On The On The WaterfrontWaterfront

John D BarrowJohn D Barrow

******

Swimmers Improved Much Faster Than RunnersSwimmers Improved Much Faster Than Runners

Men’s 400m run: 43.8 (1968) to 43.18 (2011)Men’s 400m run: 43.8 (1968) to 43.18 (2011)Men’s 100m swim: 52.2 (1968) to 46.91 (2011)Men’s 100m swim: 52.2 (1968) to 46.91 (2011)

V(run) V(run) 5V(swim) 5V(swim)

English Channel SwimEnglish Channel SwimApproximately 21 miles

Men’s record of 6hr 57m by Peter Stoychev is 3mphWomen’s record of 7hr 25m by Yvetta Hlavacova is 2.8mph

Sprint swimSprint swim

100m in 50s is 2 m/s

Record Speeds over 50mRecord Speeds over 50mStrokeStroke Men Men

(sec)(sec)WomenWomen

(sec)(sec)

CrawlCrawl>1904 Olympics>1904 Olympics

20.9120.91 23.7323.73

ButterflyButterfly>1952 Olympics>1952 Olympics

22.4322.43 25.0725.07

BackstrokeBackstroke>1904 Olympics>1904 Olympics

24.0424.04 27.0627.06

BreaststrokeBreaststroke>1904 Olympics>1904 Olympics

26.6726.67 29.8029.80

Men – Women Men – Women 3 sec 3 sec

Arms or Legs?Arms or Legs?

Legs only 100m in 80sLegs only 100m in 80s V = 1.25 m/s V = 1.25 m/s

Arms only 100m in 60s Arms only 100m in 60s V = 1.67 m/s. V = 1.67 m/s. All freestyleAll freestyle

Arms + legs 100m in 50s Arms + legs 100m in 50s V = 2 m/s V = 2 m/s

The ratio of arm pull to leg kick is 1.3The ratio of arm pull to leg kick is 1.3 The kick also plays a stabilising role in The kick also plays a stabilising role in

backstroke and freestylebackstroke and freestyle

SymmetriesSymmetriesButterfly and breaststroke are laterally symmetricButterfly and breaststroke are laterally symmetric

Crawl and backstroke are laterally asymmetricCrawl and backstroke are laterally asymmetric

Other recreational strokesOther recreational strokesTrudgeon = crawl arms + breaststroke Trudgeon = crawl arms + breaststroke

legslegsInverted breaststrokeInverted breaststroke

Slow butterfly = butterfly armsSlow butterfly = butterfly arms + + breaststroke legsbreaststroke legs

Fast breastroke = breaststroke arms + Fast breastroke = breaststroke arms + butterfly legsbutterfly legs

sidestrokesidestroke

Breaststroke Swimming is DifferentBreaststroke Swimming is Different

Speed is not constantSpeed is not constantArm recovery must be underwaterArm recovery must be underwaterPart of head above water surfacePart of head above water surface

Drag force Drag force V always decelerates V always deceleratesAccelAccelnn by moving water backwards by moving water backwardsDeccelDeccelnn by moving water forwards by moving water forwards

with kneeswith knees

Max speed of Max speed of 2 m/s 2 m/s Min speed Min speed 0 m/s 0 m/s

Created by periodic variation of Created by periodic variation of net force on the bodynet force on the body

Hydrophobic Polyurethane SwimsuitsHydrophobic Polyurethane SwimsuitsBanned by FINA in 2010Banned by FINA in 2010

Past records ‘starred’Past records ‘starred’

• Increase buoyancy by trapping air reduce water drag• Drag on body in water 780 Drag on body in air• Seamless, wrinkle-free, fibred texture, • Up to 8% drag reduction (20 world records at July 2009 Champs• 30 mins to put on, $500 each, last 1-2 races !

Water TemperatureWater TemperatureFINA Rules for Swimming competition specify 25-28C (77-82F)FINA Rules for Swimming competition specify 25-28C (77-82F)

Drag = ½ Drag = ½ AV AV22 viscosity of water

Density fall with T is a much smaller effectthan water viscosity change as Tup to about 15% on range allowed

Drag Force = ½ c Drag Force = ½ c AV AV22

Body Shape MattersBody Shape Matters

Inge De Bruin’s Drag Effect ComparedInge De Bruin’s Drag Effect Compared With Many Other SwimmersWith Many Other Swimmers

A significantly smaller c A significantly smaller c A factor at all speeds A factor at all speeds

….De Bruin formerWorld records50 &100m free100m fly

Friction dragFriction drag: in the thin layer of water near the body cAVcAV22

It is higher if flow is turbulent (c) rather than smooth (c)

Pressure dragPressure drag: fast swimmers create high pressure in front and low pressure behind AVAV22 [p(high) – p(low)] [p(high) – p(low)]

Wave dragWave drag: energy lost making surface waves. As V the wavelength and amplitude . Wavelength a bit longer than swimmerputs him in a speed-limiting wave trough. Swim more underwater!Swim more underwater!15m is the max allowed at the start and from each turn15m is the max allowed at the start and from each turn

The Three Main Drag ForcesThe Three Main Drag Forces

TurbulenceTurbulence The Onset of turbulence occurs whenThe Onset of turbulence occurs when

Reynolds Number = VLReynolds Number = VL// 500,000 500,000

Average Speed V = 2 m/sBody surface size L = 2m

Water density = 1.00 kg/m3

Water dynamic viscosity = 0.9 10-3 Ns/m2

= /

Reynolds Number Reynolds Number 450,000 450,000

Small variations in L and Vwill produce turbulence

Wavelength L= 2Wavelength L= 2VV22/g = 2m /g = 2m (V/1.8 (V/1.8 m/sm/s))22

Wave DragWave Drag

Speed

Frictional dragFrictional drag

The Dominant Drag Depends on Your SpeedThe Dominant Drag Depends on Your Speed

1.5-2m/s

Pressure dragPressure drag and wave dragwave drag (56%)Dominate Fdrag = 40(V/1.3m/s)2 N

Dominant Drag EffectDominant Drag Effect

RecreationalSwimmingspeeds

Length L = 2Length L = 2VV22/g = 2m /g = 2m (V/1.8m/s) (V/1.8m/s)22

World class

• Hand supplies energy for moving waterHand supplies energy for moving water• Don’t push water back in a straight lineDon’t push water back in a straight line• Follow a curvilinear path so as to keep on findingFollow a curvilinear path so as to keep on finding still water to push against so as to gain larger still water to push against so as to gain larger resistance and reactionresistance and reaction

Moving The Right Sort of WaterMoving The Right Sort of Water

Use Hands to Pull Still WaterUse Hands to Pull Still Water

‘‘S’ or ‘inverted question mark’ pathsS’ or ‘inverted question mark’ paths

Flow

Lift

Drag

hand

Make resultant force always forwardsMake resultant force always forwards

Optimal is about 12 deg (usual rest spacing)It has about 8.8% greater drag than wide open or closed hand

Minetti et al

Optimal Finger SpacingOptimal Finger Spacing

AE Minetti et al

Rowing and Paddling in Rowing and Paddling in NumbersNumbers

How does the speed of the boat depend on the number of rowers?

Drag on boat V2 wetted surface area of boat V2 L2

Volume of boat L3 N – the number of crew

Drag Drag V V22 N N2/32/3

Crew Power overcoming drag = N Crew Power overcoming drag = N P = V P = V Drag Drag V V33 NN2/32/3

P is the constant power exerted by each (identical) rower

V V N N1/91/9

With a cox With a cox V V N N1/31/3/[N + 1/3 ]/[N + 1/3 ]2/9 2/9 if cox is third the weight of a rower if cox is third the weight of a rower

Moscow Olympic Kayak TimesMoscow Olympic Kayak TimesAre race times T Are race times T 1/N 1/N1/91/9 ? ?

Race times in the 1-person and 2-person and in the 2-person and 4-person races should be in the ratio of

221/91/9 = 1.08 = 1.08

Men’s 1000m events:Men’s 1000m events:

Women’s 500m events:Women’s 500m events:

Results of 1980 Olympic Results of 1980 Olympic coxless races (N = 1, 2, 4) + coxed N = 8coxless races (N = 1, 2, 4) + coxed N = 8

Distance is 2000 metresDistance is 2000 metres

NN Time, Time, T(sec)T(sec)

11 429.6429.6

22 408.0408.0

44 368.2368.2

88 349.1349.1

T = (2000)/V T = (2000)/V N N-0.11-0.11

V V N N0.11 0.11 N N1/91/9

But with a coxBut with a cox N = 2: T = 422.5 s N = 2: T = 422.5 s N = 4: T = 374.5 s N = 4: T = 374.5 s

Better without one!Better without one!

The Impact of A CoxThe Impact of A CoxAdds weight to the crew but not to powerAdds weight to the crew but not to powerLightweight cox is N Lightweight cox is N N + ½ effect N + ½ effect

T(with cox)/T(coxless) = [(N + ½)/N]T(with cox)/T(coxless) = [(N + ½)/N]2/92/9

= (25/16)= (25/16)1/91/9 = 1.05 for N = 2 = 1.05 for N = 2= (81/64)= (81/64)1/91/9 = 1.03 for N = 4 = 1.03 for N = 4

1980 Olympics

Rigging Rowing EightsRigging Rowing Eights

Rowing Has Its MomentsRowing Has Its Moments

+N

-N

FF and

Moment on boat = -Ns + N(s+r) - N(s+2r) + N(s+3r) = +2Nr

Then, half a stroke later…N reverses to –N and..

Moment on boat = -2Nr

The Wiggling BoatThe Wiggling Boat

s

Size of the YawSize of the Yaw

Pair: 0.37 deg per strokeFour: 0.77 deg per strokeEight: 0.015 deg per stroke

Moment = -Ns + N(s+r) + N(s+2r) - N(s+3r) = 0

The Italian RigThe Italian Rig

No wiggle!

Four no-wiggle rigs for eightsFour no-wiggle rigs for eights

‘Italian tandem RigItalian tandem Rig ’

‘‘German Rig’German Rig’

Moment = 1-2-3+4+5-6-7+8 = 0

Moment = 1-2-3+4-5+6+7-8 = 0

Moment = 1-2+3-4-5+6-7+8 = 0

Moment = 1+2-3-4-5-6+7+8 = 0

New*New*

New*New*

Women’s European Championships 1963, Moscow Women’s European Championships 1963, Moscow

Albanian stampAlbanian stamp

Canada used the German rig to win 2008 Olympics !Canada used the German rig to win 2008 Olympics !

1-2+3-4-5+6-7+8 = 0

Oxford Use a German RigOxford Use a German Rig to Win 2011 Boat Raceto Win 2011 Boat Race

1-2+3-4-5+6-7+8 = 0

The Imperial College 2010 TrialThe Imperial College 2010 Trial

1 + 2 – 3 – 4 – 5 – 6 + 7 + 8 = 0