: Actually, there is a grain orientation, at least with some plywood.
: I found with my 3 ply 4mm Okoume that it would bend a much tighter radius
: across the panel than along the length. I assume it's because the two outer
: plys had grain orientated in the same direction, with the middle ply oriented
: the other way. I found this to quite important when I was placing
: reinforcements under the deck, since a piece cut along the length would
: not conform to the deck radius, while a piece cut the other way would do so
: quite easily.

You are correct in your assumptions. Most plywood that I have found has outer plys that are very thin compared to the inner ply. Of course what most people look for in plywood is that it has equal thickness plys which will make it not bend evenly or be as strong in both directions. The ideal plywood will have outer plys that are each half the thickness of the inner ply so that it is strong in both directions. But since the panels of a kayak are very long and but not very wide maybe it is a good thing that they are stronger and stiffer length ways. But I can imagine that if you land on a rock just in front of your seat the break will tend to run along the kayak rather than across it. So some extra fibreglass cut diagonally in this area I think would help.