"Armond Perretta" wrote in message ...
Vito wrote:
Armond Perretta wrote:

In any case a small sonar seems like a good possibility ...

Sound waves bend downward creating a blind zone near the surface.

Quite, but the sound waves generated by the target vessel do themselves
propagate in a uniform direction from the source, so they _will_ be picked
up.

The trouble is that the original poster was concerned about power consumption
on his radar. I can't imagine that a sonar solution could get away with anything
less than a fairly powerful PC running to do the signal processing, you need to
filter out all the false stuff including noises from your own vessel. Even so, for
boats with the power to keep it running, it would be very interesting technology.
The obvious use is for single-handers but, even for crews maintaining a 24
hour watch, humans can get tired and have lapses of concentration so an extra
"safety net" would be very useful.

- Julian.