Slalom racers are timed in completing a descent down the rapids of a whitewater course, in the process steering their canoes or kayaks through "gates" (a pair of suspended poles about 1 m apart), including going up against the flow, across the flow, and surfing the standing waves of the rapids. Classes include K1, C1, and C2.
The official boats recognised by the ICF as 'International Boats' are: K1, K2, K4, C1, C2 and C4, where the number indicates the number of paddlers, “K” stands for kayak and “C” for Canadian or canoe, depending on location. Kayaks have a rudder, which is operated by the feet of the frontmost paddler. The ICF rules for these boats define, among others, the maximum length, the minimum weight and the shape of the boats. For example, by ICF rules, a K1 is at most 520 cm long, and weighs at least 8 kg for marathons or 12 kg for sprints. In 2000, after the Olympic Games in Sydney, the ICF withdrew width restrictions on all boats, spurring a flurry of innovations in boat designs. Modern boats are usually made of carbon fiber and/or aramid fiber (e.g., Kevlar) with epoxy resin.
Paddles for propelling are double-bladed for kayaks, and single-bladed for canoes, and are usually made of carbon fiber with epoxy. For kayaks so-called wing paddles are generally used, the blades of which are shaped to resemble a wing or spoon. The wing blade has undergone many evolutions in the past two decades, evolving from a flatter blade to one with a more pronounced curve to better catch the water. For racing canoes, the blade is typically short and broad, with a 'power face' on one side that is either flat or scalloped out. The shaft will typically be longer than a tripping canoe paddle, because the kneeling position puts the paddler higher above the surface of the water. More recent designs of canoe racing paddles often have a slight bent shaft (a concept of Gene Jensen in the 1950s) but not to the degree used in marathon paddles. Many high-performance canoe paddlers prefer the feel of a carbon-fibre shaft mated to a wooden blade, while nearly all high-performance kayak paddlers use paddles made completely of carbon fiber.