Also the available ranks on any ship (Unless they're taken) for a pirate ship is.
In order:
Captain- Leader
Lieutenant- Second in command
Boatswain- Ropes, anchors, flag raising, (Anything with string in it basically) very important.
Gunner- Artillery and cannon maintenance
Carpenter- Ship repairs and maintenance
Sailor- The cannon fodder (Cooks, soldiers, look outs etc.)