3.4 Mayday Relay Protocols & Coast Guard Coordination
Key Takeaways
- A Mayday Relay is transmitted when a vessel observes another vessel in distress that cannot transmit a Mayday itself, or when a distress alert has gone unacknowledged by the Coast Guard.
- The voice proword MAYDAY RELAY (spoken three times) indicates that the transmitting station is repeating distress details on behalf of another casualty.
- Ship stations MUST NOT transmit an All-Stations DSC Distress Relay unless specifically instructed by a Coast Guard station or in isolated offshore conditions.
- Voice Mayday Relays are transmitted on VHF Channel 16 using High Power (25W), addressed either to ALL STATIONS or a specific Coast Guard station (e.g., SOLENT COASTGUARD).
- The relaying station must clearly differentiate its own identity and position from the identity and position of the vessel in distress.
3.4 Mayday Relay Protocols & Coast Guard Coordination
A Mayday Relay is an emergency transmission used to re-broadcast distress information on behalf of another vessel, aircraft, or person in grave and imminent danger. Understanding when a vessel is obligated to transmit a Mayday Relay—and the strict limitations placed on DSC Distress Relays—is a vital topic in the RYA SRC syllabus.
Circumstances Requiring a Mayday Relay
Under international ITU Radio Regulations, a ship station or coast station MUST transmit a Mayday Relay under any of the following three specific conditions:
- Casualty Unable to Transmit: The vessel or person in distress is physically unable to transmit a distress message (e.g., vessel has suffered total electrical failure, radio dismasted, vessel capsized, or observing distress flares fired from an unidentified craft).
- Unanswered Distress Call: The master or person responsible for the observing vessel hears a distress call or DSC alert that has NOT been acknowledged by a Coastguard shore station or any other vessel after a reasonable delay (typically 5 minutes for DSC alerts).
- Distance Limitations: The observing vessel receives a weak Mayday call from a distant casualty and realizes that shore-based Coastguard stations are out of radio range, requiring the call to be repeated at high power to bridge the communications gap.
Mayday Relay Voice Call & Message Format
Mayday Relay transmissions are conducted on VHF Channel 16 using High Power (25 Watts).
+------------------------------------------------------------------+
| MAYDAY RELAY VOICE STRUCTURE |
+------------------------------------------------------------------+
| 1. PROWORD : MAYDAY RELAY MAYDAY RELAY MAYDAY RELAY |
| 2. ADDRESSEE : ALL STATIONS (x3) or COASTGUARD (x3) |
| 3. IDENTITY : THIS IS + Relaying Vessel Name (x3) + Call Sign |
| + MMSI |
| 4. PREAMBLE : FOLLOWING RECEIVED FROM [Distress Vessel Name] |
| AT [Time UTC] |
| 5. RELAY DATA : Position + Nature of Distress + Assistance Req. |
| + POB + Extra Info + OVER |
+------------------------------------------------------------------+
Verbatim Voice Script Examples
Scenario A: Relaying an Observed Red Flare (Unknown Vessel)
MAYDAY RELAY MAYDAY RELAY MAYDAY RELAY
ALL STATIONS ALL STATIONS ALL STATIONS
THIS IS SEASPRAY SEASPRAY SEASPRAY
CALL SIGN GOLF ALFA NINE ONE MMSI TWO THREE FIVE EIGHT EIGHT EIGHT NINE NINE NINE
OBSERVED RED PYROTECHNIC FLARE AT ONE SIX FOUR FIVE UTC
POSITION BEARING ONE EIGHT ZERO DEGREES MAGNETIC DISTANCE THREE NAUTICAL MILES FROM ANCHOR HEAD
UNKNOWN VESSEL APPARENTLY IN DISTRESS
REQUIRE IMMEDIATE ASSISTANCE
OVER
Scenario B: Relaying an Unacknowledged Mayday Call
MAYDAY RELAY MAYDAY RELAY MAYDAY RELAY
SOLENT COASTGUARD SOLENT COASTGUARD SOLENT COASTGUARD
THIS IS WINDWARD WINDWARD WINDWARD
CALL SIGN GOLF MIKE XRAY TWO MMSI TWO THREE FIVE FOUR FOUR FOUR THREE THREE THREE
MAYDAY COMBINE RECEIVED AT ZERO NINE ONE FIVE UTC
POSITION FIVE ZERO DEGREES THREE ZERO MINUTES NORTH ZERO ZERO ONE DEGREE FOUR ZERO MINUTES WEST
VESSEL COMBINE ENGINE ROOM FIRE OUT OF CONTROL
REQUIRE IMMEDIATE ASSISTANCE, TWO PERSONS ON BOARD
OVER
Strict Restrictions on DSC Distress Relays
While voice Mayday Relays on Channel 16 are routine emergency procedures, transmitting a DSC Distress Relay on Channel 70 is subject to severe regulatory restrictions for ship stations.
| Radio Equipment | Authorized to Send All-Stations DSC Distress Relay? | Operating Conditions |
|---|---|---|
| Coast Radio Station (CRS/MRCC) | YES | Authorized to broadcast DSC Distress Relays to coordinate SAR |
| Ship Station (Class D VHF) | NO (Generally Restricted) | MUST NOT send All-Stations DSC Relay unless requested by Coastguard or in remote sea areas with zero shore response |
Exam Warning: If a ship station receives an unacknowledged DSC alert, the operator should attempt to contact the Coastguard via voice on Channel 16 or send a point-to-point DSC Relay to the Coastguard's specific MMSI. Do NOT press the DSC All-Stations Relay button on a ship radio without Coastguard authorization.
The Mayday Relay Protocol & Legal Duty of Assistance
Under the International Convention for the Safety of Life at Sea (SOLAS Chapter V, Regulation 33), every master of a ship at sea who is in a position to be able to provide assistance, on receiving a signal from any source that persons are in distress at sea, is bound to proceed with all speed to their assistance. However, there are circumstances where a vessel learns of a distress situation but the casualty vessel cannot transmit its own Mayday call—or where the casualty's low-power signal is masked by terrain or distance.
In such scenarios, a observing vessel or coast station must step in and broadcast a Mayday Relay call on VHF Channel 16 (156.800 MHz) at 25W High Power.
Statutory Triggers for Transmitting a Mayday Relay
A mariner is legally authorized and required to transmit a Mayday Relay under three specific circumstances:
- Casualty Unable to Transmit: The vessel or person in distress is unable to transmit a distress call themselves (e.g., vessel has lost all electrical power, capsized, or crew is incapacitated).
- Out of Range of Coast Guard: The observing vessel hears a distress call or sees visual distress signals (such as red parachute flares or orange smoke) and observes that no coast station or other vessel has acknowledged the call because the casualty is out of VHF range of land.
- Third-Party Distress Information: Information about a distress situation is received via another channel (such as mobile phone, satellite email, or visual observation) and must be communicated to search and rescue authorities.
Mandatory Voice Mayday Relay Format
The voice Mayday Relay call must follow a strict, standardized format to ensure coastguard watchkeepers immediately recognize that a third-party relay is in progress:
"MAYDAY RELAY, MAYDAY RELAY, MAYDAY RELAY"
"ALL STATIONS, ALL STATIONS, ALL STATIONS" (or "SOLENT COASTGUARD x3")
"THIS IS MOTOR YACHT SEA GULL, SEA GULL, SEA GULL"
"CALL SIGN: GOLF BRAVO CHARLIE FOUR (GBC4)"
"MMSI: TWO THREE FIVE NINER NINER EIGHT SEVEN SIX FIVE"
"MAYDAY"
"VESSEL NIMROD"
"POSITION 50 DEGREES 40 MINUTES NORTH, 001 DEGREE 20 MINUTES WEST"
"SINKING AFTER STRIKING SUBMERGED CONTAINER"
"4 PERSONS ONBOARD, ABANDONING INTO RAFT"
"OVER"
Strict Restrictions on Ship Station DSC Distress Relays
Under ITU GMDSS rules updated for Class D VHF radios, individual ship stations are prohibited from sending All-Stations DSC Distress Relays. An All-Stations DSC Relay sent by a vessel can flood Coast Guard networks with duplicate automated alerts and disrupt SAR operations.
If a ship station needs to send a DSC distress relay, it MUST send a Single-Station DSC Distress Relay addressed directly to the nearest Coast Guard MMSI (e.g., HM Coastguard MMSI 002320000). Only Coastguard MRCCs are authorized to broadcast All-Stations DSC Distress Relays.
Which condition requires a ship station operator to transmit a Mayday Relay on VHF Channel 16?
How should a voice Mayday Relay call be initiated on VHF Channel 16?
What restriction applies to ship stations regarding All-Stations DSC Distress Relays on Channel 70?