: The other problem is that when I cut ply with a power jigsaw and fine toothed
: blade, the surfaces are damaged along the cut with lifted fibres/splinters
: which have to be sanded off.
: I'd appreciate any ideas for clean cuts on ply.

With jig saws the teeth are oriented to cut on the up stroke, so you must cut your pieces with the "good-side" down, or... if you are cutting mirror image pieces ( one for each side of the boat ) put the faces together and clamp them. You can do that with two sticks, one on top and one on bottom and the clamps on the ends. This will prevent splintering on the face of your work piece.

If you want both sides clean and splinterless, try this method:
Set up a router with a "flush-trim" bit. Mark your cut line and clamp a straight piece of wood right up to that line, turn it over and run the flush bit along the piece. ( this assumes that you have precut the pieces to about 1/16" or 1/8" of the line. The normal "flush-trim" bit has a bearing on the end and will follow your straight edge )

Hope this helps!

Rehd