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why and why not

Why ITA can’t foil gybe and ETNZL almost cartwheeled

A small lesson on turning foiling boats and the phenomenon called heel induced lift.

When any foiling boat has heel, or is listing to one side, and the skipper turns the rudder, the path of the rudder elevator has to now travel on an inclined plane. This often causes a burst of lift or suction on the rudder elevator. Same reason on a moth if you heel the boat one way, and turn the rudder hard, you will crash 100% of the time (either nose dive or sky upwards then crash).

So when you see ITA AC72 go into every gybe with a decent leeward heel, the rudders turn and the heel induced lift drive the bow down and they crash. When you see Dean Barker wait till the boat is perfectly flat, then sends it through, it results in a perfect gybe.

When ETNZ did the wipe out at the top mark rounding, they had big leeward heel (didn’t look big but it doesn’t take much), big wheel down, rudders get a burst of lift until the leeward elevator is in the air then it’s all over, very lucky that someone on their design team knows WTF is going on. If they had kept it flat through the bear away, or even windward heel, it will never happen. Slingsby is all over it.  - Joe Turner.

 

August 22nd, 2013

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