When your sail is flapping like a flag, the wind passes down each side of it without being diverted from its course. When you shape yoursail, the wind has to split at the sail’s front edge and flow down each side of the curved ‘wing’ shape.
Air on theleeward sidehas to travel a longer distance in the same time as the air passing the inner surface; therefore it moves over the outer surface faster.This difference in airspeed creates a pressure drop on the leeward side which effectively ‘sucks’ the sail to leeward.
What does the centreboard do?• The pressure of the wind on the sails alone causes the dinghy to travel sideways instead of forward, therefore you need a centreboard to gain effective forward motion.• The aerodynamic & hydrodynamic forcescombined partially cancel each other outresulting in the ability to sail in almost anydirection except straight into the wind.
Trim, Balance & Heel Pressure of wind on the sail/s + wind on the hull = Heel
Balance - How to stop heel? •Helm & crew weight •Ease out sails •Reef sails A flat boat is a fast boat!
Sailing downwind• In this instance, the sailsare merely set to trap theair as it flows by, thus being Turbulence‘aerodynamically stalled’.• In strongerwinds, turbulence createdbehind stalled sails can leadto aerodynamicinstability, which can createan increased risk ofdownwind rolling of thedinghy.
Further info:• The air flowing at the sail surface is not the ‘true wind’. Sailing into the wind causes the apparent wind to be greater than the true wind and the direction of apparent wind will be forward of the true wind.
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