Yes, the boat is thin. I am trying to do an accurate copy of the real original and the aluminium hull is 3mm thick. I am a beginner to this so there must be something obvious I have missed cause it can be that hard to match the end of one object to the surface of another, right?

I want my board to stretch between the inner hull on both sides of the boat. The only way I know of doing it at all would be to use split ploy tool on a few faces on the hull and extrude it over to the other side. Do the same thing on that side and try to match the vertices manually and by eye measure make it somewhat straight. But that seems a very clumsy approach.