I anticipated a similar problem with my Shearwater 17 Hybrid so I prebent the plywood before laminating.  I used the two adjacent deck forms and clamped them to the plywood.  Let it sit for a few days, then covered it with rags and poured boiling water on it.  Let it sit damp for a few more days then let it dry while still clamped.  Down side it I got some water stains on the plywood, but the worst ones were on teh glue side.  Once dry I glued it to the hatch cutout.  Everything was close on the camber radius and the hatch maintained its shape.  That was all several weeks ago and all still looks good.

So, assuming you can get the existing plywood cut off, that is one approach to the reassembly.  You might also consider clamping the cover and plywood, with glue applied, to the deck forms, so you are sure to laminate the assembly to the correct radius.

Short of removing the existing plywood, I do not see any way to correct the camber.  Best of luck and let us all know how it turns out.

Paul G.

Hi Paul,

The same thing happened to me. I traced the curve of the deck across the aft side of the hatch opening (where it is more pronounced) and cut a scrap of 4mm okoume to match that curve.Then I glued it to the inside of the hatch cover to force the curvature back close to what it was before. It wasn't perfect but it was close enuf for guvment work:

http://www.antibozo.net/cgi-bin/eric/imglib/prod/image.pl/eric/pictures/Archive/Shearwater/1-resized/IMG_1239.jpg

Another approach might be to cut some kerfs into the stiffener to relax it a little, use some clamps and a form to force it back to the right curvature, then, restiffen the stiffener as follows:

I had to stiffen the aft deck up in places as I sanded it a little thin. The broad flat areas back there are easy to oversand trying to level things out (note to self: next time, be more careful sanding large flat areas). I ended up using sheets of mahogany veneer I had bought to do onlays. The sheets were about 6 by 12 inches and very thin. By epoxying layers of these veneer sheets with alternating grain direction, I could build up my own "plywood" reinforcement underneath the deck. The mahogany veneer wasn't that expensive and if I were to do this again, I might consider stiffening the hatch cover that way, rather than clamping that big sheet of plywood on. It seems like that is just asking for this problem.

Having since spent some time clambering about on the back deck doing re-entrys, it seems plenty strong.

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Ogata, eric

Hmm, guess I put the reinforcement on the forward (flatter) side of the hatch cover. Probably that is where most of my problem was, because the deck was too thin there. I think I might try cutting kerfs in the stiffener and then laminating a couple layers of veneer on top of that after the curve was reshaped if I were going to do this again? Worked out ok though....

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Ogata, eric

So, I did plan the offending pywood plate off with my block plane and the hatch magically returned pretty close to the profile of the rear deck. 

 I am now left with an ugly epoxy stain on the inside of the hatch so I intend using strips to make a plate to the profile of the hatch and probably a layer of 'glass to seal/strengthen

Disaster averted !

Paul