Newbie question: would this trimaran folding system work? (parallel hinge)

Discussion in 'Multihulls' started by Matthias S., Sep 25, 2020.

  1. Matthias S.
    Joined: Sep 2020
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    Location: Berlin, Germany

    Matthias S. New Member

    Hello everyone,

    I'm new to boat building and just signed up to this forum to ask my newbie question. I've been reading quite a lot about folding trimarans (also on this forum) and right now I'd like to try and build a W17. There's just one thing: I really need the amas to be foldable on the water, so the boat should still be stable enough while in the folded mode (for paddling or a small motor, with the sails down of course). Here in Berlin there's really only little space to get into the water. Also, it would be really good if the boat can stay in a berth in folded mode during the summer, so the amas should not be rotated too much.

    Today while day-dreaming at work I've figured out the parallel hinge system as seen in the attached pdf. The unique features it offers are:
    • Foldable while on water
    • Amas are not rotated, the top side stays at the top
    • Amas are lowered a little bit for increased stability (can be adjusted by the length of the inner and outer board pairs)
    Let me explain the system also in words. The pink circles resemble rotatable joints. The blue and green rectangles represent pairs of boards, not tubes, which form the akas. These boards should be as broad as the original akas. The purple part on top is a connector which provides the parallel faces for the parallel hinges.

    The blue boards are forming one parallel hinge, while the green boards are forming another one. You can imagine the boards as the long sides of two parallelograms, while the short sides are formed by the ama / the main hull and the purple part. In this way, the ama cannot rotate while moving to and from the main hull.

    In the extended state (top sketch), the blue boards are on top of each other as well as the green boards. This is a natural end stop, the akas cannot unfold any further. In the folded state (bottom sketch), the outer bottom and inner bottom board are touching; this is a natural end stop, the akas cannot fold any more.

    A (small) problem is, in both states, chafing as to be prevented. I imagine rubber parts would help here.

    Another problem I see is that the top boards may act as levers to lever out the joints. Special caution would need to be taken here.

    A third problem: The ama on the windward side will not stay extended if the pairs of blue and green boards are not fixed together by a locking system. This would have to take a lot of force to keep the system from folding.

    Room for improvement: I think it should be possible to have the amas rotate by a defined small angle by adjusting the distance of the joints on top of the ama and tweaking the relative length of the blue boards. In this way the top side of the amas could be rotated slightly by a fixed angle to be perfectly parallel to the water.

    I'm looking forward to your comments! Has anyone employed a similar system? It's quite simple and for sure I'm not the first one to make it up - there must be reasons why it won't work...

    Attached Files:

  2. jamez
    Joined: Feb 2007
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    Location: Auckland, New Zealand

    jamez Senior Member

    For a more simple folder check out the Brown/Marples Seaclipper designs. There is a 16 and 20, among others.

    Last edited: Sep 25, 2020
  3. upchurchmr
    Joined: Feb 2011
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    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    How will you lock the joints?
    That many joints will have a lot of freeplay.
    Getting the akas to hold the ama in one place will take a lots of weight and mechanism, and will still be floppy.
    As illustrated, the akas will flex a lot, compare the depth of each element to the depth of the original mechanism. Perhaps that is just the illustration.

    Why are you so insistent about keeping the ama vertical?
    The Ferrier system is well documented and used for 30+ years.
    If it ain't broke don't fix it!!!

    This was brought up some years ago, either here or on Woodenboat forum. You might search for it. Nothing was ever published about it being actually designed.
  4. Matthias S.
    Joined: Sep 2020
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    Location: Berlin, Germany

    Matthias S. New Member

    It's true, a lot of joints potentially mean a lot of wobbling. Self-made joints wouldn't be enough, commercial joints would have to be used, which can get quite expensive given the number of joints.

    I want to keep the amas vertical because I would worry about water entering through the inspection hatches while berthing for months on end.

    Another problem I realized: the joints of every axis of rotation (at least four joints per axis) would have to be aligned perfectly for both akas, otherwise the folding mechanism won't work. This is a very difficult task! In my opinion it is too difficult for the beginning builder, I think I wouldn't be able to do it as I don't have any boat building experience.
  5. upchurchmr
    Joined: Feb 2011
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    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    I use to work for an aircraft manufacturer.
    We had significant trouble keeping 3 hinges in line, and the tolerance or free play of the joints was a continuing problem.
    This was on very expensive structure.

    You can make such a structure fold even with some alighment problems of the joints, if you have enough power.
    But I don't really understand how you will force this to fold - what would be the mechanism.

    I think you could easier fix sealing the ports.
    Joined: Nov 2013
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    Location: Australia

    ALL AT SEA Junior Member

  7. upchurchmr
    Joined: Feb 2011
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    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    If that fold system would work without other elements it would be interesting.
    Is there a better description on how the ama stays upright, and how the aka ends up taking that path?

    Funny, the original W17 beam has a joint in the middle and it seems to work.
    Same as the old Cross 18.

  8. aussiebushman
    Joined: Oct 2009
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    Location: Taralga NSW

    aussiebushman Innovator

    The Farrier system can be replicated fairly easily - see pictures of the mock-up that should certainly be done before cutting and fitting the real thing. The key is getting the angles and fixing points right - the mockup will prove that.

    Sure this does not answer your wish to have the amas remain vertical plane, but it does work. It would still be working if some helpful soul has not stolen everything moveable, then torched the boat

    Attached Files:

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