G'day Matt and Niels, I promised to send my assumptions and calculations last week so here they are. I've reworked them to incorporate the segment approach so as to see at which parts of the stroke the Potential Energy (PE) to Kinetic Energy (KE) payback is most sensitive The vertical movements of Left and Right Hands and Elbows during a stroke on one side were measured by sitting in an office chair set to its highest seat position, while holding a half paddle. With the wall on my right I set up three positions while preventing the chair from rotating: i) the raising of the paddle to its highest position ii) spearing the paddle to enter the water at the feet iii) the first half of power stroke where the blade moved from its entry at my feet falling through the water to the side of my torso. I didn't bother with the last phase of the power stroke as no vertical positions of centre of mass should have changed. Once a position was established I rotated the chair until each segment faced the wall and put a sticky tab marker on the wall to mark hand or elbow positions. The assumptions and calculations are below: ASSUMPTIONS Cadence 30 strokes one each side per minute based on Brad's video link and personal observation time to lift blade 0.1 s Period for a one side stroke 0.9 s Period for the falling phase 0.45 s Period for the power phase 0.45 s Power needed to move kayak 18 W For a 70kg kayaker paddling at 7 to 8 km/h from Matts figures Acceleration due to gravity 9.8 m/s2 Muscle efficiency 25% Paddle 0.8 kg measured Upper arm 2.0 kg Forearm 1.7 kg based on arm segment model http://www.ulb.ac.be/medecine/anatemb/biblio/Clauser1969.pdf RESULTS Average rate at which potential energy is converted and supplied 7.35W Rate of energy use by body to propel kayak Power needed to propel a kayak / muscle efficiency 72W The above results take no account of blade turbulence losses; or losses due to such things as the action of a relaxed arm being supported by muscles as it falls, or transfer of energy from one arm to the other when changing from a stroke on one side to a stroke on the other. It is based on the following estimates POTENTIAL TO KINETIC ENERGY CONVERSIONS AS PADDLE FALLS FROM HIGHEST TO LOWEST DURING A STROKE ONE SIDE MEASUREMENTS Paddle 0.8 kg measured Upper arm 2.0 kg Forearm 1.7 kg Based on arm segment model http://www.ulb.ac.be/medecine/anatemb/biblio/Clauser1969.pdf PE TO KE CONVERSION STARTS Paddle lifted out of water to highest point - forward left hand with arm straight, aft right hand with arm bent Vertical axis positions Shoulder height constant at 109 cm measured Right hand 130 cm measured Left hand 110 cm measured Right elbow 110 cm measured Left elbow 109 cm calculated Paddle centre of mass 120 cm calculated Right forearm centre of mass 120 cm calculated Right upper arm centre of mass 109 cm calculated Left forearm centre of mass 109 cm calculated Left upper arm centre of mass 109 cm calculated Paddle speared into water - both arms straight Vertical axis positions Shoulder height constant at 109 cm measured Right hand 130 cm measured Left hand 88 cm measured Right elbow 119 cm calculated Left elbow 98 cm calculated Paddle centre of mass 109 cm calculated Right forearm centre of mass 124 cm calculated Right upper arm centre of mass 114 cm calculated Left forearm centre of mass 93 cm calculated Left upper arm centre of mass 103 cm calculated PE TO KE CONVERSION COMPLETE First half of power stroke bringing blade level with torso with both arms straight Vertical axis positions Shoulder height constant at 109 cm measured Right hand 130 cm measured Left hand 62 cm measured Right elbow 119 cm calculated Left elbow 96 cm calculated Paddle centre of mass 96 cm calculated Right forearm centre of mass 124 cm calculated Right upper arm centre of mass 114 cm calculated Left forearm centre of mass 79 cm calculated Left upper arm centre of mass 102 cm calculated CALCULATION OF VERTICAL DISPLACEMENT ASSOCIATED PE to KE CONVERTED ASSOCIATED TRANSIENT POWER CONSUMPTION Paddle fall to water phase Centre of mass displacement(m) Energy(J) Power(W) Paddle 0.11 0.86 1.92 Right forearm -0.05 -0.79 -1.76 Right upper arm -0.05 -0.93 -2.07 Left forearm 0.17 2.75 6.11 Left upper arm 0.06 1.08 2.40 Total for arms 0.13 2.11 4.68 Total for paddle 0.11 0.86 1.92 TOTAL 0.24 2.97 6.60 First phase power stroke - blade from foot to torso Centre of mass displacement(m) Energy(J) Power(W) Paddle 0.13 1.02 2.27 Right forearm 0.00 0.00 0.00 Right upper arm 0.00 0.00 0.00 Left forearm 0.14 2.38 5.28 Left upper arm 0.01 0.25 0.55 Total for arms 0.16 2.62 5.83 Total paddle 0.13 1.02 2.27 TOTAL 0.29 3.64 8.09 *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). 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