Keeping the Channel Clear

I'm in the process of compiling a documentary and photographic record of my boating in the days before Starcross, specifically in the 1970s and early 80s. In that context one of my boating mates has sent me this photo.

It's 1971. The boat is "Gardenia" and the crew are from Salford University's Inland Waterways Society. Gardenia was loaned out by British Waterways to cruising clubs and other waterways organisations to run on their local stretch of canal. In the days of commercial traffic loaded boats cut a "channel" along what F1 fans would term the "racing line" which kept boats moving more easily. The line was generally down the middle of the cut but, crucially, to the outside of bends and the replacement of loaded craft by shallow-draughted pleasure-craft that didn't need the channel was actually destroying it as they displaced silt from the shallower parts into the channel itself by not following the line. The idea was that Gardenia, loaded with ballast to around 15 tons, could help to preserve the channel by its movement (although quite what one boat was expected to achieve I'm not sure) and crews were also expected to remove obstructions and larger pieces of rubbish (mattresses, bicycles etc) from the cut as they went along. No charge was made for the hire of the boat and diesel was provided free of charge at BW depots, making it the ideal summer holiday for a bunch of students. 
The location is Knowle locks on the Grand Union and the slim, good-looking fellow with the long hair at the tiller is, er...me!