I built a "Yare" about three years ago. The hull is 3mm and is unsheathed. The bottom panels have a scarf right thru the middle. The scarf has to be "right on" becauses of the bending forces used to create the hull. Before I ever touched those four pieces of 3mm Bruynzeel I sharpened my hand planes and practiced on a dozen pieces of scrap ply. The planes dulled fast because of the glue lines. When I felt ready I used the set-up that Chris Kulczicki outlined in his book.
Mark and "stair-step" the panels on the edge of the bench. The bench has to be flat to fully support the lower feather edge properly. Cut about 80% of the scarf. Take a break. Resharpen your plane again and veeeery carefully finish the scarf. You should have two 1 in. bevels straight and flat from end to end.
This may seem a tedious process but for my money it's the only way to tackle something as thin and as flexible as 3mm.
Charlie

I've built several s&g kayaks, which have been very successful, structurally
: & design. However I only attempted scarfing ply on the first. A couple
: of the scarfs failed during building, so I backed them up with a ply strip
: epoxied across the inside of the join, which is what I did with subsequent
: boats. Not pretty, but strong.
: Is scarfing such thin ply practical, and does anyone have any ideas for
: prettier scarfless joints?

: 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.

: My first visit to this excellent site, can't understand why it took me so
: long.