Under normal conditions, I try to keep as much spray off the lens as possible, and wipe the body down when I get home. In truly bad weather, I've wrapped the camera in a ziploc bag (cut a hole for the lens at the front, and use a rubber-band for sealing), but that's generally more trouble than it is worth.
If I were sailing, I think I would consider at least the Ewa-Marine bag, and truly consider some way of seriously attaching it to the boat, myself, or both.
Of course, the "don't drop it" advice is quite serious. I lost a very nice Pentax H1a once while shooting pictures on the edge of the surf. I put my food down on some sharp local inhabitant, shifted my weight, and a four-ft tall wave swept me right off the rock. Camera was ruined by the time I could get it back to the hotel and immersed in clean water. As the phrase goes, "let's be careful out there".