Stainless doesn’t really hold up in saltwater, with the exception of a few grades. The material properties (toughness, ductility, brittleness, weldability) can

Stainless doesn’t really hold up in saltwater, with the exception of a few grades. The material properties (toughness, ductility, brittleness, weldability) can also be significantly different than non stainless. Corten can work in less aggressive environments, but it has been known to fail to provide the expected protection in places with more acidic rain than was expected. Salt water is really aggressive. Hot dip galvanizing does work, and is common for small boats, dock fittings, and other smaller items. There are also likely sacrificial anodes on the ship made of zinc.