Just to be clear, a RIB is not a dinghy, although a dinghy can be a RIB.

A dinghy is typically a small tender to a larger boat. A RIB is a rigid hulled boat, (Inflatable).

Yes, it is the local Coast Guard. They are stationed right inside the Simpson Bay Bridge. They have two of those, as well as an older grey gun boat that may or may not leave the dock.