The physics of turning strokes and hull interac5on
John Huth NSPN
Sunday, March 20, 2011
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Newton’s third law
Higher velocity = lower pressure
Lower velocity = higher pressure
Airflowdisplaced
LiftNo airflowdisplaced
Recall airflow around wing
Air is displaced downward to generate lift
Negative pressure(suction)
Positive pressure
Where Bernoulli comes in: higher flow on top generates lower pressure
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Pressure distribution
Suctionpeak
Favorable pressure gradient
Adversepressure gradient
Reversed flowTurbulent wake
Separatedboundarylayer
Generation of drag at larger attack angles
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More torque=more rotation
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Advantage: minimize Turbulent drag
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Works with no forward motion
Wake generation from hull
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Must have flow to work!
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Must have flow to work!
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Hull 5lt (heel, roll, edge, lean…)
Yes, yes, quibble over the language
Asymmetric airfoil – more lift
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Shape of waterline
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Shape of waterline
Edging
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Difference in shape of hull at waterline
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Edging: “lift” created by attack angle and conversion of wetted hull to asymmetric wing shape
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Higher flow gives lift and rotation
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Added bonus
Stern sees increased flow and lift, aiding turn
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Summary
• Most effec5ve “on the go” turning strokes – Minimize turbulence
• Edging creates ‘wing’ shape of wePed hull – Asymmetric liR creates rota5on
• Stern pry and draw accentuate flow diversion • Stern draw creates interac5on with hull
• Added liR in stern aids turn