Look no further than my hometown, Bristol in the South West of England.
Bristol was, and in fact still is, a major port from the 10th Century onwards, so a reasonable proportion of British shipping would have originated from Bristol and had Bristolian crews. Famous pirate Blackbeard, or Edward Teach, is supposed to have been Bristolian, so when Robert Newton portrayed him on screen in 1952, he did a Bristolian accent, which isn't extremely different from Newton's Dorset accent.
(Lee, Robert E. (1974), Blackbeard the Pirate)
Hi! You'll find a treasure-trove of pirate lore in the FAQ section on Piracy