"Armond Perretta" wrote in message ...
Derek Weston wrote:

... electronic means to
automatically detect vessels ... are of great value to us.

We have a radar with a watch facility which is great, except it
draws 30-odd watts, more that we can afford ...

In general your solutions appear to be a bit more complex than is absolutely
necessary. Just my point of view, of course.

For example, my small Furuno "watches" on a scheduled basis and draws very
little. You might want to consider a more energy-efficient radar.

I don't think there is one, but would certainly be happy to be
corrected. From what I have determined, 30W is typical for keeping the
magnetron "alight" between periodic scans.


... Our radar detector works well, but ships often
have their radars switched off.

Are you sure of this, and if so, how? You are suggesting that these
commercial vessels are operating illegally (which of course is possible,
but, en masse, unlikely).

Yup, quite sure of it. We have a radar detector on board.
Others have found the same:
"It's also interesting to note that during the transatlantic, an
alarming number of vessel's contacted to evaluate our radar return,
responded willingly but said, "please wait while I turn on the radar!"
from http://www.ussailing.org/safety/Stud...arenhancer.htm

2) Hydrophone systems
Perhaps a ships prop or other ship noise can be detected
electronically.

This leaves out vessels not propelled by machinery.

True.