The table on the left gives the speed of waves of different wave lengths in deep water. “Deep” in this context is not an absolute value, but is relative to wave length. The simple relationship starts to to breakdown when the depth of the water is less than 1/4 th the wave length. At that depth the bottom exerts sufficient drag on the wave to slow its motion and thus decrease the wavelength [equations and more about wave speed].
In the empty-lung technique, rowers inhale during the drive, and exhale during the recovery so that they have empty lungs at the catch. Because the knees come up to the chest when the lungs are empty, this technique allows the rower to reach a little bit further than if the lungs were full of air. Full lungs at the release also can help the rower to maintain a straighter back, a style encouraged by many coaches.
Outside of resistance type, we found the number-one arbiter of ride feel to be cord quality. Water ergometers tend to employ nylon cords, while air ergometers feature metal chains — a durability factor we anticipated would result in our favoring air. But while all three water rowers aced our expectation of smooth, high-tension strokes, perfecting the chain seems to be more difficult: Some tug with just a slight rumble, others feature bouncy, grinding chains that are incredibly loud, something akin to angry snoring. As for nylon, the best wind and unwind like elastic silk — no slack, no sound, no catching, just perfectly even tension throughout the stroke.