wrote in message ...
About how long can a fixed mount VHF radio be left on, receive only,
at anchor, engine off, before the battery is unable to crank the
engine? The radio being the only accessory switched on.


That mostly depends on the battery you have and how much current the motor
will take to start.

If you have an old, weak 24 series battery need to crank up a 6 liter diesel
the answer may be zero.

On the other hand, if you have a 400 amp-hour battery bank and only need to
crank up a 75 Hp 2 cycle outboard the answer might be weeks!


If you have the specifications for your VHF (owner's manual, or perhaps a
catalog page) it should provide the receive "standby" current draw. This is
usually the current draw when the receiver is quiet, and not driving its
speaker. I would expect a standby current of 0.25 amps or so for a modern
radio. When the radio is noisy (driving the speaker) the current draw will
be a function of how high the volume is, but I would expect it to be less
than a watt.

If you are monitoring channel 16 then there should be a fair amount of
traffic, so I would assume about 0.5 amps on an average.

A typical 27 series deep cycle battery (the larger of the standard battery
sizes) will provide around 100 amp-hours. That battery could run the VHF in
standby mode for 200 hours. In a 24 hour period it would have only drained
your battery about 12 %.

I would certainly hope that your battery has more than a 12% margin for
capacity on starting the engine. Or at least it did when the battery was
new. There will come a day, however, when the battery is getting old and
you may have no reserve at all.

Rod McInnis