This upward change in flow angle is called upwash. This is because the lower pressure on top of the airfoil pulls air up toward it. The difference in pressure across the sail holds the flexible sail into its cambered shape and produces force to pull the boat.Īn airfoil developing lift causes the flow approaching it to bend upward. The flow over the convex leeward side has reduced pressure (through accelerated flow) and the flow over the concave windward side has increased pressure (through decelerated flow). Since a sail has essentially no thickness, it exists only as camber. The shape of this camber line determines the amount of lift produced at a fixed angle of attack. If the thickness of an airfoil is ignored, it can be reduced to a thin curved line defining the camber. This lower pressure pulling upward on the upper surface of a wing produces lift. When a fluid (like air or water) is accelerated, the pressure that it imparts on an adjoining surface decreases. Velocity and Pressureįlow accelerates over the top surface of an airfoil, either because it is at an angle to the flow, or because the top has more curvature than the bottom, or both. Analyzing how a sail works as a wing is useful, not just for modern sails that look more like wings, but also for very traditional sails that, while they look like sails, operate very much like wings. Their appearance then becomes more wing-like and less sail-like. So, the problem becomes how to build and operate a flexible sail in the wind to produce a substantial force component to move the boat.Īs the restriction that sails support themselves is diminished (full battens and stiffer materials for example), sails can evolve to be more efficient. This leads to the traditional triangular planform of sails, since the material below has to hang from the material above, which eventually is reduced to a point at the top of the mast. This is a significant restriction that prevents many shapes from being built because they would not be able to support themselves in the wind.
They are normally built from a flexible material in order to allow the sail to work with the wind on either side to allow tacking. It is useful to recognize what a typical sail is. The following explanation of how this occurs can help understand how to maximize the performance achieved from sails. Sails are wings that use the wind to generate a force to move a boat. HOW SAILS WORK Understanding How Sails Are Designed To Create Power © Chris Howell
0 kommentar(er)
