The best match I can think of is to get a ham license
and then use APRS trackers.
Byonics makes a variety of transmitters with a GPS built in
. You can then use a mobile base station
with a GPS
built in to track it. Or you can put together a system yourself with any 2m ham radio, a TNC, and a laptop
to plot the position on (if there isn't already, it'd be very easy to make something convert APRS positions into NMEA
sentences for your chartplotter).
I think some countries use a different frequency for APRS than America, so you may need to read up on that, depending on where you'll be. Some of the tiny transmitters are multi-frequency.
But I think this would work pretty well, though it would not work if the dinghy
is in another bay (unless you are in a country with APRS repeaters).