How to determine the strength of the wind
Denis Korablev
  • 04.11.2021
  • 2,382

How to determine the strength of the wind

The wind "feeds" sailboats during the movement, so any yachtsman, whether a beginner on a chartered yacht, or an experienced yachtsman on good a yacht that is familiar to him, should always be interested in the direction of the wind and its speed. Many people think about the question even before leaving the marina: "Will the wind change?"

It is difficult to give a precise definition of "wind strength". Almost all captains with extensive experience behind their shoulders cannot correctly recognize "by eye" the strength of the wind. Sometimes, relying on the number of raised sails, helping the yacht's movement, experienced captains are able to almost accurately determine the strength of the wind on the Beaufort scale up to 7 points. The Beaufort scale is a conventional scale (12-point), which allows you to visually determine the strength and speed of the wind from the waves of the water surface, officially adopted in 1838. The scale was developed in 1806 by the military admiral Francis Beaufort, who, while serving in the navy, regularly observed the wind and recorded the data in a diary.

Yachtsmen are more likely to consider the magnitude of the wind force to be greater than the actual value due to sudden gusts bursting into a uniform air flow. It is believed that wind pressure is directly proportional to the square of its speed. The wind gust (with an approximate force of up to 40 knots) is quite noticeable, from the ship's heel angle, increasing 16 times. The attention of yachtsmen is usually directed to squally wind gusts, which create a dangerous list of the yacht. The sails are simply obliged (and the masts also need) to withstand such a sharp sudden wind.

On a sea voyage, it is absolutely impossible to foresee everything and the weather can bring unexpected surprises. For example, just one swift wind gust of 64 knots can easily turn a yacht, or even break the mast. Unexpected 6-point wind gusts are much more dangerous than a uniform 7-point wind, as they form "incomprehensible" waves.

Very rarely, but there are such anomalous phenomena as the formation of waves up to 30 meters high with a wind force of 6-7 points. Typically, these waves correspond to a 10-point storm in the ocean! Scientists have put forward versions that such waves can occur due to different directions of currents, the presence of shoals, changes in the direction of the wind, etc. A scientific explanation is difficult to find, and sailors call them "abnormal" or "wrong" waves. It couldn't be better!

The Beaufort scale is usually used to determine the average (not maximum) wind strength. Correctly formulated characteristic sounds like this: “storm wind with gusts of up to 50 knots”, not “storm wind of 10 points”. If wind gusts continue for a long time, then in a 10-point storm, their value increases to 64 knots.

In the Sailing Ships magazine, Alan Watts provides guidelines for the definition of "average yachting wind". It is required to add Beaufort wind strength to the average wind speed and determine the average value. For example, the gale force of the wind is 25-30 knots with regular gusts of wind up to 40 knots at intervals of 5-10 minutes.

Many people prefer to use Beaufort averages, especially since meteorologists use this system to predict weather conditions and storms for all shipping. This information is relevant for both large ships and small-size fleets. In some areas, storm winds behave differently. There is a possibility that two yachts within 30 miles of each other will be subjected to completely different tests when caught in a storm. For example, one of them will avoid a heavy wind.

Amateur yachtsmen, as well as "sea wolves" tend to increase the height of the waves, because they correlate them with the height of the mast, the value of which is known for sure. Any crew member is capable of calculating wind strength in this way, but this estimate is biased. In fact, when windy, the wave height is always less visible. As a rule, the actual height of the waves in relation to the visual one is 3/5 or even less. Oceanographers confidently declare that it is impossible to determine the height of the waves with the help of an eye.

So, a more or less accurate determination of the wind strength can only be obtained with the help of meteorologists, because they are guided by the data of special instruments.

Basic concepts - what do they mean?

  • Observation at a coastal station - provides approximate wind strength data once an hour. The station is located on the ground, so the data on wind strength is usually less due to turbulence and friction of the air flow against the land surface.
  • Breeze - local light wind at a speed of 18-36 km / h, with an enviable constant changing direction. During the day, it blows from the sea to land, and at night - in the opposite direction. The strength of the wind depends on the temperature difference between water and land; the greater the difference, the stronger the breeze.
  • Gust of wind - lightning-fast increase in wind speed, short in time (20-30 seconds). Usually occurs at 2 minute intervals. The gust value is expressed in knots. It should be borne in mind that wind gusts on water are much less powerful than on land (differences in values range from 25% to 100%). Wind gusts make it difficult to accurately determine the wind speed during a storm.
  • Flurry - a rapid increase in wind speed from 12 m / s and above. It differs from a gust in strength and duration. The minimum squall duration is 60 seconds, but can last up to 10 minutes or more. Sometimes the squall consists of several sharp gusts and is accompanied by a thunderstorm shower. Its appearance can be caused by the movement of the atmospheric front and the rapid change in pressure.
  • Stormy wind - continuous (8-point on the Beaufort scale) with a speed of 35-40 knots. The occurrence of a storm can be caused by a squall, a moving tornado, or an approaching cyclone. Meteorological centers invariably broadcast a storm warning of 8 winds or gusts of up to 41 knots, even assuming that it will not last long (10 minutes). Meteorologists do not issue a warning when they observe a local gust of wind caused by a short-term thunderstorm.

During an ordinary storm, there are high waves (up to 8 meters) and up to 150 meters long. In case of a strong storm, the wavelength is up to 200 meters, and the height is 9-11 meters. As noted by experienced yachtsmen 2yachts, it happened more than once that the appearance of a stormy wind did not cause a real storm in the proposed area, therefore a specific yacht located in the area warnings, the wind may bypass. At sea, it is difficult to make accurate forecasts of weather conditions.