There are many differing sets of rules governing racing, and these are generally defined by the governing body of the sport in a particular country—e.g., British Rowing in England and Wales, Rowing Australia in Australia, and USRowing in the United States. In international competitions, the rules are set out by the world governing body, the Fédération Internationale des Sociétés d'Aviron (FISA). The rules are mostly similar but do vary; for example, British Rowing requires coxswains to wear buoyancy aids at all times, whereas FISA rules do not.
Head races are time trial / processional races that take place from autumn (fall) to early spring (depending on local conditions). Boats begin with a rolling start at intervals of 10 – 20 seconds, and are timed over a set distance. Head courses usually vary in length from 2,000 metres (1.24 mi) to 12,000 metres (7.46 mi), though there are longer races such as the Boston Rowing Marathon and shorter such as Pairs Head.
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.