Propulsive Efficiency of Rowing Oars

Is the common folklore, that oars are less efficient at propulsion than propellers, correct? Here we examine the propulsive efficiency of the oars used in competitive rowing. We take the propulsive efficiency η of rowing to be the ratio of the energetic benefit, the energy Db dissipated by boat drag, to the energetic cost, the work Wr performed by the rower. Air drag is neglected as is the energetic cost of raising and lowering the oar out of and into the water. We calculate η first by directly using extensive data from an instrumented single scull and again using less data and extrapolating on the basis of a simple rowing model. From the data, we estimate that η ≈ 0.84. That is, about 84% of the rower’s energy dissipated during a stroke is due to boat drag and the remaining 16% of the energy dissipated is due to oar drag. The best marine propellers have efficiencies of about 80%. We also point out some subtleties in energetic calculations in rowing, discuss the essential differences between oars and propellers, and discuss how oars might be made still more efficient.