If considering stainless, I would usually recommend an austenitic such as 316 for its somewhat better resistance to corrosion in seawater. However, although the galvanic voltage for active 316 is -0.18v, the galvanic voltage of passive 316 is -0.05v.This might corrode your copper somewhat. My...
There are many alloys of stainless, some are harder than others. Unfortunately the most corrosion resistant one, called "316", is relatively soft. Harder alloys seem to have incrasing problems with seawater. If you can't get a steel alloy that supplies sufficient strength with adequate...