33 CFR §401.57

1. (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.
2. (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.
3. (c)Persons disembarking or boarding shall be assisted by a member of the vessel's crew under safe conditions.
4. (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.