Proa cruising sailboat design, help get this idea out of my head...

Discussion in 'Boat Design' started by 360weatherbound, Mar 2, 2010.

  1. rwatson
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    rwatson Senior Member

    Well, no they dont usually pivot the mast - they rotate the boom. Pivoting the mast would be a complex and unecessary ability.

    Rob Denney's proas are about the most usefull and advanced design style in Proas I have come across.

    He wasnt the first to design the accomodation to Windward, but he was the first to get a commercial plan available that I can find.

    I would consider that even an experimental builder should investigate that configuration first. The "expense" of Robs design comes from the very optimised 'streamlining' of the hulls. If you werent concerned about optimum sailing performance, you could easily adapt a much more simplified hull design.

    Sitting out on a skinny hull, exposed to the weather while a comfortable cabin is metres away ( in a the other style of Proa design) seems a bit crazy to me.
     
  2. ancient kayaker
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    ancient kayaker aka Terry Haines

    What is the advantage of a proa over, say a trimaran? At first glance it would seem to be a tri with one ama lopped off.

    The tri has the advantage of bilateral symmetry and is able to maintain forward motion thorough a tack or gybe. It's 3 hulls can be asymmetrical fore-and-aft and the amas can also be asymmetrical beamwise whereas both proa hulls must have fore-and-aft symmetry which must compromise drag and leeway performance.

    Admittedly most tris are way more costly and heavy than a proa but they don't need to be. And I suppose the proa hulls can be asymmetrical across the beam but that doesn't seem much of a hydrodynamic advantage compared with using a daggerboard.

    Am I missing something?
     
  3. marshmat
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    marshmat Senior Member

    One can think of a proa as being a trimaran that doesn't have to carry the unused ama all the time, hence cheaper to build and lighter. On larger proas, the ama may also be usable space; I've never seen a trimaran of cruising-yacht size where the amas can be used for anything more than deck gear storage.

    There aren't any proas around my area, so I can't comment from first-hand experience, but I don't see any reason why shunting through 90 degrees should be much more difficult than tacking through 90 degrees. It seems to be more a question of what we're used to, what we've come to expect as "normal". There's nothing to stop a proa from having twin daggerboards, as many cats do. There are many examples of boats that are fore-and-aft symmetrical and can turn out good speed for their length- canoes, of course, but also rowing sculls, the camera catamarans seen at Olympic water events, etc. These are all low L/D craft, and I suspect that a heavy proa (L/D in the high 100s) would be a miserable thing indeed, but if it can be kept long for its weight, good sailing performance should not be hard to come by.

    I've been doing some rough calculations and sketches for larger cruising proas over the last few months- just concepts for now, but I'm convinced the concept is feasible. It is necessary to give up some conventional ideas about how to rig a boat, and appropriate rudders are an engineering challenge, but I do think that a well designed cruising proa should be quite competitive, on performance and on cost, with a well designed cruising cat of similar displacement and with a similar level of fit and finish.

    Where the proa loses out is when you have to pay length-based fees, such as for haul-out or a marina slip. Good performance with the proa geometry necessarily results in a longer boat than a typical cat of the same displacement.
     
  4. Guest625101138

    Guest625101138 Previous Member

    Roughly half the beam. For a small one it could be trailerable without a folding system.

    Also you never have to go backwards. Makes getting into and out of tight spots easier.

    Rick W
     
  5. Bruce Woods
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    Bruce Woods Senior Member

    No your not missing anything. The pacific style proas with a small hull to windward may have advantages when low cost and good speed potential are required. The weight to windward/ harryproa style appear to have no advantage over a lightly built lopsided catamaran, with all the downsides of a proa, ie dual direction steering system required, compromised hull shape with no stern sections , handling peculiarities etc etc.

    See Joe osters web pages for some good info.
     
  6. ancient kayaker
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    ancient kayaker aka Terry Haines

    Thank you for your answers. Rick: I understood that a proa, whether of the Atlantic or Pacific persuasion, was obliged to tack in order to keep the ama on the irght side but as you not there is no reason not to tack if space is tight, and on can accept the loss of performance that I assmue would result from sailing in an unintended configuration.

    I experimented with a canoe by rigging it as a sailing proa. It was disappointing until I lifted the ama clear of the water then it went like a wasp dodging a spray can. Back then I had a lot to learn about hull design so the ama was obviously a dog. I never carried out a plan to rig the canoe with 2 smaller planing amas carried higher to provide the security of an ama on each side: probably unnecessary. A fire took my canoe to that great river in the sky ...
     
  7. Guest625101138

    Guest625101138 Previous Member

    Terry
    My OC1 is about 10% slower than the stabilised monohull for the same power. (To get 10kph on it requires about 30% more power than V14) It is not just the outrigger however it is significant. The outrigger does not carry much load but it offers a lot of drag.

    I think there is plenty of potential to improve on the design of proas. One of the benefits over a tri I did not mention was the lower windage

    As for the hulls my first thoughts are flat bottoms on both the windward and leeward hulls but the windward hull would be wider and easier to plane. Both would have enough rocker to generate good lift.

    The weight initially biased to the windward hull would have lower wetted surface at low speed in low wind. As the load comes off it at higher speed it would generate lift and move onto the plane more readily. It may make the ride a bit bumpy but it would be fast. On the hairy edge the long leeward hull would be taking almost the entire displacement.

    There is heaps of discussion on the rudders that I have not got into. The idea of twin dipping rudders either end appeals to me and is probably something I would try if I was plying with them.

    Rick
     
  8. ancient kayaker
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    ancient kayaker aka Terry Haines

    - that was my conclusion. At the time I was under the impression that it was desirable to keep the outrigger in contact with the water for stability, later I wasn't so sure. However, in one of the proa videos there is a shot of the wake and the outrigger's wake is far less than the main hull. It looked to be piercing the waves rather than riding over them.
     
  9. peterAustralia
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    peterAustralia Senior Member

    which proa style is best. weight to windward or the smaller ama to windward?

    I do not think this can be answered in rhetoric or ideas or theories. I think it is best answered in looking at real world boats. Jzerro, 37ft or so and weight of 2 tonnes, what do you get for your money? how much does it cost? what can it do, how much payload, crew can it carry? How fast does it go? What is it's motion like in a seaway? is it ocean capable? Is it safe? Is it robust and durable etc etc

    Work out all these factors, and compare them against different craft. For close inshore work and going into channels and paying mooring fees, the length of a proa, and the distance needed to shunt would probably not make it the ideal. For cruising thousands of ocean miles, the smooth motion, fast speeds, and high seaworthiness would have many many plusses.

    Some large proas
    Des Jours Meilleurs
    Equilibre
    Gaia's dream
    Jzerro and co
    Harry Proas

    Best to weigh up the plusses and misusses of each craft.

    If you look up the Equilibre proa and look at the amount of money invested to build that boat and what it can do (cross an Ocean), the amount of interior space etc etc. I think it would be hard to beat. For an equivalent cost in a trimaran I think length would be much less, probably to an extent where it is too short to cross oceans with confidence. Looking at the Equilibre proa website is says the boat weighs 1 tonne unladen. This is probably a good starting point in estimating its cost. Construction was in plywood and epoxy from memory (what does a one tonne plywood multihull cost to build in plywood?)

    So rather than a theoretical level, I think these arguments are best worked out on a practical level. Example, say I have $20K, what boat can I build that will comfortably, safely and quickly carry me across an ocean? When the question is put like that, a boat like Equilibre would come out close to the top. For the record I do not know how much Equilibre costs, but I guess you could ask. Jeremie Fischer is the fellow sailing it, I think his brother is an English speaker and from time to time drops in on the proa_file yahoo group, thus if you have questions you may well get an answer

    So I think it is best to focus on real world practicalities, as opposed to theoretical discussions on this and that.

    my opinion.. .please feel free to chastise me.. hassle me etc, I do not mind.

    n peter evans
     
  10. Guest625101138

    Guest625101138 Previous Member

    Terry
    If the boat is not length constrained then the most easily driven choice is to carry all the displacement on a single hull. Outriggers are ideally uninvolved for load carrying.

    This is what the high speed trimarans do. The lee hull ultimately carries all the displacement when reaching at top speed. So a fast tri needs three structures each able to carry all the displacement. By comparison a proa has one hull that can carry all the displacement and another that is skimming the surface with very little load when the boat is sailing on the limit.

    So you can appreciate that the proa is structurally a more efficient choice. Rob's racing displacement target for his 50ft Solitarry is 550kg. He has an actual weight of 98kg for the windward hull with a few bits still to be fitted.

    The origami method of building brings a new dimension to weight and quality control. Something like 90% of the construction of each hull is done as a single infused flat panel. When compared with other one-off methods of construction the other methods are more time intensive and more prone to unintended weight gain.

    Rick W
     
  11. gonzo
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    gonzo Senior Member

    There are some "modern" proas with rotating booms and other inventions. They evolved into shunting sailboats with mast that tilt for good reason. One of the most important is that the center of effort of the sail remains in the same spot on both tacks. Europization of the proas created some ******* designs with the worst of both worlds.
     
  12. terhohalme
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    terhohalme BEng Boat Technology

    What Europization you mean? Some examples please.
     
  13. ancient kayaker
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    ancient kayaker aka Terry Haines

    I'm not so interested in the impact of materials and construction technology as I am in the effect of the basic principles involved.

    Cutting to the chase, the tri (and cat) save energy during a tack or gybe and have consistent performance on both tacks. They are symmetrical and benefit from symmetry by unidirectional sailing which allows them greater optimization of hull design than the proa. The proa sacrifices those advantages to benefit from simplicity and reduced weight.

    With limited technology and both hulls in the water, the proa will be lighter and have less drag, and therefore be quicker in the open ocean than either the cat or the tri. In narrower waters such as lakes or where wind conditions frequently change such as close to shore the proa must be handicapped by the need to either reverse direction through a tack or gybe, or accept less than optimum performance on one tack.

    However with improving technology the proa's weight advantage must become progressively less important and the efficiency of the hull shape will ultimately favour the tri and cat. With unlimited technology, or the technology already available, the tri and cat will triumph over the proa in all situations.

    The width advantage of a proa over a tri in a marina is noted, as is the fact that the vast majoriy of boats rarely leave the marina for more than a few hours a year. But let's face it, the logical choice for a marina-dweller is a monohull powerboat, and the less said about that the better. I'm not so sure if that advantage is maintained over the cat. There are a few design options available to the tri designer to minimise width but they do not seem to be used often.

    If ultimate speed is the only object, then the one-way proa enters the picture. The outrigger devolves to a Bruce foil, then sail becomes a wing and the whole thing only lasts for one trip ...
     
  14. KSONeill
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    KSONeill Junior Member

    A proa's beams are only loaded in compression. They can be much lighter than a trimaran's beams.

    K O'N
     

  15. KSONeill
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    KSONeill Junior Member

    People only freak out about shunting and decide it's the worst thing ever on a boat when they've never done it. It's fine, in fact in many ways it's better than tacking. I raced Hobie 16s for years, now I have a beachcat sized proa. I'd much rather shunt my proa to windward in a lot of wind than tack a Hobie. Arrgh, back the jib, reverse the rudders, sheesh.

    You never blow a shunt. Never. Going to windward you shunt the sails and presto, you're on a broad reach with no depowered zone. Head the boat up, cross any big waves with speed and control, and you're on the new tack. A small light cat has to go through 90 degrees with no power, a wave in a bad place is a bad thing. This never happens when shunting.

    The amount of worry about proa rudders also kind of amuses me. In a world rife with abominations like the Sunfish rudder, for god's sake, you worry about making two rudders? Sheesh. Harryproa rudders work fine. Terho's Pingpong rudders worked fine. Des Jours Meilleurs rudders work fine. Mbuli's rudders work fine. Heck, my rudders work fine and I'm an amateur. Gary Dierking's boats sail fine without rudders, if you want a small, simple canoe.

    On the other hand, I agree that the more money you put into something the more you have to worry about selling it. That's why I have a cheap boat!

    K O'N
     
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