"I sing the bass and you sing the solo
Hob y deri dando
All about the clipper ship, the Marco Polo..."

J. Glyn Davies, a Liverpool University professor in the Celtic Department who was a friend of Stan Hugill, worked for The Cambrian Line, which sailed out of Liverpool docks. In his copious notes, he says that, whereas Liverpool shanty crews were basically thrown together with little chance of singing practice, North Wales sailors had a sense of community spirit; they grew up together and sang in chapel choirs together. The Cambrian Line employed Welsh masters, and Welsh became the working language on the ships, "except for Orders and shanties." Sadly, there were no Welsh-language shanties on board ships (apart from sea songs sung by the five-man crews out of Porthmadog and other Welsh ports), which inspired Davies to write Yn Harbwr Corc, Fflat Huw Puw and other classic shanties which have passed into the Welsh tradition.

The Cambrian Line also brought elderly ships which were past their prime, including the Red Jacket and the famous clipper Marco Polo - hence the ship's mention in Hob Y Deri Dando. I think that Stan collected the shanty from an Aberdyfi sailor; the folksong was in the Welsh language, but the shanty (for reasons which have been documented here) was in the English language.

Incidentally, I've always supposed that "Blaina" was the coal community high up in the Gwent valleys. In Welsh, Blaenau were the steep ends to the valleys - it could also mean Blaenau Ffestiniog!