My first thought was also the loss in stiffness due to crossgrain layers as described by Cedric. If you did this you would definately want the surface layers to be aligned with the longer dimension of the pieces.
- Ply would be a relatively expensive option compared to 'ordinary house framing timber' called for by Platt.
- All the glue in the ply adds weight but not strength.
- Ply will require you to scarf for lengths over 8', ie all stringers
+ if you could be bothered you could make all stringers as hollow box beams from thin (4mm?) ply
+ With very thin ply (3mm doorskin?) you might laminate ribs
The more I think about it the better it sounds to avoid ply and do as Platt suggested: framing timber stringers and steam bent ribs. Ply does not seem to offer any significant advantages. But if I did not have access to any suitable timber I would use it.
But the hollow box stringers idea has got me thinking... They would be extra work (?) but potentially would make an even lighter frame! The ribs could be done hollow too! If you really wanted to go with ply this might be a way to make smart use of its properties.
regards, Dave P
--- In Airolite_Boats@yahoogroups.com, Melcher Cedric <ichacedbodric@...> wrote:
> Plywood is appropriate for panels, hull pieces, bulkheads. For stringers and ribs the crossgrain layers might necessitate such large cross sections that the framework would get clunky, heavy, in order to be sufficiently strong.
> I wonder if you were to match the cross sectional area called out in the plans for a solid wood stringer with the cross sectional area of each layer of a piece of ply, would the resistance to bending be similar? Or higher because the crossgrain layers add a little?