Take the SEARCH out of SAR

Got DSC?Did you know that your VHF marine radio is likely equipped with a technology called DSC, or digital selective calling, that can help rescuers take the “search” out of search and rescue? Ever wonder how that red “distress” button on your radio works?

This is how. (Pay attention, this is important stuff, it could save your life.)

IF PROPERLY REGISTERED AND CONNECTED, that red button allows mariners to instantly send an automatically formatted distress alert and GPS location of your vessel to Coast Guard search and rescue units as well as other DSC equipped vessels nearby.

Notice the “IF PROPERLY REGISTERED AND CONNECTED” screaming at you in all caps. That’s the kicker… the DSC VHF radio MUST BE properly registered with an MMSI number and be connected to your GPS in order to properly work!! This applies to mounted and handheld marine radios.

Two simple steps:


This means obtaining the MMSI, or Maritime Mobile Service Identity, nine-digit unique identification number and carefully programming it into the radio.

MMSIs are regulated and managed internationally by the International Telecommunications Union in Geneva, Switzerland, just as radio call signs are regulated. Non-commercial users, for example recreational boaters, who stay in U.S. waters can obtain an MMSI through approved organizations such as BOAT US, SEA TOW, U.S. Power Squadron, and Shine Micro (primarily for AIS). Most of these organizations provide MMSIs at no charge even to nonmembers.

Important:Before programming your MMSI into your radio, read your owner’s manual. There may be a limited number of tries (likely only two attempts) before the radio locks out requiring you to send it back to the manufacturer for a re-set.

Connect to GPS.

All DSC-equipped radios, and most GPS receivers, have an NMEA 0183 two-wire data protocol allowing any model of GPS to be successfully interconnected to any model of radio, regardless of manufacture. Simply twisting, soldering or taping the wires together between the radio and the GPS will connect them. For more information, click here.

Again, it is important to consult both the GPS and the radio owner’s manuals before interconnecting the devices.

The U.S. Coast Guard offers VHF and MF/HF radiotelephone service to mariners as part of the Global Maritime Distress and Safety System. The Coast Guard’s “Rescue 21” project updates the USCG VHF distress system to include DSC capability & direction finding capabilities. Only those areas where Rescue 21 is installed can reliably receive VHF DSC distress calls.

For more information about VHF radios, how they work and equipping your boat, click here and choose the DSC Radio Tutorial by BOAT US.  For more information about Rescue 21 including FAQ, fact sheets and coverage information, click here.

Rescue 21 video

Click on the image to watch a USCG Rescue 21 promotional video by General Dynamics.

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