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Glassing a lapstrake plywood hull


timgoz

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Hi,

I intend to build a lapstrake plywood boat (cape Henry 21). The desiegner, Dudley Dix, recommends you not glass & epoxy the hull as it is tricky getting the cloth to lay properly on a "lapstrake detail". That said, some have used a ligh5t weight glass to sheath the hull. I would like to do the same. An option is Dyanol??? I think it is called. That material supposedly conforms to adverse shapes better.

Any thoughts or opinions on the above would be much appreciated. thanks.

Tim

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You can't use regular cloth on a lapstrake hull, unless you heavily radius the outside edge of the lap, which really messes up the look a lot. You also have to add a substantial fillet on the inside corner at the bottom of the lap. So, as a general rule, you don't 'glass lapstrake hulls. You can use very light cloth, like 2 ounce, but what's the point, as it doesn't protect much.

If you want protection, then 'glass the "flats", but leave the lap clear. I've used 6 to 12 ounce cloth on lapped hulls, but only on the exterior of the plank. The end grain portion of the plank was left clear. In fact I 'glassed before final trimming, cutting both the plank and 'glass sheathing to a fair line.

Dynel or Xynole could be used, but they have the same requirements as cloth, though you can get away with a smaller radius.

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Thanks again PAR. Glassing the flats sounds like a good possibility. The exposed edges I think I will totally saturate with epoxy and used thickened epoxy on the outside (any thoughts?). I like the idea of glassing the panels prior to finally cutting and fitting. Much easier & less messy that way.

Take care.

Tim

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The lap edge is all end grain, so several coats of straight epoxy. A thin smear of thickened epoxy wouldn't be a bad idea, once you've sealed the end grain. You'll waste a little fabric by pre-sheathing the planks, but it does mean you can do it on the bench, rather then the boat which is handy.

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This is a difficult question but, generally, I'd say don't bother.  It is possible but very time consuming to sheath the whole of a lapstrake boat by fitting temporary battens against the strake edges to force the material to conform to the edge and corner.  Glass is a poor choice for the job and Dynel is no better.  Xynole will do the job but, as I said, not worth the effort.  Glassing only the strake surface leaves the most vulnerable part, the edge, almost unprotected, so why do that?  

Fitting the strakes takes a bit of trial fitting and having to deal with a layer of glass just makes that job a lot harder.  Thousands of lapstrake boats have survived without this complication.  My best advice is to forget about sheathing it.

Edited to add:  In case it was not clear, I don't think much of Dynel as a sheathing material.  In fact, I find no use for it at all since there are other easier and cheaper options for non skid situations.  In my testing of the various sheathing materials, Dynel performed very poorly compared to the visibly similar, but far superior,  Xynole.

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