I’m a rower but with only a very loose understanding of the physics. My understanding of why you actually want the ‘peaks’ is because there’s a point at which

I’m a rower but with only a very loose understanding of the physics. My understanding of why you actually want the ‘peaks’ is because there’s a point at which you have to drop the blade back into the water to begin the new stroke. I’d guess you need to do that at the trough of the cycle in order cause the least disruption to the free speed generated. From experience it’s also definitely true that for a boat to be balanced it’s absolutely essential the rowers move in sync.