GAFF RIG GURU'S & SAIL PRO'S HELP

[mic]

Ok, I've been dreading to ask this question due to it's complex nature & many variables, but I've now gotten to the stage where it's time to do the work & I really want to do the right thing by myself & the boat, so here goes.
My boat is 46'Aft Wheelhouse Crayboat that I would like to rig as a Gaff Cutter, now some people tell me that my boat will never sail, others say it will sail beautifully & I'm just not sure. Here are some pic's so you can see the shape of the Hull in question.





Ok, I'm picturing a topsail on hopefully the existing mast, approx. 10' bowsprit, the existing boom is a little small so I'll use it as the gaff & get a new longer boom, I thing it will look super sexy on this boat .
Now I know you just don't go ahead & cut sails without doing stuff, so I'll give ya's some more info.
Existing mast is approx. 30' from deck top & is positioned 1/3 of the waterline Aft of the stem, existing boom is 18', boat dimensions are, LOD 46', Beam 14', Draft 6'.
Now for some questions. Do I need to find the centre of effort & reposition the mast?
& if I do, do I really need the lines drawings to find the centre of effort? as I don't have any.
How tall should the mast be?
How long should the boom be?
How long should the gaff & sprit be?
Oh hell, it's never ending
I know my boat will sail, I mean any boat will sail, but will it sail well enough to warrant all the work on a rig such as this. Although my boat will never sail like a race boat will it go to windward at all?
I'm really hoping for some professional help on this one.
THANKS EVERYONE

[Ian McColgin]

You need to find the existing stability curve. That will tell you whether you can even think of hanging a rig without first putting some ballast, preferably under the keel to give that a bit of guts as well.

Reconfiguring for sail, even from a very auxialary point of view, is something that should by a professional.

The idea may have merit. She's a handsome boat. But you can't just throw up a topmast and hope the boat will stand up.

Really really really hire a sympathetic naval architect.

G'luck

[Ken Hutchins]

Definitely hire someone to do the design. IMO without substantial changes to the keel, rudder, ballast, etc. it will probably sail mostly sideways, not foreward. Any respectable amount of heeling will probably render the current rudder useless, hence no steerage.

[mic]

If i haul her out and try to obtain the table of offsets myself with a laser level (there was a great article in W.B.#167 on doing it!) surely a navel archetect could do a sail plan and a ballast set up from that information, because most of the $$$ charged by archetects is actually to get the table of offsets and do the lines drawing. I actually did speak to one person from an archetectual firm in regards to this, he said it would cost about $7,000

[Dave Hadfield]

There must be a way to get heeling data cheaper than $7000. Sorry, I can't help you myself there, but keep trying.

My feeling is that a bit more keel, as ballast, would help her sail upright and help grip the water, but that means keelbolts and extra floors and reinforcement etc. Probably a slippery slope.

As she is, I don't think you'll get upwind with her under sail, butreaching and running, sure, why not, as long as she stays upright. Her mast, right now, to me, looks too far forward for a cutter, but do-able as a ketch or yawl.

A low C of E would be desirable, for sure.

I certainly like the look of her. Neat boat! A gaff would suit her well.

But I ain't a professional....

[Paul Scheuer]

What kind of action do you get out of that steadying sail ?

[mic]

Paul to be honest i've only owned the boat for about 2 years and i've probably spent more time working on her than using her and i've never hoisted that sail. There was a thread a guy put on about 2-3 weeks ago about doing a lines plan for his boat, in the end he found a computer programe that would do it. Anybody rember that one i can't find it!

[brian.cunningham]

Have you seen the GREYLING conversion?

[Ian McColgin]

You can't do this from a computer as you don't have the empiracle input. Gaining the data you need is a chore but the work from there on, whether by computer or by hand, is not hard.

As I mentioned above, the first thing you need is a complete stability curve. NA's sometimes make one based on how they designed the boat. Like how heavy is the engin, where are the tanks, and so on. You don't have these data.

Do a dockside stability test. Have the boat moored bow and stern a tad off the dock, hang a nice stout line from the mast truck, put a strain guage on and pull. If you've not the basic engineering knowledge to correctly vector the pull strain, you're not going to get far without more help anyway. Keep pulling at least till you get to the point of rapidly diminishing stability and serious deck flooding.

Once you have these stability data, you'll know what she can stand up to. The calculations of force per square inch from wind are simple. Make sure the boat won't capsize under bare spars if hit broadside by a mighty wind. Make a rig that will let you carry sail with no reefs up to say 15 kt.

For existing center of lateral resistance, anchor in a good current with no wind. Bend a nipper on the anchor rode and attach that about amidships, veering some slack in the rode. If, as is likely, the bow begins to point down stream a bit, move the nipper foreward till you get the balance point. How hard is that?

In motion, the CR will move forward a bit as you sail but there's a literal rule of thumb. Draw the profile of hull and rig at a scale of 20:1 or so. If the CE of the sail area is about a thumb width's foreward of the CR of the hull, you'll do fine.

A low gaff ketch might work more nicely with the pilot house you have but a schooner would look finastkind.

Just don't trivialize the project by thinking it will be cheap and easy. I did a rough cost in my head of materials and a schooner rig would be hard to set up for much less that $20G to $25G. You've done a great job on the boat. Don't blow it in the end game.

G'luck.

[ 02-13-2004, 07:49 AM: Message edited by: Ian McColgin ]

[Wild Dingo]

Gidday Mic mate have you contacted David Payne yet? he would probably help you and at a price considerably less than the 7000 quoted...

Either TonyH above or Mike Field has his email Id give it to you but since the mighty crash of me system Ive lost just about all of them... David was one of them... nice fella and helpfull if he can help he will and costs a damn sight cheeper than that and knows what hes doin!

Good lookin aint she?! keep us in the frame with how you get on mate

[mic]

It's interesting that almost all of ya's recon the boat would look better as a two masted rig, i was hoping that i could avoid the extra expense of two masts, two sets of riging and two sets of maintainance but if ya's all recon that's the way to go then so be it. Will it perform any better? Brian i've never heard of the greyling project, and Ian i realy, realy, appreciate your input, you're correct though certainly i could do the work; but recording the data in a useable way i'm definetly going to need some help in. I've never done this befor so i'm not sure what information i need, or where to turn.

[Wild Dingo]

Ive had a hunt and found this email for David Payne mic payne@hn.ozemail.com.au I think this is the right one, anyway give him a hoi he will help if he can.
Shane

[Wooden Boat Fittings]

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Mic, a couple of years back I did a tentative design for a gaff-sloop rig for a similar boat (42' oa, as I remember.) The boat had an enormous deckhouse which interfered with things a bit, which the owner wanted to retain, and which would certainly have precluded a ketch or yawl rig, but I wasn't unhappy with the sailplan we finished up with. (We provided a mast for the conversion too.) But unfortunately I don't know whether the owner went ahead with the project finally or not.

But note that it was not intended that the boat would be sailed without her engines except downwind or on a broad reach.

The boat's name was Susie May and she was then at Yaringa (where the owner intended at that time to keep her permanently.) Why not give them a ring and see what they can tell you about her?

Talking to David Payne is an excellent suggestion, and Dingo's given the right email address.

Mike

[mic]

Hi Shane thanks so much for David Payne's email address i really appreciate it, i'll definetly give him a try, hopefully he can help me out. [img]smile.gif[/img] And Mike i do know the Susie May and her owner Ken Mcdonald because my boat is still at Yaringa ,Ken now has the boat down at Flinders on a swing mooring and is currently doing fishing charters with her, he changed her name to ALCHEMIST. I'll certainly have a chat with him about the conversion. Interestingly enough there's no mast on the boat now.

[Ian McColgin]

You sound like a do-it-yourself sort so here are some thoughts that might get you going, perhaps even save a little on the final NA bill, or might lead you astray enough that you're the most annoying of a NA's clients but anyway . . .

Start with a copy of "Skene's Elements of Yacht Design" by Francis Kinney. I don't own a copy myself so I'm going from memory. But when I've a question, I can go to the library and almost always get the answer right there. I believe other members of the forum are more able to comment where the remarks below go astray.

As mentioned above, I don't put much value in low angle incline tests or in calculated stability curves. I've not done my approach on a vessel as large as your's. Largest was on Goblin, a 43' alden schooner of about 12tons. But just be careful and have folk clear if something breaks.

The lateral strains in this test are significant and the boat needs to be well moored along her centerline. Have lots of fenders as if a mooring line parts the boat will really slam into the dock.

I hove Goblin down by a line on the mast. If you doubt the strength of the chainplates, maybe try a parbuckle from the near gunnel under the boat over the far gunnel and ashore. The parbuckle will need far greater force to heel her down but it will work.

A third approach that costs some money but would be really easy is to run the end of the parbuckle up to a crane that has a strain guage built in.

With the first two systems, the further away the pulling vehicle is, the less problems. Anyway, you just hitch up a strain guage at the towvehicle end and start to pull her down, noting the strain every 5 degrees or so.

Note very carefully all distances while you're at it as the force will need to increase as the boat heels, but the effective heeling force may be declining as more of the energy is going into pulling the boat sideways rather than over.

You may also have a secure enough thing on the dock that at a certain point you can begin pulling straight down from the end of the mast. Or you may have a truck with a winch that you can keep repositioning such that the pull is almost normal to the mast all the while.

These are deatail to work out depending on what you have handy and are details that if you've any doubts at all, hire a competant rigger, crane operator or engineer who is used to fooling about with large objects.

Keep her going over till the rail is down, at least. Assuming that all is secure below and there are no surprising places for downflooding that much ought to be well safe. As you begin to immerse the deck, keep a very sharp eye on the effective heeling strain. It will lessen. The boat does not look (off hand) like she'll achieve negative stability in this sort of test but you want to be careful that she does not just turtle on you. Go as far as you dare.

Once you've dusted off your HS physics to get the parallelogram of force working, the data you've achieved will give you the heeling force it takes to get to varioius angles. These are the first raw data that will tell you how much rig she can stand up to. They are also useful data to keep aboard so's you know if you're rolling downwind in the trades some day that the roll has gotten to a dangerous point.

In the end, rig up, the metacentric will have been raised by therig's weight. Also you may lower some machinery or add some metal under the keel, lowering it. Important to record those changes, but you'll likely be able to calculate their effect on the empiracle stability curve.

You can actually calculate the heeling force of the wind fairly easily. There are tables that give force/area information. For whatever wind you want to test you can treat it as the force for the rig's sail area applied at the center of sail area.

Here's why for your boat two or (like my Granuaile) even three masts are nifty - it's the only way to get the center of sail area low. Also gives a plus to a gaff or chinese lug rig.

Now that hull with three masts supporting tan bark lug sails would look just tiddley.

As you do you're wind calculations you'll note that at increasing heel the effective sail area for the wind to push against is decreasing. This is also of comfort.

You're not going to make a boat that is a real witch to weather, but she ought to be good on a tight reach, maybe six points off the wind, and off from there. I'd do sail area calculation to have her get heeled comfortably - on that hull maybe as much as 20 degrees buy you and your NA will have to judge that - with all sail up in about 15 kt of breeze. Maybe if you've lots of calm and she's looking a pig with that little a sail, have her get to comfort heel at 10 kt breeze and figure to reef from there.

You also want to calculate the wind resistance of the bare rig. Be sure she won't just roll over if broadsided by a force 13 or so blast. On her mooring Grana will sometimes roll down to 45 degrees if she veers a point or two from the eye of a 50 knot wind so these bare pole considerations are for real.

G'luck

[Ed Burnett]

Hang on a minute.

Ian, that sounds really scary. For a start, hauling a boat of this size over that far is going to involve big loads somewhere, and I'm pretty sure that would be a bad idea until the mast and chainplates etc. have been fully sorted out. Also, the results are going to be far from conclusive and may be a long way out.

I don't know where your dislike for low angle stability tests comes from, but I would think that a straight forward incling experiment (to perhaps 3 or 4 degrees) is the way to go here. It's a classic and utterly respected approach and can be carried out in a really nice controlled and calm manner. No big loads, no urgency and no risk of damage to boat or people.

Mic, you can do a simple inclining experiment with a friend or two, a pile of weights, a pendulum and a quiet few hours. There are various books that detail the procedure. It's really rather fun and the results can be highly accurate if you are careful.

Once you have a simple righting moment at 1 degree, you can easily draw out any number of options for the rig and make assesments of stability etc. using Dellenbuagh angle (this is all in Skenes).

Large angle stability is another subject and another matter. If you want to look at that you need to spend some money with a Naval Architect. Whether or not you need to do this depends almost entirely on your intended use for the boat. If all you are going to be doing is mooching about in the bay on nice days, large angle stability is not going to concern you. If you want to cross oceans you need to know about it.

None of this is rocket science, and there is no reason why you can't do a lot of it yourself. Have fun....

[Ian McColgin]

It's hard to correctly correctly project from incline tests, as was rather ably shown by Capt Dan Parrott in his "Tall Ships Down." (McGraw Hill, NY, 2003) It can be done but it takes lots and lots of measurement.

On a boat made for sailing, I don't at all fear breakage just heeling her over as that's pretty much the strain everything takes sailing anyway but it does require great care, expecially at the higher angles of heel.

First time I ever did that to a boat was not for a stability test, but to do a repair about a foot below the water line.

But Ed's timely warning is important due to other things I'd not considered - easy to forget at a distance - and which could easily be overlooked by an inexperienced person thinking my thoughts are complete.

For example:

On a sail boat the chain plates really are big enough and the rig stout enough. No guarentee that the stick you've got is braced anywhere near enough.

On a sail boat, the tank vents will be nice and high as the boat's meant to heel and a good designer will have thought about cross tank gravity filling in vent location and so on. In a power boat, you might start spilling fuel at 15 degrees.

A lot of power boats have both fuel and water vents in the hull. You don't really want to put salt water in either water or fuel tanks.

This is a powerboat so the designer would not have worried about how stuff drains on a heel. Depending on your galley and head locations, you could get internal flooding through sink drains at a certain heel.

On a sail boat, lockers are designed to stay shut even at heels of 45 or more degrees. Properly done, they'll stay shut through a 360. Even if your lockers have latches, they may open if a little weight presses against the inside of the latch, especially if it's the stick your figer through the hole type.

And just think where your dishes and cutlery will go.

Now we hope down into the engin space. At what point do the batteries come adrift? Is that spare anchor going to fall off its shelf and smash the injectors? How many tools will enter the bilge right under the oil pan if you roll her to 30 degrees?

There is a lot of foresight needed and you might want to go in tiny increments as you get the idea.

And your marina will likely want a big insurance premium.

But it's still fun.

G'luck.

(And hire a pro.)

[Ed Burnett]

It's hard to correctly correctly project from incline tests

Ian, I agree absolutely that trying to extrapolate small angle results to apply to large angles is not going to be that reliable. By the same measure, hauling her over to 30 degrees or thereabouts still isn't going to tell you much about what happens at 90 degrees, which is what you would really want to know if going offshore. As I mentioned, if large angle stability needs to be considered then it becomes a big job.

The aim of a classical inclining experiment is to determine the vessel's righting moment at small angles, and thus confirm her VCG. This then forms the basis of either small angle "power to carry sail" sums, or more serious large angle studies which would involve a computer model.

In this case, as we don't know much about the boat's hull shape we would have to make some assumptions to get her VCG from the inclining results. But then a righting moment at 1 degree is a perfectly satisfactory basis for the sail carrying stuff which is the primary concern here. As I said above, large angle becomes a much more involved thing. The simple approach will be fine until the deck edge immerses, at which point you would be more than ready for a reef or two with this boat.

[Ian McColgin]

Ed may well be right here. The fact that I've learned things and successfully fooled about heaving down littler boats does not mean this is the best idea to come down the pike. On reason for Naval Architects is they know these things.

If you want the most dramatic small boat righting tests I ever heard of, see if you can find - there used to be - a site with the roll-up tests done on the new Coast Guard surf boat that replaced the venerable 40 footer. In a pond then floated it upside down and then timed the return.

Traditional boats and their immitators like the Leavitt have a place where stability vanishes. You want to know if that will apply to this boat and you want to snug down well before that.

G'luck

[Wooden Boat Fittings]

.
And if she's one of Ken Lacco's boats, as seems quite likely (he turned them out like he was running a sausage factory,) then her lines will look like this --

Mike


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[mic]

Hey Mike, how close do ya think Lacco's lines plan is to a Cayzer built boat. Ya havn 't got any of old man Cayzer's designs tucked away there have ya? Actually judging from the size of the wheelhouse in comparision to the deck on that lines plan it looks like a 54 footer.
Ian your advice and detailed responses on this subject have been a tremendous help thankyou very much! [img]smile.gif[/img]