Originally made from wood, shells are now almost always made from a composite material (usually a double skin of carbon-fibre reinforced plastic with a sandwich of honeycomb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.
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.