1. Sail Course ® Section 10, Sail Shape

2. Sail Course ® Figure 10–1 Air Flow Around a Sail

3. Sail Course ® Figure 10–2 Angle of Attack

4. Sail Course ® Figure 10–3 Angle of Attack Held Constant

5. Sail Course ® Figure 10–4 Angle of Attack and Streamlines

6. Sail Course ® Figure 10–5 Air Flow, Sailing Directly Downwind

7. Sail Course ® Figure 10–6 Sail Shape, Draft

8. Sail Course ® Figure 10–7 High and Low Aspect Ratio Rigs

9. Sail Course ® Figure 10–8 Wind Variation with Height

10. Sail Course ® Figure 10–9 Wind Vanes

11. Sail Course ® Figure 10 – 10 TelltalesFigure 10 – 10 Telltales

12. ® Figure 10–11 How Telltales React to Sail Trim

13. Sail Course ® Vocabulary Aspect Ratio. In general usage, the aspect ratio of a sail is taken to be the length of the luff to the length of the foot. Attached Flow. The movement of particles along a surface, such as the flow of air particles along the leeward side of a sail. Backwinded. A sail is backwinded when another sail to leeward of it is trimmed so closely as to cause increased pressure on the lee side of the windward sail thus causing the windward sail to bulge to windward. Lift. A force generated on the leeward side of a sail by air passing over the airfoil shape. It is the force that drives a sailboat. Also, when sailing close-hauled, a wind that shifts aft to allow a change of course toward the wind direction. Separation. Detachment of air in a smooth laminar flow from the leeward side of a sail. See also “Stall.” Stall. The condition that arises when the airfoil (sail) or hydrofoil (rudder) is turned too far off and the flow of air or water separates from the foil; there is no longer an attached flow.

14. Sail Course ® End of Section 10 Slides