The Only Two-Way VHF Is in the Grab Bag
While the liferaft of a 26 m passenger vessel is away for its annual service, you check the survival craft two-way VHF set that travels in the grab bag. It is a GMDSS-approved handheld with an integral antenna, a channel switch marked 16 and 6, and two battery packs: the primary pack fitted to the set is stamped with a date three months past, and the spare is a rechargeable nickel-cadmium pack that reads 7.9 V against the 8.4 V nominal on the label. The O-ring on the battery compartment is flattened and gritty, and the set's test button gives a short beep. The crew have never used the set, and one asks whether it can be used to call the coast guard from the berth "to check it". The vessel sails Saturday; the liferaft returns Friday. There is no other two-way set for the liferaft.
1. Which of the two battery packs, if either, can you rely on, and why?
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Neither, as it stands.
- Primary pack, three months past date: life-expired. A survival craft set has to deliver about 8 hours of operation on the standard duty cycle at −20 °C, and a pack past its date has lost capacity you cannot measure with a voltmeter. Replace it with an in-date pack through the manufacturer or approved agent.
- NiCd spare at 7.9 V against 8.4 V nominal: a low open-circuit reading, and voltage alone proves very little. NiCd packs need conditioning and capacity testing, and they self-discharge and suffer memory effect; a pack left idle in a grab bag can be flat exactly when needed.
- The O-ring is a hard fault. Flattened and gritty means the set is not watertight, and it is going into a wet liferaft. Replace the seal or the set.
The test beep proves only that there is some power in the set. Before Saturday you need either a fully serviced set with an in-date pack, or a second set - one radio, one battery, no backup, is not a plan.
2. What channels does the set use, and what is each for in a distress?
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Channel 16 (156.8 MHz) - distress, urgency and safety, and the channel on which a survival craft alerts and calls rescue units and ships. Initial call, MAYDAY, and the exchange of the essential facts: who you are, where, how many, condition.
Channel 6 (156.3 MHz) - intership, used for on-scene coordination between the craft, ships and the on-scene coordinator. Low power, short range, and it keeps channel 16 clear for other units and the RCC.
The standard drill: make contact on 16, then move the working traffic to 6, or to whatever channel the RCC or coordinator directs, and keep a listening watch on 16.
Channel 70 is DSC and must never carry voice; this set has no DSC anyway. Range is governed by antenna height - at about a metre above the water, expect a few nautical miles to a ship, further to a helicopter - so keep transmissions short and give position and identifying detail every time. Calling the coast guard from the berth is not a test: channel 16 is a watchkeeping channel, and the set has a proper test function.
3. How does this set fit into the vessel's on-scene communications plan, and what are its limits?
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In the plan: the set lives in the grab bag, switched off to conserve the battery, and goes into the liferaft with the EPIRB and SART. Once aboard the raft it is switched on and kept on channel 16. On contact: MAYDAY, vessel name, position, number of persons, injuries, craft type. Then obey the RCC's channel instructions. Keep it dry and warm inside clothing; keep transmissions short; never hold the key down to "listen".
Its limits - state them plainly in the plan:
- No DSC, no 406 MHz, no satellite link. It cannot alert anybody who is not already listening within VHF range.
- Range is a few nautical miles at raft antenna height.
- It works only as long as the battery lasts, and there is no charging in a liferaft.
So the EPIRB is the alert, the SART is the locator, and the VHF is the talking channel. Treating the handheld as the primary distress device inverts the whole design of the fit. Brief the crew on that hierarchy, and make sure the parent vessel monitors 16 and 6 and logs every transmission time.