Does a "steady wind" exist?

Much discussion takes place about different sails, lift to drag ratios, efficiency of rigs and many other points about sailing, but there is not very much consideration about the nature of the power source sailors use - the wind.
Most of the discussion that takes place seems to assume that the wind is always constant in both speed and direction, as would be found in a wind tunnel.
However, practical experience and also data collected about the natural wind seems to prove that this is not the case. It is easy to understand that wind which travels over land is going to be turbulent from the effect of hills trees and buildings, but it seems that even over a level surface, such as the sea, the wind still varies in both strength and direction considerably.
I have searched the web to find actual data of windspeed and there are some sites that provide information.
One such site is called "wendy windblows" (www.wendywindblows.co.uk) and it provides real time and archived readings for many sites around the uk for the use of hang-glider pilots, windsurfers and anyone who follows a wind-related sport.
A look at this website will show that in any given location the wind strength typically varies by about 50 percent. In other words the maximum windspeed in gusts is usually about (nearly) twice the minimum windspeed in lulls. So, for instance, in conditions when the wind maximum was 30 knots, you could expect lulls as low as 15 knots.
Some tests (not very extensive) I have carried out myself with a wind meter seem to confirm what I found on the wind websites.
As regards short term changes in wind direction I have not researched this, but judging by the the way that small windvanes move around, it would suggest that the direction is varying all the time.
Do windvanes move in response to minute changes in wind direction, or is it a design feature of the windvanes that make them move this way?
I have noticed that larger windvanes do not move around so much as smaller ones.
I would welcome any comments from anyone with more experience than myself who maybe knows more about steadier winds than I do.

 

Meteorologist Lewis Richardson

Yes, micro changes occur randomly and frequently. The lower the mass of the anemometer or wind vane, the faster the response. The best devices for measuring instaintious changes are acoustic anemometers or in some cases where macro measurements are required you can use extreme high frequency radar and chaff. But the structure and height above ground of the anemometer can effect the readings so it's just like haveing a watch, the measurement errors are already built in.

 

Bethwaite's Performance Sailing devotes the first few hundred pages to wind and weather. He goes pretty deeply into the nature of the wind we sail in.

It's pretty dry reading, but there is lots to learn if you can stay awake.

 

wedge-tail

Steady wing dose not exist in the nature. When I was experimenting with my Wing-Drive. I found that it was difficult to obtain the zero thrust position. The wings was always moving a few degrees on each side of the wind direction. Making tests with different tails I found that flat plate or airfoil shape did not stay steady in the wind direction. Only the wedge-tail was able to follow the wind shift without side movement. Working with different shape of wind vanes, demonstrated that the wedge shape was the most accurate.
Kjell

 

Try to find some of the writings of Dr. Stuart Walker. He was a sailor of international repute but he was also a scientist of considerable ability. He did many magazine articles over the years and I believe he might have been published as well. He explained weather and its' relevance to sailing tactics about as well as anyone I have ever read. Also there is a book authored by a Brit meteorologist and sailor. I believe his name was Alan Waites. His book was a marvelous collection of data and enabled the interested sailor to make pretty accurate predictions of wind shifts, gusts, and lulls for the short term. That is to say within the next few minutes. Invaluable to the competitive sailor. I'd have a more accurate name for his book had I not loaned the book several years ago. I'll research the books description more thoroughly if you wish to expand your quest for information from that source..

 

It's interesting that one of the major preoccupations for the fastest small sailing craft, like skiffs and windsurfers, is handling the turbulence of wind. That's probably the biggest factor in the design of speedsailing windsurfer rigs, as far as I know. Yet it seems to be much less of a factor in the calculations of less successful speedsailing craft. And Bethwaite makes an interesting case that "normal" boats, due to their speed, encounter an even "rougher" wind than speedsailing craft. Even in a simple boat like a Laser, probably most of the skill involved in getting extra speed is handling the roughness of the wind. I've always had the feeling that one of the big differences between fast sailors and slow sailors is that the fast sailors unconsciously appreciate the roughness of the wind and how important it is, while slow sailors unconsciously assume the wind is a steady-state thing and that governs their sailing.

I could be a raving loony, though.

 

No doubt about that ... but you are right about the wind.

 

I mentioned a book earlier but did not give correct information. The name of the book is "Wind And Sailing Boats" The Author is Alan Watts. This is an oldie but a definite goodie. Watts was an R.A.F. meteoroligist and avid Firefly sailor. Evidently his position allowed him to correlate his observations while sailing, with the meteorological records at his work place. Over several years, there emerged a large body of reliable information.

I agree with CT249 with respect to the success of sailors being associated with ability to play the wind. There are times when one feels a small header and soon afterward a large lift. There are other conditions where a small lift is felt, followed by a larger lift. The skilled sailor is familiar with such phenomena and uses them to advantage. Tactics used by small boat sailors are distinctly different than those to used by large boat sailors. Big boats, are more particularly interested in the general weather pattern and the prediction of what the wind may do in an hour or a day or even a week. A large boat is not going to tack for a two minute header, but the small boat may do so to advantage. It is pretty well established that strong gusts have a shorter life span than softer gusts so a small boat sailor often holds course when confronted with a strong heading wind but he will tack away from a softer header. Watts, along with others, cover all this rather thoroughly.

The big boat sailor will want to familiarize himself with Buys Ballot's Law. It states rather simply that with the wind at your back, the low pressure area and its eventual influence on wind direction, will be on your left. That is a useful piece of information for both large and small boats. That rule holds true for the northern hemisphere only. For CT249 in the southern hemisphere, the rule is reversed wherin the low will be on the right.

RHough has a tag line that addresses the sailor who operates without benefit of science. The tag line is a bit of wisdom. If you are going to sail, then it is most worth while to learn some of this stuff.

The answer to the original question; is there any such thing as steady wind ? There is the matter of time that must be used to qualify the answer. For the most part, the answer is a resounding NO! The nearest to steady state wind, that I have experieced ,is in the early evening, during a stable meteorological period. And this is in a river, lake, or bay where land is near. The sea breeze is, at those times, quite steady and without frequent shifts. That makes for very pleasant sailing. One can be sure that the wind will change as day approaches and by mid morning the sea breeze reverts to land breeze and so the answer is still no.