Why sliding seats and short stroke intervals are used for racing shells.

A theory is developed to explain why racing shell crews use sliding seats and shorter-than-necessary stroke intervals, two features that tend to waste energy in a highly competitive, power-limited situation. The theory shows that sliding seats are used because they allow the crew to move the oar blades fast enough during the stroke to transfer all available power to the water. Shorter-than-necessary stroke intervals are used to minimize the sum of the power dissipated in developing thrust, which decreases with the relative length of the stroke interval, and the power dissipated in hull drag due to fluctuations about average velocity, which increases with the relative length of the stroke interval. Using representative dimensions and masses, a typical value of average velocity for a race, and independently estimated values of drag and thrust coefficients, the theory predicts an optimum stroke fraction of 0.400, and optimum stroke rate of 45 per min, and an accountable power of 0.46 hp/man for an eight-oar racing shell, values that agree remarkably well with those used under competitive racing conditions. The theory indicates that using wider-bladed oars might improve performance; the theory also supports a suggestion made to the writer by R. A. Swanson that crossing the oars over the shell would improve performance.