I think Geoff has nailed it about the verses being written fresh to suit the theme.

"A dead whale or a stove boat" does not at all sound like an historically authentic chanty lyric, in my opinion. If the subsequent lines are based on more typical chanty lyrics, then you've come to the right place, Rickard. There are a good number of us here that are familiar with those typical "stock" or "floating" lines. However, if they are entirely new, then it is merely a very keen American-English-tweaked ear that you need -- Plan B: Joe's seeking the DVD!

Based only on what you have written, the lines that come to my mind are:

"Raise her up for a bulgine pie" (!)

and

"Old man your horse will surely die."

I highly doubt these are the lyrics used for the film, but they are "traditional" lyrics, with a true chanty quality, on which the lines might have been based.