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Understanding Winds

One of the most important things in sailing is the understanding of winds by the crew and especially the captain.
Interaction between the wind and the sails is the main speed gear of the boat; the wind is the fuel and engine of the sailing ships.

Wind is caused by temperature differences. The basic principle is the following: air is warmed both by the ground and the sun. When it gets warmer, it becomes lighter and rises. Its place cannot stay a vacuum, as we have gas medium, so the adjacent cold wind takes its place, so we have a continuous flow.

It is very rare that there is no wind in coastal areas.

Wind Direction
The direction and speed of wind is always graphically displayed on visual weather forecasts. The wind blows along the isobars, keeping low pressure to the left and high pressure to the right. The most reliable way to check wind direction and speed before you launch the yacht is to consult an anemometer (wind speed indicator). Less precise methods include looking at flags or smoke, watching boats out the water, looking at threads.

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The ideal wind direction for launching is sideshore, when the wind is blowing parallel to the shoreline. This should allow you to sail out on a reaching course, turn round, and sail back on the opposite reach.
The more offshore (blowing on to the shore) the direction of wind is, the more problems you are likely to encounter. A side onshore wind of 2-6 knots may start stacking up waves, but should still give you the opportunity to sail straight out from the beach/bay. A dead onshore wind will push in waves that drive the boat back, and mean that you have to sail out at an angle across the waves. Offshore winds, blowing away from the shore should be treated with particular caution. An offshore wind, which appears zephyr-like close in by the beach will gain strength as you move away from the shore.


Lulls and gusts
These are caused by rising and sinking air on days when cumulus clouds. The gusts come straight from above, and they will veer (turn clockwise) in a direction more closely related with the isobars. The gust may last for a few minutes, followed by a lull when the wind backs to the original direction. The difference in the wind shift direction is an important tactical consideration, for regattas.


Wind speed
On a weather map closely spaced isobars mean strong winds, while big width between isobars mean light winds. If the gap between the isobars is decreased into two, the wind speed will double.

One of the trickiest things in sailing is the saying that "Perfect sailing breeze depend on ability". People who are beginners would prefer a light wind, but not so light as not to be able to access from where it blows. For beginners 1 to 10 knots is perfectly suitable. For dinghies and catamarans the perfect speeds are from 7 to 16 knots.
17 to 27 knots should be treated with caution.
At above 30 knots' speed we highly recommend that you don't launch at all.

Summer winds
Seabreezes are created by the sun warming up the land ahead of the comparatively cold sea, and are mainly a coastal summer phenomenon.
The night wind is offshore, the seabreezes compensate and gradually cancel out it.
Lakes that are surrounded by mountains can also be affected by summer winds. A well known example is Lake Garda, a famous sailing location in Italy. There the normal wind is of mountain nature (esp. early in the morning), and also valley wind; from time to time summerbreezes appear.

There is a phenomenon called "dirty wind" - it is caused by the turbulence or blanketing effect of another boat's sails when it is anything less than three or four boat lengths ahead.
Reasons:

a boat that is ahead and to windward, when you will fall directly into its wind shadow.
a boat that is directly ahead, when you will be affected by both wind shadow and turbulence off its sails.
a boat that is ahead and to leeward, when turbulence affect the sails.

 

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