Mechanics of Rowing

Keval

Introduction

• Rowing for five years
• Always curious about rowing technique- why optimal?
• Pulling boat, or pushing boat?
• Why is the taught technique the “best” technique
• Investigate mechanics via photo analysis

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General Rowing Terminology

Blade- the flat part of the oar

Collar- the pivot point on the oar

Handle- the end of the oar

Shell- the physical structure of the boat

Bow ball- the front-most part of the boat

Rigger- the component that provides structure for oarlock

Pin/Oarlock- the component that holds the oars where the oars pivot

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General Rowing Terminology

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• Square- when blades (oars) are perpendicular to water
• Feather- when blades are parallel to the water
• Catch- the beginning of the stroke, blades are squared
• Leg drive- the first part of the stroke, where the legs are active
• Back- the second part of the stroke, where the upper body leans back
• Arms- the last part of the stroke, where the arms finish
• Finish- the end of the stroke, blades are feathered
• Recovery- the return to the catch

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Methodology

• Set up camera/tripod such that dock is perpendicular
• Row from the start past the dock
• Low current area
• Simple, constant stroke rate
• Parallel to dock
• Track bow ball of boat- stationary relative to oarlock
• Graph position v. time- extrapolate velocity, acceleration
• Determine force of friction (drag), F=ma
• Graph kinetic energy v. time
• Determine the different parts of the stroke versus graphs

Leverage

Oar as Class 2 lever- blade is fulcrum (frame of reference)

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Thus, L a / (a+b) = E

The force calculated from the motion is applied at the pin- the oar “amplifies” the force applied at the oar handle

Load (pin)

Effort (handle)

Fulcrum (blade)

a

b

Important note!!!

In terms of momentum- Must be conserved!

P= m_boatv_boat- m_waterv_water

So even though oar looks stationary, it moves- slippage

KE vs. Momentum in terms of velocity

• Squared term

Thus, easier to move a big amount of water slowly vs small amount quickly

In rowing, slippage is minimized to maximize velocity-this is why oar appears stationary- and can be defined as such

Drag

Skin resistance: R_skin=⍺v²

⍺_skin= ½ C_df 𝜌_water A_shell

C_df= 0.075/(Log Rt - 2)²

Rt= vL/ⱱ

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𝜌_water =1000 kg/m³

ⱱ= Viscosity of water = @ 20^o C = 0.0000010023 Ns/m²

A_shell= submerged surface area = 2.25 m²

L= length of run = 7.83 m

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Rowing Shells are unique from other watercraft

• 80% of drag is from skin drag
• Thus, divide R_skin by .8 to get total drag

So, F_net= F_pin- F_drag

Stroke 2

Acceleration

Velocity

K Energy

Leg drive+Back

• a=3.013 m/s/s
• v_avg=2.347 m/s
• F_net=265.75 N

Arms

• a=2.060 m/s/s
• v_avg=3.356 m/s
• F_net=181.69 N

Recovery

• a=-0.969 m/s/s
• v_avg=2.763 m/s
• F_net=-85.43 N

Stroke 3

Acceleration

Velocity

K Energy

Leg drive+Back

• a=3.926 m/s/s
• v_avg=2.772 m/s
• F_net=346.27 N

Arms

• a=.597 m/s/s
• v_avg=3.815 m/s
• F_net=52.626 N

Recovery

• a=-0.924 m/s/s
• v_avg=3.057 m/s
• F_net=-81.51 N

Stroke 4

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Acceleration

Velocity

K Energy

Leg drive+Back

• a=3.665 m/s/s
• v_avg=3.310 m/s
• F_net=323.25 N

Arms

• a=2.060 m/s/s
• v_avg=3.356 m/s
• F_net=181.69 N

Recovery

• a=-0.969 m/s/s
• v_avg=2.763 m/s
• F_net=-85.43 N

Average of Three Strokes

Leg Drive+Back

• a=3.535 m/s/s
• v=2.810 m/s
• F_net=311.76 N

Arms

• a=1.572 m/s/s
• v=3.509 m/s
• F_net=138.67 N

Recovery

• a= -.954 m/s/s
• v= 2.861 m/s
• F_net= -84.14

Using Resistance formula/0.8, ma+F_drag=F_pin, and leverage

Leg Drive+Back

• Drag=32.97 N
• F_pin=344.72 N
• F_handle=240.23 N

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Arms

• Drag=35.13 N
• F_pin=173.80 N
• F_handle= 121.12 N

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Recovery

• Drag=24.13 N
• No other forces

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Conclusion

Anatomy- Legs/core vs. arms

Seamless stroke- lower velocity variation

Minimize energy to vertical motion- very horizontal stroke (>6 cm y variation)

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Rowing is a PUSH sport, not a pull sport

References

Dudhia, Anu. “Basic Physics of Rowing.” Oxford University. http://eodg.atm.ox.ac.uk/user/dudhia/rowing/physics/index.html

Roosendaal, Sander. “Drag Revisited.” A Model of Rowing, 10 November 2010. https://sanderroosendaal.wordpress.com/2010/11/18/drag-revisited/

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Paul Mueller Company Engineering Staff. “How does the Reynolds number affect mixer design?” Paul Mueller Company Academy, 31 January 2018. https://en.paulmueller.com/academy/how-does-the-reynolds-number-affect-mixer-design

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