"Record for the Sandusky Steeplechase (Sandusky, OH to Put-in-Bay, OH on Lake Erie) is about 57 minutes, and that distance is supposedly about 21 miles."

Thanks Mary, that`s just the kind of stuff I was looking for. Average speed = 19,2 knots (according to my maths, everyone can do their own and we can see how many different answers we get.)
So an average of 19,2 knots for almost an hour of sailing, assuming they sailed a dead straight line, which they didn`t as they had to beat for a while. I think we can safely say they averaged approx. 20knots for almost an hour of sailing, given that they sailed a bit of a longer distance than the actual course ?
We could be conservative and say the race distance is only 19 miles, but they covered 110% of the distance of the race, and we`d get a similar result either way.