A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2017 Jun 24, 12:16 -0700
Lu Abel, you wrote:
"Here's a question for people (such as recent US Navy veterans) with direct knowledge"
I have indirect knowledge from chatting with active USN. And maybe others, too? Those with direct knowledge are generally prohibited from discussing any aspect of their vessels' operation.
"I can understand why naval vessels (of any nationality) do not broadcast AIS data even though commercial ships are required by law to broadcast AIS. After all, we don't want drug smugglers or the Iranians or whoever else to know the position of US naval vessels."
They do in fact broadcast AIS data occasionally, and they should probably do so more often. Look for "US warship" or "US submarine", e.g. Given that AIS is often superior to radar in its display of information and given its high popularity aboard commercial vessels, it seems to me that navies (not just USN) will need to learn that they should broadcast AIS data under some circumstances, especially like this: peacetime, at night or in poor visibility, approaching a friendly port with heavy traffic. Maybe turn on the AIS when a vessel is approaching too close?
An interesting and quite feasible experiment for private (individual, Internet-based) research would be to track the number of times USN vessels are visible by AIS over time. I would not be surprised if there is an increase either now or maybe after the release of the report on the collision.
"But do Navy ships receive AIS broadcasts and plot the positions of AIS-equipped vessels -- and sound a collision alarm if the CPA is too close??"
Yes, they do. They receive AIS data and process it in various ways including issuing alarms. Systems with alarms unfortunately suffer from one simple problem: the "mute" button. In addition USN commanders have the right, privilege, and responsibility of issuing their own vessel-specific rules on almost every aspect of vessel management and navigation. I would hate to learn in a few months time that someone aboard the Fitzgerald had ordered that electronics be turned off or alarms be muted for "training purposes" or some such.