: . . . It is less than a millimetre thick and 20 mill wide so I will
: carefully chisel and sand a groove so it sets in a little bit proud.

By my reading of this, you plan to chisel a groove the length of your boat (about 5 meters), and this groove you plan to make only 1/2 mm to 3/4 mm deep and with perfectly accurate width along the entire length.

That sounds like quite an undertaking, and I'm not sure it is necessary.

If the material is just under 1 mm thick why not just bond it directly on top of your wood. when the glu sets you can gently sand, in line with the "inlay" to bring that 1 mm edge thickness down to nearly nothing. When you apply your glass and resin over this there will not be any noticeable bump.

If the edge of the inlay casts a shadow under strong, directional light, that surely is not going to be as objectionable as any slips you might make in your chisel work. You certainly can't make the groove narrower than your inlaid material ( it wouldn't fit), so you would have to err on making it larger -- and that would give you a shadow line, too.

Since you plan to leave the inlay a bit above the surface of the surrounding wood, you are committing yourself to sand it down. If you mount it directl on the surface, you also have to sand. In this regard I see no advantge to cutting the groove first.

There are some nice pictures of kayaks that have been decorated by having veneers glued directly on the outside of the craft, without incising a home for them first. I think Nick's guillemot design is applied this way. unce they are under the glass they look as good as if they were done the harder way.

Just a few thoughts

PGJ