: I seem to remember Pete saying something the other day at R2K about the
: thickness of the layers in each type. Marine has equal thickness layers
: and lauan has a thick middle with thinner veneers on the outsides. This
: comes into play when you sand edges such as chines and can end up with
: black/dark lines where you sand through the outside layers. I know I got
: some of this on my Artic Terns, but I just tried to keep it consistent all
: the way down the edge. I might not be remembering this right. Does anyone
: else remember better (not unlikely :-)? Pete?

As far as I can figure, luan plywood is never called for as a structural load-bearing material in non-kayak building applications. Instead, it is used as a cheap decorative replacement for solid woods by having a very thin veneer of the desired wood on one face. The thick inner core sometimes, but not always, is a fairly dense wood of uncertain quality. The back will be another thin veneer of hardwood, and it might not look too bad with defects or knots, but it won't be the same variety of the face.

I just grabbed some samples from the shop:

The 4mm marine plywood is 4mm thick, 3-ply, each about 1+mm.

The 1/4" marine plywood is ~6mm thick, 3-ply, each about 2mm.

the 1/8" luan is just under ~3.5mm thick, 3-ply, with outer faces ~.5mm each.

The 1/4" luan is 5mm thick, 3-ply, with outer faces 1mm thick.

On multichine hulls, at least, you can round-off the angled panel joints by hand sanding through most of the outer ply, putting a sort of radius on it. The relatively thicker outer plies of the marine plwoods give you more depth to work with, thus more rounding. You'll know when you're approaching the glue boundry, as the wood will suddenly darken.

Rounding off the joints generally makes it easier to get the fiberglass to lay down and conform. By the time both sides are filled and 'glassed, I don't think there's a significant loss of strength incurred by doing this. Any opinions out there on this?

Pete in Snohomish.