Self-righting multihulls. How ?

Discussion in 'Sailboats' started by xarax, Sep 6, 2006.

  1. Doug Lord

    Doug Lord Guest

    Hybrid

    ---------------------------
    Thanks, Baron. I've been curious what the status was on Langmans concept. Conceptually, it is still a great illustration of innovative thinking. Do you know anything about the Bethwaite/Billoch
    "Pterodactyl"?
     
  2. Baronvonrort
    Joined: Jan 2006
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    Baronvonrort Junior Member

    Doug
    I have not seen or heard anything new about Julians Pterodactyl design and i suspect it will go no further than the drawing board.

    There are a few 18ft skiff sailors who believe Julian only gets one idea in 50 to actually work.
     
  3. sharpii2
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    sharpii2 Senior Member

    'self rescuing' vs 'self righting'

    The Gougeon brothers here in Michigan built a boat that could do that. It was thirty two feet long and eight feet wide. The hulls weere ver slim and most of the accomodations were in a really cramped deck house. The mast had a float and adjustable shrouds. Since the mast was much taller than the boat was wide, the mast had to be canted only moderately to plop the thing back on its feet. I've actually see vidios of them doing this.

    The boat was supposed to go into production, but I dont think it ever did. It was a thirty two foot week ender which was to retail at at least $50k. I wonder why it never caught on. But it was fast. Mainly because you could soop up water into the windward hull as ballast.

    Calling this 'self righting', I think, is a real stretch. 'Self rescuing' may be a more appropriate term. 'Self righting', in my view, is when the boat can pull itself back upright, with or without the assistance of the waves that probably capsized it in the first place, with no effort at all by the crew. Just about all the boats that got into trouble in the imfamous '79 Fastnet race mannaged to do this (though some later sank). I do not believe it is possible to make a decent performing multi that can do this.

    'Self rescuing', on the other hand, is, I believe, achievable with multi's with some careful effort in design. My definition for 'self rescuing' is that the boat, with dilligent efforts of the crew, can be brought back upright without outside help. That may be a more sensible goal.

    Bob
     
  4. Doug Lord

    Doug Lord Guest

    Pterodactyl/ multihull keelboat OR monohull with pods

    ----------------
    Baron, just got an e-mail from Clynton at Bethwaite Design who said the "project has been put on hold-but very interesting."
    At least it's not abandoned....
     
  5. rob denney
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    rob denney Senior Member

    self riighting multis

    G'day,

    If we assume that multis covers anything with more than one hull, then the very simple solution is a proa with a buoyant mast. The boat capsizes to 90 degrees and swings round until the mast head is pointing into the wind. There are then a number of options:
    1) Have sufficient windage in the trampoline and weindward hull to blow the boat upright. This could be augmented by unrolling a piece of canvas down the trampoline.
    2) Have a buoyant boom and arrange the sheets so it can be pulled under the rig, adding to it'sbuoyancy.
    3) Have the mast canted to leeward so the boat floats with the beams at more than 90 degrees to the water/mast. The canted mast is beneficial in light air to twist the top of the main. If the boat is wide enough, it will noit cost much in added heeling.
    4) Keep all heavy equipment down low in the windward hull so that iot helps bring the boat up.

    I have started building a 50 foot proa for the next solo Transpac. It was not specifically designed to self right, but has static capsize wind speed of 20 knots apparent. In 20 knots true, it will theoretically self right. With a canted rig, it should self right in 13 knots, with no input from the skipper. Will be interesting to see.

    This does not address pitchpole capsizes, but if the rig is low enough (12m/40') and the boat long enough, it is lee likely to happen. I will be using an Outleader kite, so pitchpoling is even less likely.

    regards,

    Rob
     
  6. CORMERAN
    Joined: May 2006
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    CORMERAN Junior Member

    " Self - Rescuing "

    To sharpii2 :

    Absolutely !!

    " Self - Rescuing " is a MUCH better term.
    Which the Wizard Brothers - from Michigan came close to doing.
    ( Proberly, before some of the gentlemen presently pondering
    this 'weighty' problem were born ! )

    PLease note: that the Gougeon Guy's vessel follows the criteria
    that I defined.

    i.e.
    A. Relatively NARROW BEAM ( for a multi - hull )
    B. Less than 35 ft overall length.

    Also, the only reason it had a good turn of speed was due to
    the water ballast.

    ( Gentlemen....
    - Canting keels and masts - pumps and movable
    ballast ( no matter how incredibly well designed) do not make
    a vessel SELF - RIGHTING !
    A boat that " rights it's self ", by definition ,
    does so - WITHOUT ASSISTANCE !! )

    Then there's the inherent, uglyness factor.........
    The Gougeons produced some great performing AND elegent craft.
    However, this boat - in my eyes - was sadly, not one of them.

    - And (as you indicate) the market place seemed to agree with
    me - so the hoped for series production, did not happen.

    There's a lesson here, perhaps..........

    The Universe and God - in her wisdom - does not give mules
    the abiliy to have children.

    Just as, with many one - off vessels, no sister ships ever get built.

    Cheers !
     
  7. djwkd
    Joined: Jul 2006
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    djwkd Senior Member

    so...what if,you put the weight in the middle,in a capsule under the bridge deck?is it possible to do it that way?

    have somem weight at the front Starboard,front port,rear port,rear starboard?
     
  8. marshmat
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    marshmat Senior Member

    I saw a two-metre model racing cat recently that was somewhat self-rescuing. It had a wing sail cored with an ultralight closed-cell foam. When it capsized (which was frequent, since the thing was way overpowered and it was gusty out), the boat would capsize only until the wing sail hit the water (about 110-120 degrees). It wouldn't rollany farther no matter what happened. The thing couldn't right itself from there without assistance, but it's an interesting step and one that I think would scale up pretty well.
     
  9. yipster
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    yipster designer

  10. sysfx
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    sysfx Junior Member

  11. Guest625101138

    Guest625101138 Previous Member

    I played around with the idea of a self-righting cat. I even took out a provisional patent on an articulation system that would allow a cat to fold and self-right.

    I tested various ideas at 1m scale and 3m scale. The photos below show the one that sailed best at 1m scale. It has a 30% ballast ratio and buoyant mast. It was self-righting without any assistance from wind, wave, or human input.

    I think you could make a fast practical boat with a rigid wing sail and less than 30% ballast ratio.

    I fear anything that articulates could create some nasty pinch points so for a serious ocean boat you would want rigid location of hulls. The loads on any connections that enable the articulation would likely be high.

    Best result from a sailing perspective would probably be a trimaran with a rigid wing sail that could cope with the high forces involved when the boat is knocked down.

    The 1m model shown was very well mannered. It would fly the hull and then balance out. Helm was almost neutral in this condition.

    Rick W.
     

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  12. Guest625101138

    Guest625101138 Previous Member

    An interesting aside to the self-righting cat is the condition of the cat after pitchpoling or nosediving. It will sometimes end up stern or bow down i.e. not always on its side. This is typically the condition that sets the required ballast because the base of the mast is higher above the water and recovery angle worse.

    For this reason it pays to avoid having buoyant ends in the hulls. To be truly self-righting you need to be able to recover from any condition not just a roll.

    Rick W.
     
  13. sysfx
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    sysfx Junior Member

    Multihulls are competitive against monohulls because they don't need ballast for stability and the consequently lighter displacement allows to sail faster with the same energy.

    In order to keep this competitive advantage, ballast should not be used in the design of a self-righting (or self-rescuing) multihull.

    I agree with the real world engineering problems arising from the self-rescuing system used in the 23 ft folding tri. I'd really like to see them solved, though. The development of safer multihulls require this feature.

    All the best,
    Luiz
     
  14. Guest625101138

    Guest625101138 Previous Member

    Luiz
    I would not want to discourage anyone from pursuing the concept of a ballasted multi-hull based on an opinion that it is a slow concept. In fact there is probably an optimum that can be achieved with a ballasted multihull that would outperform most monohulls and multihulls in the speed department.

    You gain a huge amount of form stability with the multihull and much bigger bang per kg in righting moment with the ballast. You can also very comfortably fly a hull without risk of rolling so you can cruise all day at full power in a 'relaxed' fashion. With a tall rig to overall beam ratio the boat will develop weather helm when truly pressed. (I took the photos shown previously while controling the boat. The boat would fly a hull without any control input. That was the attitude it liked to take once the wind was strong enough to lift a hull.)

    Also a long slender hull is less affected by chop than a wider hull so it powers through it rather than bobbing and pitching.

    My model had a keel that could be swung backwards to reduce draft and lift the bow so you could easily beach a large boat. It would sit flat once beached. The boat was still very stable once the keel was tilted but obviously the boat was no longer self-righting.

    So for someone looking for a roomy stable sailing boat with ultimate safety features of being unsinkable and self-righting then a ballasted cat with 20 to 30% ballast ratio and buoyant mast or rigid sail is something to explore.

    Rick W.
     

  15. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    Don't design capsize vulnerability in

    Hello all,

    I have been thinking about capsize for about 25 years. In all that time I have never capsized one of my multis although some friends did. Now I fear capsize much less than before. Our boats are safer and better built.

    A modern cat is very very stable. It imparts a feeling of safety to the crew. My 24ft 1958 Piver was much less secure than my 1977 Twiggy which is light years behind my 38ft 1998 Chamberlin cat.

    Witness the accounts from Richard Woods and the crew of Ramtha in the NZ bomb storm of how these abandoned boats got through horrendous conditions. Modern cats can take incredible punishment.

    If capsize is rare in large cats it seems sensible to make your cat as large as possible by putting all your money into length and width rather than re-righting features. Above about 38-40ft seems to give a very large resistance to capsize.

    Although the idea is intellectually challenging I think that the need for self rescuing is much less compelling than it was 20 years ago. Putting your time and effort into a parachute and spare drogue, bigger boat, learning how to sail well, capsize preparations for life upside down, having more time for awaiting better weather are better options that will usually help improve the cruise anyway. On top of this advances in 406 Epirb pricing mean that by the time the waves have died down sufficiently to try the self righting system you may have a ship going by aware of your presence. Everyone can now afford a 406. Having a dry inverted area and carrying enough food and water upside down is probably much more realistic option.

    As I owned a Twiggy ( they capsized three times in 1981-82 I bought mine in 1989 - sold in 1996) I was worried about capsize when I built our 38ft Chamberlin. I have stop cocks on the breathers on the water tanks so the water won't run away, full bulkheads at the front of the front cabins for collision and inverted bouyancy and a huge storage box instead of a cockpit for light things and inverted bouyancy. After sailing and cruising Kankama for three years I am going to cut up the box and make a normal cockpit. All of the other capsize preparations are non invasive. The chances of flipping our boat are so low that the high impact box doesn't make sense.

    The problem with re-righting is that the boats may be some much more likely to capsize that they then need the re-righting system. Floating wing sails would do this well as they would be a liability in heavy weather and may promote capsize. Therefore they are needed for re-righting. Even if they don't imcrease the capsize risk then self righting features may be so invasive that you get rid of them if they impact on the way you use the boat.

    There was a picture of a cat on this forum with narrow beam and a big cabin that could self right. These design features also meant that it would capsize easier. I have designed a folding cat that increases beam on the water so that it has far greater capsize resistance than normal trailerable cats. The real value in this approach will be proven if people feel that the boat is better to live in and use as well. The reason monos need to self right is because they can get knocked down. You can go two ways - avoid capsize or self right. For non radio control multis I think the modern multi has shown that increasing capsize resistance is the much better way to go.

    cheers

    Phil Thompson
     
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