> *reliable* and practical way to communicate digital data
> (mostly GPS position but also some telemetry) between some
> small boats and a land base (on the beach, maybe on a turret)
> distant max 10 Km from each boat?

How small?  Very small, as in radio controlled?  Or just small,
like boats you rent to tourists?

In either case, keeping antenna high enough to be above wave
crests for any line of sight frequency may be a problem.  If
R/C boat, then it's very low and even tiny waves may block
the signal.  If small passenger craft, then antenna system
has to be stout enough to withstand abuse by renters.

How high is the turret?  10 km is pushing line of sight even
for flat surfaces due to curvature of the earth (yes, I know
it's closer to 20 km but water isn't smooth).

No answer, just some things that came to mind...

						Lee Jones

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