1 Dirque: Arrr! Curse the British! They be gainin’ on us!
2 Long Tom: How can that be? We be the pirates! We should be havin’ the fastest ship!
3 Dirque: Have ye been seein’ the quality o’ our piratin’ these past few years?
4 Long Tom: Aye, ye be havin’ a point.

Pirates typically need fast ships because they need to catch up to other ships in order to plunder them. Pirates with a slow ship wouldn't be nearly as good at, you know, actual pirating.

Some pirates even go so far as to consider a fast ship more important than an eyepatch and a hook hand. Crazy, I know.