3. 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 your
sail, the wind has to split at the sailâs front edge and flow down each
side of the curved âwingâ shape.
5. 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
âsucksâ the sail to leeward.
8. Forces on the sail
What is lift?
âąThe force that pulls
the sail to leeward.
âą The Lift
combination of
lift over every
Total force
point of the sailâs
surface is called Drag
the âcentre of
effortâ.
9. What causes drag?
âą Friction on the sail, hull ¢reboard
Which of the 5 Eâs will help us reduce drag?
âąCentreboard, Trim, Balance & Sail setting
11. What does the centreboard do?
âą 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.
âą The aerodynamic & hydrodynamic forces
combined partially cancel each other out
resulting in the ability to sail in almost any
direction except straight into the wind.
12. Trim, Balance & Heel
Pressure of
wind on
the sail/s
+ wind on
the hull
= Heel
13. Balance - How to stop heel?
âąHelm & crew weight
âąEase out sails
âąReef sails
A flat boat is a fast boat!
14. Sailing downwind
âą In this instance, the sails
are merely set to trap the
air as it flows by, thus being Turbulence
âaerodynamically stalledâ.
âą In stronger
winds, turbulence created
behind stalled sails can lead
to aerodynamic
instability, which can create
an increased risk of
downwind rolling of the
dinghy.
15. Further info:
âą The air flowing at the
sail surface is not the
âtrue windâ. 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.