The official boats recognised by the ICF as 'International Boats' are the following: 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 steeringrudder, which is operated by the (frontmost) paddler with his feet; in a kayak a paddler is sitting, while in a canoe he is kneeling on one knee. 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 fury of innovations in boat designs. Modern boats are usually made ofcarbon fiberand/oraramid fiber(e.g.,Kevlar) withepoxy resin.