33 CFR 401.57: Disembarking or boarding.

(a) Except as authorized by an officer, no person, other than a member of the crew of a vessel passing through, shall disembark or board any vessel while the vessel is passing through.

(b) No member of the crew of a vessel passing through shall disembark or board except for the purpose of carrying out essential duties as directed by the Master.

(c) Persons disembarking or boarding shall be assisted by a member of the vessel's crew under safe conditions.

(d) Persons intending on disembarking or boarding a vessel shall only do so after they have confirmed with the Captain that the vessel is fully secured in the lock with Hands-Free Mooring or with mooring lines.