practical proa sailplans
For a midsize cruising proa, I want a rig that will shunt with a minimum of fuss, go well to windward, and be amenable to reefing. As nice as the traditional crabclaws are, I just can’t see dragging the rig back and forth. Likewise Bolger and Junkish rigs do not seem to have proven effective - yet. My inclination is to go with the well understood and efficient western mainsail plan, adapted of course for shunting. I’m also keen to maintain low aspect, so a multimast (cat schooner) rig seems smart. The Madness solution seem eminently sensible. Can anyone suggest arguments against this approach - for , say a 32’ boat? thanks!
If you think ‘junkish’ rigs are not that efficient, have a look at the latest development: se the JRA website.
They are just about matching a cruising Bermudian rig upwind, and leaving the completion way behind as soon as the wind frees. The ability to let the sheet go and fully weather-cock - on any point of sail, together with very quick and easy reefing makes them a serious contender for any proa, or multihull.
Mark
Are you thinking about a schooner rig or a sloop (Madness-style) rig?
My 21’ proa uses a schooner rig. I like it a lot, and if I were to build a bigger boat I’d use a schooner rig. Laurent has sailed on a bigger French proa with a schooner rig also. Both my boat and the French boat use jibs. They help balance the boat a lot. A schooner has a further aft CE than you would think, about a third of the boom length behind the centerline of the boat.
KONeil
I assume you mean a two mast schooner, with small jibs at both bows?
“A schooner has a further aft CE than you would think, about a third of the boom length behind the centerline of the boat.”
I was kicking around the idea of three masts, no jibs. This would put two of three sails behind the centerline, so yes, I see the CE problem.
SP
Yes, two masts. Three just seems like needless complication, with very little added ability. For two or three, the CE when all the sails are sheeted will be about 1/3 of a boom length aft of the centerline of the boat, so adding more masts doesn’t help you there.
I had a roller furling jib on each bow. It worked fine, but with four sheets and two furling lines it was a task to rig, and a little bit of a tangle until I got the lines routed sensibly. If I were to make any changes it might be to try to increase the rudder size and mainsail size so I could dispense with the jibs. Sailing as a cat schooner, with just two sheets to handle, is quite a lot easier.
KON
thanks for your reply
re - “two masts. Three just seems like needless complication, with very little added ability. For two or three, the CE when all the sails are sheeted will be about 1/3 of a boom length aft of the centerline of the boat, so adding more masts doesn’t help you.”
so you don’t think the lower aspect would be a significant advantage? Could make for a narrower boat for the same stability? Smaller rig, lighter, smaller sails, easier to handle…and reefing would be a matter of dropping the mid one or the outer two
“If I were to make any changes it might be to try to increase the rudder size and mainsail size so I could dispense with the jibs.”
you needed the jibs to counteract weather helm. On rigs I’ve seen they tend to be small. But increasing the rudder size would add drag (?)
“Sailing as a cat schooner, with just two sheets to handle, is quite a lot easier.”
with three masts, I’d wondered about yoking the three boom ends together. I assume they would not always be exactly parallel, but even if, ie the aft one was more close winded, the relationship would be stable till you shunted.
thanks for your reply
so you don’t think the lower aspect would be a significant advantage?
No. The primary advantage of a schooner in my experience is the ability to sheet in the front sail first, and control the boat better in a shunt and when you’re in danger of going aback. With a single main the boat can head up a lot in a shunt, and can sometimes be hard to control.
Beyond that, a low aspect ratio is bad, not good. The boat goes to windward better with a higher aspect ratio. My boat has 17’ luffs on the sails, and 8’ booms. With two masts that’s about a 1:1 aspect ratio. Certainly you don’t want less than that.
Could make for a narrower boat for the same stability?
Right, but as long as I’m going to trailer it I might as well make it 8’ wide. At 8’ wide I have righting moment to burn. I don’t need a lower CE.
Smaller rig, lighter, smaller sails, easier to handle…and reefing would be a matter of dropping the mid one or the outer two
Yeah, but seriously, the faster you go, the more you’re going to windward. AR is important. My 1:1 is really too low, and you can see the difference when I sail against a higher AR boat like Laurent’s boat with the A cat rig up on it.
with three masts, I’d wondered about yoking the three boom ends together. I assume they would not always be exactly parallel, but even if, ie the aft one was more close winded, the relationship would be stable till you shunted.
On my boat, the rigging for a mere two masted schooner proa has proven complicated enough.
“Beyond that, a low aspect ratio is bad, not good. The boat goes to windward better with a higher aspect ratio. My boat has 17’ luffs on the sails, and 8’ booms. With two masts that’s about a 1:1 aspect ratio. Certainly you don’t want less than that.”
understood, but in my understanding the total luff length is what is important. Say I have 3 x 25 luffs,(each with, say, an 8ft boom) thats 75ft of luff, with slot effect, and AR fro each is ~ 3:1 (isn’t it?) or am I calculating AR wrong? I thought it was luff: foot ratio.
“Beyond that, a low aspect ratio is bad, not good. The boat goes to windward better with a higher aspect ratio. My boat has 17’ luffs on the sails, and 8’ booms. With two masts that’s about a 1:1 aspect ratio. Certainly you don’t want less than that.”
understood, but in my understanding the total luff length is what is important. Say I have 3 x 25 luffs,(each with, say, an 8ft boom) thats 75ft of luff, with slot effect, and AR fro each is ~ 3:1 (isn’t it?) or am I calculating AR wrong? I thought it was luff: foot ratio.
I think the definition in Marchaj is actually height squared divided by sail area. So if you figure the total AR of the whole rig you actually get about 1.6:1 for my boat. I’m not sure how valid calculating the AR of an entire rig is, but it’s how I think about it. I think adding up luff lengths is overly optimistic, that would imply that two or three smaller sails together have as good a combined AR as one tall sail, that can’t be right.
At any rate, there’s a lot of advantage to getting up high, there’s more wind up there, in an absolute sense. Having sailed with Laurent a bit when he had a much taller rig than mine, I can tell you that he often sailed past me on wind my masts just didn’t get into.
So what kind of boat are you planning? How big? Trailerable?
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so you don’t think the lower aspect would be a significant advantage? Could make for a narrower boat for the same stability? Smaller rig, lighter, smaller sails, easier to handle…and reefing would be a matter of dropping the mid one or the outer two
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with three masts, I’d wondered about yoking the three boom ends together. I assume they would not always be exactly parallel, but even if, ie the aft one was more close winded, the relationship would be stable till you shunted.
Simon,
Unfortunately, you cannot have your cake and eat it…
If you tie the 3 sheets together, to simplify the handling, you then loose the “smaller Sails, easier to handle” aspect of such a rig. And as you noted, you will need to sheet in the aft sail more than the foresail; how do you do that with tied sheets, on both tacks?
The only advantage I can think of, is the reefing by dropping completely one sail, in the middle, or 2 sails, at both ends.
But for the size boat you are talking about (in 30+ feet long range, correct?) I do not believe that such gain overweight the hassle of the extra sheets, hardware, mast, rigging, etc…
As always, designing a boat is a compromise… Too much of a good thing, can become a bad thing on another aspect of the use of the boat.
Cheers,
Laurent
” I think adding up luff lengths is overly optimistic, that would imply that two or three smaller sails together have as good a combined AR as one tall sail, that can’t be right.”
why not? In any case, what you loose in height you might gain in slot effect?
“At any rate, there’s a lot of advantage to getting up high, there’s more wind up there, in an absolute sense.”
I know, but a touted advantage of the crabclaw is more power lower down.
“So what kind of boat are you planning? How big? “
~ 32’
“Trailerable?”
hard to imagine at around 32’x12’, (with detached ama), unless I can lie it on its side 😊
Laurent
“Unfortunately, you cannot have your cake and eat it…”
I know, sailboat design is endless compromise, as you say.
“But for the size boat you are talking about (in 30+ feet long range, correct?) I do not believe that such gain overweight the hassle of the extra sheets, hardware, mast, rigging, etc…”
yes, right now I’m thinking 32’ (four sheets of ply 😊
why not? In any case, what you loose in height you might gain in slot effect?
Aspect ratio is much about lifting surface/tip vortex ratio. The upper end of the sail will create a big vortex adding lots of drag, and three masts will have three vortices = 3 X the drag of a single mast + sail.
The tip-losses is so big that three shorter masts would probably have a bigger overturning force than a single twice as tall rig.
Cheers,
Johannes
Johannes
interesting.
So what qualities (I won’t use the word aspect) of the tip of the mast sail contribute to the large vortices? How do you tame them?
http://bateaubois.free.fr/file/rigs.pdf
http://www.christinedemerchant.com/sail_sprit_sail.html
Aerodynamics is a quite large subject. I post two links above as some interesting reading to start with.
Cheers,
Johannes
I would like to try a modernized sprit rig with high aspect, carbonfiber sprit spar and the mast in a luff pocket, similar to the Wharram gaff wing sail.
http://wharram.com/site/how-we-design/wharramwingsail
If the sprit spar is placed 5 - 10 inch back from the mast on the boom, the sail is easy to pull from side to side in front of the spar and over the boom to avoid the bad tack where the wind press the sail-cloth against the spar.
This is an idea Sven Yrvind gave me.
Cheers,
Johannes