I've always heard Cyril sing it 'as it DIVES away' and the gangplank as the walk-ashore.
Cyril wasn't a bigot about his words in that he didn't sing his songs word-for-word every time, though. He sometimes 'danced on down that silver lane.' In ST peter's shoes.
I suppose every-one knows about the 'spar' verse, how a club-member took it to America, and Cyril forgot it until someone brought it back many years later?