'squeeze boxes are no more traditional for sea songs than any other instrument.'
Not sure about that, Steve. My friend the distinguished folklorist Bob Thompson [with whom I visited, & collected from Harry Cox - see the definitive Topic "Bonny Labouring Boy" Harry Cox collection] once said to me that he thought the association of seamen with the concertina was one of those bits of 'folklore about folklore', no older than Bert Lloyd's partnership with Alf Edwards; but he changed his mind when I pointed out the concertina-playing pirate in Barrie's 'Peter Pan' [1904], and the ref to sailors 'dancing to the wheezy music of the concertina' in the penultimate paragraph of Somerset Maugham's 'The Moon & Sixpence' [1919]. The concertina is a small but robust, portable but powerful instrument, small enough to fit into a sailor's dunnage without taking up too much of limited fo'csle space, &, unlike the harmonica to which it is so closely related [particularly in its anglo avatar], usable by a singer for simultaneous accompaniment.