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Electronic Communication and Safety

-or how to live with the Global Maritime Distress Safety System (GMDSS)


We all have mobile phones nowadays and the fact is you may make a call to tell someone you are in trouble on your boat. What happens though if you are out of mobile phone range?

A marine system independent of phones has been set up by international agreement to improve the safety of both professional and recreational mariners. It combines technological advances in satellite and radio communication and puts them into a structure that works all worldwide. The system is called GMDSS for short and in Australia, the authority that manages the system is Australian Maritime Safety Authority (AMSA)

If we look at the system today we have firstly the Emergency Position Radio Beacons or EPIRB. They are only switched on in an emergency and they send a signal to a satellite. The better EPIRB’s have a built-in GPS system so that the satellite knows immediately where you are instead of having to work this out, and who you are.


The “who you are” is known because when you purchased the EPIRB you took the trouble to register it with AMSA either online or with the form provided in the box you purchased. One of the vessel identifiers that can be provided to AMSA is the MMSI number. MMSI stands for Mobile Maritime Service Identity and it is an internationally recognised number and it is very important for the next item on the GMDSS list.

A vital part of the maritime safety system is marine VHF radio. This is a short-range communication system (line of sight only). Every ship keeps a listening watch and there are countless shore stations which do the same. Modern VHF transceivers have a function called Digital Selective Calling (DSC). When used such a system can restrict communication to the privately selected station or stations but this is not its safety function. Its safety function is to immediately transmit a distress call to those vessels or shore stations in your line of sight. The difference with the EPIRB system then is that on the one hand, the satellite tells the national officials that one is in trouble, the DSC system alerts those that are the nearest help that one is in trouble. Activating both is the best method of effective help. It is an essential part of the DSC system that the vessels identity MMSI is programmed into the VHF transceiver along with a connection of the VHF transceiver to a GPS device. Thus, when in distress, one lifts the spring loaded flap and pushes the red distress button on the VHF your location and identity is automatically transmitted on Channel 70 to those in the best position to provide quick assistance.

One can now purchase HF radios that operate the same DSC system to get your distress known to vessels and shore stations over the horizon but closer than the national authority alerted by the EPIRB. There are two other items that will be more familiar to big ship operators than small boats so they are only mentioned here. They are SARTS and NAVTEX

The other place the MMSI number is useful is when programming an Automated Identification System (AIS). These devices transmit data on the VHF frequencies. Typically the data transmitted is who you are (name and MMSI number) your size, location, speed, and direction so that other vessels have an idea as to whether a collision is possible or likely. This information might prompt a call from other vessels on VHF channel 16 voice so that avoiding action can be agreed upon.


Grab a coffee and watch this video....

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