Synchronystic rowing for speed

The Quick Study about rowing (Physics Today, June 2017, page 82 ) by Jean-Philippe Boucher, Romain Labbé, and Christophe Clanet was interesting, but I think the authors missed the real answer to their question. To understand why rowing in sync is faster than rowing asynchronously, consider the authors’ plot of velocity versus time. As the boat speed increases, the exertion of a given force by the rowers becomes increasingly difficult and the stroke time decreases; as a result, the per-stroke momentum imparted to the boat decreases. By reducing the boat speed during most of the stroke, synchronized rowing increases the effective power output of the rowers and thus raises the average speed.

I experienced the phenomenon during my brief time with the freshman crew at MIT in 1969: The faster the boat is going, the harder it is to pull effectively on the oar and the shorter the duration of the power stroke.