When cooking pasta (or hard boiled eggs, a luxury for the first week or so out) I just dunked the pot into the drink for enough water. If you like the pasta al dente, though, instead of cooked to death, cut it by 1/4. Leftover cooked to death pasta just seems to save better, whether by freezing or refigeration. For rice, I used about 3/4 fresh to about 1/4 sea. More, with rice, is okay (I learned when a crewmate didn''t get it quite right) when combining the rice with items such as beans or meat, provided you don''t used additional salt to flavor. The rice will be stickier, though.
And, I agree, never ever use heavily salted water to initially cook dried beans. They will stay as tough as the day they were picked, but I learned that from growing up in the country, not from sailing. Adding salt or fatback a bit later will add to the flavor, but not toughen the skin.