A very good analysis and sensible comment by BoatyardBoy.
We sail 4,000 nm per year and have over 200 ship interactions. We follow the rules, negotiate passings frequently on the VHF and unless we have a problem are as considerate as we can be to commercial vessels.
If the tug/tow was claiming rights as a RAM (restricted in ability to maneuver) we would get out of his way, if not we would call on the radio but would have a very low threshold for getting out of his way. We often find that a few degree change in our course will avoid all problems, providing you pick them up and make the change at 10 miles plus. AIS has significantly improved our ability to easily handle interactions and make the correct course changes. We transmit on AIS and use the radio so the large course changes I used to make, showing them the other light, is now rarely necessary.
Even when we are not in a narrow channel or inshore shipping lane we are far more considerate when in crowded waters. In open waters we frequently ask ships to give us a wider margin explaining that as a sailboat we need a little more room. However, once a second or third vessel is involved we are less likely to ask for a course change unless we are being squeezed between two big ships. In a situation like that we would talk to both bridges and make sure they were aware of our position. Occasionally we use their MMSI number to 'ring the phone' on their bridge to ensure that they are aware of our position.
The only ships out there that have given us a problem are ones with watch officers with Eastern European accents and the US Navy who like to maintain radio silence and do not transmit on AIS. Not a very sensible precaution when 50 miles from Jacksonville in heavily trafficked waters.
When communications are poor we start the engine for added maneuverability under Rule 2...Good seamanship and get out of the way!
Oh, if you think anyone is watching... http://www.maib.gov.uk/publications/...mor_stream.cfm