6. When must AIS be in operation?
Per 33 CFR 164.46(d), vessels required to have AIS must operate it in U.S. navigable waters (as defined in 33 CFR 2.36) at all times that the vessel is navigating (underway or at anchor) and at least 15 minutes prior to unmooring. Should continual operation of AIS compromise the safety or security of the vessel or where a security incident is imminent, the AIS may be switched off. This action and the reason for taking it must be reported to the nearest U.S. Captain of the Port or Vessel Traffic Center and recorded in the ship's logbook. The AIS should return to continuous operation as soon as the source of danger has been mitigated. Note, vessels equipped with AIS--either by mandatory carriage or voluntarily--must abide by the requirements set forth in 33 CFR 164.46 which state an AIS must be: properly installed, use an officially assigned MMSI, that its data be accessible from the primary operating position of the vessel, and, always be in effective operating condition; which entails the continuous operation of AIS and the accurate input (see USCG AIS Encoding Guide) and upkeep of all AIS data parameters. Although Coast Guard AIS authority (46 USC 70114) does not extend beyond U.S. navigable waters or to all voluntary users, mariners are reminded that Navigation Rule 7 requires that every vessel use all available means to determine risk of collision. AIS is one of the most effective means currently available, particularly when coupled with radar and sight, to not only determine the risk of, but, also mitigate collisions. Thus the Coast Guard exhorts all AIS users to maintain their AIS in effective operation, at all times.
Note that you do leave it on when anchored.
We leave ours on while docking and until all settled in. Then when we start to prepare to undock, we turn it on. So typically 30 minutes or so before we actually leave.
I don't think it hurts greatly if boats that are docked have their AIS on, but it does create more boats to observe, some of which don't really need to be observed. It's like saying "look at me" when you aren't doing anything meriting being looked at.