It's a softer wind
08 December 2016
“It's a softer wind.” Ken Quant and I were discussing the difference between the wind in the tropics and our home sailing waters of Lake Michigan.
When I raced Veloce (28' boat that wWeighed only 4,000 pounds) I loved a 10 to 12 knot day. When the forecast was for 20 knots of wind, we knew we were going to get our butts kicked. Veloce sailed very well in these conditions but it was work and we were going to get wet. We had heard that the trade winds in the tropics were always blowing 15 to 20 knots. Well, we better prepare for some heavy weather sailing.
But Uproar is a 42.5 foot boat and weighs over 20,000 pounds. She sails just fine in lighter winds with a large genoa and stands right up in a blow. Being a cruiser/racer, she has more sail area than most cruisers but with the bendy mast is easy to depower. Still the idea of being in the upper wind ranges left me with some trepidation. I can report that we have rarely been in winds that have been uncomfortably high. When the forecast is for 20 knots we just go sailing with no worries. What's the difference?1
It is a softer wind here. Wind force is directly proportional to the density of the air and the square of the velocity. I did some rough calculations and warm, dry air in the tropics is about 10% less than a cold, spring day on Lake Michigan. That doesn't seem like much but 15 knots here is not the same as 15 knots on Lake Michigan. Warm, moist air is more stable and stays in layers. You don't get many strong gusts. Colder air near warmer land and colder water has a lot of vertical mixing. You go get some strong gusts near the shoreline on Lake Michigan.
When wind speed changes from 14 knots to 15 knots, the increase in wind force is 15%! Those gusts really mean a lot on Lake Michigan. But the largest factor is the feel of the warm, tropic air. There is no slap in the face by a frigid wave crashing over the deck. Yes the wind is softer here and the sailing is delightful!