Not to mention, I still don't understand what all
these ground based RECEIVERS are supposed to do.
How does a receiver on shore assist navigation
for a vessel in the water?


AIS is not only an aid to navigation, it's just like APRS for ships, it
allows those ashore at remote locations to monitor the position of vessels.
On a river system I guess it could be used to monitor traffic flow, optimise
lock usage, find out when your vessel is likely to arrive for unloading etc.

73
Jeff