Ply trimaran - which repair, if any?

Discussion in 'Sailboats' started by Tiny Turnip, Jul 10, 2018.

  1. Tiny Turnip
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    Tiny Turnip Senior Member

    20180710_220719.jpg 20180710_220518.jpg 20180710_220421.jpg 20180710_220259.jpg 20180710_221053.jpg 20180710_220154.jpg 20180710_220802.jpg 20180710_220310.jpg

    This is my 16ft Solway Dory trimaran.

    [​IMG]

    It carries about 8 sq metres of sail.
    A couple of years back, while pushing it hard, the leeboard partially popped a flake of ply out of the hull, just below the pivot. The leeboard is 1.3metres long, and is quite a powerful foil.
    I repaired the fracture, and built a much bigger reinforcing plate with more gussetts on the inside of the hull. - See picture attachments.

    However, when I push the boat hard, it still makes cracking noises from the area of the new reinforcement and pivot, which is very disconcerting.

    I have been told that a repair like this needs a layer of glass between the hull and the ply reinforcing plate. I can't honestly remember whether I put any in, but I think I didn't. I did thoroughly scarify the inside of the hull with an angle grinder.

    I'm planning a sailing trip soon, and if I'm going to conduct a further repair, I've got about a week to do it.

    So... do I...

    1) Leave it be, and put up with the cracking noise on the grounds that it is unlikely to fail catastrophically.
    2) Put a bunch of brass screws through the hull into the reinforcing plate?
    3) Bite the bullet, rive it all out, and re resin it in, with a layer of glass in between? (chopped strand mat rather than roving? one layer? two layers?)
    4) As 3 but brass screws as well?

    Many thanks

    Adrian
     
  2. Tiny Turnip
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    Tiny Turnip Senior Member

    The original damage, and the current cracking noise occur on port tack only.
     
  3. Doug Lord
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    Doug Lord Flight Ready

    I'd suggest adding a couple of layers of 6-8 oz woven glass/epoxy IF you're sure the wood in the vicinity is dry. That way you get it fixed right-no more worries. Anyway, good luck and have a great trip!
     
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  4. Corley
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    Corley epoxy coated

    From what you are describing it doesn't sound like it will fail catastrophically so I'd go sailing given how close the trip is. As you have mentioned above the best solution would be the major one, grind out the area and extend glass out over a larger area to reinforce the pivot and normalise the loads into the hull. Brass screws don't hold much load and once again it's a point load which it's good to avoid in a light craft.

    Extending that idea I wonder if you filleted the outside bracket onto the hull surface with epoxy and carried some double bias out over the plywood whether that would help with the problem. It's a skin load but spread over enough area it might well solve the problem. If you wanted to avoid the potential skin load issue you could stitch the outer bracket through the hull using glass or carbon tow. My other observation is the washer that holds the board on it's outer side seems rather small. A larger washer might spread the load over more area and help to reduce the cracking noise you hear. Finally there could be an issue where the bolt loads the face of the plywood when on the port tack. One approach to that could be to drill the area out with a hole saw and back fill with a thickened epoxy then redrill the bolt hole. The epoxy helps to spread the load more effectively into the plywood skin than the bolt bearing directly against the hull.
     
  5. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Pretty boat, must be a hoot and a houl to sail.

    The first few pics show a very solid repair.

    The last two indicate that the lee board is flopping around. The face of the offset block is scarred and doesn't mate perfectly to the foil. There are cracks and a small gap between the base block and hull which indicate it is moving. I believe this is the source of the disconcerting noise.

    Corley has some good ides on how to strengthen the lee board's attachment. Also, consider adding plastic wear plates into the system. Old coffee can lids with parameters removed might work well.

    Enjoy your outting.
     
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  6. Angélique
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    Angélique aka Angel (only by name)

    My view in a few pictures . . .

    leeboard support 1.jpg - leeboard support 2.jpg - leeboard support 3.jpg - leeboard support 5.jpg - leeboard support 4.png

    Note: the difference with picture 4 & 5 is that the tri less heels and has only one board which is on the starboard side of the vaka (main hull).

    For picture 2 * see post #4.
    P.S. - Just in case the blue top text in the 2th picture isn't so well readable, it says...
    ‘‘ The new support full length abut the leeboard of course, it's just a simplified drawing in a not so well angled picture to show this. abut ’’
     
    Last edited: Jul 12, 2018
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  7. Doug Lord
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    Doug Lord Flight Ready

    =====================
    Good thinking, Corley!
     
  8. alan craig
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    alan craig Senior Member

    I agree with Angelique: the leverage is huge because the support below the pivot is very short and the leeboard is long. I think there should be a longitudinal external support near or just below the chine, like the picture of the dutch yacht or a Thames barge.
     
  9. Angélique
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    Angélique aka Angel (only by name)

    Right Alan, but the lower support only helps on the starboard tack, in my view the counter forces of the port tack board moment are best dealt with on the top side of the board.

    For this I've added a note in black to the bottom of pic 1, and drawn a proposed board extension in orange at the board top side in picture 2 with a side note.

    The just recently in post #6 added notes are:

    pic 1 ‘‘ The tri has only one board, which is on the starboard side of the vaka, the here shown forces are for the port tack. ’’

    pic 2 ‘‘ * Proposed board extension at the top, to lengthen the short arm of the leverage, and so relieve the port tack reaction force on the hull, which probably requires a whole new board. The port tack board moment on the hull top side stays the same while doing so, but in this way it's better lead to the existing inside hull reinforcements, which looks to be well capable to counter the opposite moments of the port and starboard tack, of which the latter is the easiest to deal with. ’’
     
    Last edited: Jul 12, 2018
  10. Tiny Turnip
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    Tiny Turnip Senior Member

    Many thanks all for your thoughtful and helpful comments. I think I have a plan coming together, and I will post some drawings soon and respond to your comments in detail. Just done in after a full on day! Really appreciate your thoughts and help.

    Very best

    Adrian
     
  11. Angélique
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    Angélique aka Angel (only by name)

    The forces of the board on the hull topside in the port tack can be further reduced by lowering the pivot point in both the hull topside and the board, so the board stays at the same height when down.

    Operation of the board would also become lighter, since the hand that operates the board needs to travel a bit further.

    leeboard support 7.jpg - leeboard support 6.jpg
     
    Last edited: Jul 12, 2018
  12. Angélique
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    Angélique aka Angel (only by name)

    A longitudinal slot outside the boat just above the waterline is also an option to counter the board to hull forces on both the port and starboard tack. In that case the pivot point could be best as high as possible to lengthen the short arm of the leverage.

    leeboard slot 1.jpg
     
    Last edited: Jul 12, 2018
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  13. latestarter
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    latestarter Senior Member

    This is puzzling me.
    If the damage at issue is the crack/slit highlighted by Angelique in photo 1 of post 6, on port tack the pressure on the board would be pushing onto the hull not levering it off, as shown by the 5th picture.
     
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  14. Angélique
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    Angélique aka Angel (only by name)

    Latestarter, maybe you mistake the bow for the stern in the 5th picture in post #6 . . ?

    Or I have a mistake in my terminology in the jargon in English ?

    In the below pictures is how I understand it . . .

    leeboard support 4.png

    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

    leeboard support 8.jpg
     

  15. Zilver
    Joined: Nov 2007
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    Zilver Junior Member

    Did you ask Solway Dory ? The whole setup puzzles me a bit, because I don't understand why there's a second layer of ply on the outside side of the mount. That makes the bearing surface much smaller (as Angelique altready pointed out). Also I think Solway Dory rely on the aluminium angle bracket to take all the forces. The extra layer of wood on the outside makes the arm/lever to that bracket longer so that is not benificial either. You might be overthinking/overbuilding. It could be that a bit bigger aluminium angle piece would do the job.
    Cheers, Hans

    BTW how does the ketch type of rig work in practice ? I'm curious. It looks very practical but "they" always say it's not good for windward ability.
     
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