RYA SRC GMDSS 3 — Questions and Answers
Question 1: What is the primary purpose of Digital Selective Calling (DSC) on Channel 70?
- To broadcast weather forecasts to all vessels
- To send automated digital distress alerts and calls to specific stations (Correct answer)
- To transmit navigational warnings to ships in the area
- To relay NAVTEX messages to coastal stations
Correct 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.
Question 2: When a DSC distress alert is received on Channel 70, what should you do first?
- Immediately transmit a DSC acknowledgement
- Switch to Channel 16 and listen for the associated Mayday voice call (Correct answer)
- Call the vessel on Channel 67
- Relay the alert on Channel 70 to all ships
Correct 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.
Question 3: What is an MMSI number used for in GMDSS?
- It identifies the radio operator's licence number
- It is a unique 9-digit number that identifies a ship or coast station in DSC transmissions (Correct answer)
- It is the frequency code for the vessel's working channel
- It denotes the vessel's ITU radio licence expiry date
Correct 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.
Question 4: A UK vessel's MMSI number always begins with which digits?
- 00
- 99
- 23 (Correct answer)
- 06
Correct 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.
Question 5: How should a DSC distress alert be acknowledged by a coast station compared to a ship station?
- Ships should acknowledge immediately on Channel 70; coast stations should not
- Coast stations acknowledge on Channel 70; ships should NOT transmit a DSC acknowledgement and should listen on Channel 16 (Correct answer)
- Both ships and coast stations acknowledge simultaneously on Channel 70
- Ships acknowledge on Channel 16; coast stations acknowledge on Channel 70
Correct 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.
Question 6: What does the Nature of Distress field in a DSC distress alert indicate?
- The vessel's current speed and heading
- The type of emergency, such as fire, flooding, or collision (Correct answer)
- The number of people on board the vessel
- The vessel's port of registration
Correct 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.
Question 7: 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?
- Cancel the distress alert and call on Channel 16 voice only
- Send the DSC alert with position fields left as 'no information' and follow up with a voice Mayday (Correct answer)
- Wait until you can obtain a GPS fix before transmitting
- Send the alert only if the DSC is linked to a GPS receiver
Correct 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.
RYA SRC GMDSS 3
What is the primary purpose of Digital Selective Calling (DSC) on Channel 70?