I did it in '85 and '86 on a Catapult. The tide was low one of the years and we had to be careful crossing the sands before turning into the river and the stretch of river up to the bridge was very narrow. It looked like a wide strip of water, but in some areas the channel was only a few boat lengths wide. Maybe they time it these days so that the tide is high during that part of the race. It was great fun.