33 CFR 81.1: Definitions.

As used in this part:

72 COLREGS refers to the International Regulations for Preventing Collisions at Sea, 1972, done at London, October 20, 1972, as rectified by the Proces-Verbal of December 1, 1973, as amended.

A vessel of special construction or purpose means a vessel designed or modified to perform a special function and whose arrangement is thereby made relatively inflexible.

Interference with the special function of the vessel occurs when installation or use of lights, shapes, or sound-signaling appliances under 72 COLREGS prevents or significantly hinders the operation in which the vessel is usually engaged.