46 CFR §143.240

1. (a)This section does not apply to an excepted towing vessel as defined in § 136.110 of this subchapter.
2. (b)Each towing vessel must be fitted with a communication system between the pilothouse and the engine room that:
   1. (1)Consists of either fixed or portable equipment, such as a sound-powered telephone, portable radios, or other reliable method of voice communication, with a main or reserve power supply that is independent of the towing vessel's electrical system; and
   2. (2)Provides two-way voice communication and calling between the pilothouse and either the engine room or a location immediately adjacent to an exit from the engine room.
3. (c)Towing vessels with more than one propulsion unit and independent pilothouse control for all engines are not required to have internal communication systems.
4. (d)When the pilothouse engine controls and the access to the engine room are within 3 meters (10 feet) of each other and allow unobstructed visible contact between them, direct voice communication is acceptable instead of a communication system.