Energy balance of locomotion with pedal-driven watercraft

Abstract

In this study, we examined the mechanics and energetics of locomotion with a paddle-wheel boat and a water bike. Power output ([Wdot] _tot) was measured directly on the water bike by means of an instrumented chain-ring. The simultaneous assessment of oxygen uptake ([Vdot]O₂) allowed the computation of the “overall” efficiency of locomotion (η _o = [Wdot] _tot / [Vdot]O₂). Mean η _o was 0.27 (s = 0.02), which was unaffected by the speed, and was assumed to be the same for the two boats as both are semi-recumbent bicycles. For the paddle-wheel boat, [Wdot] _tot was then obtained from η _o and measures of [Vdot]O₂. The power to overcome (passive) drag was calculated as [Wdot] _d = D · v (where D is the force measured by means of a load cell when towing the boats at given speeds). Propelling efficiency was calculated as η _p = [Wdot] _d / [Wdot] _tot, which was lower with the paddle-wheel boat (mean 0.35, s = 0.01) than with the water bike (mean 0.57, s = 0.01). The observed differences in η _p and [Wdot] _d explain why at the highest speed tested (∼3 m · s⁻¹), the energy required to cover a unit distance with the water bike is similar to that required to move the paddle-wheel boat at 1.3 m · s⁻¹.

Keywords:

• Hydrodynamic resistance
• propelling efficiency
• energy cost of locomotion
• human-powered boats

Acknowledgements

The technical assistance of Franco Mazzante (Lamar, Udine) and Ciro Di Piazza is gratefully acknowledged. We also would like to thank Marco Pasianotto (Nautilago, Udine) for his support during the experiments and all the participants for their patience and kind cooperation.