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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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