Yes, polyurethane will seal wood just fine. I've even used it in hulls in spray form to reach places I could not otherwise reach (in a hydro hull). You will want to put several coats (at least 3) to make sure. It is chemical resistant as well. It does not add any strength as epoxy will, but it does seal wood. On a wood hull it can also lay down a very nice finish that can be buffed to a very high gloss if desired.