AIS aids to navigation
With AIS receivers becoming more common on cruising boats, boaters need to be aware of "virtual" aids to navigation--that is, electronic aids rather than physical buoys, lights, etc. Currently, the virtual aids are experimental, but the expectation is that eventually they will replace many of the existing physical aids. Currently, they are not shown on government charts, but show up only on AIS recievers. For example, in the Straits of Mackinac, right now there are 4 virtual aids at the Mackinac Bridge, 1 at the Round Island light off Mackinac Island, and 1 in the south passage off Cheboygan. None are depicted on charts. Here's the Coast Guard's info on these virtual aids:
"In the near future, the U.S. Coast Guard and other authorized agencies and organizations (i.e., U.S. Army Corps of Engineers, Marine Exchange of Alaska) will begin transmitting AIS ATON messages and marine safety information via AIS for testing and evaluation. The exact content, location, and times of these broadcasts will be announced in future Local Notices to Mariners
"AIS is an internationally adopted radio communication protocol that enables the autonomous and continuous exchange of navigation safety related messages amongst vessels, lifeboats, aircraft, shore stations, and aids to navigation (AIS ATON). AIS ATON stations broadcast their presence, identity (9-digit Marine Mobile Service Identity (MMSI) number), position, and status at least every three minutes or as needed. These broadcasts can originate from an AIS station located on an existing physical aid to navigation (Real AIS ATON) or from another location (i.e., AIS Base Station). An AIS Base Station signal broadcasted to coincide with an existing physical aid to navigation is known as a Synthetic AIS ATON. An electronically charted, but non-existent as a physical aid to navigation, is identified as a Virtual AIS ATON. The latter two can be used to depict an existing aid to navigation that is off station or not watching properly or to convey an aid to navigation that has yet to be charted. All three variants can be received by any existing AIS mobile device, but they would require an external system for their portrayal (i.e., AIS message 21 capable ECDIS, ECS, radar, PC). How they are portrayed currently varies by manufacturer, but the future intention is for the portrayal to be in accordance with forthcoming International Standards (i.e., IEC 62288 (Ed. 2), IHO S-4 (Ed. 4.4.0)).
"Mariners capable of receiving and displaying these test AIS messages are encouraged to provide feedback and report any anomalies to the USCG NAVCEN Website: http://www.navcen.uscg.gov | Contact Us Tab | Subject: AIS | Category: AIS Testing."