The White Cart and the Black Cart join to become the River Cart but they are much further up river at Renfrew. I'm not sure what you're seeing? There are one or two possibilities but I need some more information. If you are crossing Erskine Bridge from Erskine towards Old Kilpartick is the water you're seeing on your right or left and the Erskine side or the Old Kilpatrick side of the Clyde?
And the AIS site is the one I use to track shipping. At this moment, for example, the Waverley is doing 13.4 knots at the south tip of Arran and her destination is Glasgow, so I could see her again this evening if I wanted to.
For the benefit of others:http://marinetraffic.com/ais/