Tobie,

Congratulations!
Sounds like you are well ahead of me.
I've been very vaguely considering both autonomous boat and autonomous
aeroplane projects.
Like you, I have no great reason for a boat project - just seemed like fun.
The aeroplane had rather more point but much less range.
It's highly likely that I will never do anything about either :-(.
We have several offshore islands and also Australia is about 2000 miles from
here.

Can you provide some outline details of your proposed boat.
Say size, propulsion, control, power sources etc.

I envisaged a sailing craft like a broad low catamaran with power needed
only to control sail setting and course.
Possibly an inefficient but high survival symmetric design which could sail
upside down (!) so that it could survive a capsize.
The idea was to have a mast which lowered between the hulls and could be
erected "under" the boat if it was "upside down".

For position location you could consider a series of high energy radio
signals at very well defined times of the day.
Say a burst every 10 seconds for a few minutes at fixed times each day.
At say 100 watts x 0.1 seconds x20 bursts x 4 times/day this is 800 watt
seconds/day or a mean continuous power of under 10 milliwatts!
You could probably get this level of power from solar cells in the middle of
a hurricane :-). (being daytime would help)

If going ship to shore then something around 14 MHz would probably be best
(best at night too).
There is an ISM band at 13.560 MHz afair, which would be near ideal.
This is internationally allocated and this IS an ISM application.
Also happens to be the frequency used for some RFID equipment so high power
use close to shore may be frowned on.
Diathermy units and plastic welders and cheap walkytalkies work on the 2nd
harmonic at 27.120 MHz but propogation there may not be as good.

These signals could be searched for with directional equipment from numerous
positions on both sides of the boat-pond and a fair fix could be obtained.
Using high power bursts for very short periods would allow a very low
average power consumption. If you used relative slow speed data modulation
of these burst to contain position information, so much the better.
GPS would give you very accurate position and data sent need only be a few
bytes.
You should be able to get enthusiastic involvement from the amateur
community.

I believe Iridium is still alive although dying. If so then this or similar
would be probably the most reliable "on demand" method.

Even with GPS and satellite phone the mean power would be very low.





regards


            Russell McMahon

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