Terry Spragg wrote in message
I seem to recall some one devising an 'all around' lens that
focuses on a colour ccd camera. Any red or green light and it's
bearing would be detected in logic, and no scanning mirrors would
be required.

Right. Thanks for the info and comments.
I'm discouraged by my observation that night capable CCDs all seem to
have peltier cooled sensors.

If you have ever heard powerboat engine and prop noise
transmitted through the water and hull while enjoying a quiet
sail, you would think it possible to detect approaching ships
like submariners and antisubmariners do. Speech recognition logic
can recognise any sound it is trained to. As it can be sensitive
to specific voices, it could be attuned to high speed or heavy
props, or both, along with whales, which talk and blow a lot,
seemingly, and slop sounds from semi submerged containers of
certain volume and exhibiting audible resonances, etc. Three
hydrophones should be able to determine bearings of noise
sources, if not their source noise echos near shore. A high rate
repetiton sonar pinger and interleaved range gating logic may be
able to catch repeated MTI type returns, as opposed to wave face
clutter in deep waters. There is no reason why sophisticated
analysis engines could not be mass produced on microchips except
cost, which depends on scale of production. In the meantime,
logic development might have to do. What more engrossing passtime
could a long distance sailor wish for?

Indeed. I think I may do some experiments along this line.
Wouldn't help detecting other yachts, but none of the options
(including a good human lookout) is perfect.