Rowing is a cyclic (or intermittent) form of propulsion such that in the quasi-steady state the motion of the system (the system comprising the rower, the oars, and the boat), is repeated regularly. In order to maintain the steady-state propulsion of the system without either accelerating or decelerating the system, the sum of all the external forces on the system, averaged over the cycle, must be zero. Thus, the average drag (retarding) force on the system must equal the average propulsion force on the system. The drag forces consist of aerodynamic drag on the superstructure of the system (components of the boat situated above the waterline), as well as the hydrodynamic drag on the submerged portion of the system. The propulsion forces are the forward reaction of the water on the oars while in the water. Note also that the oar can be used to provide a drag force (a force acting against the forward motion) when the system is brought to rest.
Major domestic competitions take place in dominant rowing nations and include The Boat Race and Henley Royal Regatta in the United Kingdom, the Australian Rowing Championships in Australia, the Harvard–Yale Regatta and Head of the Charles Regatta in the United States, and Royal Canadian Henley Regatta in Canada. Many other competitions often exist for racing between clubs, schools, and universities in each nation.
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.
Some rowing enthusiasts claim that the disproportionate number of tall rowers is simply due to the unfair advantage that tall rowers have on the ergometer. This is due to the ergometer's inability to properly simulate the larger rowers drag on a boat due to weight. Since the ergometer is used to assess potential rowers, results on the ergometer machine play a large role in a rower's career success. Thus, many erg scores are weight-adjusted, as heavyweights typically find it easier to get better erg scores. Also, since crew selection has favored tall rowers long before the advent of the ergometer, and bigger, taller crews are almost universally faster than smaller, shorter crews on the water, being tall is a definite advantage ultimately having little to do with the ergometer.
The rowing machine itself is unlike any other on the market with its patented water filled flywheel. It is hard to exactly copy the action of a scull on the water, but the mechanics of the flywheel spinning in water comes in a close second on dry land. The fact that the water is 800 times denser than air means that there is no need for any extra resistance or dampening that you will find in normal air rowers. The faster you pull, the more resistance is generated giving it infinite variability. However, if you want to be able to practice rowing with a faster stroke, you will have to reduce the amount of water in the tank unlike an air rower where you just have to adjust the baffle.