Forces on sails (3 m) = 5-m/s (≈10-knot) wind at 3 m above the water would be approximately "V" (15 m) = 6 m/s (≈12 knots) at 15 m above the water. In hurricane-force winds with "V" (3 m) = 40-m/s (≈78 knots) the speed at 15 m would be "V" (15 m) = 49 m/s (≈95 knots) with "p" = 0.128. This suggests that sails that reach higher above the surface can be subject to stronger wind forces that move the centre of effort ("CE" ) higher above the surface and increase the heeling moment. Additionally, apparent wind direction moves aft with
Forces on sails sail and the apparent wind ("α" ) exceeds the point of maximum lift on the "C"–"C" polar diagram, separation of flow occurs. The separation becomes more pronounced until at "α" = 90° lift becomes small and drag predominates. In addition to the sails used upwind, spinnakers provide area and curvature appropriate for sailing with separated flow on downwind points of sail. Again, in these diagrams the direction of travel changes with respect to the apparent wind (V), which is constant for the sake of illustration, but would in reality vary with point of sail for a constant true wind. In