Marine 911

— By John Payne

Digital selective calling takes the "search" out of search and rescue. When properly registered with an MMSI number and interfaced with GPS, just one push of the red button automatically transmits the boat's identity and position to a shore-based rescue coordination center.

The technologically advanced global maritime distress and safety system (GMDSS) was fully implemented in 1999 for all commercial shipping. This new system has a significant impact on recreational boaters. Previously, safety communications systems were based on voice systems that included both VHF and HF radio. Distress calls were generally though voice signals, with those familiar “mayday” transmissions and, for those who had invested in an EPIRB, a satellite signal distress alert that improved one’s chances of rescue at sea. While you could hope that your voice distress signals would be heard by one of the thousands of merchant, naval and fishing boats underway, it might not and tales of people repeating mayday messages over the radio as the water rose above their knees were the tragic consequences.

Satellite-based systems have brought tremendous advances in the success of at sea rescue efforts. For decades boaters relied on Morse code and a VHF radio, which were the primary “mayday” resources in the merchant ships I served on in the mid-70s. These technologies are now virtually extinct and mariners rely on radios with digital selective calling (DSC) and Inmarsat C for distress messaging along with satellite EPIRBs, Inmarsat C and NAVTEX transmit weather and navigation information. GMDSS is a multi-layered system that ensures maximum coverage. The discussion of EPIRBs, Inmarsat and NAVTEX is separate from this article but each is a part of the GMDSS system.

Safety Net
The principal function of GMDSS is to coordinate and facilitate search and rescue (SAR) operations. This applies to both shore-based rescue groups and other boats. The system is also designed to react to distress calls with minimal delay and locate those in distress with maximum accuracy. The system also provides marine safety communications and maritime safety information (MSI). This includes navigational and meteorological warnings, weather forecasts and other urgent safety information.

The adoption and installation of GMDSS is not compulsory for pleasure boats but, due to its global implementation on commercial vessels, most boaters will want to install partially GMDSS compliant equipment simply to remain “plugged in” to the system and DSC radio is the entry point for most small boat owners and, arguably, is the most important safety device onboard.

GMDSS certainly maximizes SAR situations for boats so, in most cases it will enhance offshore safety, and these changes are good for the recreational boater. GMDSS equipment accurately identifies your own boat (all the physical details) and your current position (exactly where you are) and this information is broadcast automatically. Push one button and you automatically activate alarms at coast stations and on other boats.

Why DSC?
VHF Channel 70 is the nominated DSC channel and a VHF marine radio with digital selective calling is a primary component of GMDSS. It improves the accuracy, transmission and reception of distress calls.

Digital signals in radio communications are at least 25% more efficient and significantly faster than voice transmissions. Consider the time it takes to say “mayday” and give all the position information versus the moment in which the one button pushed takes effect. A DSC VHF transmission typically takes a second and MF/HF takes approximately 7 seconds, and both depend on the call type you are making.

A DSC radio requires the use of an encoder and decoder. A dedicated DSC watch receiver continuously monitors the specified DSC distress frequency. This means that your DSC radio is always listening ready to decode and always ready to encode and send your distress alert. Affordable VHF DSC radios are available from Horizon, Icom, Raymarine, Simrad and several others.

Identity Alert
DSC radios enable the transmission of digital information that is based on four priority groupings: distress, urgency, safety and routine. This information can be selectively addressed to either all stations or to a specific station or to a specific group of stations.

Every owner of a DSC radio must register the radio and obtain an ID number called a Maritime Mobile Selective Call Identity code or MMSI. The radio’s owner, a vessel description and emergency contacts are all collected as part of the registration and forwarded to a SAR database kept by the Coast Guard. In the U.S., the numbers are issued by the Federal Communications Commission (FCC) and in Canada, by Industry Canada. Once issued, the boat owner programs this unique, nine-digit number into their radio.

MMSIs are managed by each nation for its own registered boats and the first three digits are a country code. For those cruising internationally or who otherwise require an FCC license, it will include an MMSI if the applicant requests one. For boaters who do not need a license, BoatU.S. and Sea Tow have been authorized by the FCC to assign MMSI numbers to boats with DSC capable radios. To get a free MMSI number from BoatU.S., go to BoatUS.com/mmsi. There is also a list of frequently asked questions at this site as well as a free radio tutorial, “Can You Hear Me?” that anyone can take online to become more familiar with DSC radios. Canadians who need an MMSI may register with Industry Canada, also free, at http://sd.ic.gc.ca.

A DSC distress alert message is configured to contain the transmitting boat’s MMSI, the exact time, the nature of the distress and the boat’s position, all of which comes from your interfaced GPS unit. One common problem is that owners don’t properly interface the GPS with the DSC radio and, without a position, no one will know where you are. Similarly, many don’t program in the MMSI code, so when you are in distress, the rescuers don’t know anything about you and the alert may get overlooked. The same applies to proper registration of an EPIRB.

Distress Chain
So, what happens in the various GMDSS distress call situations? A distress alert is activated from a DSC VHF or MF/HF radio, a 243/406 MHz EPIRB or Inmarsat B and C terminals from a boat to shore. Other boats within the area may hear your alert, however, it’s important to understand that the shore-based rescue coordination center (RCC) is responsible for responding to and acknowledging receipt of your alert and not other vessels.
When the RCC receives and acknowledges an alert, the RCC then relays this alert to other boats in your geographical area. This properly targets the local resources available and does not involve boats that are outside the distressed boat’s area. Alerts are received on a DSC VHF or MF/HF radio, Inmarsat terminals or a NAVTEX unit MSI message. When a boat receives the distress relay message, it should contact the RCC to offer assistance.

When the SAR phase of the rescue commences, the previous one-way communications channel changes to a two-way channel for efficient coordination of both aircraft and other rescue vessels. Local communications between various SAR elements use short-range, terrestrial MF or VHF on the various specified frequencies. Large ships have a SAR transponder and/or a 121.5 MHz homing frequency of an EPIRB that allows the precise location of the boat in distress.

Coverage Limitations
The GMDSS system categorizes requirements for equipment and services into four specific sea areas, though only two relate to most pleasure craft. This effectively defines a boat’s specific communications’ system requirements.

Area A1. This is for boats that are sailing within shore-based VHF radio range. Typically, that distance is in the range of 20 to 60 nautical miles (nm). You require a DSC VHF radio operating on channel 70 and of course, channel 16. You should also have a 406 MHz EPIRB. I also have a handheld VHF radio in my abandon boat kit. In general, this category fits most boats that enjoy coastal waters.

Area A2. This area is for boats within shore-based MF radio range and that distance is around 100 to 300 nm. The same VHF requirements as Area A1 are applicable, as are survival craft requirements. I have a Navtex, as it’s useful (and permitted) in both A1 and A2 areas and there are several good yacht and small boat units available.

For now, Channel 16 remains the primary distress channel in the U.S. as the Coast Guard is not officially monitoring Channel 70 in all regions. Rescue 21 is the $730 million upgrade of all Coast Guard coastal communication equipment that will utilize DSC technology. It’s being installed, by region, through 2011. For a map of the current installation schedule, go to www.uscg.mil/rescue21/about/impsched.htm.

If you go cruise any distance, a DSC radio is a valuable investment in your safety at sea. It’s not complicated and it’s easy to operate.