Self-righting multihulls. How ?

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

  1. xarax

    xarax Previous Member

    "A monohull retains at least one major advantage over most multihulls in that it can be made self-righting."(John Perry)
    An obvious way to achieve self-righting on a multihull is to put a keel, weighting a little more than the (insubmersible) mast. If the mast weights, say, five percent of the whole boat, a keel weighing ten to twenty percent would do the job, and the boat would still be lighter and faster than a monohull. Why we have not seen any such sailboats?
     
  2. Crag Cay
    Joined: May 2006
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    Crag Cay Senior Member

    Oh we have seen them. Do a search on the history of multihulls and you will see that during the 1950's and 60's lots of people experimented with ballasted multihulls.

    They also sailed around with huge floats on the top of the most to stop them inverting. However the 'holy grail' of the self righting multihull proved as elusive as the real thing, despite periodic claims by some that they have at least got a sighting of it.

    But James Wharram proved that if you wanted stability, then his ideas were perfectly workable, and if you wanted outright speed - well, learn to be careful.
     
  3. yipster
    Joined: Oct 2002
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    yipster designer

    recall or imagin there is a way by canting a free standing mast level to boat / surface with the shrouds
    than all sit on top of the mast and reverse the proces to get airborne, something like that, bit foggy today
     
  4. terhohalme
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    terhohalme BEng Boat Technology

    Self righting multihulls?

    Why? Have you ever sailed one?
     
  5. yipster
    Joined: Oct 2002
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    yipster designer

    nothing personal but...

    i did in a wet suit, but even if i had not, i dont think its very helpfull asking why without answering a question
    soo... as a fellow multi sailer can you tell about rightning a cat?
     
  6. terhohalme
    Joined: Jun 2003
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    terhohalme BEng Boat Technology

    Yipster, just want to know if xarax ever have sailed a multihull and what could be the possible reason for demand of self-righting. A little more backround and it would be easier to consider better answers.

    Beach cat or cruising? Sheltered waters or offshore?

    "A multihull retains at least one major advantage over most ballasted monohulls in that it can not sink" :)
    At least if multihulls are designed by EU standards.

    No means to be inpolite. English is just a foreign language for me...

    Terho
     
  7. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    No prob Terho, we appreciate the effort you and all the other non-English folks put into translating their thoughts!
    Now as for the cat.
    I think the main reason for discussing self-righting is that, apart from marina fees, self-righting ability is one of the few advantages that monohulls still have over multis. It's also one of the few things that make traditionalists a bit worried about sailing on multis. A self-righting offshore cat would be the ultimate dream boat for many people, with huge accomodations, comfortable at anchor and safe at sea.
    Not sure how this would scale to a full size craft, but at the SailBot race earlier this summer, one of Waterloo's cats (LOA a bit under 2 m, I think) had a nearly-rigid wing sail. Their setup was a bit top heavy but the boat fell over in the gusts many times, and the wing sail floated- thus the cat never rolled, or pitched, past about 110 degrees.
     
  8. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    Self righting is hard

    Hello all,

    No expert myself but as stated before there have been several attempts at self righting but now people don't really worry about it.

    During the seventies and eighties many designers tried various different approaches to design the ultimate multihull. In the 1976 multihull symposium Carlos Ruiz showed a simple model using waterbags to re-right his cat. Later a builder of one of Derek Kelsall's designs capsized and re-righted his 36 Tonga in a lake in England. Then no one bothered much afterwards.

    It is probably because capsizing is very rare and requires huge compromises in the structure of the boat. Hatches need to be made watertight, pumps rigged and much more. It is probably better to put half the effort into making the boat not fall over on the first place - get a good parachue and drogue and then making sure the boat is habitable up side down.

    Many modern production cats are heavy and so are stable. However they may be unsuitable for inverted flotation. There have been a few fatalities when cats have capsized and people stayed inside and asphyxiated.

    There is no ultimate boat and those who want full self righting are best to stay on a mono. As Jim Brown (the fab tri designer said) you only need self righting if you fall over a lot anyway.

    If you want to read about the attempts at self righting and why it may not work in reality buy "The capsize bugaboo" published by Multihull mag and read "The case for the cruising trimaran" by Jim Brown and "The cruising multihull" by Chris White. All great reads and a must for the multimariners library.

    cheers

    Phil Thompson

    www.foldingcats.com
     
  9. Doug Lord

    Doug Lord Guest

  10. CORMERAN
    Joined: May 2006
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    CORMERAN Junior Member

    Self Righting - The Myth of......

    Guys...

    I think it's time we all chipped in and paid for xarax to
    go on some voyages on the various types of vessels he mentions.

    Study all these hydrodynamic questions first hand.....
    before asking any more questions. That to be kind - indicate
    a certain absence of real world experience.

    To xarax:

    The huge waste of time trying to make a sizable multi - hull
    self righting has been explained well by catsketcher.
    This is old news to most of us...........

    So I will go futher and challange your basic assumption !
    Based on third hand info.

    THAT SELF RIGHTING IS A GIVEN WITH ALL MONOHULLS
    - AND SOME HOW, THIS WILL SAVE YOU, WHEN THINGS GO BAD.

    It just isn't true. The laws of physics are working against it.

    Mr. Perry is a skilled and respected designer - however.........
    He has been quoted out of context.

    Most of the vessels he has been involved with, I suggest,
    and other craft that HAVE successfully self righted are:

    A. Narrow across the beam.
    B. Seldom much over 35 ft in length.

    There was a monohull yacht race that was hit by a very
    severe storm.
    In which, much to the dismay of the sailors involved, a lot
    of the yachts showed an extreme reluctance to right themselves !

    These boats had extremely high ballast ratios.
    With NARROW beams they would have spun like tops.

    However.............
    They, were designed like beach boats.
    With very WIDE beams and FLAT planning bottoms.
    They had the same HIGH STABILITY- up side down
    - as right side up ! ( Just like a multi- hull ! )

    The very opposite of the Wineglass vessels of yore.

    So REAL WORLD evidence gives lie to this cherished truism
    that, " We're all right, Jack ! She will bring us back....."

    Even when a yacht does self right - this is no guarantee
    it won't sink.
    Like when a former Prime Minister of Britain sank his Gold Cupper.
    This I'm sure was a very " Bristol " monohull.

    However.............

    If memory serves:
    They hit a rogue wave in the Channel.
    Did a 360 roll over......
    Lost a man overboard.
    Went back to find him.
    Hit the SAME wave pattern.
    Did another 360 ...... and proceeded to sink.

    The huge stresses on the rigging, rolling over - and over
    - ripped the hull to deck connection apart........
    The ingested sea water and wave action reduced the
    freeboard to zero...
    So down she went.
    With all that wonderfull self righting ballast, pulling the boat down.
    Fast !

    Once you get much over a certain displacement - self righting
    will cause so much collatral damage - that it becomes
    a danger. NOt a safety factor.

    Finaly:
    Talk to the Captain of any commercial, monohull, vessel
    - say from 500 ft - 1000 ft long.
    And ask him,
    ".......what is the self righting capability of your ship ? "

    We, all, look forward to his answer.
     
  11. xarax

    xarax Previous Member

    Sailboats have either keels or amas. Having both (a keel AND an ama) is a road seldom taken. I am not convinced it is an impasse, though. Modern technology ( materials, pumps, etc) could well produce some hybrids that we can not foresee.
     
  12. Doug Lord

    Doug Lord Guest

    Self-righting multihulls?

    There has been much discussion about the Reynolds 33 narrow beam cat. Here is an article worth reading all the way thru by Randy Reynolds. Xarax, he is working on a 100% "self-righting" system:
    Reynolds Sailing Catamarans Randy Reynolds and Morrelli and Melvin.
    Address:http://www.r33.com/en/update/sept05.asp
    --------------------
    Here's a self-righting tri description by Paul Kruse:
    THE FLIP FLOP CONCEPT
    Address:http://www.trikini.com/FlipFlop/Untitled2A.htm Changed:9:32 AM on Tuesday, March 4, 1997
     
    Last edited by a moderator: Sep 12, 2006
  13. CORMERAN
    Joined: May 2006
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    Location: Vancover,BC, Canada

    CORMERAN Junior Member

    Self Righting

    To Mr. Doug Lord:

    Like Mr. Perry - messers Morrelli, Melvin
    and Reynolds have the respect of their peers.

    However...........

    If you read their statements carefully - the objective
    is to come back from only 90 degrees.

    Coming back from 180 - like a classic monohull is another story.

    Given that they will have some future success.
    - please note that the vessel concerned is less than 35 ft.
    - with a relatively narrow beam.
    - which is close to the criteria I suggested before.

    This whole self righting thing is in essence only really viable
    to a very narrow range of boats. - And I emphasize the word boats.

    To Mr. xarax:

    The objective of many of us participating in these forums
    is to further the State of the Art.
    To get REAL answers to serious, PRACTICAL concerns.

    So I don't think people will be willing to let you to cop out
    - when the poor logic of your presumptions start to unravel
    - and you glibly suggest that some mythical tech. in the
    far distant, misty future will make your wishfull thinking valid.
     
  14. Doug Lord

    Doug Lord Guest

    "......To Mr. xarax:

    The objective of many of us participating in these forums
    is to further the State of the Art.
    To get REAL answers to serious, PRACTICAL concerns.

    So I don't think people will be willing to let you to cop out
    - when the poor logic of your presumptions start to unravel
    - and you glibly suggest that some mythical tech. in the
    far distant, misty future will make your wishfull thinking valid.[/QUOTE]
    =============================
    Well, I think Mr. Xarax deserves better than a comment like that because he is 100% right-at least he MIGHT be right.
    Here is a concept done by Sean Langman/ Andy Dovell-hardly crackpots- a multihull with a canting keel(or a monohull with buoyancy pods?)-a hybrid by any definition:
    langman1.jpg
    Address:http://www.sailinganarchy.com/innerview/2005/images/langman1.jpg Changed:9:27 PM on Sunday, October 23, 2005
    ---------------
    And here is another hybrid done by Julian Bethwaite and Martin Billoch -this one with a fixed keel:
    billochcut.jpg
    Address:http://www.sailinganarchy.com/fringe/2005/images/billochcut.jpg Changed:7:21 PM on Wednesday, September 28, 2005
    ----------------
    If you're seriously interested in the "State of the Art" than you cannot ignore the work by these respected designers and sailors.Nor can you so lightly dismiss Mr. Xarax' comments.
     

  15. Baronvonrort
    Joined: Jan 2006
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    Baronvonrort Junior Member

    Doug

    I know Sean Langman and i recall his first 18ft skiff was called "Corinthian Doors".
    Sean Langman gave up on that concept quite some time ago along with his other canting rig with canting keel monohull concept.

    Sean uses these concepts to interest potential sponsors so i have to burst your bubble on that one.

    Sean Langman is doing this years Sydney to Hobart on probably the oldest and slowest boat he has sailed in many years.
     
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