The U.S. Coast Guard is replacing many of its fixed sound signals with foghorns that mariners themselves activate. All we have to do is set our VHF radios to a specified frequency and key our mics five times. This activates the foghorn in question for either 15, 30, 45 or 60 minutes before shutting off. Each new Notice to Mariners lists additional foghorns that are being converted to MRASS, which stands for Mariner Radio Activated Sound Signal.
Most of the MRASS signals are being installed in lighthouses and other fixed applications, such as the signals marking the end of a jetty. For example, one prominent navigation aid that will soon feature a MRASS sound signal is Boston Light. Under the plan, keying the mic five times on channel 81A would activate the Boston Light fog signal for 45 minutes.
Heretofore many of these signals were activated either by visibility detectors, also called fog detectors, or by remotely activated phone line switches, both of which tended to cause continuous signaling, even when no boats were nearby. (And sometimes even when there was no fog; just sea spray in the air, for example.) The low-frequency signal, ideal for propagation through fog, also travels far enough to annoy local residents who complained of noise pollution.
The problem is that infrequent boaters or visiting cruisers may not know of the presence of MRASS signals, and even if they did know, might not be aware of which channel to use to key their mics. One suggestion is to add (RA) for “radio activated” to be used with a chart note referring the user to the Light List.
But not everyone carries a current List of Lights or Sailing Directions, the government publications that list details about the various MRASS locations. While the obvious answer seems to be labeling the MRASS signals on government charts, NOAA worries about clutter. Stay tuned and we will update you on this issue as policymakers sort it out.