[PlasmaKrab]

Don, don't get me wrong, I don't find boats in general to be too easily sunk on the whole. When I say that soe get sunk by what I find to be too small-caliber weapons. In the end. After being showered with other small-caliber weapons for some time.

In a test scenario I set up, it took me in at least one instance a half dozen LSTs firing all they had (12.7 to 57mm, four slots each) for two turns full to get one small gunboat under. Nevertheless, the gunboat was still taken under by a weapon with WHS<3. And yes, I lost at least one LST to a LAW, again not the first shot. This is my only (little) peeve on this subject.

As little as I have learned from historical accounts, it seems to me you have to put a significant amount of HE to sink a boat of any significant size (larger than your average Rigid Raider).
Of course, you can render it utterly useless (no crew, no movement, no carry, no weapons) with nothing but MG fire, but in this case, realism would call for the floating hulk to linger on as 'abandoned' or something.

As I said before, I understand there may be no way to do this in the game, and 'sinking' a boats altogether may be the only way to render it completely useless.
If a threshold in Warhead Size to 'kill' naval units is introduced in the game, and naval units that are not 'killed' still have some fight (or can land their complete carry, as observed), then they would indeed become unsinkable islands.