I checked Peter Kennedy's _Folksongs of Britain and Ireland_ and it seems I was wrong about there being "a lot" of songs involving the sea. I remember at least a couple in the sections of Gaelic and Welsh songs and there's a song called "The Soldier and the Sailor", I believe, in the chapter "Songs of Occupations". I didn't look at it, though.

"La Paloma" is another song about the sea. I have it in the form of sheet music and it's published by Schott. However, it only has the lyrics in Spanish, French and German, not English.