These are the ranks on which you may choose to be but some may require permission of approval.
Ranks and Descriptions
Captain
Highest rank upon a ship and thus holds the most authority.They are the ones who tell everyone what to do,who to fight,and where to sail basically.They are understanding of every duty there is on the ship as well as know how to do each duty if there were any emergency.
Lieutenant or Captain's Mate
Second in command to the captain and thus hold the most trust from them.They are loyal to their duties and are often put in charge if the captain is ill or off the ship on other duties for the time being.Usually picked by the captain.
Doctor
On rare occasions there is a doctor on board of a ship and if so high chances they were signed on by contract,or in otherwords kidnapped but placed under contract,kidnapped by captured ships,or volunteers to the captain and his crew.Their rank is just below lieutenant due to their specialty.They are required to take care of the general health of the crew and treat injuries.
Master
The person who steers the ship and generally does any other navigation for the captain.They are excellent with maps and know just where to go to get to where the captain orders to sail.They are also keen onto where the captain's ship can sail through safely and know the waters like the back of their hand.Normally seen on larger ships.
Boatswain or Mates
Most important men aboard the ship.They may not be high in rank but they are the ones who do all the hard work that the lieutenants or captains bark at them.These things include any ropes to the ship,anchors,sails,cables,flags,and anythiing else depending on the situation.Other occasions they will take a carpenter's job and repair any damage to the ship as well as clean the deck.They really are the hardworking bunch!
Gunner
Only one person can be the gunner and they have to be top notch at artillery,especially if they want to live for the next fight.They are in control of cannons and during battles they direct the master where to move so that the ship's cannons have clear shots at the enemy ship.When it comes to the ship's artillery there is no one the smarter.
Quatermaster
Generally the man who speaks for the crew,or more importantly the heart of the hardworking men.They are the one that the captain will listen to as to the opinion of their crew and have the most willingness to speak for the crew straight to the captain no matter the case may be.They have high popularity on the ship for this but their ranks are still that of a mate.