Marathon competition is conducted in divisions; the lower divisions can use any sort of kayak (or canoe in canoe classes) but higher divisions use specialised marathon boats, long, narrow and VERY unstable when stationary! Kayaks can also be single (K1) or double (K2) and occasionally even K4; marathon canoes are also narrow and involve the paddler kneeling on one knee whilst paddling with a single-bladed paddle; again, classes are held for C1 and C2.
Ben Jones in action at Wolfreton Marathon