46 C.F.R. § 35.35-42

(a) No vessel may come alongside or remain alongside a tank vessel in way of its cargo tanks while it is loading or unloading cargo of Grade A, B, or C without permission of the Person in Charge of the transfer on the tank vessel.

(b) No vessel may come alongside or remain alongside a tank vessel in way of its cargo tanks while it is loading or unloading cargo of Grade A, B, or C unless the conditions then prevailing are acceptable to the Persons in Charge of cargo handling on both vessels.