Thanks. I've opted for a solution like the one suggested by Bob the Postman. I've chosen three versions of the ballad, for two of them, the British ones, I'll make a reference to the Netherlands (the first is the version in the Penguin Book of English Folk Song and the second is the one sung by Johnny Doughty). The third is that sung by the Carter Family: I'll evoke the loneliness and vastness of the sea. Les from Hull is also right, but it is a pity to make the line just a nonsense rhyme, loosing what it hints at.