GMDSS Flashcards

What is the primary purpose of Digital Selective Calling (DSC) on Channel 70?

Answer: To send automated digital distress alerts and calls to specific stations

DSC on Channel 70 is used to send automated digital calls, including distress alerts, to specific vessels or coast stations without occupying voice channels.

When a DSC distress alert is received on Channel 70, what should you do first?

Answer: Switch to Channel 16 and listen for the associated Mayday voice call

On receiving a DSC distress alert, you should switch to Channel 16 and listen for the accompanying Mayday voice message before taking further action.

What is an MMSI number used for in GMDSS?

Answer: It is a unique 9-digit number that identifies a ship or coast station in DSC transmissions

An MMSI (Maritime Mobile Service Identity) is a unique 9-digit number programmed into the DSC controller to identify the vessel in all digital calls.

A UK vessel's MMSI number always begins with which digits?

Answer: 23

UK vessel MMSIs begin with 232, 233, 234, or 235, all starting with '2' followed by '3', reflecting the UK's MID (Maritime Identification Digits) of 232–235.

How should a DSC distress alert be acknowledged by a coast station compared to a ship station?

Answer: Coast stations acknowledge on Channel 70; ships should NOT transmit a DSC acknowledgement and should listen on Channel 16

In GMDSS, only coast stations should acknowledge DSC distress alerts digitally; ship stations must avoid transmitting DSC acknowledgements to prevent confusion and channel congestion.

What does the Nature of Distress field in a DSC distress alert indicate?

Answer: The type of emergency, such as fire, flooding, or collision

The Nature of Distress field in a DSC alert encodes the type of emergency (e.g. fire, flooding, man overboard) to help rescuers prepare an appropriate response.

If your vessel is fitted with a DSC VHF radio but you are uncertain of your position, what should you do when sending a DSC distress alert?

Answer: Send the DSC alert with position fields left as 'no information' and follow up with a voice Mayday

You should send the DSC alert immediately even without a position — use 'no information' in the position fields — then follow up with a voice Mayday on Channel 16 giving all available details.