Although the oar can be conveniently thought of as a lever with a "fixed" pivot point in the water, the blade moves sideways and sternwards through the water, so that the magnitude of the propulsion force developed is the result of a complex interaction between unsteady fluid mechanics (the water flow around the blade) and solid mechanics and dynamics (the handle force applied to the oar, the oar's inertia and bending characteristic, the acceleration of the boat and so on).
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.