11. Using a moderately sized sail, a foil windboard can achieve speeds over 6 knots faster than the apparent wind . 12. Additionally, as their speed increases on the broad reach, their apparent wind changes to allow them to point lower. 13. Figure 1 shows the relationship of the true wind and apparent wind vectors as differing by the yacht velocity. 14. The 4000 is fast enough to make use of the apparent wind to reach the bottom of the racecourse sooner. 15. Depending on the alignment of the sail with the apparent wind , lift or drag may be the predominant propulsive component. 16. On running the spinnaker is angled for maximum drag, with the spinnaker pole at right angles to the apparent wind . 17. The Windex, a wind indicator that measures the apparent wind generated by a boat's movement across water, was their invention. 18. Pressure differences result from is the chord line of the sail and the apparent wind velocity ( "'V A "'). 19. These devices can be calibrated to measure the true wind speed and the apparent wind speed ( speed that a sailor would'feel'). 20. Also note that the optimum speed sailing angle is equal to the apparent wind angle ( Beta ) below a beam reach.