On The Waterfront John D Barrow Swimmers Improved

On The Waterfront *** John D Barrow

Swimmers Improved Much Faster Than Runners Men’s 400 m 100 m run: 43. 8 (1968) to 43. 18 (2011) swim: 52. 2 (1968) to 46. 91 (2011) V(run) 5 V(swim)

English Channel Swim Approximately 21 miles Men’s record of 6 hr 57 m by Peter Stoychev is 3 mph Women’s record of 7 hr 25 m by Yvetta Hlavacova is 2. 8 mph Sprint swim 100 m in 50 s is 2 m/s

Record Speeds over 50 m Stroke Men (sec) 20. 91 Women (sec) 23. 73 22. 43 25. 07 24. 04 27. 06 Breaststroke 26. 67 29. 80 Crawl >1904 Olympics Butterfly >1952 Olympics Backstroke >1904 Olympics Men – Women 3 sec

Arms or Legs? Legs only 100 m in 80 s V = 1. 25 m/s Arms only 100 m in 60 s V = 1. 67 m/s. All freestyle Arms + legs 100 m in 50 s V = 2 m/s The ratio of arm pull to leg kick is 1. 3 The kick also plays a stabilising role in backstroke and freestyle

Symmetries Butterfly and breaststroke are laterally symmetric Crawl and backstroke are laterally asymmetric Other recreational strokes Trudgeon = crawl arms + breaststroke legs Inverted breaststroke Slow butterfly = butterfly arms + breaststroke legs Fast breastroke = breaststroke arms + butterfly legs sidestroke

Breaststroke Swimming is Different Speed is not constant Arm recovery must be underwater Part of head above water surface Drag force V always decelerates Acceln by moving water backwards Decceln by moving water forwards with knees Max speed of 2 m/s Min speed 0 m/s Created by periodic variation of net force on the body

Hydrophobic Polyurethane Swimsuits Banned by FINA in 2010 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 Temperature FINA Rules for Swimming competition specify 25 -28 C (77 -82 F) Drag = ½ AV 2 viscosity of water Density fall with T is a much smaller effect than water viscosity change as T up to about 15% on range allowed

Body Shape Matters Drag Force = ½ c AV 2

Inge De Bruin’s Drag Effect Compared With Many Other Swimmers …. De Bruin former World records 50 &100 m free 100 m fly A significantly smaller c A factor at all speeds

The Three Main Drag Forces Friction drag: drag in the thin layer of water near the body c. AV 2 It is higher if flow is turbulent (c ) rather than smooth (c ) Pressure drag: drag fast swimmers create high pressure in front and low pressure behind AV 2 [p(high) – p(low)] Wave drag: drag energy lost making surface waves. As V the wavelength and amplitude . Wavelength a bit longer than swimmer puts him in a speed-limiting wave trough. Swim more underwater! 15 m is the max allowed at the start and from each turn

Turbulence The Onset of turbulence occurs when Reynolds Number = VL / 500, 000 Average Speed V = 2 m/s Body surface size L = 2 m Water density = 1. 00 kg/m 3 Water dynamic viscosity = 0. 9 10 -3 Ns/m 2 = / Reynolds Number 450, 000 Small variations in L and V will produce turbulence

Wave Drag Wavelength L= 2 V 2/g = 2 m (V/1. 8 m/s)2

The Dominant Drag Depends on Your Speed Dominant Drag Effect Length L = 2 V 2/g = 2 m (V/1. 8 m/s)2 Frictional drag Recreational Swimming speeds Pressure drag and wave drag (56%) Dominate Fdrag = 40(V/1. 3 m/s)2 N 1. 5 -2 m/s World class Speed

Moving The Right Sort of Water • • • Hand supplies energy for moving water Don’t push water back in a straight line Follow a curvilinear path so as to keep on finding still water to push against so as to gain larger resistance and reaction

Use Hands to Pull Still Water Flow ‘S’ or ‘inverted question mark’ paths hand Lift Make resultant force always forwards Drag

Minetti et al Optimal is about 12 deg (usual rest spacing) It has about 8. 8% greater drag than wide open or closed hand

Optimal Finger Spacing AE Minetti et al

Rowing and Paddling in Numbers How does the speed of the boat depend on the number of rowers? Drag on boat V 2 wetted surface area of boat V 2 L 2 Volume of boat L 3 N – the number of crew Drag V 2 N 2/3 Crew Power overcoming drag = N P = V Drag V 3 N 2/3 P is the constant power exerted by each (identical) rower V N 1/9 With a cox V N 1/3/[N + 1/3 ]2/9 if cox is third the weight of a rower

Moscow Olympic Kayak Times Are race times T 1/N 1/9 ? Race times in the 1 -person and 2 -person and in the 2 -person and 4 -person races should be in the ratio of 21/9 = 1. 08 Men’s 1000 m events: Women’s 500 m events:

Results of 1980 Olympic coxless races (N = 1, 2, 4) + coxed N = 8 Distance is 2000 metres N 1 2 4 8 Time, T(sec) 429. 6 408. 0 368. 2 349. 1 T = (2000)/V N-0. 11 V N 0. 11 N 1/9 But with a cox N = 2: T = 422. 5 s N = 4: T = 374. 5 s Better without one!

The Impact of A Cox Adds weight to the crew but not to power Lightweight cox is N N + ½ effect T(with cox)/T(coxless) = [(N + ½)/N]2/9 = (25/16)1/9 = 1. 05 for N = 2 = (81/64)1/9 = 1. 03 for N = 4 1980 Olympics

Rigging Rowing Eights

Rowing Has Its Moments +N F and -N F

The Wiggling Boat s Moment on boat = -Ns + N(s+r) - N(s+2 r) + N(s+3 r) = +2 Nr Then, half a stroke later…N reverses to –N and. . Moment on boat = -2 Nr

Size of the Yaw Pair: 0. 37 deg per stroke Four: 0. 77 deg per stroke Eight: 0. 015 deg per stroke

The Italian Rig Moment = -Ns + N(s+r) + N(s+2 r) - N(s+3 r) = 0 No wiggle!

Four no-wiggle rigs for eights ‘Italian tandem Rig ’ Moment = 1 -2 -3+4+5 -6 -7+8 = 0 New* Moment = 1 -2 -3+4 -5+6+7 -8 = 0 ‘German Rig’ Moment = 1 -2+3 -4 -5+6 -7+8 = 0 New* Moment = 1+2 -3 -4 -5 -6+7+8 = 0