WINDSURFING: A LITTLE THEORY

WINDSURFING: A LITTLE THEORYWindsurfer strikes the imagination at first sight. Everything in his appearance unusual, does not fit into the established way of sailing, even just a little, ship. Instead of the housing Board, the mast is hingedly fixed to the steps and held only in the hands of the athlete, no line of the Scots, the halyards and other rigging. But the most unusual and unfamiliar in the windsurfer is the lack of steering, which place was occupied by a stationary fin.

 
But despite the lack of steering of the windsurfer is perfectly controlled and can maneuver as good as any yacht.
 
What is the secret that allows the windsurfer to do without the helm?
 
Consider the forces acting on the windsurfer moving under the action of the wind.
 
The flow around the sails with the stream of air directed at a slight (15°) angle to the sail, flow rates on the windward and leeward sides of the sail will be different. By virtue of the laws of aerodynamics (similar to the wing) on each elementary portion of the surface of the sail will be a force directed .perpendicular to this area (see Fig. 1 on the tab). The point F of application of the resultant of all aerodynamic forces will be called the center of the sail (CPU). The CPU is located approximately at the geometric center of the sail.
 
Arising on the sail the force F through various communication mast, rigging, and rider and through the body of the athlete affects the vessel’s hull and causing it to move.
 
Decompose the force F into two components (Fig. 2), one of which Ft acts along, and the other FD is perpendicular to the hull. The first force causes the movement of the vessel forward and is called thrust: the second creates a lateral movement of the vessel under wind (drift) and is called force drift.
 
If the resistance to motion of the hull was the same in all directions, the ship could only move in one direction — to the wind and could be managed. To prevent this from happening, try the resistance to movement of the vessel forward is to reduce, and the resistance to drift the lateral resistance increased. This is achieved by setting in the diametrical plane special vertical plates Vertov, sverzov, fins; increased underwater part of the hull and giving her a special form, as it is with keel boats.
 
The physical principles of operation of the centerboard, and all other above-mentioned plates are the same as that of the sail. The only difference is that the centerboard operates in a different, more dense environment.
 
In the flow of the centerboard stream of water to develop a hydrodynamic force directed in the direction opposite to the force of drift. The point of application of the resultant of the hydrodynamic forces acting on the centerboard and the underwater part of the hull is called the center of lateral resistance and is denoted by CLS.
 
The strength of the drift and force of the lateral resistance attached to the body of the vessel at different points (Fig. 3 a and 3 b) form the moment of forces that deploy it.
 
If the projected center of the sail to the diametrical plane located behind the projection of the center of lateral resistance closer to the stern (Fig. 3 6), the resulting moment of the forces will begin to deploy a ship towards the wind (to cause wind) until, until it stands precisely against the wind to head to wind.
 
WINDSURFING: A LITTLE THEORY
 
When the front location of the projection of the center of the sail relative to the center of lateral resistance (Fig. 3 a) resultant moment of the forces will begin to deploy the ship from the wind (to evaluate) to the position when the wind blowing directly aft (the wind).
 
And finally, if the projection of the center of the sail and the centre of lateral resistance are on the same line, the forces of drift and lateral resistance compensate each other (Fig. 3), and the ship moves in the direction of its longitudinal axis. For ordinary sailing ships, moments of forces, causing the casting or uvarivanie are harmful as they complicate the management of the vessel, reduce speed, and in some cases can be downright dangerous. Therefore, when designing a sailing craft hull shape, and relative position of the centerboard or keel and sail are selected to produce under different sailing conditions the moments of the forces that deploy to the ship was minimal.
 
When creating windsurfer designers went the other way — harmful torques, they made useful and forced them to operate the vessel by the will of man.
 
To do this, they fixed the mast is hinged on the housing in only one point. This design allows a wide range to change the position of the mast, and hence the position of the center of the sail relative to the center of lateral resistance. Such a bold decision allowed the use of the arising torques to control the windsurfer.
 
There is one interesting feature in the management of the windsurfer. If conventional sailing craft, the direction of rotation depends only on the rudder (the rudder on the left side — turn to the left, rudder on the right side — turn to the right), windsurfer direction of rotation when moving the sails in the same direction depends on which side the wind is blowing, that is, from the gals. This is because by moving the sail, and hence the center of the sail forward or backward, the athlete brings the rider to the wind or velivet it.
 
Thus, if the windsurfer is starboard tack (wind coming from the right), then tilt the mast back will cause a change in its course to the right. Conversely, if the windsurfer is port tack (the wind is blowing to the left), then tilt the mast back will cause a course change to the left (Fig. 4 a).
 
When tilting the mast forward, the reverse pattern — when uvarivanie windsurfer goes starboard tack, change course to the left, and reaching port tack to the right.
 
This feature of the control requires some skill: you have to measure your actions when maneuvering with the position of the surfer relative to the wind.
 
B. Evstratov, engineer

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