Wayne.B wrote:

Does the SPOT device also double as a useful GPS, and is it waterproof
enough to take on a dinghy, leave on the flybridge, etc. ?

All it does is blink at you so it can't double as a GPS. If you have an
Internet connection, you could use the tracking to find out where your were
within the last half hour which might bail you out if your primary GPS(s)
failed.

It's made for backpackers and looks as though it's pretty waterproof. It
was originally supposed to function floating with the antenna up but they
forgot to have a naval architect check the stability and it floats on its
side If you are in the water with it, you will have to hold it out of
the water which would be a serious energy drain.

--
Roger Long