Asynchronous Rowing

© 2001 Atkinsopht (09/29/04)

This computer modeling project began with the idea that asynchronous stroking in fours (or eights) could increase average speed through a significant reduction in the cyclical shell speed excursion. Because the power required of rowing increases as the cube of shell speed the gain realized in the low speed portion of the stroke cycle is not recovered in the high speed portion. Making the stroke period of each rower one-fourth (or one-eighth) out of phase with the others should increase efficiency by reducing shell speed excursions correspondingly.

Not so, it turns out. Confining the shell speed to its average value makes impossible the transfer of useful work to the boat through the footboard. It is as if the footboard were fixed--like that on a rowing ergometer.

The work so transferred in a free moving boat is a significant part of the total effort required to advance the shell--as ROWING shows in the summary of the work done on the shell.

ROWING made this determination by assigning an infinite inertial mass to the shell (but without altering the displacement or wetted surface). The resulting constant speed loss for an eight at 30 1/min is about two percent.

                                     Conventional  Asynchronous
                                     ------------  ------------
  Inertial mass of shell, kg            227          6030   
  Shell speed avg., m/s                   5.63          5.52
  Shell speed excursion (amplitude)       2.1           0.3
  Peak oarhandle effort, avg., N        617           617 
  Stroke rating, 1/min                   30.0          31.3
  Positive work at footboard, J *       104.8           0.5
  Total rower power, Watts              575           575
  System mechanical efficiency            0.533         0.481
                                * Contributes to advance of shell
The work lost at the footboard just about cancels the hull gain from maintaining constant speed.

See the centipede for a clever animation and some history of this concept.

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