Tornado hull modifications

Discussion in 'Multihulls' started by tamkvaitis, Nov 28, 2012.

  1. tamkvaitis
    Joined: Aug 2005
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    Location: lithuania

    tamkvaitis sailor/amateur designer

    So, it all started in this thread .
    Basic idea was to convert Tornado catamaran into trimaran. Although idea is still very interesting, but various commitments does not allow to spend as much time on this project as I wanted and as it is needed.

    At the moment we are planing to do a slight face lift to our tornado catamaran this winter, as it involves, sanding old paint down and a lot of fairing and painting afterwards, I started to wonder about extending the standard tornado bows, so it would be more similar to modern catamaran bow shape. So I am starting a new thread in order to stop confusion regarding trimaran conversion and shape modification.

    So the basic arguments for bow extension are:
    a) Increase waterline - waterline equals speed, so everything looks straightforward with this point.
    b) Decrease entrance angle - this should give softer ride with less wave resistance, also this should slightly reduce piching as fine bow would first of all gently cut into a wave and upwards motion shouldn't be so violent as it is now (usually we are sailing in very chopy conditions)
    c) Increased bow volume - this should add a slight safety margin regarding pichpoling danger. If hull drag is decreased with finer entry angle and forward buoyancy increased this boat could be pushed harder.

    Arguments against this modification are:
    a) increased weight
    b) increased weted surface area

    So is this whole idea worth the effort?

    Second question is what is the best way to extend the bows? Idea at the moment is to add a layer of foam to existing bows, shape it in desired way and cover it with several layers of fiberglass. Is this approach feasable?

    I already have one suggestion from another thread:

    It looks straightforward regarding construction, but I am not sure If the advantages of this modification is worth the effort, I am pretty sure that You guys are more than capable of assisting me.
  2. Samnz
    Joined: Nov 2008
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    Samnz Senior Member

    you would be better off extending the stern
  3. dantnz
    Joined: Apr 2008
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    dantnz Junior Member

    I can't see how this would have a significant effect without much bigger modifications to the hull. Plumb and reverse bows are usually the result of the cross section shape of the hull, ie a hull having more bouyancy at the waterline and or a flatter 'planing' hull bottom. To get this in the T you would have to start your bow mod almost back to the front x beam. I can't see that the extra volume or length in just changing the bow profile would have a beneficial effect outweighing the extra drag and weight - if any positive effect at all.

    Much better would be to concentrate on upgrading the rig if you haven't already. The square top and spin arrangement is much easier to control both upwind and down.
  4. idkfa
    Joined: Sep 2005
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    Location: Windward islands, Caribbean

    idkfa Senior Member

    Having a larger submerged transom increases top-end speed, think that's were most of the recent gains have been (also lifting foils), not bow fineness (Cp high good) or planing shapes???

    Still there is not one ultimate hull shape, it is an optimization for your particular speed potential, (read & grok S# - Sponberg) and that is mostly dependant on displacement (which also dictates beam)

    So your speed will be largely dictated by the weight and (lesser) shape of the vaka. If it is heavy (and fat), like a Farrier, then you're stuffed upwind, not so much downwind.

    You really shouldn't treat them independently.

    imho idkfa
  5. aussiebushman
    Joined: Oct 2009
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    Location: Taralga NSW

    aussiebushman Innovator

    You might be interested in this mod, though I think you have a different reason in mind, because mine were intended to complement a new centre hull for a cruising tri. The amas started life as A Class cat hulls but thanks to help from various members of this forum, it became obvious that there was insufficient volume.

    Probably not the easiest way to do it, but using foam formers epoxy glued to the original hulls, then strip planking in Paulownia with glass sheathing, the result was very strong, high volume asymmetrical hulls without excessive additional weight. Doing it this way means that virtually any desired shape can be achieved


    Attached Files:

  6. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member


    just do one side and see if there is any benefit.

    One improvement that has been mentioned in the past is taking off the bow deck and putting in stringers to spread the bow at 1/2 height, then putting back the original deck.
    Giving more bouyancy to the bow to provide less nose diving when on a reach.

    It would be a pity if you changed the "look" of the bow just for fashion.

  7. Martin Goodman
    Joined: Jul 2019
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    Martin Goodman Junior Member

    Hi Alan,
    Noted its an extremly old post (>10 years) just a quick question if you recall, how much weight overall did you add to the each ama?

    many thanks

    Martin Goodman
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