One of my favorite musical instruments is the accordion--yes, the accordion. Although often mocked now, thanks, in part, to Lawrence Welk, the accordion was the electric guitar of its day. It was portable and versatile with a modern mechanical sound. There's a reason it became so popular, showing up later on in everything from polka to Tejano to sea shanties.
The accordion became such a common instrument among seafarers that it is, along with its cousin, the concertina, an essential part of any pirate movie. That, for a historian, is a little bit of a problem. The accordion was patented in 1829. The concertina dates from about the same time. That means that neither instrument existed in the classic age of piracy which is usually set in the late 16 and early 1700s. Sailors then played whistles or fiddles for musical accompaniment.
They might also have used my other favorite musical instrument, the bagpipe, which actually has a much wider range of use than just Scotland. A truly ancient instrument, the bagpipe has been part of traditional music from Iberia to the Baltic to the Middle East. Somehow, though, a pirate crew dancing to a bagpipe just doesn't seem quite the same.
Anyway, I love accordions and I love ships so I'm willing to forgive the glaring historical inaccuracy in pirate films. I still wince, however, each time someone in a tricorn hat and buckled shoes breaks out an accordion to serenade his fellow swashbucklers.