You'll need to complete the Avast Ye, Admiral! quest and you'll need to be friendly with the Bloodsail Buccaneers in order to get it!

The only way to gain rep with the Buccaneers is to kill Booty Bay Bruisers. The amount of time it takes to get to Friendly really depends on how much rep you have with Booty Bay. Each Bruiser will award you 5 rep with the Bloodsails at level 80.

After you have reached Friendly you can complete the first part of the quest chain Avast Ye, Scallywag which starts with "Pretty Boy" Duncan (27, 67) just North of Booty Bay. He'll send you to Fleet Master Firallon (30, 90) on the ship South of Booty Bay to begin the Avast Ye, Admiral! quest. You'll need to slay Baron Revilgaz and Fleet Master Seahorn which are both located on the upper floor of the inn at Booty Bay. Good luck and have fun!