Lead and weather helm

[Duncan Gibbs]

I've been exploring this issue on the Eric Jr (http://forum.woodenboat.com/showpost.php?p=2578565&postcount=131) thread (http://forum.woodenboat.com/showthread.php?t=111226), and wanted to seek advice on aspects of tuning the rig design to ensure what James McMullen says is more weather helm than fun in a blow on Eric Jr. You'll see that I've done some drawing on the subject in the post linked to. I wanted to find out what people's thoughts are in including/not including the rudder in CLR calculations.

I would have thought that the double ender forms the CLR/CE relationship would remain reasonably static even when the boat is well heeled. But James' experience of Eric Jr says otherwise and the examples shown in that thread and on the Atkin web site show a different sail plan, as Lee Baxter pointed out in the OP of the Eric Jr thread.

If people post specific comment on the Eric Jr to that thread I would be most obliged, however this one could be used for a more general discussion of the subject.

Cheers
Duncan

[Roger Long]

The whole lead and balance thing is a crock. I posted a long diatribe about it here and other places but am too tired from working frantically on getting my boat ready to launch to go over it again. The search function should turn it up.

[Paul Pless]

The whole lead and balance thing is a crock. I posted a long diatribe about it here and other places but am too tired from working frantically on getting my boat ready to launch to go over it again. The search function should turn it up.if it looks right it probably is?

[Canoeyawl]

The whole lead and balance thing is a crock. I posted a long diatribe about it here and other places but am too tired from working frantically on getting my boat ready to launch to go over it again. The search function should turn it up.
What he said...

I took liberties with a noted design and moved the sail area forward and the center board aft (about three feet :eek:).
It sails very well. The helm is balanced in most conditions. 2° rudder angle in about 15 knots breeze with the whole rig up.
That weather helm in is like having the brakes on!
If you have real world experience sailing that design that indicates weather helm, fix it.

(I really like the Eric jr. -
I surveyed one years ago and fell in love with it, eventually it came around for sale, but by then it was in pretty rough shape so I passed)

[PeterSibley]

The whole lead and balance thing is a crock. I posted a long diatribe about it here and other places but am too tired from working frantically on getting my boat ready to launch to go over it again. The search function should turn it up.

That wasn't really the advice Ed Burnett gave me here http://forum.woodenboat.com/showthread.php?t=97232&page=7 on the MM thread , a very different hull of course .

[john welsford]

I've been exploring this issue on the Eric Jr (http://forum.woodenboat.com/showpost.php?p=2578565&postcount=131) thread (http://forum.woodenboat.com/showthread.php?t=111226), and wanted to seek advice on aspects of tuning the rig design to ensure what James McMullen says is more weather helm than fun in a blow on Eric Jr. You'll see that I've done some drawing on the subject in the post linked to. I wanted to find out what people's thoughts are in including/not including the rudder in CLR calculations.

I would have thought that the double ender forms the CLR/CE relationship would remain reasonably static even when the boat is well heeled. But James' experience of Eric Jr says otherwise and the examples shown in that thread and on the Atkin web site show a different sail plan, as Lee Baxter pointed out in the OP of the Eric Jr thread.

If people post specific comment on the Eric Jr to that thread I would be most obliged, however this one could be used for a more general discussion of the subject.

Cheers
Duncan

WHen drawing a new sailing boat hull I do a series of calcs to determine the center of bouyancy at increasing angles of heel, and graph the movement of the center to ascertain the chance in fore and aft trim, and from that the shift in lateral plane.
A boat that has a marked change in that respect ( If for some reason I dont redraw it to a less extreme shape) gets a rig placement with a bit more lead than otherwise, and a boat that is very neutral will have just enough lead to counter the assymetry in her hull as she heels.
Twin hulls, no lead, and trimarans, about 2 or 3% but that depends greatly upon the shape of the outrigger hulls.
I do find that the lead of sail area over lateral plane can make a big difference to the way the boat sails and handles, but it should not be considered in isolation as different hull shapes react very differently to different treatment in this respect, and different rigs also behave differently.

I dont use the rudder in the lateral plane calc unless its one of the occasions where I am drawing a boat with the centerboard way forward in what what will essentially be a tandem centerboarder with the after one steerable, in which case I might include up to 60% depending upon just how far forward the main board is.

Experience helps a lot. You get experience by making mistakes and fixing them.

John Welsford

[James McMullen]

The Eric Jr I sailed wasn't stricken with disastrous weather helm by any means. Probably could have just put a reef in the main to restore a little more balance if you weren't trying to go as fast as possible. And the hull of that boat is about as balanced and symmetrical of any boat you've ever seen. Please don't take my endorsement of a slightly larger foretriangle as evidence that there was anything particularly wrong with the Eric Jr--she was a fine boat to sail.

[Duncan Gibbs]

James, would you mind commenting on the proposed cabin layout alteration on the Eric Jr thread, since you've had a good deal of experience with her.

[Roger Long]

That wasn't really the advice Ed Burnett gave me ...


That's what makes someone an expert, when they can disagree with another expert about the same subject. I see someone has bumped my original discussion up. Read it and decide for yourself.

[PeterSibley]

That's what makes someone an expert, when they can disagree with another expert about the same subject. I see someone has bumped my original discussion up. Read it and decide for yourself.

I read it ,a very thoughful post and I see that things seem to vary quite a lot depending on rigs and hull type .
Seeing Ed is a designer who specialises in traditional British hulls and rigs , on my hull I'll take his advice .:)

[Ed Burnett]

So many factors to discuss, so little time to do them all justice!

I wouldn't say the whole lead and balance thing was a crock, but then it's not exactly the most sophisticated measure either. Many people do however take it to be a "rule" or "law" that has some theoretical basis. That certainly is a long way from the truth and as an approach is liable to lead to dissapiontment. Knowing the shortcomings of a method is equally as important as knowing how to apply it.

As with many things in our field, the real situation is far too complex to reduce to one simple rule, and the real mistake is to apply a rule of thumb incorrectly or beyond it's range of validity. Used with a little understanding however, rules of thumb are effectively an amalgamation of decades of accumulated knowledge that can be of great service to us. They aren't an alternative to experience - they ARE experience.

[Duncan Gibbs]

Okay then: Let's apply them to the hull shape at hand, which is the Atkin-ised Archer double-ender.

Rather than the Eric 32', which was fairly much a scaled down 'direct copy' of an Archer, the subsequent boats from Atkin's drawing board were far more slender - about 25 to 30% beam to length ration - and draw less, but still have those big full stern post rudders.

I guess that - in dealing with foils - both in sail plan and hull plan - the idea is to achieve balance between and efficient lift from both shapes. Where would the main points of drag that may induce a negative through neutral to positive helm balance, from light winds through to wher the boat is at its maximum heel.

All his slender double enders have an aperture for the prop, plus there's the trailing end of the keel/rudder junction.

I had a crazy notion that small cast bronze winglits, two to the prop aperture and one to the keel/rudder end may help there?

[Duncan Gibbs]

Hello Duncan,

Sorry for not answering your question better.

As a starting position, for the boat in question, I would be looking for a lead of between 13 and 15% of LWL. (excluding rudder area, and using the area of the sail set in the foretriangle rather than the foretriangle itself). That's a lot more than the original sail plan shows, and it wouldn't surprise me in the least if she carried a fair weight of helm. In the photo posted you can actually see the chap has the tiller behind his back.

I'm intrigued by your winglets idea around the prop apperture, there might be something in that, but it would be a complex one and a trial and error job to sort out. There are probably improvements that could be made to the rudder planform anyway though that would be more readily achieved.

With traditional boats we are frequently coming at helm imbalance problems from two sides. In many cases, adjustments to the rig to balance the helm may require a compromise from a handling point of view (big jib on a long bowsprit) that is a step too far. So, if the "disease" can't be cured fully, one has to look at making the "symptoms" easier to deal with and that is where rudder efficiency comes in. It's nice to have an efficient rudder either way of course.

Hope that helps.

Best regards,

ED.

ps. please feel free to copy this into the appropriate thread if you like.

Done! Thanks Ed! :)

http://www.boat-links.com/Atkinco/Photos/EricJr/Tyke1955.jpg

[PeterSibley]

Interesting , I hadn't noticed the angle of the tiller in the above photo .

[Duncan Gibbs]

Maybe a reduced main and a small mizzen sail may help with rudder trim? Did you see my gaff rigged yawl option Peter?

[PeterSibley]

Nice , I like yawls but for anyone considering sailing to the Hobart WBS ,they get in the way of a vane ....and vanes are wonderful .Much better than sheet to tiller before you say it !

[Duncan Gibbs]

Yeah! On a nice long keel like that!... You read my mind Pedro! :D

[Canoeyawl]

Interesting , I hadn't noticed the angle of the tiller in the above photo .
Photo studies are great. If you look at images of older yachts under sail, this weather helm position is often the case. The old magazines are a treasure trove for this sort of image.
The poor fellow is sitting up to weather more to get room to pull that tiller up into his lap than for a righting effect!
There are a lot of lines plans available for older designs and you can readily place the theoretical balance/lead point as a study for helm position to compare to a photo.
*note in the above photo that the condition is pretty fair weather.
I sailed a much loved early design of William Garden for a season and it had a wicked helm. A real eye opener. Evidence of broken tillers, and subsiquent repairs abounded. A lovely symmetrical hull form, but just wrong! That experience caused me to study very carefully any action images of smaller yachts, and in particular canoeyawls, with a jaundiced eye.

[Ed Burnett]

Photo studies are great. If you look at images of older yachts under sail, this weather helm position is often the case. The old magazines are a treasure trove for this sort of image.
The poor fellow is sitting up to weather more to get room to pull that tiller up into his lap than for a righting effect!
There are a lot of lines plans available for older designs and you can readily place the theoretical balance/lead point as a study for helm position to compare to a photo.
*note in the above photo that the condition is pretty fair weather.
I sailed a much loved early design of William Garden for a season and it had a wicked helm. A real eye opener. Evidence of broken tillers, and subsiquent repairs abounded. A lovely symmetrical hull form, but just wrong! That experience caused me to study very carefully any action images of smaller yachts, and in particular canoeyawls, with a jaundiced eye.

This is very true. Assuming an old boat (even a well respected old boat) had a balanced helm can be a mistake.

The lead method of assessing helm balance is really just a way of comparing one boat with another. In other words, it is simply a way of describing how the areas of the sails and the underbody relate to each other that we can use in order to learn from a sample of example boats. For the comparison to be useful, you need to know how the example boats felt on the helm - there's no point faithfully copying something that was actually a complete dog.

As I mentioned above, the recomended or suggested values for lead are merely an accumulation of past experience; a guide as to what has been found to be acceptable in other boats of similar type, measured in the same way. For the method to be used relaibly, you need to know how the other boats were measured (eg was the rudder included?) and you need to have a bit of faith that the vessels used as source data were good ones!

The one thing about photos however is that they only show the helm postion at one instant. Looking at the photo of the Atkin boat again, we could argue that the chap on the helm is in the process of bearing away. He's on his own, and has tucked the tiller behind his back to start the boat bearing away, freeing up his hands to ease the jib sheet at the same time. He seems to be smiling, and the dog looks happy enough, so passing judgement on the basis of this one photo might be a bit harsh!

[maxcampbell]

Old boats and assuming balance! Essex smacks generally carry so much weather helm as they heal that they are complete pigs. Everyone admires them, from the photos. Try sailing hard to windward.

[Duncan Gibbs]

I think that I will use James' assessment of the qualities of Eric Jr as a good guide. AFAIKT his Eric Jr had the rig as designed and a reef in the main when beating to a stronger wind would have helped. I could see then how three things may help:

1. A larger foretriangle;
2. A smaller main;
3. A small yawl mizzen.

More drawing and study is needed before settling on anything. I would assume that LCB, CLR, CE, VCG, hull shape and foil development, among a host of other design aspects, all come into play on the helm feel and performance when sailing upwind.

[Duncan Gibbs]

Now for the results in my first lead study of the various rigs and a comparison with Albert Strange's last design 'Venture' featured in CB Magazine (Sept 2008 No. 243).

Here is the lead percentages of the original rig and the reduced main and enlarged fores'l. Note that lead is calculated as a percentage of LWL:

http://pic80.picturetrail.com/VOL1913/10058894/23178147/386955180.jpg

Here is the Bermudan Yawl with the three possible sail combinations' lead calculated: [edited to add the lead with main & fores'l alone is 22% and mizzen & stay alone 10.86%: These figures are unclear in the drawing as printed to PDF and saved as jpeg.]

http://pic80.picturetrail.com/VOL1913/10058894/23178147/386955185.jpg

Here's the first Albert Strange inspired rig with a larger main and the mizzen located directly over the stern post top:

http://pic80.picturetrail.com/VOL1913/10058894/23178147/386955184.jpg

Another variation with a smaller main and the mizzen brought inboard:

http://pic80.picturetrail.com/VOL1913/10058894/23178147/386955183.jpg

Here's the sailplan and underwater profile with the lead percentages for Venture:

http://pic80.picturetrail.com/VOL1913/10058894/23178147/386955182.jpg

I've found that the lines for the underwater hull shape are remarkably similar with a few small exceptions: The half breadths of Venture are more rounded in the aft quarters whilst the diagonals are sharper; The beam is slightly greater in Eric Jr and the LWL is longer in Venture by 200mm and Strange's design is 100mm (4") greater in draft. The mizzen is also raked forward.

http://pic80.picturetrail.com/VOL1913/10058894/23178147/386955181.jpg

This exercise has taken quite some time but I'm not sure what conclusions to draw from it, so I'm throwing the results out into the ether to see what kind of comments and thoughts may be generated from the drawings.

I guess the first question that this exercise generated considering James McMullen's comments about the efficiency of a yawl rig, that the mizzen isn't so worried by the dirty air off the main as it's not a driving sail, more of a rudder is should it really be included in any type of lead calculation (whether lead be a crock or not) in the same way a rudder is not included in finding the CLR centroid for the underwater profile?

[Ian McColgin]

Include the mizzen? Depends on the design. There are yawls and even a couple of ketches with such poorly designed sail plans that the mizzen isn't worth much except as an auxillary rudder of dubious efficiency on the wind and a stick to hold up the mizzen staysail off the wind. A mizzen like that costs more in added windage and weight aloft than ever it can give back. Leave it out and stick up a tower for your windmill.

A good mizzen drives the boat. Drives the boat first. It's a sail and it either drives the boat or it's really really stupid and the designer should be returned to designing tupperwaretunnatowerterrors. If it drives the boat, then also it will be rather nice for balancing, giving power to certain turns, especially low speed quick tacking and really hard rounding up. It will also help the boat lie head to the wind at anchor. And while the whole "jib and jigger" bit is way over-rated for storm conditions, it is rightly well-loved as a way to super fast shorten sail while you take a breather or figure out where you are or look over a strange anchorage.

But first, if you're making a mizzen that does not drive the boat, you've really missed the point.

[Canoeyawl]

Having gone through this same exercise in great detail I agree with Ian, very well said sir.
(I will add that unless you have sailed the boat that is being used as a datum, or have sailed and designed many similar boats, the execise may be useless)

[Duncan Gibbs]

I am then at a disadvantage and know not which way to turn! I was actually going to suggest that my effort was an exercise in futility!! :eek:

Here I am with what looks to be a greatly admired design that every extant example I've seen has changed the rig, and had Mr McMulllen's testimony that, under a good press of wind, she has "more weather helm than is fun." He has suggested that a yawl plan would be a glorious variation to her rig. I've found Mr Strange's Venture to be rather similar in below water lines and any use of her sail plan on Eric Jr results in a very similar gaff headed tops'l yawl rig in configuration and total sail area.

If a mizzen is indeed a driving sail then I've been correct to include it in the CE calculations for the various rigs.

I suppose I'm looking for answers, or even suggestions of answers, as to how the inclusion of a properly designed mizzen (for I'm not interested in any way, shape or form in an improperly design mizzen) will affect helm balance and general handling of Eric Jr, amongst the other aspects of the overall design. I'm quite serious about a desire to build her, as I have ready access to a good quantity of excellent boat building timber for no money aside from the cost of milling. Her draft will allow me to day sail on the Tweed, which is quite shallow in parts as well as take her out over the horizon.

I may yet change my mind! :rolleyes:

[John B]

Well you can flag the cocked mizzen arrangement, that looks weird, mostly because strange would be a gratuitous pun.
Just think of the mizzen as a reef, factor it in and be assured that you'll be dropping it at 18 or 20 knots, at which time you'll be rapturous to have some sail area relatively forward anyway.

[Ian McColgin]

There are a couple of different ways to look at mizzens on yawls - and how and why they happened.

At one time the mizzen was unpenalized sail area. So you see a lot of things that would be, often once were, happier with a nice long boom but someone sawed off about 10 or so of boom and stuck a broomstick with a handkerchief on it. The penalty of a rig that barely gave move push than it's rig cost in resistance was off-set by the savings in the rating.

Another approach is more like a ketch but the mizzen is further aft. The mizzen is bigger, more inboard, and far better stayed than the sawed-off boom approach. It may have been chosen to divide the sail area and perhaps bring the CE down a big rather than having all that sail in the main but still wanting the tall mainmast advantages of a sloop or cutter.

It is positivly amazing how often you'll see yawls of the first type actually being sailed as sloops with the mizzen never going up except maybe at anchor.

But I must say, in each of the examples drawn, I'd be more inclined to put a few feet on the boom and maybe even the mast for some sail area. I don't like mizzens where the conflict between rudder post and mizzen step is resolvable only by strange, possibly ficticious, engineering and where the stay base and sheeting base are both hopelessly narrow. Of modernish designs, the Concordia yawl is about a much porportional difference between main and mizzen as I can stand.

There are things that work for different types of sailors, different conditions, different goals. I't not take something that weak very far off.

[John B]

Just re weather helm, somewhere in amongst the tens of thousands of words I've read about old boats/ designers etc etc over the years , I did read a very interesting article where it pointed out that the belief amongst designers of say 1900( to pick a circa date) was that a boat needed to be hard on the helm to perform to weather. A default hunting up to windward you might say, to help with the deficiencies of the historical rigs and materials.
Anyway , that always rang true to me. Not what you want now.

[Duncan Gibbs]

The other thing I've read somewhere is that the mizzen can greatly improve pointing ability to windward. I'm assuming that that would be a generalisation of the worst kind, but generally true to the greater degree.

[johnw]

I like the old terms, ardent for weather helm, crank for lee helm.

A narrow boat or a scow won't pick up a lot of lee helm as the boat heels, because they don't have that huge curve to the lee waterlines. My old Yankee one-design had neutral helm at pretty much any angle of heel.

A lot of older designs do seem to have plenty of weather helm. I've seen a version of the Eric Jr. that had the main from the original design, a foresail that looked like the jib from the original design, and a masthead jib on a three- or four-foot bowsprit that filled the full foretriangle outside that sail. The boat balanced quite well. Of course, it heeled more in the winds usually encountered, which would feed weather helm into the balance. And it didn't match any of the pictures in post #22.

[johnwill]

The excellent sail diagrams posted by Duncan lead to questions. How are the individual sail centers of pressure determined? Is it a result of experiment, calculations, guesswork, what? They appear to be about 40% to 45% of the sail chord and span, to use airplane wing terminology.

Subsonic airplane wings generally have a center of pressure closer to 25% of chord. Are sail aerodynamics that much different?

And finally, the underwater center of effort appears to have about the same location as the sails (40% to 45%) span and chord. Given the very low aspect ratio, I would think it would be a lower percent of span.

I am well acquainted with airplane measurements to verify all these variables, but know nothing of similar ship characteristics. Fascinating stuff, in any event.

[johnw]

I believe those are centers of area, not centers of effort, which are more complicated to calculate. That's part of what complicates the discussion.

[Duncan Gibbs]

I believe those are centers of area, not centers of effort, which are more complicated to calculate. That's part of what complicates the discussion.

The ones I created in AutoCAD for the original sail plan matched exactly those drawn by Billy Atkin. I used the following process described on the boat design forum in post 8 from this thread (http://www.boatdesign.net/forums/sailboats/center-lateral-resistance-1898.html).

To recap this process here, I drew a closed polyline and turned it into a region, of which the centroid can be located using the "massprop" command. This same command can find the centroid of several regions (mizzen, main, top & fore/mizzen & fore/ main, top & fore and for each individual sail un-reefed). I tried using the same method on a gaff sail and checking it via the manual method as described in both Mariano (Sailmaker's Apprentice) and other texts: It's deadly accurate. Of course someone like Todd Bradshaw may chime in here and suggest other factors that may be at play aside from centroids that give a true determination of CE in any particular sail and sail plan.

[Ian McColgin]

As Roger Long and almost every serious instructor on things sail point out, the center of area is a useful fiction. The two most obvious things "wrong" with it are that it is a center of area, not center of effort, and it is based on a plane view of the sails amidships - a place they never are when working. At the hull end there's an analogous pair of "errors": The static center of lateral resistance - about the same as the center of underwater plane - is always abaft the center of lift, which moves ahead with increased speed; and as the boat heels the sloped lateral planes of keel and skeg change their centers.

Center of area v. center of effort and effect on weatherhelm - You're hard on the wind and the boat has a wicked weather helm. So you ease the sheet putting a little luff in the main and thus also moving the center aft a little. Normally moving the sail's center aft increases weatherhelm but here other factors are more important and you reduce weather helm.

Amidships - what's wrong with this picture is most blatantly shown in catboats where the big long boom and lowish sail place the sail's center on almost all points somewhere out past the lee rail, rather like having an outboard out there.

All that CE/CR stuff is a useful rule of thumb. Litterally sometimes - Pete Culler felt that if you did the plans at 1-1/2" per foot, then the lead should be one thumb's width ahead of the hull's center.

The NA mantra: Design, build, correct. Redesign, build better, correct. And on.

[Duncan Gibbs]

Interesting Ian; or as a shipwright mate of mine down in Sydney says, "If it looks right it usually is!" At the end of the day I am asking those with much greater experience than I for advice and sifting through it for that nugget that will help me make a decision one way or another on a final rig.

The timber is yet to arrive, the shed is being built and I have a trove of MoToR Boating Magazine articles with plans and offsets drawn by the same hand. I should have enough timber for two boats....

[Canoeyawl]

Just a note* There is an overlay lines drawing of my little yawl Sally (a similar hull form) in the WB magazine #142:42 that shows the changes we made to the "lead"or theoretical balance. The boat "looks" like it will sail well without the centerboard but in fact it develops a significant weather helm and is a completely different boat that would be an extreme disapointment to weather without changes.
This "lead" business is always a wrenching decision and an interesting excercise.

[johnwill]

Thanks to all for your enlightening comments. Ian's last comment seems to sum it up best.

Airplane aerodynamics seems relatively simple, more scientific, but perhaps less fun.

[Duncan Gibbs]

Canoeyawl, if you please I would be very interested to hear your account, as concisely or as detailed as you care to put it, of how you went about this same exercise and exactly what drew from the experience. Had you already built your Wenda at the time?

[Canoeyawl]

It was a pretty big deal, but to sum it up I hired independently two experts.
One an N.A. - Al Mason, I spent a very enjoyable day with him in his studio going over the design.
And another, a friend, an aeronautical engineer (USNA) that had a passion for boat design (Hobby for fifty years) with several successful designs under his belt.
After my input on how I would sail the boat i.e. the mizzen would be a primary sail, not a rule cheater, they both came close to the same agreement, but I tended to put more faith in the airplane guy because I knew his history designing aircraft and his methods.
Other than this I would rather communicate off the forum if you want more details.
And No, the boat was unbuilt at the time
canoeyawl at hotmail