Another good way to get the feel for the shanty is to find a "traditional" rendition (done at pace). The generally slower tempo than modern entertainment versions, the measured beat, the rests involved - all really help to emphasize the nature of the work they were meant for. Capstan shanties tend to have a steady beat throughout, without lenghty rests. Long haul shanties (Paddy Doyle's Boots is a great example of a hauling shanty in general) tend towards heavy line-by-line call and response, with rests built in. Foc'sle tend to sound more "entertaining" (as they should, being generally for the crew's entertainment).

At the heart of it, it does really help to at least have a slight amount of knowledge about sailing ships from the Golden Age. Knowing every detail isn't as needed, but knowing what the capstan is, the foc'sle, the quarterdeck, that sort of thing - those will go a long way towards helping decipher what the shanty is likely for.

M