I spent over two years aboard a ship ( Aircraft Carrier HMS Eagle )and never did I see or hear a melodeon . There was a CPO who played a rather nice piano-accordion, but that was it , squeeze-wise. It wasn't that the ship wasn't musical ; we had a full Royal Marine band, a group of "Singing Chefs " , a Bluegrass duo , and a 6-man Folk Group ( with whom I played the banjo ) , but there just were not any melodeons ,or , indeed , concertinas . And we were fully air-conditioned ,with plenty of locker-space , per man, for storing things in ; imagine taking a melodeon , or expensive concertina ( who could have afforded either, indeed ??) on board of a dank,cold,mouldy old wooden sailing vessel ,with nowhere to store what few personal possessions one had (or was allowed ) . Not to mention the ever-present danger of one's instrument being dashed to pieces by enemy broadsides ! No , all romantic nonsense ,I think !