A bosun is a high-ranking warrant officer aboard a ship, in charge of a number of tasks associated with running the ship.
Bosun, also written bo’s’n or bos’n, is short for boatswain, deriving from an old form of the word swain ('young man'). In many other languages, the name for this rank means 'boatman.' The rank is the oldest one in the Royal Navy and can be traced back to 1040.
The bosun was originally in charge of a ship's running rigging (all the moving parts of the rigging), but also cordage in general, anchors and boats. As such, he would also be the direct superior of the ship’s rope- and sailmaker. His duties would include supervision of maintenance, even if the individual tasks were carried out by skilled tradesmen. Being a type of foreman to the deck crew, the bosun could also be partially in charge of discipline among the crew.
Most famous among the bosun’s duties was certainly the commanding of maneuvers, using a type of pipe known as a bosun’s call. The bosun’s call would also be used to pipe (call) the crew to meals, assemblies etc.
Bosuns were mostly highly experienced seamen who had risen to their position from the ranks. A bosun would be expected to be familiar with all aspects of seamanship, especially ropework and maneuvering, and capable of performing them himself.
Aboard the Obra Dinn
The Obra Dinn’s bosun was a man of Austrian origin named Alfred Klestil. He had only one mate, Frenchman Charles Miner. As the Obra Dinn did not carry a Master-at-arms, the bosun and his mate seem to have been in charge of discipline among the crew, as suggested by the order given to them in Unholy Captives, part 4. Neither of them survived the voyage.
Strangely enough, the Obra Dinn had neither a rope- nor a sailmaker.