I like Fenix lights, I have two of them and while they are bright and have nice light options (strobe, SOS, Turbo et al), they are not waterproof, only dunkable. With saltwater, a dunkable light might not work at all. The cheap light this guy got from his local sporting goods store was reported as waterproof.

If I was going to sea, I'd go with dedicated gear designed to get real wet, dunkable is fine for non-survival gear, not for gear your life hangs on.