Originally made from wood, shells are now almost always made from a composite material (usually a double skin of carbon-fibre reinforced plastic with a sandwich of honeycomb material) for strength and weight advantages. FISA rules specify minimum weights for each class of boat so that no individual team will gain a great advantage from the use of expensive materials or technology.
John Duke, creator of the WaterRower, was inspired to try his hand at invention while working at a subsidiary for U.S. Steel. He wanted to make an indoor machine that felt as much like real rowing as possible, with a focus on aesthetics. It took him two years to get the design right, moving past failed ideas such as a flipper in the tank instead of a clutch. What began as a series of doodles at his desk turned into a sculptural piece of exercise equipment that upends expectations in two ways: by bringing water indoors, and by looking elegant and artful when stored.
Ergometer rowing machines (colloquially ergs or ergo) simulate the rowing action and provide a means of training on land when waterborne training is restricted, and of measuring rowing fitness. Ergometers do not simulate the lateral balance challenges, the exact resistance of water, or the exact motions of true rowing including the sweep of the oar handles. For that reason ergometer scores are generally not used as the sole selection criterion for crews (colloquially "ergs don't float"), and technique training is limited to the basic body position and movements. However, this action can still allow a comparable workout to those experienced on the water.
Fitness experts as well as health professionals agree that rowing machines provide one of the best workouts possible. Exercising on a rower will allow you to target the great majority of your muscle groups and give them as hard and challenging a workout as you feel like giving them. On the better rowing machine models, you’ll be able to track your progress and see how your splits are improving.
Water rowers feature a tank that is actually filled with water as a means for resistance. As you increase the pace of rowing, the resistance naturally increases as well. This means that you can set your own pace and resistance in a single motion. The same is true for air rowers. Air rowers use a fan or flywheel to create resistance, and you have control over the intensity of the workout due to the fact that the air resistance depends on your pace. Most water and air rowers come equipped with -- or at least have as an option -- monitors that track various functions such as distance, strokes, strokes per minute and calories burned.

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.