And the Lords Commissioners of the Admiralty do hereby further give Notice, that the Uniform directed, in pursuance of His Majesty's Order on the 17th November 1787, to be worn by the Warrant Officers of His Majesty's Fleet, viz. Blue Cloth Coat, with Blue Lappels and round Cuffs, fall down Collar, Three Buttons to the Pocket and Cuff, white lining, but not edged with white; Button with an Anchor, same as the Captain's former one; white Cloth Waistcoat and Breeches. Shall be worn only by Gunners, Boatswains and Carpenters; and the subordinate classes of Warrant Officers shall not be allowed to wear Lappels.
From the Admiralty Rules, 1807
It it generally believed that the seated fellow visible at the left through the doorway/window in the Ibbetson painting above, is a Bo'sun given his mode of dress and the chain about his neck. See enlargement detail.
Above Left: Bo'sun, HMS Venerable, 1799. Above Right: Bo'sun's Mate, HMS Gloucester, 1812