33 CFR §89.1

As used in this subpart: Inland Rules refers to the Inland Navigation Rules contained in the Inland Navigational Rules Act of 1980 (Pub. L. 96-591) and the technical annexes established under that act. 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 the Inland Rules prevents or significantly hinders the operation in which the vessel is usually engaged.