MOTIVATION ARTICLES - SURFING
CHASING THE WIND
Depending on the wind direction, i.e. the angle that the wind closes along the longitudinal axis of a windsurfing board, the sail will change a variety of conditions, by which it will sail in very different ways. These are called the 'types of sailing '.
The main types of sailing are:
Sailing upwind – when windsurfing board sails down the course that closes an angle with the wind direction that is less than 90 degrees. Sailing upwind goes from 'sailing totally upwind'(angle up to 40°- 45°) to sailing ‘upwind' (angle from 45° - 90° with regards to the wind direction).
Sailing downwind (favourable wind) – When the angle between the wind direction and the longitudinal axle of the windsurfing board is about 90 degrees or above, windsurfer sails down a favourable wind or downwind.
Wind is nothing but a mass of air molecules moving from one place to another. If the air molecules encounter obstacles on their way, they mount on such an obstacle and change their direction, extending their movement along the very obstacle. The sail is also an obstacle, with a special form and so the impact of all molecules, that fall onto the face of a sail, windward, determines its total pressure onto the sail. It is, however, important to bear in mind that this is not a blow and turning of isolated mass of air, but a continuous and constant flow of molecules, similar to a river flow in a bend. Molecules that continually arrive will have to adapt their movement in the vicinity of the sail, because they are hit by the previous ones that were rejected by the sail and flow along it. They will not hit the sail with the same strength like the ones in front of them, but if the turning from their direction is insignificant, they will be able to bulge slowly along the sail.
When, due to large angles of sail inclination, the turning of molecules from their path becomes larger, the arriving molecules will not be able to turn from their path with such an ease. They will clash with the ones that hit the sail before them at a distance greater than the previous one, thus creating a swirling motion that significantly reduces wind pressure onto the sail. Molecules that pass leeward, along the inlet edge of the sail, will have to significantly modify their movements to reach the depression present there, creating that way a swirling motion.
The above, totally unscientific interpretation, however, sufficiently explains this phenomenon. We are actually interested in the essence of it and how it can be used in sailing. The impact onto a sail is increased by increasing the exposure angle, as the greater amount of air is in motion. Therefore, there is more impact onto the face of a sail and stronger suction effect leeward.
We conclude the following:
- The sail has to have a depression (concave) surface exposed to the wind pressure, which depends on the turning that the sail makes under the wind.
- The sail must have dimensions developed rather by height than by width.
- The impact on the sail changes with the change of depression of the sail and its inclination
- The impact achieves the highest value for a certain depression and for a precisely determined angle of inclination.
In other words, for a determined sail surface there are a determined ideal sail depression and an angle for every strength of the wind with regards to the wind for which there will be maximum movement. This conclusion is very important for surfers, because they encounter a large number of combinations of sail size and wind power which will determine their choice of sail and windy surroundings. Let’s not forget experience as an important factor contributing to the right choice in every situation. The aim is to achieve maximum satisfaction during the time spent on the water holding a boom and enjoy that 'special' feeling . . the feeling for which we are ready to put out all our sacrifices and efforts.
Here are some useful tips concerning wind and weather.
Natural signs indicating the change of direction or wind strength:
- The presence of waves coming ashore with no wind and becoming progressively greater can be a sign of fresh wind coming from the open sea towards mainland.
- When breeze slowly disappears and appears back again in increasing intervals_this is a sign that a peaceful period is coming or that wind will change its direction.
- If there is a constant breeze or worse, if it gets stronger when it should be calming down_a sign of bad weather.
- Rain, if not followed by a storm, usually brings silence and in any case, reduces the strength of wind and calms the sea or river.
- If the sky is gradually covered by grey clouds covering the sun, whilst there are no black clouds, it means that breeze is likely to fade away and that it will be quiet_a windless period.
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