View Full Version : Larch thwart twist
05-24-2011, 03:13 AM
Hi everyone, I am about to put in the thwarts which are made of larch (22mm thick). One of the thwarts has a slight twist in it ie. it is not completely flat. I wonder whether I should (or can) sort this out before screwing the thwart down to the thwart cleat, or let the action of screwing it down flatten it out. I am a little worried about the stress this may place on the hull (6mm ply).
As always, grateful for tips, suggestions etc,
05-24-2011, 06:41 AM
How much twist and how difficult is it to unwind?
If it's not bad,say 10mm on a 100mm x 1m thwart,it should be alright
05-24-2011, 10:11 AM
I had exactly the same problem recently with the old 4/4 DF thwarts that came with my dory skiff. If I'd noticed the issue earlier, clamping flat to a form before installing would have been my first solution, but as it was I just installed it and shimmed up the slight twist under the seat rail.
05-24-2011, 05:12 PM
Never a good principle to use screws to pull items together.Can you apply force from an inwale or other part of the boat?If a bit of persuading won't close the gap,do as Thorne suggests and shim.The point about how slight the twist is is very relevant as is the type of wood you will be putting the screws into.
05-24-2011, 07:11 PM
I reckon the twist means one corner of the 880x200x22mm thwart is 6-8mm above an even surface (garage floor) when I lie it down. I will be screwing it into cleats I cut from a block of glued up marine ply. They are a little bit thicker than the cleats in the plans. Creative use of clamps would enable me to press the thwart down before screwing, is that the way to go, John?
Yes, using screws to bring things together is a very bad idea, that's one thing I have learned on my first build.:o
05-25-2011, 06:58 PM
I would definitely recommend using clamps to hold the thwart in place and then applying screws.This almost eliminates the risk of shearing the screws by trying to tighten them as you attempt to pull the twist out of the wood.
05-30-2011, 03:51 AM
Well, clamping the thwart down just put too much stress on the Mouse's delicate hull, and shiming wasn't pleasing to the eye: the bad angle was quite noticeable. So I'm going to do the simple thing and just get another piece of wood. The local cabinet maker will swap it for free.:)
Don't try to take all the twist out in a few minutes. Lay the stick,outside in the grass,until it picks up enough moisture to straighten, then screw it in place. The stress will be taken up slowly as the stick dries, with luck, not straining the hull.
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