Wave Drag on Human Swimmers

Swimmers at the surface experience wave drag due to the energy required to form the waves in wake behind them. A new paper presents measurements in the Otago University swimming flume which show wave drag is very important. A mannequin was towed at a range of speeds and depths. The measured drag when towed at the surface was twice the drag when towed at 0.7m below the surface. Thus wave drag of humans is up to 50-60% of total drag. A figure much higher than the 5-20% previous research had suggested.

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Wave drag on human swimmers

Ross Vennell, Dave Pease and Barry Wilson

Journal of Biomechanics Volume 39, Issue 4 , 2006, Pages 664-67

PDF article 250kB

Abstract

Drag measurements from a towed mannequin show total drag at the surface is up to 2.4 times the drag when fully immersed. This additional drag is due to the energy required to form waves in the wake behind the mannequin. The measurements show that passive wave drag is the largest drag, comprising up to 50-60% of the total at 1.7m/s, much higher than any previous estimates. Comprehensive measurements spanning human swimming speeds and tow depths up to 1.0m demonstrate that wave drag on the mannequin is less than 5% of total drag for tows deeper than 0.5m at 1m/s and 0.7m at 2m/s. Wave drag sharply increases above these depths to a maximum of up to 60% of the mannequin's 100N total drag when towed at the surface at 1.7m/s. The measurements show that to avoid significant wave drag during the underwater sections of starts and turns, swimmers must streamline at depths greater than 1.8 chest depths below the surface at Froude number (Fr) =0.2, and 2.8 chest depths at Fr =0.42. This corresponds to speeds of 0.9m/s and 2.0m/s respectively for a chest depth of 0.25m and toe to finger length of 2.34m.