Steve, This may seem like a dumb question, but….How does the height above the water affect the anemometer readings? The reason I ask this is that my mast is 56ft off the water and it seems that the wind speed readings I get are consistently higher than mates of mine that have shorter (i.e. 35ft) masts. I have B&G gear so it should be accurate….is there a formula that we can apply to get surface wind speed, knowing the height of our instruments ? Thanks Cheers Alan
Hi Alan: The wind increases with height. However, the amount it increases varies with the type of air mass, water surface conditions, temperature differentials between water and air, etc. There have literally been millions of dollars spent on trying to figure this out, as all racing polars are based on true wind speed. In addition, there is upwash and downwash to consider. These kick in more when reaching, and vary from boat to boat. For example, on Beowulf, we can be running in 10 knots true, and then start reaching and the true wind speed will climb to 13 knots. The higher end B and G systems, like the 790, have correction tables to roughly zero out these factors–but they are only as good as the day’s conditions are like those when you originally made up the table. Our solution–we look at the water and make our own estimate. Steve
Posted by Steve Dashew (November 30, 1999)
