That makes sense...
Forgot to mention - it is still possible for modern non-steel hulled vessels to literally burn to the waterline, of course, and some steel-hulled civilian vessels/boats have managed it too. In the latter case, it’s because the very thin steel hull has its internal supports burned away/melted and then the hull collapses. Amusingly, the most notable and numerous example of the latter are party barges which literally burn down to the actual waterline on lakes with dreary regularity. :P