That most useful (not to say hackneyed) reference, which alerts the solver to the fact that the word to be entered as a solution in the grid contains the letters ab, derives from the common abbreviation for able-bodied seaman.
A calling which, in both senses of the word, would be familiar to even small children in the days when the British navies were of a size to be reckoned with.
But as I was solving one such clue the other day I suddenly thought How could you have a seaman who is not able bodied?
Perhaps one who cannot climb the mast or the rigging, must stay on deck or even be confined below?
One who cannot swim?
In fact there is some confusion over whether it means able-bodied or simply able, one with more training & experience than a mere ordinary seaman. As an abbreviation the OED rules that A.B. stands for ‘able seaman (formerly able-bodied seaman)’.
Me no’ able wi’ that
Searching for further elucidation on the web brought me to a charming website which, as well as giving a very helpful description of the jobs available at sea, is about a volcano:
