A ship's officer is a person responsible for the navigation, operation, and maintenance of a ship. The four most common positions are MATE, PURSER, BOSUN, and BOATSWAIN. A MATE is a senior deck officer who is in charge of the deck crew and is second-in-command to the captain. A PURSER is responsible for the financial and administrative duties on board the ship. A BOSUN is a senior deck officer who is in charge of the deck crew and is responsible for the maintenance of the ship. Lastly, a BOATSWAIN is a senior deck officer who is in charge of the deck crew and is responsible for the navigation and operation of the ship.