieve or have I misunderstood your post?

No ,thats about it .
I'll draw up a new plan but I'm off for a sail on the bay for a day or so .I need to be reminded what all this is about !:D

[PeterSibley]

Ed , on the subject of topmasts , it seems they need to be long enough to reach from deck to hounds when lowered as a first requirement .That way the head could be secured in the housing that holds the foot ( it has a name ?) while the foot rests on deck ....when it is lowered ,spaced away from the mast a little to allow the ties to work .Otherwise where do you store a reasonable sized pole of that length ?

It's advantage for me would be a shorter more easily handled pole mast .

The disadvantage would be all the extra gear .

[Larks]

No ,thats about it .
I'll draw up a new plan but I'm off for a sail on the bay for a day or so .I need to be reminded what all this is about !:D

Ahh...what's this? Leisure time? Surely not!!!:D What on and who with??

[PeterSibley]

A mate with a nice little 32 foot ketch , it's a Redland Bay and we'll go for a wee sail then take it up the river .Good work if you can get it ! :)

[Larks]

I hope the weather is kind for you mate, have a great trip. Also thanks again for the wood, I've roughly shaped the cedar and bought it back to start carving and also sliced off a couple of "slithers" of the black bean to see if I can do something interesting as an inlay with some huon pine. I'll post some pics (if it works out OK and looks like it's wrth posting).

[PeterSibley]

My pleasure Greg ,it was great to see you I the flesh !
I'd love to see your carving , not something I've ever tried .

[Larks]

I sort of missed the chance to talk to you about stability and buoyancy and so on the other day. I thought we had a post here about weight and CG but can't find it, (maybe I imagined it or typed it and didn't send it??) Anyway, at the risk of repeating, have you done any weight estimates on the hull as yet that we can do some Centre of Gravity calculations/estimates from? If not, do you know the weight of your cast ballast? I think from memory Skenes may have some guidance on construction weight estimates.

If I can establish the CG I think I can start giving you some stability calc's based on the general sail area that you already have. Otherwise I'm wondering about the concept of working backwards - Ed/Michael can this be done??? Should it be done? IE working out an ideal CG then establish the weight/build distribution to achieve that?

[Larks]

I'd love to see your carving , not something I've ever tried .

Nor have I other than for doing art at school and the recent half hulls. Something that I'm interested in trying though, I have a cunning plan!!:D

[PeterSibley]

Greg , I haven't done the build weight yet .I will but probably not for a while .The outside ballast casting is 5600 pound IIRC , Skenes sample calculation is a pretty good guide to how to do it ..a bit time consuming but interesting .

[Larks]

If you are interested in it and think it's worth doing I might have a play with it anyway - or at least make a start, I don't know how far I will get as far as distribution of weight goes but the exercise will tell us what we don't know.

I have a density for the Tallowood frames of 1010kg/m2, what did you say the hull and deck would be? Also any ideas on what the sizes of your frames might be and a guess at what the weight of the backbone would be now?

[PeterSibley]

Off the top of my head the backbone is 9x6 tappering to 5" at the ends ,yellow stringy ,20 foot long.
Stem 9' of 10x6 iron bark
Stern similar + a big knee and a doubler .:confused:

Greg , I reckon I'll have to do this as I really have to work through it stick by stick .....and there are a lot of them .

No time right now , I'll have a go in a few days .

[Ed Burnett]

Hello Peter, hope the sailing was good (entirely justifiable design research!).

The topmast vs. pole mast discussion could run and run. Why not sketch up a sailplan for both options (allowing each to run it's course in terms of development for sail area and balance), and then see which looks like the best bet all things considered. I know which way I would go, but it's not up to me!

As for the weight and stability issues, a full estimate of weights and centres would give a greater degree of security, however if you don't do it thoroughly that security is unjustified. It really is a pretty dull process, I spent most of last week working on one for an 83' schooner, and the fact that I have been posting here is as good an illustration as any that a diversion was called for every now and again!

In terms of Peter's boat, there are certain factors that mean he can safely proceed without a full estimate. Firstly, the boat is of a type for which we have ample empirical data, and providing the design stays within the bounds of this and follows the established path the chances are that she will work out. Peter and I had a bit of off forum discussion on this to look at a few numbers and check that the boat was in the right area.

Secondly, she has a large proportion of her ballast inside, which makes it adjustable. If Peter had to commit to a fully external ballast keel weight and shape now, a full weight estimate would probably be needed.

One thing you might consider is to plan to weigh the hull and deck before the internal ballast goes in. With a project like this it is an entirely realistic thing to do, and is both more accurate and substantially less time consuming than doing an estimate now.

[Ed Burnett]

Otherwise I'm wondering about the concept of working backwards - Ed/Michael can this be done??? Should it be done? IE working out an ideal CG then establish the weight/build distribution to achieve that?


Sorry Larks, forgot about this question....

In terms of LCG, certainly one aims to distribute ballast such that the boat floats level. If one had to commit to all fixed ballast now this would require some sort of weight estimation process at this stage.

In terms of VCG however, I expect in practice you would end up with so little ability to control it that it would be wasted effort. It is also the case that (from where things are now) the ideal CG is more or less as low as you can get it! At least in this sort of boat, the purpose of the weight estimate for VCG is not so much to place it where you want it, but to check that it is low enough for the vessel to have sufficient stability.

With the basic proportions of the boat now set, the external ballast cast and the general configuration of the structure more or less established, the outcome from a VCG point of view is pretty much determined at this point. We may not know exactly what it is, but there is no longer much we can do about it (This is why it is so important to take care in establishing the overall proportions of the boat). From here on, the structure will weigh what it will weigh, as will all the other bits. The final amount of internal ballast that will be required remains to be confirmed, but you would have to come up with a pretty convincing argument to put this anywhere other than in the bottom of the boat, whatever ideal CG you might have decided on!

[Larks]

Thanks for answering that ED, it makes sense. I've been using Peter's design process to understand some of the practicalities of the Naval Arc' assignment that I've been doing and thought I may be able to "prove" the concept of his original question about the stability of the different hull shapes. cheers

[Bob Cleek]

Great thread! I overlooked it previously. Not much to add, since you seem to have the hang of it, but as the long time owner of one of these boats, I'm surprised you haven't considered J. Laurent Giles' designs. He's pretty much recognized as having brought the type discussed to its highest level of development with his 25' Vertue, 30' Wanderer and 46' Dyarchy designs.

Vertue:

http://www.tc.umn.edu/~parke120/Boats/images/giles_vertue.jpg

http://newimages.yachtworld.com/1/1/7/9/3/1179316_1.jpg

Wanderer:

http://www.cheoyleeassociation.com/Owners/Members%20Photos/Wanderer.jpg

http://www.cheoyleeassociation.com/images/Wanderer/Wanderer_int.jpg

Dyarchy:

http://www.betty-ck145.de/cruisers/smalljpgs/riss_dyarchy.jpg

http://www.betty-ck145.de/cruisers/smalljpgs/dyarchy_ii.jpg

These designs, particularly the Hiscocks' Wanderer, are extensively discussed in their "Cruising - Voyaging... Under Sail" series. There's a ton of articles on the very famous Vertues. This one is pretty good: http://www.viking-boats.com/Pdf/Vertue.pdf.

Plans to build all these designs with their original gaff or later Giles designed Marconi rigs, and with various Giles designed cabin and doghouse variations, in traditional wood or now even in welded metal, are available from the Laurent Giles offices in England and New Zealand. http://www.laurentgiles.co.uk/ I see where Giles partner Barry Van Geffen is running the NZ office now. If you are down that way, tell him I said "Hi!"

[RFNK]

Bob, correct me if I'm wrong but a friend (sailed a Vertue from England to Oz) tells me that plans from Giles are very, very expensive (i.e., thousands of dollars). Do you know if that's right? Rick

[Bob Cleek]

Many who are used to seeing "study drawings" of vessels in magazines and books, or sometimes full lines and offset tables (such as are frequently provided in Chapelle's books) are shocked at the cost of a proper set of plans and a "license to build" from a naval architecture firm. I don't think the Giles firm's services are at all expensive when compared to any other design firm of comparable prestige. Founded by J. Laurent Giles in the late 'twenties, the firm is still going strong and in addition to their archive of pedigreed classic yacht designs, remains one of the foremost designers of "megayachts," sail training "tall ship" vessels, and commercial small craft. But... yes... their services do cost money, which is how they make their living.

It must be remembered that when dealing with a naval architectural firm you aren't just "buying plans." Rather, you are buying a "license to build" a vessel to those plans. What you are paying for isn't simply the printed paper drawings, but the intellectual property rights in them and, thus, the right to build a "Vertue" or other specific design. Then, also, you will have available to you the architectural firm's resources while building when questions arise. Giles will provide all services required, at an hourly fee, if you wanted, say, to make custom modifications (e.g. calcualte for a lead, rather than an iron ballast keel) or have them inspect and approve the construction in stages when done by a commercial builder and so on. There is no question that building a specific classic design to the plans under a "license to build," when it comes time to sell the boat, will enhance its value in an amount far, far, greater than the cost of the license, assuming the vessel was properly built as designed. And, owning such a vessel is a lot like owning an old Rolls Royce. Despite the passage of time, when you call the "factory," they know your boat and they know your name because they keep track of the "works of art" they've produced over the years. (For example, one of the "perks" of owning a "licensed build" was that when I wanted to have some sails made and inquired as to certain measurements and centers of effort on my Vertue, I immediately go back a set of the Vertue sail plan and rigging drawings and a letter in response answering my question... at no charge.)

Some years back, subject to an agreement that I would not build a full sized vessel, but only a model, the firm sold me all the drawings for "Dyarchy" (less the offset tables, which I did not need for modeling purposes) for $250. These comprised a LOT of very detailed drawings of every construction detail of the hull and rig. At that time, the "license to build" was quoted, IIRC, at around $2,000 and, if I ever wanted to build a full sized version, the $250 I paid for the drawings would be credited against that. I found those prices very reasonable. It would be interesting to find out what Sparkman and Stephens would charge you today for a license to build a comparably sized boat of the same era, such as Dorade. I'd expect it would be much the same, if not more.

There are "study drawings" published many times over in various books for both Dorade and Dyarchy. One could, certainly, approximate the same shape by enlarging and lifting the offsets for such hulls and build a boat very similar to either. (In which case, you'd be completely on your own as to scantlings and construction details.) A small alteration in the lines might save you the grief of losing a copyright infringement lawsuit (although perhaps not the cost of defending it!), but calling such a boat a "Dorade" or "Dyarchy" without having bought the rights to do so would certainly end up costing you a LOT more money than the license to build ever would have if the designers caught wind of it and enforced their intellectual property rights.

These copyrighted designs should not be confused with other fine designs which may, for whatever reason, have found their way into the "public domain" and are no longer "owned" by their creators, but are "fair game" for anyone who wishes to use them. For instance, many of Atkin's designs published in MoTorBoaTing issues and later in their "Ideal Series" reprints, are in the pubic domain and can be built by anyone who wishes and properly called an "Atkin Whatever." Atkin's beautiful cutter "Benbow" is very similar to the designs discussed in this thread and is in the public domain and available to anyone without paying a license to build. Full sized (not magazine reprints) for "Benbow" are available for purchase from the Atkin estate for $250. http://boat-links.com/Atkinco/Sail/BenBow.html Not to besmirch the Atkins, whose work I appreciate, but, having seen the full published Benbow plans, I can assure you the Giles Dyarchy drawings for the same price were much more detailed and comprehensive.

When the cost of a "license to build" is considered as a percentage of the vessel's overall cost of construction, the licensing fees for the Giles archival designs start to look like a real bargain. I'd expect any naval architect would be looking for something in the range of at least a ten percent commission on the construction cost to design a boat. Their fees for an already designed boat are far less than that.

Finally, I'd add that, as much fun as we amateurs have "noodling" boat designs in an imaginary quest for the "perfect boat," there is tremendous value in a "tried and true" proven design. There aren't any surprises with a "pedigreed" boat. Built to the plans, it WILL float on its lines and it WILL sail every bit as well as its sisters. That's worth a lot of money. Nothing is sadder than a really well built (and expensive), beautiful boat that, due to an often unanticipated design feature, falls short of the mark in performance. More often than not, even with professional naval architects using state of the art CAD software, such surprises occur. With a proven design, somebody else already took that risk for you.

Atkin "Benbow:"

http://boat-links.com/Atkinco/Sail/images/BenBow-1.gif

http://boat-links.com/Atkinco/Sail/images/BenBow-2.gif

http://boat-links.com/Atkinco/Sail/images/BenBow-3.gif

[RFNK]

Thanks Bob, very enlightening. I'd have to agree that where this price includes ongoing support through the build etc., it seems reasonable. I certainly wasn't aware that purchase of plans would include this. Rick

[Larks]

Peter, here's a link to "Germain" which I found on Daniel Skira's web site links (I hope he doesn't mind me copying it), I found the lines quite interesting. Although a little slab sided she looks lovely in the photos and has an interesting looking rig set up with the main mast looking quite forward both in position and rake.
http://www.port-rhu.com/jolieplaisance/Germaine_fr.htm

[peter radclyffe]

yes alden plans seem reasonably priced

[PeterSibley]

Peter, here's a link to "Germain" which I found on Daniel Skira's web site links (I hope he doesn't mind me copying it), I found the lines quite interesting. Although a little slab sided she looks lovely in the photos and has an interesting looking rig set up with the main mast looking quite forward both in position and rake.
http://www.port-rhu.com/jolieplaisance/Germaine_fr.htm

She's a remarkable looking craft isn't she !:) Beautiful !

Ed , I noted your comments about the balance of traditional sailing craft , a quick look at many in light of my recent calculations would suggest heavy relieving tackles in use .:D

BTW ,the research trip was excellent ,10 to 20 knots , 14C and rain .:) Perfect winter weather for us !

[Larks]

BTW ,the research trip was excellent ,10 to 20 knots , 14C and rain .:) Perfect winter weather for us !

photos!!!!!???:confused::)

[Ed Burnett]

I noted your comments about the balance of traditional sailing craft , a quick look at many in light of my recent calculations would suggest heavy relieving tackles in use .:D

It's a fascinating subject, and one which rather defies technical analysis without resort to some pretty expensive tank and wind tunnel work. We have a few useful rules of thumb, but there remains plenty of scope for individual judgement.

I sometimes wonder if our measure of what is "acceptable" weather helm has changed over the years, but I do also feel that a few modern influences have had an effect.

Firstly, I am sure modern materials used in the rig make the whole boat feel more taught and the feedback more direct.

Secondly, our desire for centreline props and the aperture that results has a huge effect on the feel of the helm. The efficiency of the rudder is seriously harmed by digging a hole in the middle of it, and so any imbalance in the rig is more noticable at the helm. There remains a pretty good argument for a quarter prop if you can stand the manoeuvring issues.

[Andrew Craig-Bennett]

It's a fascinating subject, and one which rather defies technical analysis without resort to some pretty expensive tank and wind tunnel work. We have a few useful rules of thumb, but there remains plenty of scope for individual judgement.

I sometimes wonder if our measure of what is "acceptable" weather helm has changed over the years, but I do also feel that a few modern influences have had an effect.

Firstly, I am sure modern materials used in the rig make the whole boat feel more taught and the feedback more direct.

Secondly, our desire for centreline props and the aperture that results has a huge effect on the feel of the helm. The efficiency of the rudder is seriously harmed by digging a hole in the middle of it, and so any imbalance in the rig is more noticable at the helm. There remains a pretty good argument for a quarter prop if you can stand the manoeuvring issues.

Hooray! Bravo, Ed!!! :):):) Well said!

The quarter prop is so, so much better and with the modern hydraulic set up and twin folding props you get marina manoevring that puts fin keelers to shame.

Years ago I experimented by taking the Stuart Turner out of my two and a half tonner (an "illegitimate" Harrison Butler) and filling in the hole. She was transformed from a hard mouthed little bitch into a boat that was really fun to sail.

Dinghies of course have gone the other way with modern materials because they all now have bendy masts, (which Uffa Fox would have thought a worse heresy than unballasted centreboards!) so the sail flattens in a puff.

[Ed Burnett]

Not sure I would go the hydraulic route on a boat of this size. It's complication and noise that one can do without, and the efficiency is not great. Far better to avoid marinas anyway....

But we digress. Interesting to note though how seemingly unrelated aspects of the design in general have a bearing on eachother. The best boats are the ones where each and every element has its place in the well thought out whole.

[Andrew Craig-Bennett]

Not sure I would go the hydraulic route on a boat of this size. It's complication and noise that one can do without, and the efficiency is not great. Far better to avoid marinas anyway....

But we digress. Interesting to note though how seemingly unrelated aspects of the design in general have a bearing on eachother. The best boats are the ones where each and every element has its place in the well thought out whole.


(excuse the digression - I must do something about Mirelle's engine one of these decades - its 42 years old and very wheezy, and the stern A bracket is the 72 year old original Kelvin one. So we do avoid marinas...ideally I'd take it out and have done...)

[PeterSibley]

I agree with you Andrew , the only short coming from my point of view is that the hydraulic drive system is either bulky (in tankage and cooling ) or very expensive .
Zane Lewis has contributed to a few very useful threads .
http://www.woodenboat.com/forum/showthread.php?t=65976&highlight=hydraulic+drive

http://www.woodenboat.com/forum/showthread.php?t=90723&highlight=hydraulic+drive

A hydraulic anchor windlass seems relatively simple to achieve however .

[PeterSibley]

The boat I spent yesterday on had a 45 year old Yanmar 20 hp ,a Lister clone from the appearance and sound .900 rpm is a pleasant speed to have a motor running at ...not nerve shattering the way some of he modern ones are .

[PeterSibley]

Secondly, our desire for centreline props and the aperture that results has a huge effect on the feel of the helm. The efficiency of the rudder is seriously harmed by digging a hole in the middle of it, and so any imbalance in the rig is more noticable at the helm. There remains a pretty good argument for a quarter prop if you can stand the manoeuvring issues.

That is worth taking on board Ed , I've chopped a half apperture in the sternpost , but a repair isn't inconceivable .

[Larks]

There's probably a world (or thread) full of discussion just on the topic of stern tube/prop placement Peter. "The great man" (LFH) is adamant that an offset prop is the way to go in justifying his design with the H28 but, if I recall reading correctly, in other designs he does an about face and promotes the benefits of a centreline prop'.

[PeterSibley]

Hmmm ! Well I'm open to suggestions and discussion :) .This thread is an education !

[Larks]

I came accross this blog on a Lyle Hess Falmouth cutter build last night while searching for deck/hull join ideas, very nice work:

http://images.google.com.au/imgres?imgurl=http://3.bp.blogspot.com/_F8a8fpmJkls/ScCg4o5eSpI/AAAAAAAAAD0/PTadj0YROfo/s320/glassing%2Bdeck%2Bhull%2Bseam.jpg&imgrefurl=http://knjwoodworking.blogspot.com/&usg=__obIEDgvj4pcYqVomxd_9ppsjPPE=&h=240&w=320&sz=18&hl=en&start=69&um=1&tbnid=-QWLZmxEwkHdZM:&tbnh=89&tbnw=118&prev=/images%3Fq%3Dwooden%2Bdeck%2Bhull%2Bjoint%26ndsp%3 D18%26hl%3Den%26sa%3DN%26start%3D54%26um%3D1

[RFNK]

came accross this blog on a Lyle Hess Falmouth cutter build last night while searching for deck/hull join ideas, very nice work:

http://images.google.com.au/imgres?i...%3D54%26um%3D1 (http://images.google.com.au/imgres?imgurl=http://3.bp.blogspot.com/_F8a8fpmJkls/ScCg4o5eSpI/AAAAAAAAAD0/PTadj0YROfo/s320/glassing%2Bdeck%2Bhull%2Bseam.jpg&imgrefurl=http://knjwoodworking.blogspot.com/&usg=__obIEDgvj4pcYqVomxd_9ppsjPPE=&h=240&w=320&sz=18&hl=en&start=69&um=1&tbnid=-QWLZmxEwkHdZM:&tbnh=89&tbnw=118&prev=/images%3Fq%3Dwooden%2Bdeck%2Bhull%2Bjoint%26ndsp%3 D18%26hl%3Den%26sa%3DN%26start%3D54%26um%3D1)


Wow! How about that interior joinery! Rick

[PeterSibley]

I came accross this blog on a Lyle Hess Falmouth cutter build last night while searching for deck/hull join ideas, very nice work:

http://images.google.com.au/imgres?imgurl=http://3.bp.blogspot.com/_F8a8fpmJkls/ScCg4o5eSpI/AAAAAAAAAD0/PTadj0YROfo/s320/glassing%2Bdeck%2Bhull%2Bseam.jpg&imgrefurl=http://knjwoodworking.blogspot.com/&usg=__obIEDgvj4pcYqVomxd_9ppsjPPE=&h=240&w=320&sz=18&hl=en&start=69&um=1&tbnid=-QWLZmxEwkHdZM:&tbnh=89&tbnw=118&prev=/images%3Fq%3Dwooden%2Bdeck%2Bhull%2Bjoint%26ndsp%3 D18%26hl%3Den%26sa%3DN%26start%3D54%26um%3D1


That blog is a great find Greg ....some brilliant photos ! Thanks mate :)

[PeterSibley]

Andrew and Ed ,
re the hydraulic drive idea .I think in it's normal form it's too expensive and complicated but here is a possible alternative .It isn't as flexible but far simpler ....the idea is a bare engine of say 20 hp ,no gearbox but a fixed short stub shaft .Off this ,by cogged belt ,two gearboxes are driven ( probably the original and another with reverse rotation ).

As you can probably envisage ,if the port box is forward and the starboard in reverse you will be changing direction rather quickly ,the speed could be varied by "feathering" the engagement of one of the gearboxes .At low revs this could be quite useful and it's realitively simple .....I wonder if it's been done ?

[Larks]

I'm reminded of an Indonesian Phinisi I got a lift on a few years ago, the only controls in the wheel house were the helm, and a transistor radio. When we left the dock one of the guys ran down to the engine room and started the engine backwards to give him a reverse gear then when we wanted to go forward he killed the engine and restarted it forward.

[PeterSibley]

Hmmm! Not quite that primitive Greg :D

What do you think of the idea ?

[Andrew Craig-Bennett]

Peter - I'd stick with single offset prop (FOLDING!!)

The manoevreability is quite good because you can turn towards the prop using the rudder to deflect the wash.

[PeterSibley]

Yes , an offset position is really were a folding prop comes into it's own ! I wouldn't need one of those lovely but horribly expensive feathering things .:)

[Ed Burnett]

Hello Peter,

Well, I don't doubt it is technically possible, but there would be all sorts of problems to sort out and the bespoke engineering would proabably end up costing more than the hydraulics.

Think also about the amount of length all this stuff would take up in the aft end of the boat, and how this would effect the companionway and so on.

With any of these systems on a boat of this size, the danger is that you get too caught up in the detail and loose sight of the basic requirements. Think a bit about the sort of sailing you are going to be doing, and what your priorities are regarding handling under sail and power, and the efficiency of the engine installation. Let these things drive the solution.

[PeterSibley]

It's OK Ed , I wasn't planning to do it ,it's just that there have been a few quite educational discussions about hydaulics over the last few years .It's attractive but bulky (tankage ) ...unless the most expensive components are used ....then it becomes just very expensive .:D

It was just an exercise in imagining an alternative solution ....while driving home from my sail .:)

As to bespoke engineering ...it is the kind of thing I would do myself without too much drama .

[Ed Burnett]

Well it's always fun to work through ideas, and good to consider various options before settling on the best solution.

The bulk of the hydraulic tank isn't really the biggest problem, but the various hoses and bits and bobs do take up a surprising amount of space. Noise and efficiency are cetainly issues. We have done a few of these installations in original BCPC's, I'm not convinced it stacks up in anything smaller.

Anyway, how's the rig sketching going?

[PeterSibley]

Several attempts ,but life has been interfering .Tomorrow will see me with sufficient hours to do it properly ....and it will be raining so I won't be able to do any building here .....always a good excuse !

[Larks]

Just caught up with this Peter, I can see that it's an interesting concept to work through for the sake of working through it. I can't see that it'd achieve much though, as Ed says, there's the issue of space, both for the stub shaft and the prop shaft and the gear boxes, though I guess they'd not need space between them, just enough length for the drive belts. Also the need to still locate the prop shaft and a means to keep it in place from falling out as well as balance it against whichever gear box belt is driving it and wanting to pull it off centre. But I'm a bit like you I think, I still like to play with ideas and work them through one way or the other.

[PeterSibley]

Belts are the way to go with a low hp installation like this, the new toothed variety or the Seigling multi vs are brilliant and can be back tensioned with no problem ,so no tensioning problems ....it lets the central shaft and the boxes be solidly mounted or if the engine was on soft mounts the 2 tensioning pulls would even each other out .A small Hurth box is only about 250mm on a face ,very small .Actually I think it would be quite fun to play with .

The idea was for someone who needed a close maneovering ability .

[Peerie Maa]

The Lancashire Nobby Venture http://easternyachts.com/venture/images/venture.jpg
was fitted with a really innovative solution, belt driven. The wing shaft was bolted to a front hub from a Mini, which accepted the thrust and misalighment whilst allowing the engine to be mounted horizontal. The Mini hub was secured to the bed frame by its suspension wishbone. That allowed the engine to be mounted alongside the shaft, with out worrying about alignment whilst the pulleys were mounted on drive shafts supported in plummer blocks.

[PeterSibley]

Hi Ed , here is the latest attempted sailplan .The main has shrunk to 317 square feet ,jib 163 ,staysail 258 Topsail 123 .

A total of 738 square feet on the 3 lowers , 861 total with the topsail .

The lead has moved forward to 12% ,the bowsprit has grown to 12 foot .I'm wondering about the bobstay angle too ,it looks a bit ineffective as drawn ?

Sorry about the image , I can't seem to post a larger one !

http://pic40.picturetrail.com/VOL282/9443996/17245530/369162761.jpg

[rufustr]

Is this a bit clearer?

http://i359.photobucket.com/albums/oo39/rufustr/369162761.jpg

[PeterSibley]

I need you Rufus ! :D:o

[Ed Burnett]

Hello Peter,

Ok. Plenty of tweaking probable on that sail plan before it gets built, and that no doubt will be worthy of its own thread in due course.

The reason for looking at the rig at this point was to see if it was going to be possible / practicable to balance the helm before signing off the hull lines. We now know what you have to do in terms of sail area distribution to achieve that aim and are in a position to assess whether or not this is going to be acceptable.

Looking at what you have to do rig wise, it might be worth thinking about the sternpost a little more. Exactly how far have you got with this? Might it be possible to dissasemble it and trim a little off the knee to bring the sternpost more upright? Would you consider some sort of secondary wedge of sternpost aft of what you have built. Is this all completely out of the question (would you rather live with a heavy helm or an enormous jib)?

There will have to be a compromise here, but I think we have now touched on the main contirbuting factors so you should be in a position to decide on a course of action.

[dhic001]

Looking better Peter. I'm not sure that you have your staysail quite right though. The luff is a little long, and I can't see how there is enough space to fit the block at the head of the sail. Sure you can make the luff that long, but can you actually hoist it?

Still think you need to get rid of that spar on the topsail, and go for either a topmast or a longer pole mast (aka Dynarky). That flying jib is a nice light winds sail :p
Daniel

[PeterSibley]

Thanks Daniel ...the whole thing is a box of compromise but the topsail is the "Curlew " type ...I have a friend with one and I'm a convert ,very easy to set !
Frankly I'm reasonably happy with everything except the ridiculous staysail ! It might just have to be a little smaller ,a heavy helm at low wind ( but proportionately less ) with the first few winds of the roller main giving a lighter helm back .Am I correct ?

Ed , I'll have a look at the stern post assembly again ....but I think it is very unlikely to be even possible !

[PeterSibley]

http://pic40.picturetrail.com/VOL282/9443996/17245530/364808956.jpg

Ed , it's interesting to compare the original MM rig .I'll have to work out the Centre of Effort of the various combinations ,it's marked but there are quite a few sails drawn .

It looks as if it would have a fairly heavy helm , the underwater profile is very similar to my drawing .

[Ed Burnett]

Yes, the staysail won't work as drawn. Too long on the luff, and too much overlap to be able to sheet it inside the forward lower without the leech getting interfered with. And that jib, well, to be honest, the first thing you will want to do when it starts to get breezy is change that for a smaller one, and we know what that will do to the helm.

Tricky.

[PeterSibley]

A bowsprit with varying positions may be a possibility Ed .What do you think ?

[Ed Burnett]

It's a possibility, but you are treating symptoms, not the disease.

[PeterSibley]

I suspect the disease , as you put it , is pretty well locked in ! The centre of lateral areas is where it is , the centre of effort seems required to be around 12% forward ,if I have understood my lessons .

The cure eludes me .

[Ed Burnett]

Check your email Peter.

ED.

[Bob Cleek]

Given that this is the design that the Pardeys sailed around the world, I would think it's sea keeping abilities have been well proven.

http://www.ukhalsey.com/newsletter/oct2005/Pardeys_sm.jpg

My preference aesthetically is for plum or nearly so stems and sterns.

Measuring any design by the voyages (or voyage, singular) it may have made is always a dubious proposition. The classic example of such folly was the Westsail 32 and similar "Colin Archer" clones. While it is true that some famous and remarkable small boat voyages were made in "Colin Archer" designed double ended lifeboats, this was so because nothing else was available to perform such a feat in those days. Those early voyagers would surely have picked something better suited for the task, had they had the choice. In this instance, the Pardeys' seamanship was the determining factor... not the "sea keeping" abilities of the Serrafyn design, which, while very pretty and entirely adequate, is nothing particularly special. It's just one of many similar designs which happens to have enjoyed much more widespread media exposure. Truth be told, if Lynn and Larry had been able to afford it, they'd have built a different boat. As soon as they could, they did.

[Peerie Maa]

All due credit to the Pardeys seamanship, they also knew enough to chose the right boat. Those short ends evolved in some of the most arduous seas in England, and as work boats, it was not "can't earn my living today, its a bit rough", they needed a boat that could work.

[peter radclyffe]

there is the story of an itchen ferry boat travelling out from the isle of wight, every day, for 60 years

[PeterSibley]

Reassuring :)

[PeterSibley]

Here is a slight improvement ,10% lead .Not finished but progressing I think .A few comments would be helpful ,as I've said sailplans aren't my forte .:o

http://pic40.picturetrail.com/VOL282/9443996/17245530/369316812.jpg

[rufustr]

http://i359.photobucket.com/albums/oo39/rufustr/369162761.jpg

[PeterSibley]

Thanks Rufus ....you have a job ! :D

[PeterSibley]

Here is another , .5% more lead but a shorter bowsprit , the mast moved forward 20" or so ,similar areas .The forward movement of the mast makes the cabin area more useful with a wider sole .

I think this is an improvement ,the staysail is more managable .

http://pic40.picturetrail.com/VOL282/9443996/17245530/369407562.jpg

[Larks]

Peter, I wish I knew more about sail and rig design but for what it's worth, when I line all three designs up side by side the last one just "looks" more right than the others, particularly in terms of mast and cabin position. Just wondering though why the headsails don't hoist right up to the mast? Is that something to do with a gaff rig set up? If I saw a yacht with headsails hoisted like this I'd think they weren't cut for that vessel. Also is there any reason why you couldn't bring the inner one further back to at least amidships or a bit beyond?

Not trying to pre-empt how you plan to sail her but I'd like to see you with furlers on both headsails so that you can take her out by yourself with the girls and not need anyone up on the foredeck, so in that case you could probably afford to cut both sails a bit bigger.

[Larks]

Having just typed that I went back and had another look at the original Marie Michon drawing and saw the pulley set up for hoisting the headsails...do you plan to do the same set up??

[PeterSibley]

Greg , the set up will be rather MM ,no furlers although for inshore sailing with the kids ....great !
The sails are very likely to be used to start with , money is kind of scarce and to start with at least , yes used and recut if necessary .When all the bugs are out and I've saved a few more dollars ..new would be lovely !

As to the size and shape of the foretriangle ,at the moment it's all about trying to get the centre of effort around 10% + forward of the centre of lateral plane to ensure ?? an easy helm ,she has something of a forefoot ....identical to MM in fact .

[PeterSibley]

It's been an interesting exercise Tony , trying to get the centre of effort forward , I made an assumption that a large foretriangle was the way to go ...and set the mast at 40% wl from the stem (11 foot 4inches ) .Something I had seen recommended. The numbers have actually worked out better with the mast 10 foot from the stem !

What I want is a traditional but easily handled rig .I'll be using a roller reefing gear on the main ,which should make mainsail reduction realitively simple ,keeping the foretriangle handlable is something I'm very keen on .That said ,I don't trust headsail furlers .

The mast will be keel stepped and the cabin structure and bulkheads will be aligned to the mast .

[Ed Burnett]

Hello Peter,

Looking better as you tweak. There are still a few practical issues to work out, but the basic shape of the rig seems to be heading in the right direction.

Incidentally, it looks like you are using the geometric method described by Chapelle to find the centre of the main. With the proportions the sail now has, the angles at which the lines cross are getting very fine so its accuracy probably isn't great. I would suggest you revert to a "two triangles" method.

I think trimming the backbone profile a little by the stern (as per your email) is a good idea. From a drawing point of view you won't have to change the rest of the shape much and can leave the sheer as it is. Looking at the photos of your sternpost assembly, I would also suggest you consider adding an additional wedge of external sternpost aft of your current trailing edge. You have a bit of overlap in the deadwood to spare and you need not adjust the line of the rabbet. Adding up the effects of these things will get you as much as 1.5% more lead which I think will be worth having.

[PeterSibley]

Hi Ed ,
I'm glad you think things are coming along ,it's been a bit of a learning curve but I feel that I'm starting to get a feel for the changes that various modifications make .

Here's the photo of the sternpost assembly .

http://pic40.picturetrail.com/VOL282/9443996/17245530/369423904.jpg

How much wedge would you suggest ? As much as possible I assume !

[Ed Burnett]

Yes, more or less.

In an ideal world, I would be suggesting you dissasemble the lot and cut angles on each part (knee, inner post and sternpost) to bring the trailing edge more upright, but I appreciate the work involved and also the fact that the bolt holes would then become rather less than perfectly straight!

So, how about cutting as much of an angle as you can on the current sternpost and adding another slab on the aft edge, again tapering towards its upper end. You could chase the existing bolt holes through to the new trailing edge.

The question of course is whether it is worth it. In conjunction with a bit of trim as already discussed, I think it may be.

[PeterSibley]

I'll do a few measurements Ed , the tab of timber I've left at the bottom is about the limit , around 6" IIRC .

It almost looks as if I have enough to go on with , the aft addition , redraw (if I can bring myself to do it ! ) the aft stations to gain 800 pound displacement aft ,the sail plan looks workable and gives me a position for the step and which frames need to be especially solid .

At this point I think I should publicly thank Ed for taking an interest in this project , it would have been both a hard slog and probably a disaster without him !

Thank you Ed !:):)

[Ed Burnett]

No problem - it's a fun process to work through.

As you suggest, we have probably talked through most of the issues at this point, and have a reasonable idea of how each will reflect on the boat as a whole. Over to you for the final blending of compromises!

[PeterSibley]

Thank you Ed !

[maxwaterline]

Speaking of thanks, I would like to thank Peter, Ed, Andrew,Larks, MMD and others for a great thread. Haven't been able to fully understand everything but this has been very interesting regardless.

Cheers

Adrian

[Larks]

Ditto that Adrian, one of the much more interesting and valuable threads here, thanks Petern for incuding the rest of us on the forum in the process.

[PeterSibley]

You're probably right Tony , but the thought of a jammed furler in the middle of the night is just as scary ! I have read of the same , but can't find a reference .

They are very attractive ...I agree !

Perhaps a good subject for a thread ?

[Larks]

Well, I hear what you say Peter, but (sincerely without any disrespect) I think you're crazy. In my experience, headsail furlers are one of the best things to hit short-handed bluewater sailing since (ideal metaphor escapes me!:confused: you get the idea, anyway!:rolleyes:). On a dark, windy night somewhere off (choose whichever nasty rocky bit of coast you particularly don't want to hit) it's very nice to be able to wind in a nice slab of jib/genoa (whichever) without having to leave the comforting safety of the cockpit - or even wake up the crew off-watch. I've not heard of one failing, although I've no doubt it has happened on occasion (everything fails sooner or later!).

Just my two cents worth!:)


I've got to agree Tony. Having done a couple of Sydney Hobarts and hung on for dear life with one hand while trying to hank on a new sail with the other while also trying to stop the one that I've taken down flying off over the side with whatever spare appendage I can utilise, then spending a year cruising with the luxury of a furling headsail before doing the hanked on headsail thing all over again for six weeks up the Red Sea and a few months in the Med……..sheesh!!!

It can be difficult enough changing down or dousing a hanked on sail before the weather gets up when you are on your own, but when you need to do it in a sloppy sea it quickly looses its element of "excitement".

What I did find particularly different with a furling headsail when crusing is that I had no trouble reefing early and reefing often because it was particularly easy to shake out afterwards.

The problem with the hanked on sails was that I tended to "think about it" often a bit too long and too late because of the effort involved in dragging out a new smaller sail from below, get it up on deck, hanked on, drag the lazy sheet around for the new sail, raise it outside the current one, douse the old one, tie it up before it lets loose over the side, drag the new lazy sheet back around the other side and reverse it all an hour later when the expected blow doesn't materialise. And when you do leave it too long……well between getting soaked, bucked off the bow, loosing fingernails grasping at flogging sails, banging your knees and elbows and hips on rails, deck and hatch, getting smacked around the head with flying sheets and shackles, chipping your teeth by chomping down too hard on the mini mag light in your gob when you bounce of the deck, cursing yourself for leaving it too late or your mate for not waking you earlier, you spend most of the time wishing you had a furling headsail.:o My two bobs worth as well:o

[PeterSibley]

I'm listening , you're getting more and more convincing .:D:o

[Ed Burnett]

I've got to agree Tony. Having done a couple of Sydney Hobarts and hung on for dear life with one hand while trying to hank on a new sail with the other while also trying to stop the one that I've taken down flying off over the side with whatever spare appendage I can utilise, then spending a year cruising with the luxury of a furling headsail before doing the hanked on headsail thing all over again for six weeks up the Red Sea and a few months in the Med……..sheesh!!!

It can be difficult enough changing down or dousing a hanked on sail before the weather gets up when you are on your own, but when you need to do it in a sloppy sea it quickly looses its element of "excitement".

What I did find particularly different with a furling headsail when crusing is that I had no trouble reefing early and reefing often because it was particularly easy to shake out afterwards.

The problem with the hanked on sails was that I tended to "think about it" often a bit too long and too late because of the effort involved in dragging out a new smaller sail from below, get it up on deck, hanked on, drag the lazy sheet around for the new sail, raise it outside the current one, douse the old one, tie it up before it lets loose over the side, drag the new lazy sheet back around the other side and reverse it all an hour later when the expected blow doesn't materialise. And when you do leave it too long……well between getting soaked, bucked off the bow, loosing fingernails grasping at flogging sails, banging your knees and elbows and hips on rails, deck and hatch, getting smacked around the head with flying sheets and shackles, chipping your teeth by chomping down too hard on the mini mag light in your gob when you bounce of the deck, cursing yourself for leaving it too late or your mate for not waking you earlier, you spend most of the time wishing you had a furling headsail.:o My two bobs worth as well:o

Dont' forget guys, that we are not talking about a bermudian sloop here. The arguments all change once you change the rig configuration.

Firstly, Peter's staysail will be probably hardly ever be changed. It may have a reef in it, but otherwise it's either up or down and will most likely live on it's stay. It's small enough and should be built strongly enough to deal with most conditions (certainly more than your average roller reefing genny would be), and when it does come to changing it down for some sort of serious storm staysail, I would far rather be dealing with a hanked sail then some sort of wretched headfoil!

The jib is a rather different kettle of fish. There are any number of options for handling it, but one thing for sure is that you don't want to be playing games on the end of that bowsprit. Whatever system is adopted will involve a ring traveller on the spar so the whole shooting match can be handled on the foredeck, and that rules out a fixed roller reefing system. Roller furling (Wykeham Martin or modern equivalent) is a very likely option, but that's as far as it goes.

[Andrew Craig-Bennett]

Ed is right.

Just for the record, Mirelle's staysail gets hanked on at the start of the season and unhanked when she is laid up. It has a sail cover. It is dropped when the tow foresail is set but it is not un-hanked; it sits at the foot of the stay.

It has two rows of reef points; the second set got used once...

I personally quite like the Wykeham Martin furler, and change jibs using it, but its not essential.

To expand on this, one of the main attractions of the gaff cutter rig, to me, is the ease of handling headsails. No fighting large acreages of Dacron, no huffing and puffing with two speed winches, etc.

I usually drop the mooring with just the jib, unrolled on the Wkyeham Martin furler, and set the staysail once we are clear of everything and don't need a good view forward; likewise when entering a port or a creek with a lot of moorings or going to anchor I stow the staysail early. The jib does in fact have a pair of simple Murray bottom action winches but it does not really need them.

[PeterSibley]

The Wykeham Martin seems quite workable , what are the modern equivalents Ed ?

[PeterSibley]

Thanks Andrew , we must have posted simultaneously .The Wykeham Martin gear is a bit rare over here ,how do you furl the jib as the breeze increases , run off and shield the jib with the main ? Is it easy to clip on a smaller jib under these conditions ?

[Andrew Craig-Bennett]

The Wykeham Martin seems quite workable , what are the modern equivalents Ed ?

"The replacement for a DC3 is another DC3"!;)

The replacement for a Wykeham Martin gear is a Wykeham Martin gear!

The practical issue with a W/M gear on a bowsprit traveller is keeping the furling line taut as you bring the traveller in - not impossible to do, espescially if you use the furler line as the inhaul.

Remember that you need to keep the jib halyard blocks separated on the mast - though using braided rope helps.

[Ed Burnett]

The Wykeham Martin seems quite workable , what are the modern equivalents Ed ?

Facnor do quite a nice one: http://www.facnor.com/uk/main.asp?url=http://www.facnor.com/uk/products/gennaker__code_0_furlers/default.asp and there are others.

It is fun to see the old way of doing things being re-invented and developed with modern materials. The look of the modern versions is rather different of course (and the price isn't the same either...), but there is no doubt that the bearings are better and the modern luff ropes are a nice alternative to stiff wire when it comes to stowing the sail.

With that said however, the good old WM gear works just fine providing you follow the rules.

The over-riding benefit of these systems is that when it goes wrong you still have the option of running the bowsprit traveller in and lowering the whole lot onto the foredeck.

[PeterSibley]

I just had a look at the Classic Marine site , there's a photo of a WM furler there but rather a small one .I'm assuming that it is essentially a bearing assembly with what looks like bicycle steering head bearings (?) top and bottom plus a line furling drum at the bottom .

The bearings look very light ! But they are recommended above by Andrew and Ed so they must be OK .
That said, a couple of taper rollers would be nice .

Is there anymore to it ? Am I missing anything ?

[Andrew Craig-Bennett]

Mirelle has a Size 4 (from Classic Marine, long ago) which is overkill but better too large than too small. Jib luff wire is 8mm.

Since these are pretty much indestructible they are another item
which you can just leave an Ebay search running for and/or prowl the boat jumbles.

[PeterSibley]

Thanks to the search function ,all my questions are answered here .http://www.woodenboat.com/forum/showthread.php?t=43700

[PeterSibley]

Thanks Andrew , you answered most questions on the thread I noted .The continuous Ebay search would be a very good idea , in the UK though .It would be fruitless here .

[Andrew Craig-Bennett]

A thought: in a cruising boat, I like to have the boom quite well steeved up, for two reasons - firstly it is much less inclined to drag in the sea when running and secondly it won't brain anyone standing in the cockpit in a gybe.

I was lucky in that when I went to Gayle Heard for a mainsail he built this in without my asking for it. I noticed when Tom Cunliffe's book came out that he also recommends it.

[Don Kurylko]

Andrew, what is the sail area of the jib you are using. Just curious.

[Andrew Craig-Bennett]

"'bout a hundred and summat" ...

Scotch cut, heavy oil and ochre dressed cotton/Dacron mixture; 9" panels.

[PeterSibley]

Tony , it looks as if a furler would be unusable with this rig anyway but .....the thought of a failure gives me the shudders !

[Ed Burnett]

My little gaffer does have a bowsprit (about 3 feet long!:p) and it does have a furler on the end, which works fine in the enclosed waters of Sydney Harbour. Peter's boat will be a much larger and more substantial proposition, so the tried-and-tested set-up used by generations of English working craft I'm sure will be the ticket (although a furler on the staysail might be just as good as a Wykeham Martin furler!;)). The point that I was trying to make to Peter is that his distrust of furlers is, I think, misplaced.

That is all perfectly valid comment. A lot of this does come down to personal preference (influenced by sometimes unpleasant experience!), but it is also important to evaluate each sail and each rig in the context of the whole boat and the way in which she will be sailed.

For example, Tony's boat, being small and with a short bowsprit sounds like she might have just the one headsail. The bowsprit is short enough to be able to reach the end of it relatively easily. So, all in all, a nice neat furler sounds just the job. Quick, convenient and not too huge a drama if it goes wrong.

Peter's somewhat larger cutter however brings a few more considerations into the reckoning. The main difference is that with her two headsails, one can usually manage things so handling the staysail is a pretty leisurely affair. The boat will balance and manoeuvre well with just jib and main, so when leaving and entering harbours etc. the staysail can be stowed. One less set of sheets to handle, a slightly depowered rig, a good view forward and a nice clear foredeck for playing with anchors or whatever. In other words, just the sort of versatility that drives one to split a rig into smaller sails in the first place. Given these thoughts the roller on the staysail doesn't really achieve as much as it would in a sloop, and bearing in mind my earlier comments above, the balance (in my view at least) shifts towards a hanked sail.

The jib on a cutter of 30' and up does start to require a bit more thought. It is extremely important in getting the boat to sail at all well, but I try to to make them as independant of the rest of the rig as possible in terms of structure at least. In essence, you want to be able to lose it and still have a workable and strong inboard rig. When sailing around in harbours, jib and main is great. In stronger winds offshore however, it is really nice to be able to get the emphasis off the jib and shorten sail to a reefed main and a nice strong staysail. Most of these boats need some sort of jib (just a little one) to be able to work to windward in a blow if there is any sea running, but it's nice if the heavy jib can be just a little thing which holds the nose of the boat steady, with most of the sail area and drive coming from the main and staysail. At the opposite end of the weather scale, there is nothing like a really big light yankee jib to get the boat going in light airs.

Given half a chance, I will specify three different jibs for a boat like this. Two is workable (ditch the big yankee first and make the working jib a little larger), but it's hard to see how one sail set on some kind of roller reefing gear could be expected to cover all three jobs. There is also the problem of the roller gear itself, which with its fixed length foil becomes a permanant installation at the end of the bowsprit. Even if it always operates perfectly, that hugely complicates changing sails, not to mention running in the bowsprit. So, we come back to setting the sail on a bowsprit traveller. There might be some kind of running forestay to which it is hanked (Dyarchy style), or it could be set flying. The Wykeham Martin gear is simply a means of getting a sail set flying to roll around it's own luff - you retain the ability to drop it in the normal way if it doesn't roll properly (which does happen in certain circumstances).

All good fun to think about, but the important thing to recognise is that the variety in boats in general goes all the way through the boat. In other words, there isn't much point chosing one rig configuration (for whatever reason) and then applying the same approach to gear and handling that you would for something totally different. The best arrangements are those that are appropriate for the boat and the way in which she will be sailed. That doesn't mean one has to be a stick in the mud and always follow what might be parroted as the "right" way of setting things up. Quite the opposite in fact, as it encourages one to think freely and adopt or devise solutions that work for the case in hand, bearing in mind all the various considerations. There are a huge number of solutions out there that one can draw inspiration from.

[Eric D]

Thank you Ed, Peter, MMD and all, truly inspiring to read, bit over my head here and there, but it is forcing me to "learn outside my box".

Have a great weekend guys, keep it up, loving this thread.

[Don Kurylko]

Awhile back, just for fun, I made up this reefing sequence diagram for a topmast cutter. It’s a cartoon really, but it does help illustrate some (though by no means all) of the sail combinations possible with this rig. The boat shown is 34’ LOD, 29’ DWL, 8 tons displacement (half load). It’s similar in size to Andrew’s Mirelle, but with a harder turn to the bilge than the MM type being discussed.

The numbers in green denote sail areas. There is also a light air sails cartoon, if anyone is interested.

http://www.dhkurylko-yachtdesign.com/archive/Reef%20Sequence.jpg

[PeterSibley]

Thanks Don ,I've saved that ! I have to say I've drawn all of the above but without the assurance you display !

[Don Kurylko]

Auto-Cad, easy peasy! :D

[floatingkiwi]

Awhile back, just for fun, I made up this reefing sequence diagram for a topmast cutter. It’s a cartoon really, but it does help illustrate some (though by no means all) of the sail combinations possible with this rig. The boat shown is 34’ LOD, 29’ DWL, 8 tons displacement (half load). It’s similar in size to Andrew’s Mirelle, but with a harder turn to the bilge than the MM type being discussed.

The numbers in green denote sail areas. There is also a light air sails cartoon, if anyone is interested.

http://www.dhkurylko-yachtdesign.com/archive/Reef%20Sequence.jpg
Is the dot in the sails the CE (or centre of effort)?

[Don Kurylko]

No, just sail areas. CE's, CLR's, etc., are on the master drawing. It's very cluttered. My intent with this series was to just play with the sail combinations to get a feel for the rig. Nothing more than a visual aid really. I just thought it might be useful for viewers unfamiliar with a "traditional" cutter rig. Not much of a contribution to the discussion, I'm afraid.

[PeterSibley]

Auto-Cad, easy peasy! :D

Ahhh ! jealousy !:D

I have a very good 2H pencil ,rule and battens .Slow , but I know how to drive them !:D

[Andrew Craig-Bennett]

That drawing will do very well for Mirelle.

I prefer to reef the staysail early on, and to keep a small jib on the bowsprit. This little sail does very little to achieve forward motion but it certainly helps to keep control of the boat. The staysail on the other hand is a driving sail, and reefing it helps a lot.

I've never yet run the bowsprit in at sea, but no doubt the day will come.

In general by the time I get round to reefing the staysail I will be thinking of heaving to, if I've got water to do so.

I agree with the choice of a gaff trysail; it's hopeless trying to get a gaff cutter to stay through the wind with a pointy headed trysail.

The worst job by far is getting the mainsail off her. Headsails are easy of you run her off whilst working on the foredeck.

Actually Mirelle has one other condition - a very handy one - she will lie-to under close reefed staysail only.

[PeterSibley]

Andrew , how close is Mirelle's underwater profile to my drawing ?

More vertical sternpost ? More or less forefoot ?

[Andrew Craig-Bennett]

About the same, but being an East Coast of England boat drawn to a limited draft she has a little less drag to the keel.

[Don Kurylko]

Thanks for the comments Andrew. I expect each boat will have its preferred sail combinations, to be discovered in actual practice on the water in real conditions. I am hoping that my cutter will also be handy under staysail alone, but, with a cutaway forefoot, I’m not so sure. We shall see once she gets launched.

I too think that a gaff trysail is a good choice, even though it may be harder to rig than a jib header. And I have often wondered if a lug trysail would work. It might be simpler to rig than a gaff, but it might be harder to control in a blow. I thought I saw a photo once of Taberlay’s Fife with a small passage making lugsail rigged in lieu of the large main. It seemed very handy.

[Andrew Craig-Bennett]

Actually, Don, I reckon its the cutaway forefoot that allows my boat to get away with it! Sheet the foresail in hard to leeward and lash the helm half down and she seems to settle very happily with the forebody skidding to leeward every time she wants to luff. We end up with the one knot square drift which is what I reckon you want when hove-to.

I thought Pen Duick had a gaff trysail and made passages under that.

[Don Kurylko]

I hope that trick with the staysail will work for me. It’s going to be fun learning the secrets of a new boat.

I was sure it was a photo of Pen Duick in Classic Boat magazine, but I have not since come across it again. I could be wrong. It was years ago and …………………...............................… what was I saying again? :D

By the way, what is your current sail inventory, if you don't mind my asking? And what would be your "dream" inventory if you could go out and order it today?

[Andrew Craig-Bennett]

Could have been a bust gaff jaw - it produces a lug-like effect! :D

[Don Kurylko]

Okay, now I'm going to have to go through all those back issues! :p

[Andrew Craig-Bennett]

I hope that trick with the staysail will work for me. It’s going to be fun learning the secrets of a new boat.

I was sure it was a photo of Pen Duick in Classic Boat magazine, but I have not since come across it again. I could be wrong. It was years ago and …………………...............................… what was I saying again? :D

By the way, what is your current sail inventory, if you don't mind my asking? And what would be your "dream" inventory if you could go out and order it today?

Mainsail, boom staysail with two rows of reef points, working jib and spitfire jib (both fitted for use on Wykeham Martin gear) - all heavy oil ochre dressed cotton.

Jackyard topsail, tow foresail, 7 oz blue Dacron

Light big jib - 4oz dacron
Three cornered trysail - dacron

I would like two sails:

A conventional staysail (not on a boom) of the same material as the working sails

A gaff trysail

[Don Kurylko]

Huh, interesting. No desire or need for light air sails, like a big Yankee, asymmetrical spinnaker or light drifter?

Thanks Andrew - something to ponder. Would you care to expound on Mirelle’s sailing characteristics?

[PeterSibley]

That would be interesting Andrew , should you have the time ....

[Andrew Craig-Bennett]

How to describe the behaviour under sail of my beloved boat?
Well, the first word that comes to mind is “docile”.
In 25 years we’ve seldom missed stays – the occasions when we have done have usually been when over-reefed in lumpy stuff.
New helmsmen take a firm grip of the substantial ash tiller, rather like a batsman about to face fast bowling; then they say “Isn’t she nice!” and steer with two fingers.
A little fiddling with the inside ballast will trim out the helm balance to neutral, which is undesirable, so I leave slight weather helm, enough to do the “party trick” of “Look Mummy, no hands!” going to windward on the starboard tack (because the drag of the fixed three blade prop to port counteracts the weather helm).
Wooden rudder stock and wooden gaff jaws mean that in light stuff we go everywhere to a “Hollywood sound track” of creaks, groans, and, when at anchor in wind over tide, loud banging noises! On the other hand we very seldom get water over the deck in bouncier conditions, and you can stay dry at the helm.
Gybing is interesting; she sort of asks, “Do you really want me to do this?” before the helm goes dead, which is a couple of very long seconds before the boom goes over, at which point you do need to be firm in applying counter-helm to stop the luff.
Under power, she is, frankly, a swine. Not enough horses, and a lot of windage, forward, so if motoring into a stiff headwind the bow can blow off; in this event the only way to recover is to do a swift 360 and pray you have room! All three owners have disliked this. Going alongside port side to is usually disastrous – a slight touch astern to stop her causes the stern to leap six feet sideways off the quay just as you were thinking of getting a line ashore. Starboard side to, we can do.
Running in a sea, she will get a little twitchy, but I’ve never thought that she might actually broach.
Beating in a sea, frankly, we need to tack through at least 110 degrees – the old smack rule of “Stand, facing ahead, and then look over your shoulder to see where you’ll go!” applies.
Going to windward I usually lash the helm and leave her to get on with it. She does it at least as well as I do; probably better.
Like all gaff cutters, we like reaching, but we really, really, like it, and pass all sorts of boats when doing so. This is probably because the tiller is not half across the weather deck like on some boats I could name…

[PeterSibley]

Interesting Andrew , it sounds as if she is a joy to sail and the moveable ballast is very worthwhile for trimming ! But motoring is to be avoided , I can see why you enthuse about a double prop setup .How many hp does Mirelle have ? I have a 20hp engine and know it's insufficient but would like to get by with less !

[Andrew Craig-Bennett]

The little Volvo had 15 hp when it was young; frankly I doubt if we see more than ten ponypower out of it now - good for all of three knots in a calm.

[PeterSibley]

That pretty miserable Andrew , what would be ideal ? I'm at the stage were such things are a lot easier .

[Andrew Craig-Bennett]

Well, a lot more horses!

My real limiting factor is propeller diameter - 14".

I don't know what hp one could usefully put through a 14" diameter prop at low hull speeds.

It is something that I should find out, in relation to standard engines and gearboxes.

My interest in hydraulic systems stems from this. Two props, twice the possible power.

I don't see another way to get say 4hp per ton of displacement.

[PeterSibley]

45 hp ! That's quite a lot of engine ,but as it happens I have quite a good 4 cylinder Isuzu in an old ute , the vehicle is a little sad but the engine is excellent .The reason I've not really considered it is that it requires a glow plug start , probably the norm for everything these days but the Bukh doesn't .A glow plug and a big engine means the batteries must be fully charged ,something of a challenge on a boat ...says I from experience !

Did you see my thoughts on 2 gearboxes powered by one engine Andrew ? It sounds a little weird but I really see no reason why it wouldn't work well ....that would give you 2x14" props .Bespoke engineering in Ed's words but a solution that I could build without too much trouble , the modern toothed belts are very ,very good .

[Don Kurylko]

Thanks for that Andrew. Mirelle sounds a treat to sail. I can see why you love her. Can you comment a bit about light air performance and the sails you use?

[Andrew Craig-Bennett]

In light airs, it is just a case of "hang out more kites!"

Jackyard topsail, then if slightly free of the wind the tow foresail (reaching staysail) and in very light stuff we have a jib that fills the fore triangle. Have to be careful with this one, though, as there is no masthead preventer backstay.

We will probably sling a jib under the boom as a watersail ifracing in light airs (it gives the crew something to do...)

Edited to add - I forgot a couple of light nylon spinnaker cloth drifters, which come in very handy - one stands in for the tow foresail when the wind won't fill that and the other one stands in for the jib - but they both MUST come down at the top of F1 or they will be ruined - having no hanks they drop easily.

They are not any bigger than the other sails but they find a wind where the heavy sails don't.

We can carry the tow foresail up to the top of F4 on a reach, or F3 on a very close reach (it can sheet inside the shrouds, but, since it is not a heavy genoa, one needs to exercise self discipline with it or it will lose its shape)

[Ed Burnett]

Sounds like Andrew's engine has seen better days, or that the prop doesn't match it very well, or quite probably both (ie. the prop used to match the engine but doesn't any more).

It takes a surprisingly small amount of power to move a heavy boat well in flat water, but this does require the installation to be efficiently worked out. That means the right reduction and the right sized prop in good clean flow. Where you really start to need power is when you are pushing up into higher speed / length ratios, or into a headwind and lumpy sea.

The most efficient arrangement is a single slow turning prop. As soon as you go for twin props you loose a bit of efficiency there, and also in the more complex transmission system - particularly hydraulics.

So, if you are trying to get the best out of a small engine, go for a relatively large reduction ratio and have a nice big prop on the quarter. If you don't mind not being able to stop, make it a folding prop to reduce drag under sail, and then you can make the prop diameter even bigger with little drag penalty. If you do need stopping power, then you have to spend a bit more on a feathering prop or accept the (rather seriously depressing) drag of fixed blades.

For your information Andrew, a 14" three bladed prop can soak up about 20hp at a shaft speed of 1450 rpm. Pushing up to 25hp would require a shaft speed in the region of 1600 rpm, which is getting pretty quick.

[Andrew Craig-Bennett]

Thank you very much indeed, Ed.

To be honest, I have stuck with a 42 year old engine for far too long, because I always find some other part of the boat to spend the money on (if I could get away with it, I would have no engine).

All it has to do is to charge the battery for the navigation lights and put me on the mooring in a calm.

However, I have had a daydream of an hydraulic set up for years, because the "received wisdom" is 4hp per ton, and I cant see any other way to get that.

The stern installation belongs to the original 1937 Kelvin E2 (7.5hp) which had a 14" two blade folding prop; it now has a 15 x 10 three blade fixed prop which comes within half an inch of the planking. I can't fit a bigger prop or we are into the rudder, unless I make a new shaft log, etc.

So I think I need to stick to 14" diameter, and obviously fit a folder and look for a 20hp engine...

Thanks very much

Andrew

[Ed Burnett]

Based on the way it sounds like you use the boat Andrew, I would think 20hp would be fine if you can get most of it into the water.

One of the UK firms that puts together twin screw hydraulic drive setups acknowledged that having tested it they find they lose around 25% of the power in the transmission system. Coupled with the additional losses from two props rather than one I really do feel that you have to want to do a lot of going round in tight circles to make it worth it.

Have you seen these?: http://www.kiwiprops.co.nz/ Looks like a good and cost effective solution for a wing installation. A two bladed folding prop will require greater diameter, or given your restriction on this, higher shaft speed.

[Andrew Craig-Bennett]

Thanks again, Ed. I hadn't seen those - they look like a neat answer, given that I can't shift the blades much aft to fold.

Dunno about their restriction on mud berths, though!

I am now having a rethink about whether I can get away with 20hp.

[PeterSibley]

I sail with friend who has an 18" 3 blade fixed prop , it's a horror ! He has finally found an 18" feathering prop at a price he can afford .I'm looking forward to it !

edited to add .... the one he has bought is from the company you linked Ed , http://www.kiwiprops.co.nz/

[Andrew Craig-Bennett]

Their smallest size is 15.5" diameter so I will have to have a careful look to see if we can shoehorn one in. They do say the tip clearance matters less with their design.

[Ed Burnett]

Their smallest size is 15.5" diameter so I will have to have a careful look to see if we can shoehorn one in. They do say the tip clearance matters less with their design.

Hmm. You might ask if they could trim a bit off the tips for you.... Tip clearance is a variable feast anyway. 10% of prop diameter is the usually stated minimum, 15% is nice, but I have known far less to be ok, particularly when the clearance is to a solid piece of timber.

Otherwise, watch the tips don't catch on the hull further forward when the blades are swung around into their astern position. Not sure how big an issue this is with the Kiwi prop.

The amount of power installed in boats has increased generally of the years. I suspect this is partly due to the shift to smaller and faster reving props (being less efficient), but it more likely reflects the modern desire to get where one is going at an earlier and more predictable time.

Very approximately, it might take twice the power to drive a displacement hull at a S/L ratio of 1.4 than it does to get to S/L of 1.2. For a 28' waterline that is the difference between 6.3 and 7.4 knots. Frequently these days, people also expect to have sufficient reserve of power to be able to continue at near hull speed into a headwind and sea. If you don't want to go that fast under power, and like to slow down a bit when it gets nasty anyway, a relatively small engine can be just fine. Pick one with modest maximum revs however, as you will be living with it running at nearer it's maximum power when cruising.

[PeterSibley]

"Pick one with modest maximum revs however, as you will be living with it running at nearer it's maximum power when cruising".

That seems to be the nub of it .The boat I mentioned above has a Yanmar 20 hp ,a Lister clone from the early 60s IIRC ,it moves the boat along at 5 knots at 900 rpm ,max around 1400 ,not that I've ever heard it at such astronomical speeds .Such engines are just not available now .My Bukh gives 20hp ,but at 3000 rpm .I haven't got a hp graph but at 2200 I would probably be down to 13 or so .More than 2200 and I start to feel uncomfortable .That is the main advantage of a larger engine , you can operate at reasonably low rpm and still move along ....not good for the engine , but better for your nerves .

[Andrew Craig-Bennett]

Hmm. You might ask if they could trim a bit off the tips for you.... Tip clearance is a variable feast anyway. 10% of prop diameter is the usually stated minimum, 15% is nice, but I have known far less to be ok, particularly when the clearance is to a solid piece of timber.

Otherwise, watch the tips don't catch on the hull further forward when the blades are swung around into their astern position. Not sure how big an issue this is with the Kiwi prop.

The amount of power installed in boats has increased generally of the years. I suspect this is partly due to the shift to smaller and faster reving props (being less efficient), but it more likely reflects the modern desire to get where one is going at an earlier and more predictable time.

Very approximately, it might take twice the power to drive a displacement hull at a S/L ratio of 1.4 than it does to get to S/L of 1.2. For a 28' waterline that is the difference between 6.3 and 7.4 knots. Frequently these days, people also expect to have sufficient reserve of power to be able to continue at near hull speed into a headwind and sea. If you don't want to go that fast under power, and like to slow down a bit when it gets nasty anyway, a relatively small engine can be just fine. Pick one with modest maximum revs however, as you will be living with it running at nearer it's maximum power when cruising.

Thank you very much, Ed.

You are quietly converting the "new engine project" from the wilder shores of pipe dream at around £12,000 for twin screws and hydraulics to possible practicality at half that.

The one time when I really, really, want an engine is to be able to punch over the Deben and Alde bars against a flood tide and a sea breeze (the two have a habit of occurring together, of course!)

Five knots would do that, comfortably, allowing 20% for seamargin, so an S/L of 1.2 is enough, so 20hp does the job (?)

[Ed Burnett]

Well, 3000 rpm isn't much for a modern diesel. Most now rev to 3600 or so, so I would be inclined to take the 3000!

The Kubota based marinisations (such as Beta and Nanni) seem to be a pretty good option these days, but even in these you have to be up around the 40hp mark before the revs drop from 3600 to 3000.

One thing about fitting an overly powerful engine is that you will tend to match the prop to near the maximum output (or there isn't much point). Fixed pitch props have a power absobtion curve that is very different to the power production curve of the engine. In essence, at say half revs, the engine may be capable of developing around 60% of its maximum power, but the prop will only be demanding 10% or so. This is why underloading of engines can be an issue.

It also further illustrates the point that it takes very modest power to move a displacement hull at modest speed - compare boat speeds at half and full throttle, and bear in mind that the actual ratio of delivered power is closer to 1:10.

[Ed Burnett]

Five knots would do that, comfortably, allowing 20% for seamargin, so an S/L of 1.2 is enough, so 20hp does the job (?)

Well, the one thing we don't know is how much power it takes to move Mirelle at five knots. So far we have been speaking in relative terms.

My gut feeling is that 20hp, efficiently delivered, ought to get you over five knots, but this really is just a gut feeling.

[Andrew Craig-Bennett]

My boat spends the winters in Robertsons Boatyard, which, thanks to Peter Norris, is a Nanni State, so I was thinking of the 21hp Nanni, espescially as it comes with a 70amp alternator as standard (option on the Beta)

[Andrew Craig-Bennett]

Well, the one thing we don't know is how much power it takes to move Mirelle at five knots. So far we have been speaking in relative terms.

My gut feeling is that 20hp, efficiently delivered, ought to get you over five knots, but this really is just a gut feeling.

I'll take that.:)

I see the Kiwiprop can have the blade angles fiddled with to adjust the pitch, which may help.

The variances are probably down to the owner keeping the bottom clean and I can usually motorsail to some degree over the bars.

[Andrew Craig-Bennett]

Well, 3000 rpm isn't much for a modern diesel. Most now rev to 3600 or so, so I would be inclined to take the 3000!

The Kubota based marinisations (such as Beta and Nanni) seem to be a pretty good option these days, but even in these you have to be up around the 40hp mark before the revs drop from 3600 to 3000.

One thing about fitting an overly powerful engine is that you will tend to match the prop to near the maximum output (or there isn't much point). Fixed pitch props have a power absobtion curve that is very different to the power production curve of the engine. In essence, at say half revs, the engine may be capable of developing around 60% of its maximum power, but the prop will only be demanding 10% or so. This is why underloading of engines can be an issue.

It also further illustrates the point that it takes very modest power to move a displacement hull at modest speed - compare boat speeds at half and full throttle, and bear in mind that the actual ratio of delivered power is closer to 1:10.

Very good point.

I "know" that in relation to ships, which are my day job, but I have tended to forget it when playing boats! ;)

[Andrew Craig-Bennett]

Hmm. You might ask if they could trim a bit off the tips for you.... Tip clearance is a variable feast anyway. 10% of prop diameter is the usually stated minimum, 15% is nice, but I have known far less to be ok, particularly when the clearance is to a solid piece of timber.

There's a good 5/8" between the 15 incher and the sternpost! As you rightly say, it does not seem to cause any trouble.


Otherwise, watch the tips don't catch on the hull further forward when the blades are swung around into their astern position. Not sure how big an issue this is with the Kiwi prop.



I recall that it scuppered an earlier plan of mine involving a Bruntons Autoprop.

[Ed Burnett]

It is perhaps the case Andrew that you are somewhat limited in what you can achieve anyway. If the most you can expect a single prop to soak up is 20hp, then the performance from 20hp is all you are going to get!

The alternative, as you have found, would be to install very much more power (as in 2 times as much) to make up for the various inefficiencies of the hydraulic twin prop option and achieve marginally better real performance.

[Andrew Craig-Bennett]

RIP the twin screw hydraulic drive... it's not worth spending that much money, weight, and space on something that gets used very little (I find I use 20-30 litres of diesel per year in the boat...)

This isn't really a hijack of Peter's thread, as he is thinking of the same issues - I was just trespassing on Ed's good nature! :)

Thanks!

[PeterSibley]

Andrew , i'm very pleased to see you expand on these issues and if Ed is good enough to off advice ...go for it !

[PeterSibley]

Well, 3000 rpm isn't much for a modern diesel. Most now rev to 3600 or so, so I would be inclined to take the 3000!

The Kubota based marinisations (such as Beta and Nanni) seem to be a pretty good option these days, but even in these you have to be up around the 40hp mark before the revs drop from 3600 to 3000.

One thing about fitting an overly powerful engine is that you will tend to match the prop to near the maximum output (or there isn't much point). Fixed pitch props have a power absobtion curve that is very different to the power production curve of the engine. In essence, at say half revs, the engine may be capable of developing around 60% of its maximum power, but the prop will only be demanding 10% or so. This is why underloading of engines can be an issue.

It also further illustrates the point that it takes very modest power to move a displacement hull at modest speed - compare boat speeds at half and full throttle, and bear in mind that the actual ratio of delivered power is closer to 1:10.

Ed , could I ask you to expand on the highlighted section ? Are you saying that a prop that can use 20 hp at say 1350 shaft speed might only need 2 or 3 hp at 800 ? Or have I misunderstood ?

What are the effects of underloading a diesel for long periods ,long being relative in a yacht ! An 8 hour motor is a marathon !

[Ed Burnett]

Ok then, a quick aside on props.

The first thing I should do is point out that propeller theory and design is a very large subject. What follows applies to slow speed boats, and what most of us would view as "normal" props with fixed (as opposed to controllable or variable) pitch. It is valid for folding and feathering props, but not the Brunton AutoProp jobs. There is plenty more that could be said.

The solid line in the graph below shows the power curve for a natually aspirated diesel:

http://www.burnettyachtdesign.co.uk/images/power_000.jpg

Max rpm is 2800, at which the engine is capable of developing something like 43hp. A little further to the left, at say 1800 rpm, you can see that the engine is capable of developing around 33hp. If you were running it out of gear however, it wouldn't be developing anything like this amount of power as it would only have to overcome its own resistance.

That last point sets the precedent for what is going on with the prop. The broken line on the graph shows the amount of power it takes to turn the propeller (this is an exponential curve, the exponent is commonly around 3). The diameter and pitch of the prop in this case has been determined so that at 2800rpm, it is absorbing 43hp. The prop has been "matched" to the engine's power curve at the maximum rpm.

So, at full revs, everything is great. The engine is developing its full power and all of this is being soaked up by the prop, which if it is a good one will be converting about 55% of it into thrust. Throttle back to 1800 rpm however and things are different. Sure, the engine can develop 33hp or so, but it only takes about 13hp to turn the prop at this speed, so that is all it can extract from the engine, and 55% of that is all it can put into the water.

Essentially, the engine is not being fully loaded at anything other than full rpm.

The prop can be matched to any point on the power curve, but only one point. Reduce revs from the point at which engine and prop are matched and each will follow back down its own curve. It is pretty common to match a prop to a little less than full rpm so you can be sure you are getting most of what the engine can deliver. For example, looking at the engine power curve there isn't much increase in power from 2600 to 2800 rpm, so you might choose to aim for a match at 2600 to be sure the boat isn't under propped. (If underpropped, at the maximum revs the prop still wouldn't be able to soak up the full power of the engine, so that potential performance is wasted).

I am not an expert on diesel engines, so am not the best qualified to say what effect the underloading would have. Opinions do vary - some say the results are dire, some say it isn't a problem. The reality most likely varies by degrees depending on the specific circumstances in each case.

Either way, this all further serves to illustrate that going for a slightly smaller engine will not result in so large a drop in performance as one might think - at least in flat water. As discussed, it is when the resistance goes up due to wind and waves that the reserve of power becomes necessary to maintain the same speed.

Incidentally, the prop curve also has a bearing on fuel consumption. Frequently, the consumption figures quoted for an engine are based on it's maximum output at a range of speeds. The more accurate (and substantially more econmical) assesment comes from applying the specific fuel consumption (gallons per hp per hour) to the prop power curve.

[PeterSibley]

Thank you Ed ! ...very informative .I'll C&P that to email to a friend of mine trying to work out just those questions .

The heart's desire would be a prop that matches the engine curve a bit more closely than the graph .

[Ed Burnett]

The heart's desire would be a prop that matches the engine curve a bit more closely than the graph .

Well, that's the idea with a controllable pitch prop, and the Brunton AutoProp aims to do it automatically.

[Andrew Craig-Bennett]

http://www.bruntons-propellers.com/index.htm

Excellent bit of kit; made in the (otherwise less than lovely) town that I grew up in! Bruntons are part of the international group that makes most of the world's big ship propellers.

Merchant ships that are fitted with variable pitch propellers, usually ships like ferries and tugs, have "pitch combinators" which gear the propeller pitch to the engine rpm and fuel settings, as, otherwise, it would be horribly easy to overload the engine

[Ed Burnett]

Merchant ships that are fitted with variable pitch propellers, usually ships like ferries and tugs, have "pitch combinators" which gear the propeller pitch to the engine rpm and fuel settings, as, otherwise, it would be horribly easy to overload the engine

That is interesting Andrew.

The theory with variable pitch is that you always have the "right" prop. Incorrectly used however, the more likely reality is that you always have the wrong prop!

[PeterSibley]

That is interesting Andrew.

The theory with variable pitch is that you always have the "right" prop. Incorrectly used however, the more likely reality is that you always have the wrong prop!
True , but it looks from your graph as though for anything but a very narrow rev range we all always have the wrong prop . Disconcerting !

Either way some form of feathering prop looks as thought it will be the choice .A fixed 3 blade is for launchs only !

[dhic001]

If I may be allowed a little space on this thread... I know you guys are talking side mounted props, but just incase anyone is reading who has a centreline shaft, beware of changing from an old slow revving engine to a new fast revving one. As you all know, most wooden boats have a fairly solid sternpost and rudder, which limits the amount of water getting to a centreline prop. The brigantine Breeze has a very large sternpost and rudder, with a centreline shaft. She used to have an old slow revving 60hp Lister, with a correspondingly large prop, probably not great for sailing, but effective. When the Lister needed some attention, she was fitted with a new 85hp Ford, against the advice of someone who knew Breeze extremely well. The Ford has a small prop, which just pokes its tips past the sternpost. The result is a loss of performance, 6 knots cruising under power instead of the former 10 knots the Lister gave, and god help all on board if you have to battle into a head wind!
Appologies for the drift, please feel free to resume normal service :)
Daniel

[PeterSibley]

Thanks for the input Daniel , surely it was just the wrong gearbox on the Ford ?Replace the engine but make sure to match the gear box to the original prop and old rev range ?

[Ed Burnett]

Thanks for the input Daniel , surely it was just the wrong gearbox on the Ford ?Replace the engine but make sure to match the gear box to the original prop and old rev range ?

Absolutely. Not really the fault of the engine - a larger reduction would have maintained a shaft speed and prop diameter more appropriate for the vessel. Still an entirely fixable problem if the owners wanted to look into it.

[PeterSibley]

I have to say it ! 500 posts on a discussion of an old design ...with slight metamorphosis .:)

Thank you very much to all concerned , a remarkably informative thread !

[dhic001]

Absolutely. Not really the fault of the engine - a larger reduction would have maintained a shaft speed and prop diameter more appropriate for the vessel. Still an entirely fixable problem if the owners wanted to look into it.

I don't believe a large enough reduction was available, either that or the option wasn't allowed by the powers that be. The better solution would have been a minor overhaul of the original engine. As for it being fixable now, there isn't the will to deal with minor things, let alone major ones :(
Daniel

[TomF]

I've nothing to add - except gratitude. This is a simply stunning thread, and the generosity of people like Ed, mmd etc. is jawdropping.

Thanks all.

t

[mmd]

Sorry I haven't been able to do more than drop by occasionally to read during these past few months. However, the fireboat is delivered (I'm in Portland now, finishing up the delivery paperwork & reports), then I'll have a couple more weeks of wrap-up back at the yard, and then I'll be happily unemployed for a bit. Time to find my home office, re-acquaint myself with my wife & daughter, and work on my boat for a while.

Peter, I'll look forward to discussing your proposed yacht further, especially as it takes shape under the watchful eyes of the WBF!

[PeterSibley]

A beautiful boat Tony , perhaps a little bigger than I need ! :)

Michael ,there will definitely be photos ...although I have a cabin to finish before I can get back to the boat .It's coming along pretty well though ,a few months should see it do and the boat startup again .

[Andrew Craig-Bennett]

That boat, with its utterly impractical accomodation, looks a real 1920's day dreamers' vessel.

In my opinion, a real lead mine, of the plank on edge type.

Actually the abovde deck form looks not a million miles from T. Harrison Butler's "Khamseen" design - which was smaller - 31ft? best known as Peter Tangvald's "Dorothea".

[PeterSibley]

I wouldn't be that critical Andrew , I'd like a bit more displacement aft ...the way she comes to that transom is a trifle strange .....following he midship section aft would improve things .It seems a little similar to one of the shapes I drew ....much to Ed's disaproval .:D Otherise I quite like her ....I'm sure we will find things to criticise though !:D

[Andrew Craig-Bennett]

Peter - you took the words out of my mouth - "looks like an amateur design". But she wasn't.

Since she actually was built, does anyone know what became of her.

OK, here we go:

Stern sections are much too weak.

Wall sided topsides do nothing for strength (much better with some tumblehome) and will make her as wet as a half tide rock.

Keel profile will be a stinker if you want to slip her or dry her out.

[PeterSibley]

Doing well ! :D

I agree about the bottom of the keel ... silly ! Just as easy to have something that will sit on a cradle .

I won't criticise the slab sides , I've seen it done well and I rather like the mid sections .

If she is the work of a professional designer....I'm a little surprised !