Hatches warping?

I'm got the hatches cut into my front deck made out of 1/2" plywood, and they have been working great until I noticed the other night they started warping slightly. The boat is kept in a open barn, so it doesn't get direct sunlight or rain, but does sometimes get covered in dew in the morning. Is there anything I can do to keep this from happening? The wood has been treated with 2 coats of Thompsons water seal

could reinforce the hatch with a piece or two of angle aluminum.

Plywood is funny stuff. Wood in general tends to warp or cup in the direction is is drying. So if you laid a piece of plywood on the floor the top surface would tend to dry out and the board would warp in that (upward) direction. Plywood is not a particularly stable product. Unless you spend a lot on marine plywood you can expect some warpage. In general, plywood made of more plys will tend to be more stable than plywood with fewer plys. Some 1/2" plywood has only 4 or 5 layers while other more expensive types will have more. CDX plywood is usually made of few layers - intended to be nailed to roofs or walls as sheeting. The glues of course make a difference too although they're more likely involved in delamination due to moisture. The best you can do is to coat all sides evenly with whatever sealer you're using to try and minimize it drying out in one direction. As suggested above you could reinforce with alum angle or you could replace the hatch covers with a better grade or thicker plywood.

Try using spar urethane or give it three coats of paint instead of the thompson's.

This is the only reason I am thinking about doing 3/4" instead. I need to save weight but I may try that elsewhere. Good Luck

I would not blame the Thompsons, I use it all the time for various things.

I had a similar issue with my 5/8" bcx ply

but on my hatches, they started warping before I even finished the boat

I blame it on the wood being too new and wet. When I bought it I had to sort though a pile of sheets that looked like bananas.

Now, after about a month after being on the boat (has not got wet) the hatches have settled back into place.

I think the wood just needed to dry out some

but then, I could be all wet

:LOL2: