Do you sail faster in fresh water or salt water? It’s a question you’ve probably never had to ask yourself, but it’s one the SailGP teams in Chicago this weekend have been delving into.

Explore the question for conventional sailing boats and you’ll come across a couple of differing arguments, one being that the increased density of salt water equates to increased buoyancy, so for heavy displacement yachts (and particularly large ships), less volume of boat is in the water, so reduced drag equates to increased speed.

The other view is that the increased density of salt water equates to increased resistance moving through the water, and slower boat speeds. Either way, for most yachts and sailors any difference is likely to be negligible.

The only way to settle the discussion is with real, empirical evidence, and if there’s one sector of sailing which has endless data on relative boat speeds of multiple, equally matched boats in different sailing areas, it’s SailGP.

Ahead of today’s first day of racing for the Chicago stage, the 10 teams have been training on inland Lake Michigan, and recalibrating foil handling for sailing on fresh water has been a key focus. There’s no question that for the foiling F50s, fresh is faster.

Fresh water is faster

“It’s about 2 knots difference,” Russell Coutts told me after the pre-event press conference.

“They have to be selling a little faster for the take off, but the top speed is about 2 knots faster. It’s a pity we’re not going to get a windy weekend because we…