Anti Capsize / Damage and Sails

Discussion in 'Multihulls' started by Fanie, Dec 8, 2007.

  1. tuks
    Joined: Jun 2007
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    tuks Junior Member

    I disagree, I suspect that you will find that most of these pitchpoles are a result of sailing on the edge of controll and then stuffing the bow into a wave(except the VX40). The sailplan with a high center of effort, pressing the bow down is obviously an important factor, but the reason they capsized is the waves. Keep in mind these guys are racing, they will keep adding sail area untill they are on the limit of crashing.

    [​IMG]
    This is the other type of capsize that happens from the wind gusting.

    I seriously doubt a simple auto release cleat will work. Any cleat that would release when the hull lifts, would also release any time the boat is sailing in any waves or even from the sudden loading when the sails fill.
     
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  2. masalai
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    masalai masalai

    tuks, I am with you on that point, in racing situations and pushing the limits (not cruising by any stretch of the imagination).

    Fantastic images, how about sharing some new & similar posts on Random images?
     
  3. Petros
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    Petros Senior Member

    The cleat release may help some of the time, but this happens so fast that once the bow is buried the sails are already spilling a lot of air (and forward thrust), it is the momentum (both rotational and forward) of the whole ship that carries it over.

    As pointed out this happens when pushing it hard, and it happens very suddenly (consider they may be going as fast as 30 knots or more). With a simple "tilt" release it might also get triggered with a sudden impact on the hull, the shock could register the same as a tilt.

    This happens as a simple matter of physics, the high aspect ratio sail is generating a lot of forward thrust high on the mast, that puts downward pressure on the bow. This is also why you often see the crew toward the back of the hull, to counter balance the rear lifting up. If a wave or sudden gust drives the lee bow downward (as you can see in those great pictures!) there is a sudden drag increase, and at the same time your pivot point move back relative to the CG, as it dives deeper the amount of righting moment goes down! So over it goes.

    I think a cleaver bow design might fight this, one that not only increases displacement, but also generates some dynamic lift too (as in little wings or vortex generators as noted earlier in the thread). Notice the bow shape on the first pic, there is no increase in buoyancy as they dive deeper into the water. how about retractable Wings that deploy with a pressure switch, or even manually deployable when there is high risk of a pitch pole.

    Again, great pictures. I did a quick search but all I found was the monohulls. I did not have enough time to brows all the cat sites, where I had seem many similar pics.
     
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  4. tuks
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    tuks Junior Member

    I suppose I should, I usually avoid the >1000 post threads, will check it out when I have a moment.
     
  5. Richard Atkin
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    Richard Atkin atn_atkin@hotmail.com

    How about a sheet release system that is triggered by a simple laser or camera device that measures the angle of the boat (and the rate that the angle changes). A little bit of electronics and software can be a very cheap solution.
    But as Petros says.....momentum
    I think there could definitely be a place for a sheet release system on cruising boats (less momentum)
     
  6. Richard Atkin
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    Richard Atkin atn_atkin@hotmail.com

    Does anyone have any ideas on how to make a self-righting catamaran? Do any exist (other than radio controlled models)?
     
  7. Fanie
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    Fanie Fanie

    I have been fiddling with an idea lately after seeing Tuks's pictures... How about a trimaran with three hulls :rolleyes: BUT positioned in a large trangle. You could probably even steer with the front hull, almost like a wheelburrough. Since it's for racing only you only need a lightweight structure. Even four hulls could be utilized this way.

    Dipping the hulls could be solved easily with some 'wings' and the angle is turned upwards to elivate the hull upwards towards the surface if the water sensor or pressure sensor senses the water at a certain depth
     
  8. Fanie
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    Fanie Fanie

    Not an easy one... Worst case is somewhere where you cannot touch bottom with an anchor, no other boats...

    Maybe a pneaumatic / hydraulic combo. If the cat is upside down you let a large sea anchor out ... far. Then flood one hull while pumping air in to the other. From the aired hull winch the anchor in over the flooded hull. If it is possible to submerge the flooded hull with the drag from the anchor it may well be possible to get the inflated hull over the submerged one, thus tipping it over. Another large sea anchor tied to the submerged hull that would help drag it under the 'inflated' hull could also help a lot.

    O-hor, how about inflating a large baloon on the mast - like an air bag. This may get the cat to float on it's side and the sea anchor may pull it over more easily. Sounds like a mess any way you look at it.
     
  9. masalai
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    masalai masalai

    Where does one stop? In a large cylindrical hull with multiple hull forms all the way round the outside. That will never tip upside down because every side is both up and down?

    I thought a cat was a non tiping mono & a tri a non tiping cat and a penta-thing an abortion? Non tiping requires a VERY buoyant mast tip?
     
  10. Fanie
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    Fanie Fanie

    You're right, a cat is not supposed to capsize. However, when that does happen for whatever reason...

    I suppose it's the same risk getting your car on it's roof. I'm sure the sea has other challenges than the roads though, I've heard of freak waves and swell's, don't know how common they are.

    It seems some people succeed often in getting in some problematic situations, others either avoid it or handle it differently. If you don't have a choice like bad weather and no tropical island with dancing girls on it you can sit it out behind, it probably boils down to your choice of handling the situation.

    If you have in the mast tip something that can inflate... ie similar to an emergency raft or whatever those blow up things (not dolls) are called, it may well be possible to get the cat or tri half-way up. Don't know how practical it would be, someone may have to try it out. There should be some way of correcting a capsize.
     
  11. masalai
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    masalai masalai

    Fanie, Maybe the Aussy sardonic "tongue-in-cheek" humour takes a bit of getting used to. See cylindrical hull line and use vivid imagination, only a septic would think that a good idea and successfully sell it to the pentagon. I do not that kind of "hutspa" of which I am jealous / envious.
     
  12. Alan M.
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    Alan M. Senior Member

    It's been done.

    http://www.boatdesign.net/forums/showthread.php?t=17142

    I don't know how successful it would be in self righting, but it certainly would be far more likely to need that capability than a more "normal" design.

    The fact is, cruising catamarans are far less likely to invert than similar sized monohulls, and THEY won't neccessarily self right either, despite what the myths say . (The angle of vanishing stability for a Beneteau oceanis 38 was quoted as only being 109', with probably only about 25% of the righting moment of a 38 foot catamaran.)

    For a cruising boat capsize is very unlikely. IMHO less likely than sinking is for a ballasted monohull. It's probably easier to prevent capsizing too, when you think of the number of things that could sink a mono, such as failed through-hulls, failed wet exhuasts systems, broken rudder shafts, etc etc. Why go to great lengths to be able to self-right, when the need is probably never going to arise anyway? How many monohulls have systems built in to recover from sinking?

    You just have to use some common sense - if you are going to be fishing, or reading or whatever and won't be able to pay attention to the boat, then reduce sail. Reduce sail even though you don't need to, if you can't watch what's going on properly.
     
  13. Richard Atkin
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    Richard Atkin atn_atkin@hotmail.com

    I think its worth considering these 2 points:

    1. people buy cats because they are fast and comfortable.

    2. people don't buy cats because they don't tip back up like mono hulls.

    How profitable would it be to form a TIDY self righting system?? I think it would be HUGELY successful. You would convert thousands of monohull sailors and would-be sailors to the catamaran experience. I think this thread posted by Fanie is very important.
     
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  14. Alan M.
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    Alan M. Senior Member

    A lot of people just follow the herd. Mono's don't always tip back up. Sometimes they stay upside-down, and sometimes they sink. Doesn't stop people from buying them.

    IMHO even if you built a good looking, fast, comfortable, cheap, roomy, self righting multihull, a lot of these people would still buy mono's.
     

  15. GTO
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    GTO Senior Member

    I just had a great idea to self-right a cat or tri.

    Strap a JATO rocket on the side! WHOOSH..BAM!!!!

    Oh yeah.

    Could get a little fancy with the installation and as the boat returns to near level the JATO rotates aft and off ya go! Might as well make up some lost time. Well, thinking further, the rocket could ignite before the hull rotates a full 180 degrees. Never even hit the water. FLIP...WHOOSH...BAM!!! Self righting in less than 5 seconds. Sweet!

    Hmmm, most places don't even allow a pistol, not sure a military grade rocket would get through customs though.
     
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