Joy,
It being a nautical song I am not surprised. I have noticed, among the merchant seamen that I know, that there is an "inverted snobbery" associated with deliberately mispronouncing place names and names of ships.

A very similar snobbery exists among Cockneys who often deliberately mispronounce words of three syllables or more; or even replace them with different words.

They will also comment on other peoples use of long words with sayings such as "We had one of those but it died" or "We had one of those and crossed it with a Flemish Giant"

It's a whole different branch of folklore.

Bert.