Crab claw Sail

Discussion in 'Boat Design' started by blackdaisies, Oct 23, 2008.

  1. blackdaisies
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    blackdaisies Senior Member

    Some of the crab claw sails I've seen have masts in the center of the boat. A Bermuda sail is similar to crab claw, but in relation to the mast, can the crab claw rig be used on a the same mast? What type of other available mast will a crab claw sail work best on?

    They are shorter and the crab craw sail is turned in every angle even upright above the sailor appearing like a boat top canvas. I don't think the Bermuda can move above the boat, but it is the most similar.
     
  2. blackdaisies
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    blackdaisies Senior Member

    I meant Lanteen sails are similar to crab claw sails, not Bermuda. sorry!
     
  3. rwatson
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    rwatson Senior Member

    No you dont - you mean LATEEN sails.

    Crab Claw sails dont work well on any boat - you can read about the replica Hawaiian Canoe that found Crab Claw sails were very inneficient for most kinds of sailing performance.

    The only good point about them is they spilled strong gusts very quickly, thereby avoiding gear breakages.

    Crab Claw rigs were designed like that because of tradition and material availability.

    Interesting reading on the subject at
    http://www.proafile.com/view/weblog/comments/rig_options_crab_claw/

    including debunking of some dubious performance figures that did the rounds.
     
    Last edited: Oct 24, 2008
  4. blackdaisies
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    blackdaisies Senior Member

    This one says he didn't think crab claw sails did that well, but said just like the site you gave me, it needed fine tuning, but had possibility.

    http://www.rclandsailing.com/catamaran/results.html

    Am I wrong to assume most of the problems are for racing and not just for ocean cruising?

    Here's another forum discussion describing their opinion of it.

    http://www.wharram.eu/cgi-bin/yabb2/YaBB.pl?num=1025071115

    They say it's not really good for bad weather conditions unless it's really bad so much that the crab claw is easy to take down in those conditions.

    There is also discussion of whether the sail should be tightened or not. Most say yes, but I read of another that said they didn't think so.

    There are other types of crab claw sails including the one that is shaped like a U instead of a V. I don't see how a sail can find wind with the wider ends to the bottom. Crab claw sails were referred elsewhere as kite sails. It does give a better comparison to kites being it is sails in midair and turned in any direction like a kite.

    The best bad weather sails I read were Gaff rigged, but I would imagine very heavy to carry. Weather would be a important factors in if a rig is good or not.
     
  5. keith66
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    keith66 Senior Member

    I have had practical hands on experience of sailing a 20 ft proa with a crab claw rig, it is very different to other rigs and many people CA Marchaj included have refered to it generating a dual vortex over the upper & lower yards. we did some crude smoke tests with the boat ashore and this proved to work occasionally! we put a strut between the yards with a tackle to tension the sail and this worked well. It was apparent that it is necessary to allow the lower yard to swing out & upwards this gives a limited kite effect. Sailing the thing was huge fun and it was very fast on a reach, of the wind it generated huge weather helm & was frankly hard to control. The owner changed the rig to a Gibbons rig which was not nearly as powerful & fast though easier to handle. I think that the rig is peculiarly suited to flying proas and not much use on anything else!
     
  6. garydierking
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    garydierking Senior Member

  7. blackdaisies
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    blackdaisies Senior Member

    The first video looked like he was going pretty fast, but that just shows you what you can get from that type of rig.

    The plans that look most like what I want are this:

    http://catamarandesigns.com/lotek.htm

    [​IMG]

    But in a 15 foot version with a berth down under, kitchen area, and maybe even a chemical toilet or compost toilet. Open deck for the sail would be the only option. A trailer sailer cruiser , but in catamaran take apart version or folding catamaran. Preferably made from ferro crete, but I don't know if that can happen.

    do you think two small sails would work better than one? A jib type of crab craw? I'm not sure if that makes more sense.
     
  8. tom28571
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    tom28571 Senior Member

    A couple points:

    If you want a 15 foot catamaran, you are looking at no more than 18" beam for the amas to get decent drag numbers. This is scant room for anything of a cruising nature. Even a 24' cat has little interior room. Fatter beams will result in a clod of a boat that is slow and even more reluctant to tack than a normal cat. Small cats usually opt for a deck structure for limited habitation.

    I think the advantage of the crab claw sail is related to where it originated. That is for sailing in the Pacific ocean swells. The large sail area up high is still able to grab a bit of wind when the hull is in a trough between wave crests. It also means that the CE is up high and heeling moment is high, calling for a high stability hull system.
     
  9. blackdaisies
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    blackdaisies Senior Member

    They make some catamarans with just two dories side by side, so if a dory made to hold the framing for a cubby cabin is used for each catamaran, there would me more than enough room for one big berth, a bathroom of some type in one hull, a small kitchen of some type and sitting room in the other however small. The deck would be used for the sail. If I really get creative, I can get a folding room on the deck and put the sail above the room. It would be heavy, but sailable with two small sails.
     
  10. blackdaisies
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    blackdaisies Senior Member

    I changed my mind for a monohull instead about 15 feet by 6 foot, but with a crab claw and a jib or spinnaker of some type. I would prefer two smaller crab claw masts, but in case of emergency, how would you use a heavy weather sail? One crab claw and one jib for an emergency sail sounds safe.

    I'm dead set on crabclaw sails. I don't know why, but it makes more sense that the wind is in the air, so those triangle squares bigger at the bottom, than top like the crab claw, can't be as good.

    The rig looks flimsy and never needed to be complicated because it's dead set in the middle of two stable hulls. On it's own with ballast and some nice minor adjustments, I think it will do fine.
     
  11. blackdaisies
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    blackdaisies Senior Member

    I wrote one of the boat plans sellers and he suggested I could use the Lynx 14 or 16 for the crab claw sail alterations.

    [​IMG]


    [​IMG]

    http://www.selway-fisher.com/PCup16.htm#LYN

    The rig can be two different types: gaff/gunter rigged and a mizzen mast and sail.

    The crab claw is supposed to have a pivoting mast, but do all crab claws have pivoting masts?
     
  12. lunatic
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    lunatic Senior Member

    Sailed several lesding edge vortex sails http://proafile.com/view/weblog/entries/C12 compression strut between yards to flatten sail helps. Long trailing telltails will show vortex flow sailing, never could get lower vortex to form. Best sailing for area was with all surface flow up into top vortex. Sailed some rigs without a sheet, with neutral helm interesting sail especially offwind but limited upwind both in theory and in my practice
     
  13. rwatson
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    rwatson Senior Member

    Well, maybe in light air when pressure is hard to find, the higher aspect could grab more air - but with such un-aerodynamic design, I doubt it would outperform a more tradional rig even with more mass in the air. Light air is where proper flow control is so critical.

    In heavier winds, it just makes for greater capsize tendency (especially in a monohull) with no other benefit.

    I am sure its fine to have an interest in "non standard" sail designs, but from a purely practical point of view, you are just making lots of problems for yourself with no chance of creating a better performing rig.
     
  14. blackdaisies
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    blackdaisies Senior Member

    Do you think a gaff rigged or junk rig would catch the same or more air from the top? Lateen, which is close to crab claw anyways, would also do as well? The vortex has to be because of the upper end being bigger than the lower. The little swirls of air run down the sides of the sail, but I would imagine they would or could do the same in an inverted sail. The Spirit rig doesn't move, but is inverted. A spirit rig is not able to be moved around but is probably the same as a crabclaw sail, but not really. The crab claw can do outward sideways and upside down, however you turn it.
    What other sail give the most sail on top other than crab claw?

    Thanks for all your replies.
     

  15. blackdaisies
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    blackdaisies Senior Member

    http://www.friend.ly.net/users/dadadata/oddsails.html

    [​IMG]

    [​IMG]

    http://www.friend.ly.net/users/dadadata/odd/mini_gunter_1.gif[img]

    [img]http://www.friend.ly.net/users/dadadata/odd/mizzen_1_tiphys.gif

    [​IMG]


    These look odd, but what experience with the bat wing gunter has anyone had? I thought these still looked better than the traditional triangle sails.
     
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