50'Self-Righting, 1200lb, Single Foil Proa-Rob Denney

Discussion in 'Multihulls' started by Doug Lord, Nov 20, 2006.

  1. Doug Lord

    Doug Lord Guest

    This is without a doubt one of the most innovative multihull designs I have ever seen. Check out Rob's site for a detailed explanation of the extraordinary concepts involved. Anybody considering a multihull of whatever size should check this out carefully:
    harryproa/solo transpac
    Address:http://www.harryproa.com/SoloTranspac/SoloTranspac_1.htm Changed:4:01 PM on Monday, November 20, 2006
     
  2. Doug Lord

    Doug Lord Guest

  3. Vega
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    Vega Senior Member

    Interesting boat, but he didn’t say that his boat is self-Righting. He says that the boat MAY self right after a capsize.

    And he is talking about a knock down, not what I call a capsize (inverted position):

    "May self right after a capsize. Because the sealed mast is canted 7 degrees to leeward and is in the lee hull, the boat will only capsize to 83 degrees. When capsized, the boat swings around until the mast is pointing into the wind. The combination of the offset ww hull weight and the windage will right the boat, in which case we have the world's first self righting, unballasted multihull. If not, it is a pretty simple operation to add a little more windage or weight (water) without the skipper leaving the cabin in the windward hull."

    If the boat is really capsized (inverted) I don't understand how he wants to add more windage or weight and certainly, it don't look simple to me:p
     
  4. Doug Lord

    Doug Lord Guest

    50' selfrighting proa design

    I don't know Vega: the design is clearly for a self-righting boat. Rob is hedging his bets when he says "May" because it hasn't been tested on the 50 footer yet. Wise move.
    It was tested on his 25 footer but because of the pocket luff's filling with water it didn't work.
    I think it's a brilliant idea and seems likely to work. IF it does work, it will represent a significant achievement in multihull design.
    In all my early sailing "capsize" always(almost always) meant a 90° knockdown; in many boats such a knockdown was always recoverable with crew effort. "Turtling" was the next step....
    Did you pick up on the single foil?
     
  5. Vega
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    Vega Senior Member

    I guess that the notion of capsize has to do with the kind of boat, small sailboat or yacht. I understand what you mean, in a small boat, with the sail and the crew out of the boat, in most cases the boat will not go turtle and even if it is not a ballasted self-rightening boat, the crew can right the boat.

    But regarding a yacht I don't think you should call a knock-down a capsize. The crew will remain in the boat and the boat will right itself up without the crew assistance.

    Do you call this a capsize?
     

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  6. Doug Lord

    Doug Lord Guest

    50' selfrighting proa

    Vega, your picture looks like partial knockdown as a result of a broach? Not a capsize. Interesting to ponder: I always considered a "knockdown" a keelboat knocked flat with it's mast parallel and/or touching the water(from which it should recover with very little, if any, crew assistance). Since 95% of my sailing experience has been in dinghies/small multies capsize always refered to a boat knocked 90° and supported in that position by the buoyancy in the mast(hopefully preventing a turtle) from which crew effort could right the boat. A capsize could lead to a turtled boat but capsize did not mean turtled(bottom up).
    As I understood Robs description of his boat, the physics of what happens (should happen) are more similar to the keelboat since no(or very little) crew assistance is required for the thing to right itself. It does ,however, have in common with the dinghy the requirement that the rig remain intact and that the mast is buoyant enough to support the boat with the mast nearly parallel to the water-though ,theoretically, not for long.
    --------
    PS- I make no claim that the above "definitions" are the REAL definitions-just the common understanding I've picked up from close to 50 years of sailing and racing on the Gulf Coast of the US and Florida's east coast.
     
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  7. Vega
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    Vega Senior Member

    Fair enough.;)
    Anyway It is an improvement and possibly it will work if there are not breaking waves involved in the capsize. If there are, the forces involved are so big that the mast will broke and in this case, that system will not work.
     
  8. rob denney
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    rob denney Senior Member

    vega
    Anyway It is an improvement and possibly it will work if there are not breaking waves involved in the capsize. If there are, the forces involved are so big that the mast will broke and in this case, that system will not work.

    G'day,

    Vega, You are correct, it is only a 'maybe' at this stage as I have yet to try it. However, the numbers stack up, so it may only be a case of tweaking the mast cant angle or weight in the windward hull to make it happen.

    You are less correct about the definition of a capsize. For a proa with a buoyant mast it is 90 degrees. For all other multis it is 180 degrees, although for most of them, by the time they get to 60 or 70, they are past the point of no return.

    Re the mast breaking: to make it stiff enough, the mast has far more strength than is required so it should stand up to a fair bit of abuse. My experience with the half size model is that once the boat has capsized, and swung round so the mast points upwind, the chances of damage are pretty neglible, the whole thing slides sideways with little to impede it. Reasonable size waves help a lot to lift the mast and aid righting. I hope I neve get to test it in serious Tzu Hang type waves. Hopefully I would have dropped all sails, lifted the rudder, put out the sea anchor and gone below to read a book long before the seas got to this stage.

    regards,

    Rob
     
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  9. Vega
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    Vega Senior Member

    G'day to you too (here is blowing 70K and floods everywhere):rolleyes:

    Rob,
    I have been following the development of your cruising Proa for some years. It is a very interesting concept and I believe that the concept makes a lot of sense for cruising. I agree that regarding stability and safety, it has advantages, compared with a trimaran or a catamaran.

    Regarding the buoyant mast, I think that possibly it will work with a small Proa, but not with a big cruising one. I believe that in this case it will brake, as it normally brakes on cruising monohulls.

    But I think that if you utilize a kind of self deployed big air bag on the hull ( on the side of the sail) and a small bulbed weight mounted on a retractable foil on the other side, the boat will right itself up in most of ocean circumstances. The air bag will also prevent the mast from breaking.

    For being commercially interesting, at least here in Europe, the Proa will also have to have a system that permits it to be “foldable”, I mean, to be able to fit in just one marina berth (not two), but that doesn’t seem difficult to me. Marinas are really expensive here.

    Regards
     
  10. rob denney
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    rob denney Senior Member

    G'day,

    70 knots would be a good test of the "drop the sails, lift the rudder, deploy the sea anchor and go below with a bottle of scotch" theory of survival!

    Glad you like the boats. A big proa may well break the stick if it capsized. However, there are very few large cruising cats that have ever capsized. The proas have very large righting moment, plus the bendy rig, so I suspect they would be even less likely to do so.

    Air bags are pretty unreliable in salty environments, and extra weight is anathema to multi sailors, so I suspect that neither would be acceptable. The canted to leeward mast is more likely to gain acceptance, which, if the heavy weights in the windward hull are low enough, should give it positive righting moment up to 90 degrees of heel, making it effectively uncapsizable by wind strength,

    regards,

    Rob
     
  11. catmando2
    Joined: Sep 2006
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    catmando2 Malaysia bound....soon

    G'day Rob, how do the rigs go on the French 60' tri's when they go over?

    Surely if your section is fat enough you'd be looking pretty good.

    Dave
     
  12. Alan M.
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    Alan M. Senior Member

    Unless it sinks.
     
  13. Alan M.
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    Alan M. Senior Member

    Rob, given that mistakes happen, what happens with a proa if you end up with the "leeward" hull to windward? I imagine this would be a reasonable possibility when sailing downwind, much like an unitentional gybe.
     

  14. rob denney
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    rob denney Senior Member

    The 60 footers go upside down and require assistance to get them up. If they don't lose their mast in this situation, then it is probably overdesigned and could be lighter.
    On my small proa the mast is 7m.24' long with an average diameter of 60mm/2.4". It holds the boat at 90 degrees easily. The big boat will have a 500mm/20" chord wing mast, so should indeed look pretty good. If it is canted outboard, it may not even need to be sealed as the boat will have self righting ability at the point where it is in the water.

    On my boats, the sheet goes from the end of the boom directly to the windward hull. If the boat is caught aback, the sail weathercocks and the boat stops. It is then fairly simple, and totally unstressful to drift downwind and steer it back onto the correct course. Unintentional gybes are unlikely as the boat is light enough to sail the apparent wind angles downstream, but if one does occur, the boom swings around until it is pointing upwind and the boat slowly loses way. No banging, crashing or breakages. Unstayed rigs are the solution to so many problems on modern boats, it amazes me that there are not more of them.

    regards,

    Rob
     
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