what are boatswain and who are they

A boatswain is an officer on a ship, thus, the leader of the crew. In the first scene, the boatswain suggests that men, despite their power, are still subject to nature; "what cares these roarers for the name of king," he asks, when the king's ship is being pummeled by the storm (I.i.16-17). The boatswain's statement makes sense in the context of that scene; however, it becomes ironic in the second scene, when Miranda and Prospero reveal that it was Prospero himself who caused the storm.