Radio-Activated Sound Signals

The new MRASS system allows boaters to activate sound systems on aids to navigation by themselves.

March 24, 2014

This story updated with the addition of the USCG video, 06/2018



The Coast Guard’s new MRASS system will allow boaters to activate sound signal on aids to navigation such as this jetty marker simply by keying their VHF microphone. Grafton Smith

The U.S. Coast Guard is implementing a system that allows boaters to activate sound signals integral to aids to navigation (AtoN) by keying their VHF radio microphones, thus improving navigational safety when visibility is limited.

Many boaters believe that navigational sound signals jetty lights and navigational buoys are activated automatically when visibility becomes limited, but most are not.


Under the old system, a boater needed to hail the Coast Guard on VHF channel 16 in order to activate a sound signal. However, the new Mariner Radio Activated Sound Signal (MRASS) system allows the boater to skip that step and activate the AtoN sound signal himself. Once activated, the sound signal will continue for 30 minutes, which is the same as how they operate currently.

In order to activate the sound signal, you need to key the mic five times on a designated frequency. Provided that you within VHF range, the AtoN will begin blaring sound signals at its designated intervals. Each MRASS will be on a different VHF frequency. Authorized channels include 81A and 83A; however, if those frequencies are used as working channels in a port, a different frequency will be designated. The correct frequencies will be placed on current NOAA nautical charts. While the NOAA no longer provides printed charts, you can download PDFs of the most up-to-date charts at NOAA/charts.

No timeline has been established for full operation, according to Coast Guard Lt. Melissa Smith. “The plan is for this to ultimately to be a Coast Guard wide change,” she said.


Mariner Radio Activated Sound Signals (MRASS)

What is it? Let’s you turn on navigational sound signals yourself.

How does it work? Key your VHF mic five times on the designated channel.


Which channels? Check current NOAA charts. Most use 81A or 83A.

How long will the signal operate? For 30 minutes after you turn it on.

When will MRASS be fully operational? The Coast Guard has not set a deadline. Sign up to receive the Local Notice to Mariners for your district for updates.


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