Triple keeled boat plans/vs trimaran vs swath boat for stability and searworthiness

Discussion in 'Stability' started by blackdaisies, Sep 23, 2008.

  1. blackdaisies
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    blackdaisies Senior Member

    I was hoping to get information on tripple keeled boat types. I know they are very seaworthy, but cause problems in shallow drafts. What is your opinion of the stability of long keel with twin keels on the outer edges? Do you think they offer stability equal to that of a swath boat? Egual to a trimaran?

    I read long keeled boats were self righting, so with 2 extra keels, is it still self righting? For small boats, they do well on the ocean, but how much more stable do you think a keel boat is even compared to a flat bottomed dory?

    If anyone has any ideas I'd love to hear them, plus have you ever heard of a trailerable model? I've seen this one:


    I like the longer bilge or twin keels as opposed to the more narrow ones. Is it more difficult and what problems do they cause? I know there are tons of benefits, especially since the boat can sit on them while being trailered or before the tide.
  2. Brent Swain
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    Brent Swain Member

    Twin keelers can be almost as fast as a single keeler if the keels are angled out enough to minimise interaction between them. Triple keeled boats are as slow as a government bureaucrat, as there is no way to minimise the interaction between three keels.
    The stabilty of a boat , regardless of how many keels she has, is determined by the draft. Two identical hulls with identical deck structures, of the same draft, have the same stability , regarless of how many keels they have.
    Single keelers only gain stability by having deeper draft than most twin keelers.
  3. blackdaisies
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    blackdaisies Senior Member

    What about two identical long keels 6 feet deep? Would that be slow? To go all the way to the end of the boat or start to decline until it blends with the tip?

    Do you think the long keel boats sail very well even better than multihull designs? I don't care for speed, but I don't want to lug dead weight either. I want a boat that can go in any kind of water, not necessarily shallow, but in very bad water conditions. Do you think a keel boat is best for this compared to non keeled boats? What about non fixed keels? Do you think they are equally as effective as fixed long keels?

    Thanks for the reply. I was hoping someone would still know about keel boats, not flat bottom boats, being I think they are mostly obsolete or just not used.

    What about double keels that are made as long, not as wide, as single long keeled boats? I know they make them 4 feet for double and 6 feet usually for long keeled, so two double keels at 6 feet, do you think that is equally as good?
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    FAST FRED Senior Member

    The most efficient twin keels would be open in planform.

    The leading and trailing edges would be the lifting surfaces to get you to windward ,

    the bottom would hold required ballast weight ,to have stability under way and enough structure to be able to take the ground with ease.


  5. blackdaisies
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    blackdaisies Senior Member

    Would you prefer keeled boats over a tirmaran/catamaran? What type of sailing boat would be better for ocean traveling? I"ve seen keels fan out at an angle and most of them do. If you had a 33 foot boat and you put two fanned out or something at an angle keels about 15 feet long and 6 feet deep, with the ends tapering at both ends so to make better turns, do you think that sounds good or bad?

    How possible is that? Plus the two keels would enable the boat to sit on a trailer better or in low tide.

    How well does a boat sail under heavy ballast? A sailing double keel would be about equal to that of a swath, or maybe a swath boat is to the extreme, but it works with the same methods.

    Thanks again for the reply.
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