Report Text:
Smoke alarms can damage your safety. Whilst motoring in calm weather in a 10m motor sailor with the wheelhouse doors closed, suddenly (within 5 seconds) the whole yacht filled with acrid smoke, such that it was not possible to see from the wheelhouse through to the fore cabin, some 5m. There was no indication of the source and no flames visible. The engine was stopped, an engine fault being the immediate thought even though there was no change in engine noise; then it was realised that for the whole boat to fill with smoke so quickly it must have been dispersed through the (diesel-fired) blown air heater. The heater locker was opened gingerly, with a fire extinguisher at the ready, but there were no signs of smoke or flames. It was later found that the diesel cut-off solenoid had shorted, the heat generated being enough to vaporise the solenoid packing and the resultant thick smoke was sucked into the intake and dispersed round the boat. The intake is deliberately from that locker in order to provide forced circulation of air. So far, so good: the unexpected problem was the smoke alarms. There are three, one in each cabin (each can be closed off): all three sounded within seconds of the smoke appearing. The problem was that the resulting noise made it difficult to think clearly and would have made it completely impossible for the Coastguard to have distinguished the words of any transmission, or for me to have heard their reply. I could have taken the microphone outside the wheelhouse, but would still have been unable to hear their reply. The alarms are the common domestic type: it would be possible to fit a switch in the wheelhouse controlling them, but this would be complex and give scope for failure. There seems no easy answer to this problem and it is perhaps one which does not occur to most yachtsmen: it didn’t occur to me until it happened.
CHIRP Comment:
A number of accident investigations have established beyond doubt that smoke alarms can save lives. In this incident the alarms did exactly what they are supposed to do and provided prompt warning of a problem and had the crew been asleep, for example, this warning could have been a life saver.
The report does highlight the need to consider what is the best smoke detection system for your needs, where sensors should be located and what impact they might have on communication should they be activated. It is always a good idea to have a plan for the worst, whilst hoping for the best.
