building hatch covers?

[109jb]

I'm getting closer to having the deck back in my boat and am thinking about things to come. From the factory, the access holes for the storage compartments were covered by the seat bottom cusions that had a 1/2" plywood bottom. My plan is to be able to use the boat for fishing by removing the bench and bowrider cushions, so obviously having big holes exposed won't work too well. I am going to make hatch covers (non-locking), but am worried about the plywood warping over time. At least in the bow I won't be able to use the molded plactic hatches because the covers need to be sort of triangular shaped. I may or may not use hinges. My thought is to make the hatch out of 2 layers of plywood and then putting the "same" sides toward each other. For example, if I use A-B exterior plywood I would glue the B side of one piece to the B side of the other piece (screws too). That way they would want to warp in opposite directions and therefore stay straight. The hatch would get covered with fiberglass once done. What do you think?

 

[CheapboatKev]

Re: building hatch covers?

Why not glass and resin the ply instead of waiting (expecting them) to warp?

 

[Boss Hawg]

Re: building hatch covers?

Why not glass and resin the ply instead of waiting (expecting them) to warp?

Agree- if you wait for any type plywood to warp-------it will

 

[109jb]

Re: building hatch covers?

From my original post:

...The hatch would get covered with fiberglass once done. What do you think?

I have no confidence that a single fiberglassed piece of ply will stay perfectly flat. Hell sheets of plywood aren't really flat when you buy them unless you get cabinet grade. Maybe I'll just get some cabinet grade birch ply for the hatches.

 

[lowkee]

Re: building hatch covers?

Birch ply warps just as easy. I used it for a bar I made. By the time I had the poly on and was ready to install it, it had warped almost to the point where the screws were about to strip rather than screw in. Amazingly it hasn't popped off and killed someone with a flying screw yet

I agree with others, glass them and never worry again.

 

[coastalcruiser]

Re: building hatch covers?

I made my own hatch cover out of ply
the trick is that you must coat both sides.
On mine I used matt on the top and gelcoated the whole thing.

 

[erikgreen]

Re: building hatch covers?

From my original post:



I have no confidence that a single fiberglassed piece of ply will stay perfectly flat. Hell sheets of plywood aren't really flat when you buy them unless you get cabinet grade. Maybe I'll just get some cabinet grade birch ply for the hatches.

Hmm... don't know where you're shopping.

Get plywood from a real lumberyard and it'll generally be quite flat.

Or alternatively get a piece that's not too curved and place two 2x4s on one side, then screw through them into the plywood to straighten it.

Glass the side without the 2x4s, then remove them. It'll stay pretty flat, at least to the limit of the stiffness of the ply. Glass the other side and it'll be even stiffer.

Despite intuition, a properly glassed piece of ply will stay in whatever form it was in when glassed. You can even pre-curve pieces and then glass them, and they'll hold that curve forever. The glass won't let the plywood move, and it's much stronger than the wood. The wood can even rot out completely and the glass will hold that shape.

Don't mess around trying to second guess warping, just get good ply to start and make sure it's flat or in place when you glass it. Once it's glassed it won't move unless it gets completely soaked and swells up. Seal it and you won't have that problem either.

Erik