Last I remember playing while at sea was Steve Hillages' version of Hurdy Gurdy Man from "L". Othervise, the obscure and overlooked Canadian group "Klaatu" has produced some arch-maritime stuff like "Sir Bodsworth Rugglesby III" from 3-47 E.S.T. Oh, Deep Purples "Sail Away" from "Burn". Then there's all of Zappas "Sleep Dirt" album, the instrumental version, which haunting music
for me invariably produce a strong yearning for The Big Blue and much contentment when I'm there (most would probably beg to differ, in more or less civil tones... like a certain harbour chief.