2.7 Survival Craft Radio Equipment & GMDSS Distress Alerting

2.7 Survival Craft Radio Equipment & GMDSS Distress Alerting

Core Principle: Column 3 of Table A-VI/1-1 requires you to be able to operate location devices, including radio equipment. Pyrotechnics tell a ship two miles away that you are there. Radio equipment tells a rescue coordination centre on another continent who you are and exactly where you are — within minutes, and before anyone has started looking.

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1. What the Ship Must Carry

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2. Two-Way VHF Radiotelephones

These are the handhelds stowed in brackets on the bridge, taken to the survival craft when the ship is abandoned.

• Purpose: communication between survival craft, between craft and the parent ship, and between craft and rescue units — not long-range alerting.
• Channels: must be capable of operating on channel 16 plus at least one additional channel; typically 16 and 6.
• Power source: a sealed non-rechargeable primary battery with a long shelf life is required for the emergency set, so that it is always full when grabbed. Rechargeable batteries may be used only for routine on-board work, and the emergency battery is replaced by its expiry date, not by charging.
• Construction: yellow or high-visibility orange, or marked with a surrounding yellow/orange marking strip; waterproof; capable of operation by a person wearing gloves; buoyant or fitted with a buoyant lanyard.
• Range: effectively line-of-sight. From a liferaft, with the antenna barely a metre above a wave, useful range may be only 2–5 nautical miles to a ship and rather more to an aircraft.

Practical point: ration transmissions. The primary battery has a finite life and you may be in the raft for days. Agree a listening schedule — for example, transmit on the hour for two minutes and listen continuously only when an aircraft or vessel is seen or heard.

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3. Search and Rescue Locating Devices

Radar-SART (9 GHz)

A transponder, not a transmitter. It is dormant until a searching X-band (9 GHz, 3 cm) radar pulse interrogates it, at which point it replies with a swept-frequency response that paints a line of 12 dots on the searching radar's screen, extending outward from the SART's position along the bearing.

• Battery: at least 96 hours standby plus 8 hours transmitting while being interrogated.
• Mounting height matters enormously. The device must be mounted at least 1 metre above sea level; from 1 m the detection range from a ship's radar is roughly 5 nautical miles, while an aircraft at 3,000 feet may detect it at 30 nautical miles or more. Mount it as high as the raft's telescopic pole or lashing allows.
• X-band only. A 3 GHz (S-band, 10 cm) radar will not interrogate a radar-SART. A rescue vessel searching on S-band alone will see nothing.

AIS-SART

An alternative permitted since 2010. It derives its own GNSS position and transmits AIS safety-related position reports on the VHF AIS channels, appearing on a rescue vessel's ECDIS or AIS display as an active SART symbol — a circle with a cross — with an identity beginning 970. Its advantage is a precise position rather than a bearing line; its limitation is that the receiving vessel must have AIS switched on and monitored.

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4. The 406 MHz Satellite EPIRB

The Emergency Position Indicating Radio Beacon is the ship's automatic long-range alert.

• Stowage: in a float-free bracket with a hydrostatic release unit, sited so it will float clear if the ship founders. It can also be released manually and taken into a survival craft.
• Activation: automatic on immersion after float-free release, or manual.
• Transmission: a coded digital burst on 406 MHz to the Cospas-Sarsat satellite constellation (low-earth, geostationary and now medium-earth orbit repeaters), carrying the beacon's unique registered identity — for a ship beacon, normally derived from its MMSI. Modern beacons embed an internal GNSS position, giving a fix accurate to a few tens of metres within minutes.
• Homing: a low-power 121.5 MHz signal that SAR aircraft and helicopters home on during the final approach.
• Endurance: the battery must support at least 48 hours of transmission.

Registration and False Alerts

An EPIRB is only as useful as its registration. The 406 MHz message carries an identity, not a name — the rescue coordination centre resolves that identity against a national beacon register to learn the ship, the owner and the shore contact. A beacon that changes ship must be re-registered.

The rule that is always examined: if an EPIRB is activated by accident, do not simply switch it off and say nothing. Switching it off leaves an unresolved alert that will launch aircraft. The correct action is to switch it off and immediately notify the nearest rescue coordination centre — by DSC, radio, or telephone — cancelling the alert and giving the ship's name, position and the reason.

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5. Putting It Together: The GMDSS Distress Sequence

   1. DSC ALERT      VHF Ch 70 / MF 2187.5 kHz / HF or Inmarsat
                     Carries MMSI + position automatically
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   2. VOICE MAYDAY   VHF Ch 16 / MF 2182 kHz
                     "MAYDAY x3, this is <ship> x3, MMSI, position,
                      nature of distress, assistance required,
                      persons on board, OVER"
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   3. EPIRB          406 MHz float-free -> Cospas-Sarsat -> MRCC
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   4. SART / AIS-SART Terminal homing for the on-scene search unit
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   5. TWO-WAY VHF    Craft-to-craft and craft-to-rescue-unit traffic
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   6. PYROTECHNICS   Final visual confirmation when the unit is in sight

Each layer works at a different range. The EPIRB gets a rescue tasked; the SART gets the search unit to the raft; the handheld VHF and the pyrotechnics close the last mile. Deploy them in that order — and never burn a hand flare because you think you hear an engine.