I would also vote for something lighter than 1/4 inch plywood, which I think would be serious overkill for a day hatch bulkhead. However, I would be hesitant to use doorskin as the glue is unlikely to be waterproof, so if you ever get water intrusion, you would have delamination in short order. I used some ~1/8" cedar for my bulkhead cores, which is plenty strong enough glassed on both sides, and is very light. As mentioned already, commonly available mat most likely will not form a strong bond with epoxy. If I was going to make a membrane bulkhead, I would use a few layers of glass cloth which I knew was chemically coated so as to bond properly with epoxy.

If you use a rigid bulkhead, fit the bulkhead with 3/16 or so space along the hull edge, and glue it in with a good bead of lexel. It can be held in place for the caulking operation with a few dots of hot melt glue near the shear line and under the deck. The space filled with lexel will give you a bit of flexibility if you hit something, but not as much as with a minicell bulkhead. OTOH, a minicell bulkhead will use up 2-3" of the space you have available for your storage volume. The most likely consequence of a bulkhead that is too stiff is just cracked gel coat, so I would not be too worried about it.

Good luck,

Allan Edie

: I removed a chimp pump from my Valley Pintail. I plan to replace it
: with a Beckman deck plate and add a bulkhead to make a day
: hatch. I plan to use plywood for the bulkhead. That's as far as
: I've gotten. I'd like advice as to plywood thickness (1/4",
: 3/8" etc.), should I add a wooden lip to give more surface
: area for better bonding? should I get a good fit and epoxy it in
: with a Lexel bead to finish it off? Any advice would be great.

: I've built several SOFs, some with fabric bulkheads, but this is my
: first venture into modifying a glass boat.

: Thanks in advance.

: -Eric