If you can't eat off the bottom, it's too dirty. I wash and wax my boat (and daggers and rudders) the day before I go to a regatta, then wash the hulls again when I arrive at the regatta, before I take it off the trailer.

Road grime picked up while trailering to the regatta is slow. In the book mentioned above Frank did drag tests of hulls that had been washed after trailering and not, it was very clear which were always faster.

Shall we talk about the dirt on the mast and sails now? Anyone know of a good aluminium polish? ;^)