Plywood warping

Submitted bytriad onSat, 03/02/2019 - 13:32

Its been a while since I’ve been on this forum but hello again. I feel the older version was easier to use but I should stop complaining and get with it. 

Im currently building Eric’s Shearwater Hybrid 17 and I opted to cut my own hull pieces out of 4 mm marine plywood from Noahs Marine up here in Ontario, Canada. I’ve currently cut out and scarfed the pieces together over a couple months time. What I’m finding is the panels are warping and cupping. My hope is that after I stitch them together they will straighten. 

Has anyone had the same experience of the panels distorting? Is it possible to flatten these panels with heat and/or moisture or does it even matter since stitching and then installing the forms will pull them into submission?



Sat, 03/02/2019 - 15:29

How have the panels been stored, and where?

If they have been stacked, there may be moisture differences between the surfaces now - especially with (dry indoor) winter conditions in Ontario.

There are 'tricks' to flatten panels, but just storing them on edge or with stickers for a few days may cause some improvement.

mick allen

Sat, 03/02/2019 - 16:46

in addition to John's comments - as most surfaces of a kayak are curved surfaces,  probably all slight warping of the flat plates will be eliminated once the curved edges, that force the curving of the whole surface, are stitched in place. If there is localized cupping [in the middle of a flat area] this will not be enough however but that would mean some quite severe surface deviations. 

Of course I can't speak to  your situation, but I'm on the wet west coast where my bare newly stained panels have been inadvertently rained upon which in turn meant that I had to wash the panels down and then restain and then 're-dry' before cutting out with no noticeable effect that I can discern . . . but it could be that I had a severely curvaceous boat that really forced surface control and also that I don't care that much. ymmv.

Right off the bat the 4 x8 sheets of plywood had some waviness to them. Maybe my concerns are unfounded and stitching them will solve the issue. We will be ready in a couple weeks to stitch them and I’ll follow up with what happened after. Thank you