I was wondering that Brian but presumably it cannot be too high as it was supposed to be used for pulling out boats? Low gears must be usable.
Why do you suppose it was set up like that? Perhaps to carry more weight on the tractor. The chains look a bit HR.
Someone on the Brit Farming Forum has found out a little more and it apparently has a top spd of 7mph. Very low geared therefore and had moved a boat weighing 300t (presumably on the hard).