Avandar Chief of the Boat
The Chief of the Boat (COB) is a senior enlisted crewmember on a starship in the Federation Starfleet who assists and advises the Commanding Officer and Executive Officer on matters regarding the good order and discipline of the crew. There is only one COB on a vessel, and he is generally responsible for the day-to-day operations of the ship's non-commissioned personnel and for their morale and training.
While it is usually true that the COB is the most senior enlisted crewmember, it is not strictly required. The CO is neither required to select the highest ranking crewmember or the most senior in time aboard nor to replace his COB with a more senior crewmember who reports aboard after the COB's selection. The position of COB should obviously be considered as a senior staff position on a starship.
When a new enlisted crewmember joins a ship's crew, the COB is usually one of the first people he will meet. While the COB is outside the direct chain of command for crewmembers junior to him, he has a tremendous amount of authority and carries a lot of weight, generally being thought of as the top of a virtual enlisted chain of command.