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(Derek Weston) wrote:

We shorthand frequently on our sailboat, and electronic means to
automatically detect vessels in our area 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 as we're primarily solar panel
powered. Our radar detector works well, but ships often have their
radars switched off.

Our radar is a LCD which I think doesn't take that much power. THe
real power hog is the Autohelm. If you are on watch alone or are
singlehanding, are you not using some form of steering? Of course
maybe you are using a wind vane, which doesn't take power. However
IME, people don't use wind vanes much unless they are experienced BW
cruisers.

Someone has suggested a wind generator. When we are sailing (which I
presume you are, else the power needs of the radar wouldn't be a
problem), we don't get a lot of use from the wind generator even
though it isn't dependant on the light. Either the wind is too light
to put in any amps, or the sails blanket it so it doesn't get any
wind.

In any case, of the suggestions made, I think an auto radar detector
or a less power hungry radar are the best solutions. Or perhaps a
battery bank that can store more amps so that you have more of them
available.

Two ideas I've been mulling over to which others may be able to
contribute useful ideas:

1) Nav light detectors
I think it may be possible to devise an electronic system which can
detect red and green coloured lights, and distinguish these from the
moon and the stars.
I'm imagining a rotating system with a cylindrical lens and both
red-filtered and green-filtered detectors, and triggering an alarm on
the basis of the magnitude of the difference between the two sensor
outputs. With appropriate relative gain settings, the moon and the
stars could give a near null result, while coloured nav lights may
give a greater output sufficient for the alarm trigger.
This may be close to the limits of present technology. I can imagine
the sensors may need to be cooled (with consequent condensation
problems).

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

Any thoughts, previous work, intelligent comments....

Derek Weston
Talking Marine Instruments
http://www.alphalink.com.au/~derekw/mit/apps.htm

grandma Rosalie