D.B. of Marina del Rey, California, asks:
"Not long ago I received a phone call from my dockmaster telling me a loud alarm was coming from my boat. I told him I’d be right down, and to keep an eye on things until I arrived. When I went aboard I found the sound was coming from my RayMarine Ray 240 marine VHF. How could it possibly go into an alert mode after being turned off?"
Gordon West replies:
This popular VHF radio incorporates a Class D Digital Selective Calling (DSC) receiver that continuously monitors VHF Channel 70. If anyone in range transmits a DSC distress call it will sound a loud distress alert warble. “To conserve battery power, you can put your marine VHF on standby, with the internal DSC receiver and audio alerting stages still on,” says Raymarine’s Chuck Anderson. “The behavior in question is consistent with the original design of the Ray 240, and a free software update is now available through RayMarine’s factory repair center (raymarine.com/support.com) that will eliminate a DSC alarm when the unit is in standby.” Of course this same feature might save a life if you are out sailing with the radio turned off and someone nearby broadcasts a DSC distress call.
On the other hand, back at the dock when no one is aboard, the feature can be a nuisance, as you discovered. The best way to make sure the radio won’t make noise when you’re away is to turn off the circuit breaker that feeds the power to the unit.