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. Verf.-Referat