It should be noted that the pirate accent is rather similar to the Bristol and West Country accents, found in the South West of England. This is presumably because many pirates of the Atlantic came from this area. Bristol was a major merchant port in the Golden Age of piracy (16th-18th Centuries), and was a primary apex of the slavery and tobacco trading triangle between colonial America (especially the Caribbean), England and Africa.
Those who are vaguely familiar with the accent may find it helpful to recall the band The Wurzels and how a stereotypical English farmer may say the word "combine harvester". One of the main differences between talking like someone from the West Country and talking like a pirate is that a gruff, throaty voice is unneccessary for imitating the gentle folk of the South West.
One of the interesting things about these accents is that the "R" sound is dissimilar to that of most of the British accents, and has more in common with the American accents. For a quick technical analysis, see how to pronounce an English "R".
If one wishes to talk like someone from the West Country, one should include gratuitous references to arable or dairy agriculture, the "arrr"s of a pirate, as well as the Bristolian phrase "my lover" (pronounced moy l'verr) when talking to people who may even be complete strangers. As with the pirate accent, this may also lead to unintended violence.