First the good news. Throughout most of the continental United States, calling the Coast Guard on your marine VHF radio now ties you into one of the most modern marine radio networks in use anywhere on Earth. As of November 2010, the 26 Sector Command Centers in the Coast Guard’s Rescue 21 radio network can monitor transmissions along nearly 37,000 miles of coastline.
On the East coast from Maine to the Florida Keys, on the Gulf coast all the way through to Corpus Christi, and on the West coast from San Diego to Seattle, you are covered. If you’re a Great Lakes sailor, you’re also covered along the eastern shore of the state of Michigan, and by the end of this year you should be fully covered on lakes Michigan and Erie as well. By next year coverage may also be extended to the Ohio and Mississippi rivers.
What’s so great about Rescue 21? For starters, the system all but eliminates the 88 known coverage gaps where the Coast Guard’s old transmitters and receivers, which date back to the 1970s, often could not hear incoming calls. In addition, within this expanded coverage area, Rescue 21 has great reception.
“While we routinely pick up calls from less capable devices, the system is designed to minimally pick up a 1 watt signal from an antenna 2 meters off the water up to 20 miles offshore,” explains Lt. Commander Michael A. Edwards, Rescue 21’s Technical Manager.
No more worrying that the Coast Guard’s squelch control is set too high or that the volume control is turned too low. Any radio sound, including a lightning strike, will get the immediate attention (most likely) of multiple Coast Guard watch-standers on the air. Any working marine VHF transceiver will be heard, from an old crystal-controlled 5-channel set to the latest in fixed-mount synthesized VHF equipment.
All receiving stations in the new system are also linked together in a digital TCP/IP (Transmission Control Protocol/Internet Protocol) network that makes it possible within one second to triangulate vessel positions for incoming voice calls on Channel 16, given minimum signal strength and quality factors.
“Right off the bat, a watch-stander has a visual display, so we can not only hear the radio transmission, but can also see which towers are picking it up, and from which direction, and where the signal bearings intersect,” says Chief Petty Officer Lawrence Beatty, Operations Specialist at Sector Baltimore. (During a two-hour period last July, Beatty responded to 37 distinct distress calls, resulting in more than 77 people being assisted or rescued during an unexpected powerful storm that erupted on Chesapeake Bay.)
“Rescue 21 Channel 16 voice calls are also digitally stored for 30 days,” Edwards adds. This allows for instant retrieval and playback analysis through digital signal processing, which helps the Coast Guard to decipher and interpret nearly inaudible calls for help.
Rescue 21 and DSC Radios
The new system’s most important function is to take full advantage of the automatic distress signaling feature on modern DSC (Digital Selective Calling) VHF radios. If your DSC radio is properly registered and installed, you can simply press the red distress button in an emergency and Rescue 21 will instantly receive your automatic call, including your identity and current GPS position, on Channel 70.
After transmitting automatically on Channel 70, your radio then dutifully switches to Channel 16, where numerous agencies will be responding to your call for help. Other vessels in the vicinity with DSC radios will also see the bearing and range from their stations to your station.
Now for the bad news—about 90 percent of the DSC radios currently in use don’t have properly registered MMSI (Maritime Mobile Service Identity) numbers and/or are not connected to GPS receivers. Without embedded identity and position data, a Channel 70 digital distress call, delivered in a very short, efficient transmission burst, can actually be less effective than a traditional voice call.
“Receipt of distress alerts over Rescue 21 without either position or MMSI data causes watch-standers much frustration,” explains Edwards. “The system will pick up these distress alerts and can indicate what tower or towers heard the call, but cannot always triangulate a position. Instead of ‘X marks the spot,’ we’re forced to consider the entire coverage area of the site receiving the call as a possible search area.”
In many cases the area in question can exceed 600 square miles and is much too large to search. Without additional information, SAR planners are forced to declare an “uncorrelated” Mayday and must issue an Urgent Marine Information Broadcast (UMIB) over VHF rather than deploying SAR assets.
What you should do
The U.S. Coast Guard has accomplished its job by finally getting most of its Rescue 21 system up and running. Now there’s no excuse for not having a DSC radio aboard your boat. Once you have a DSC radio, it’s your job to obtain an MMSI number, input it into your radio and connect your radio to your GPS receiver.
MMSI numbers are now included with all new FCC-issued Ship Station licenses. They can also be obtained for free by logging on to boatus.com/MMSI or seatow.com/boating_safety/mmsi.asp.
As an added measure of safety, the Coast Guard advises that if you ever need to make a VHF distress call you should also, if possible, make a voice call on Channel 16 after sending an automatic digital one on Channel 70.
If your radio ever receives a DSC distress message, you should write down the MMSI number of the vessel in distress. Then listen for the rescue action on Channel 16. Have the other vessel’s MMSI number on hand in case someone needs a relay. Instructions for relaying DSC distress calls, and for making DSC radio-check calls, can be found here.