"Is that relevant? Are kilometers the same whether measured on land or on water? If so, assuming a race is 100 kilometers, don't you still have to convert the kilometers to nautical miles before you can get average speed in knots? Or convert the kilometers to statute miles in order to get miles per hour?"
See now this measurement thing is getting confusing. Kilometres are always the same, no matter where you measure them. If you have ten fingers you can figure out the metric system quite quickly.
Mary, in my case, every time someone quotes mph I have to convert it to km/h, then to knots . Depends what you`re familiar with.
The common language for sailors and pilots is knots, so lets try keep it that way. People who quote windspeed in mph, or km/h, or metres/sec always get me, I have to find a calculator to figure out what they mean.

"Wind over the water is supposed to be measured and reported in terms of knots, while wind over the land, even if it is only 50 yards away, is supposed to be measured and reported as miles per hour. And it is often hard to know which it is."
See now I`m totally lost, and I`m beginning to fully understand the following :
"Wouter, I am talking about the United States. I know you think we are archaic. "

So, if the wind passes from the land to the water, you guys change the unit of measurement. Does the wind then speed up, or slow down ??