33 CFR § 155.785 - Communications.
(a) During vessel to vessel transfers, each tank vessel with a capacity of 250 or more barrels of cargo that is carrying oil or hazardous material must have a means that enables continuous two-way voice communication between the persons in charge of the transfer operations on both vessels.
(b) Each vessel must have a means, which may be the communication system itself, that enables a person on board each vessel to effectively indicate his desire to use the means of communication required by paragraph (a) of this section.
(c) The means required by paragraph (a) of this section must be usable and effective in all phases of the transfer operation and all conditions of weather.
(d) Portable radio devices used to comply with paragraph (a) of this section during the transfer of flammable or combustible liquids must be intrinsically safe, as defined in 46 CFR 110.15–100(i), and meet Class I, Division I, Group D requirements as defined in 46 CFR 111.80.