paul culver

Member III
Noticed this abbreviation on my chart next to the fog horn location at the entrance to my harbor, so I looked it up. Its a system that allows boaters to turn the horn on by way of VHF radio. Makes sense since you might be in a fog bank off shore when its clear at the harbor. Look up the VHF channel for the horn and key the mike five times to turn it on. Its like some airstrips that let the pilot turn on the landing lights via radio. Cool stuff. Half of you probably already know this but I'm posting it for the other half.

Christian Williams

E381 - Los Angeles
Senior Moderator
Blogs Author
New one on me, too. I'll have to make a note that: "Channels 81A (157.075 MHz) and 83A (157.175 MHz) are the frequencies allocated to MRASS use."


The U.S. Coast Guard is slowly replacing many of its Aid to Navigation (ATON’s) sound signals with signals that mariners themselves are able to activate. This new system known as the “Mariner Radio Activated Sound Signal” (MRASS) allows the mariner to activate an ATON sound signal if the aid is so equipped. Once activated, the signal will continue to sound for a period of up to 1 hour with 45 minutes being the norm before shutting down and going into standby mode again.

While this system is somewhat new for the mariner, this is not new technology. In fact this has been available to the aviation pilot for decades allowing them to turn on airport runway and taxi lights and in many cases allowing them to adjust the brightness of those lights as well simply by use of the aircraft’s radios.

How to Identify a MRASS Aid to Navigation

As can be seen by the chart segment below, every ATON that is MRASS equipped is noted on the chart. Occasionally the frequency used to activate the sound signal is also published on the chart, but if not then you will need to refer to the appropriate USCG Light List volume for that area.

MRASS shown on Chart

How to Activate

Each MRASS sound signal operates on a specific VHF frequency. Channels 81A (157.075 MHz) and 83A (157.175 MHz) are the frequencies allocated to MRASS use. In areas where these frequencies may be being used for other purposes, such as port operations, other frequencies may be designated.

To use this system; tune your VHF radio to the specified frequency and then key your microphone (5) times in succession. If you are within VHF range of the ATON, the sound signal will be activated.

Keith Parcells

Contributing Partner
That is a new one to me, too. Sounds great!

Couldn't they have thought of a better name (acronym?) than, "Mister A**," though??? Oh well, maybe that makes it memorable!