We all have experienced some wind conditions that really makes life hard out on the pond. The wind conditions I'm writing about are the ones that makes your model sailboat do things that you don't want to do. These ill wind conditions are gusts, eddies, and whirlwinds. Since a person can't change or alter the wind conditions, at least a person can understand what causes these conditions to occur.
The first of the ill winds is a gusts. Gusts are a brief increase in wind speed above some average value. Gusts are caused by either random turbulence due to ground friction and by wind shear at the ground level or by convection currents in the atmosphere with the mean wind. In other words when wind blows around buildings, trees and hills (turbulence) its speed is increased in an area for a short period of time.
A wind shear is the result when wind changes in height; this change could be in direction or speed. Generally speaking a large amount of moving air is being dump down and then across a body of water at a high rate. In any case a wind shear can greatly over power a model yacht without warning.
The last condition to cause wind gusts is convection currents in the atmosphere. Convection currents are rising and falling air currents that occur in an unstable atmosphere. Convection currents are one way to create clouds. When an area of air is warmed at the earth's surface, it becomes more buoyant (a thermal) and starts to rise until it meets cooler air. The warm moist air then cools and starts to condense and a cloud is formed. What occurs next is air around the cloud cools, and starts to sink back towards the ground. This descending air is a common cause of wind gusts when cumulus clouds are being built.
Eddies are the one thing that causes skippers the most grief when sailing their model boats. Eddies are for what we are concerned about are bodies of rotating air caused by surface friction or obstacles to the wind. If a model boat gets caught or sails into one, the boat can come to a stop, sail in a different direction or the boat literally spins around like a top. Whatever the results, eddies are a real pain for the skipper.
The last ill wind is the worst one of them all, and thankfully not very common, it is the whirlwind. This nasty wind condition can cause a model sail boat some real damage. A whirlwind is a small but rapidly rotating wind made visible by dust, sand, and debris it picks up from the surface. It develops best on clear, dry, hot afternoons. It is made up of a hot area of air at the surface and forms in a vortex when wind causes the hot air to rotate. When this rapid rotating, upward column of wind picks up dust and dirt, we call it a dust devil.
Normally a dust devil doesn't cause any problems to a skipper so long it stays on land (where they are formed), but when a dust devil moves on water look out! I won't go into too much detail but when my 36/600 got caught in one I could only stand there and watch. Luckily no damage was done to the boat when the whirlwind laid it on its side and spun it around violently. It was interesting to watch the whirlwind move across the water, and watch the water being drawn up into the rotation (see photo below as an example). I heard another 36/600 got caught in one a few days earlier, and this whirlwind literally picked up the model yacht and flipped it over hitting a mark! No real damage was done to the boat but the skipper suffered from a quick case of anxiety!