# Understanding the Wind

Discussion in 'Hydrodynamics and Aerodynamics' started by brian eiland, Oct 28, 2015.

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### brian eilandSenior Member

Understanding the Wind .....(that powers our sailboats)

I had some thoughts rumbling around in my head today, and thought I might try to find some answers via the search engines. I was looking for some statics on WIND, and more specifically gusty winds....

Are there some general statics (averages, or distribution graphs, or etc) on how much the wind speed changes in 'gusty conditions'?
Are there some general statics on the range of angles these gusts can appear from?

We have numerous subject threads about how our sails make power from the wind, but not that much on the wind itself. When I ran across this article, I went looking thru old postings, and saw very little if any discussions of the WIND as an entity. This article also inspired the title of this subject thread.

There is nothing more important for a sailor to understand than the wind. Kenn Batt explains the basics of wind in this informative article
Read more at http://www.mysailing.com.au/news/understanding-the-wind#J7rbhSzZviWyM2Yw.99
http://www.mysailing.com.au/news/understanding-the-wind

There is some more to the article, but mostly some info on measuring wind speed. And of course no statistical analysis of the variations in gust directions

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### tspeerSenior Member

You might find more than you ever wanted to know in the ESDU Wind Engineering data sheets.

Section 2: Wind Speeds and Turbulence - Mean Hourly and Gust Speeds, Extreme Speeds, Turbulence Characteristics
ESDU 82026
Strong winds in the atmospheric boundary layer. Part 1: hourly-mean wind speeds.
ESDU 83045
Strong winds in the atmospheric boundary layer. Part 2: discrete gust speeds.
ESDU 74030
Characteristics of atmospheric turbulence near the ground. Part I: definitions and general information.
ESDU 85020
Characteristics of atmospheric turbulence near the ground. Part II: single point data for strong winds (neutral atmosphere).
ESDU 86010
Characteristics of atmospheric turbulence near the ground. Part III: variations in space and time for strong winds (neutral atmosphere).
ESDU 87034
World-wide extreme wind speeds. Part 1: origins and methods of analysis.
ESDU 88037
World-wide extreme wind speeds. Part 2: examples using various methods of analysis.
ESDU 88038
Estimation of hours per year when mean wind speed exceeds specified thresholds.

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### Doug HalseySenior Member

I highly recommend reading Frank Bethwaite's High Performance Sailing. The 1st quarter or so of the book is about wind, and it's really the best discussion of the subject I've come across!

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### Ad HocNaval Architect

You might find these of interest too

#### Attached Files:

• ###### WMO Wind factors.pdf
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### SukiSoloSenior Member

The fun bit is the 'invisible' mini tornado 'gust'...

Not sure how you predict these, but I have been capsized by one before now!. Never seen any data on this phenomenon, probably because so localised and near a mini waterspout. Very little on water surface except a normal slightly stronger gust (fan) type pattern, ie if you want more pressure or better angle you head towards it.

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### Manie BSenior Member

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### CT249Senior Member

A few years ago I went in to Frank's office to go to lunch with him. When I got there he was sitting in front of an anerometer, marking minute fluctuations on a chart. Such a Frank thing to do!

Much of HPS came from a series called "The Magic Circle" in Australian Sailing magazine in the '70s. It was all about the fact that in every fleet, there was a circle of people who shared all the wins. His description of the wind as an ever-fluctuating thing made a huge difference (eventually) to my sailing. Before that I'd thought of 'real' sailing as the thing you did in steady winds.

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### CT249Senior Member

We used to race high-performance cats alongside Sydney airport. Sometimes in calm conditions you'd get bombed from above by what must have been wingtip vortices spiralling down from 747s coming in to land on top of the race course. If the first thrust of the incoming vortext came from behind you would madly bear away to stop from capsizing but you'd have to keep on going around in a circle as the vortex seemed to spin around you. I'm sure we did a 270 degree turn, on the edge of capsize all the way with the true wind at the same angle to the boat as we span around inside the vortex. Fun stuff, but very disorienting!

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### brian eilandSenior Member

Sorry I have not had time to get back to my own generated subject thread...'home projects' in the way
Looks as though some interesting links have been provided, I just need to find time to read them

I wondered if there were some extensive studies carried out in preparation for the America's Cup races quite a number of years ago off the western tip of Australia, that were held in pretty open ocean, windy conditions if I remember correctly? Usually these well funded events are supplemented with well funded studies of local conditions.

I realize there are numerous land-based objects that can influence our winds, but what I was searching for with my inquiry was more of an 'ocean-based' observations that might be experienced by the world wide cruiser,...how the wind itself behaves in general without the influence of land based objects.

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### SukiSoloSenior Member

Thanks for that insight CT, good to know others have experienced similar 'vortex' conditions....
Just so hard to stay upright (upwind) as you let the sheet out but the sail is still full and luffing hard still does not ameliorate it!. I've had it a couple of times including on Rutland Water (1500 hectares) but the only aircraft round there are military, though I did not notice any at the time. Where I now sail we get RAF Chinooks coming down to 15-20 meters off the lake surface.....
not been caught with that downwash yet...

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### jehardimanSenior Member

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### SukiSoloSenior Member

Well it's past Halloween, so I won't meet him/her yet.....

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### jehardimanSenior Member

You really don't want to meet it. I saw an ocean racer on a run in from the light bucket in an Ocean-Vallejo race get hit by the demon and round up washing the mast fly... they slipped the halyard, blew the sheet, and stood her up just in time for the vortex to force an unintended crash gybe then rounded DOWN!...both boom and pole in the water with the kite, sheeted by the water, pulling the masthead, and the rest of the boat, forward and under. Took so long sorting out, they never made it to Vallejo.

http://www.latitude38.com/lectronic/lectronicday.lasso?date=2009-03-23#.Vjg5UIddF9D

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### brian eilandSenior Member

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