if you really want to use screws then adding a small strip outlining the profile of the hull section of the frame gets around screwing into plywood edge. And of course you can use lighter ply for the frame to conmensate for the extra wood. We only use the thickness of ply because we want to attach something to the edge. In effect what we want is a something to attach the longitudinal pieces to and keep them a certain distance apart
Niven
: Bill, for my own information, how strong and flexible does the
: frame-to-stringer joint have to be? Flexibility requirement
: probably depends on how heavy the frame is - a heavier frame
: would need to have more rigid joints to distribute stresses
: whereas a lighter frame would need the flexibility to absorb
: shocks.

: I imagine lashing is more than enough, and flexible too, but it
: sounds a bit fiddley and rough on (my arthritic) hands.

: Screws would be fast with immediate hold, but I can see then
: working loose with the flexing of such an open structure.

: As for nailing, all the hammering is going to disturb the previous
: joints IMHO.

: Joint area is not enough to do the job with glue: it would need
: around x10 area I suspect to prevent joint failure because the
: joint would not flex.

: Oh for a really long Pop rivet . . .