Rob. Interesting point.
As you know I too also sail in a very busy shipping area. As I understand it all port area, estuaries and commercial sea area's are covered by their respective VTS - Vessel Traffic Services. VTS Humber in my case, VTS S'ton/Thames/Tyne etc elsewhere.
I would imagine the procedures are the same everywhere where it is a legal requirement (bye law) to monitor the respective channel in the area you are sailing, we use Chans 12, 13, 14, and 15 when in my VTS sea area.
Indeed in my experience you would be very foolish not to do this. There is always plenty of information published from VTS's (Reeds, internet etc) on what channels to monitor at what point and what your responsibilities are.
Ships bridge crews also call us direct and speak to us if they are at all concerned of our intentions, on the respective VTS channel NOT Ch16.
The Coastguard monitor Ch16 in their respective area's, including their VTS area's, but I understand it is not a legal requirement for you to monitor Ch16, (and I am open to correction on this), as opposed to VTS' channels where it IS a legal requirement.
I think it would be fool hardy in my opinion not to monitor Ch16 out of VTS area's, eg Last year I was anchored over night in a perfectly safe anchorage on a beautiful calm night, when the inshore life boat appeared checking on my welfare (!) as they'd had a report of a vessel in distress! Our VHF set had been switched off by a crew member keen to save on the battery supply, the CG were calling, got no response so they activated the RNLI!
If you have an AIS Transponder then you will appear on VTS and CG screens and they will be aware of you and any potential issues that you may get yourself into with commercial traffic. In my area they definitely will call you up to request your intentions in respect to the 50,000 ton tanker bearing down on you at 20 kn!
To be honest we have found it sometimes beneficial to go into 'stealth' mode so they don't keep hassling you. Having said that they also monitor radar and I now understand, high powered CCTV as well.
But at night or in low visibility, VTS is your best friend ever .. They are always helpful and really not that often sarcastic - and not just to yachties!
Hope that helps with your query - respective VTS websites will tell you what chans you are required to monitor. But outside of the VTS area's, monitor Ch16 for calling direct and request a chan change to 6 or other inter ship chans to talk direct or of course - and preferably, use DSC direct if you have a DSC set.
Andy and Equinox