The modern raft is an inflatable boat, consisting of very durable, multi-layered rubberized (hypalon) or vinyl fabrics (PVC) with several independent air chambers. The length varies between 3.5 m (11 ft) and 6 m (20 ft), the width between 1.8 m (6 ft) and 2.5 m (8 ft). The exception to this size rule is usually the packraft, which is designed as a portable single-person raft and may be as small as 1.5 metres (4.9 ft) long and weigh as little as 4 pounds (1.8 kg).
Rafts come in a few different forms. In Europe and Australasia, the most common is the symmetrical raft steered with a paddle at the stern. Other types are the asymmetrical, rudder-controlled raft and the symmetrical raft with central helm (oars) or Stern Mounts with the oar frame located at the rear of the raft. Rafts are usually propelled with ordinary paddles and or oars and typically hold 4 to 12 persons. In Russia, rafts are often hand made and are often a catamaran style with two inflatable tubes attached to a frame. Pairs of paddlers navigate on these rafts. Catamaran style rafts have become popular in the western United States as well, but are typically rowed instead of paddled.
Grades of white water
Grade 1: Very small rough areas, might require slight maneuvering. (Skill Level: Very Basic)
Grade 2: Some rough water, maybe some rocks, might require some maneuvering. (Skill level: basic paddling skill)
Grade 3: Whitewater, small waves, maybe a small drop, but no considerable danger. May require significant maneuvering. (Skill level: experienced paddling skills)
Grade 4: Whitewater, medium waves, maybe rocks, maybe a considerable drop, sharp maneuvers may be needed. (Skill level: whitewater experience)
Grade 5: Whitewater, large waves, large volume, possibility of large rocks and hazards, possibility of a large drop, requires precise maneuvering. (Skill level: advanced whitewater experience)
Grade 6: Class 6 rapids are considered to be so dangerous as to be effectively unnavigable on a reliably safe basis. Rafters can expect to encounter substantial whitewater, huge waves, huge rocks and hazards, and/or substantial drops that will impart severe impacts beyond the structural capacities and impact ratings of almost all rafting equipment. Traversing a Class 6 rapid has a dramatically increased likelihood of ending in serious injury or death compared to lesser classes. (Skill level: successful completion of a Class 6 rapid without serious injury or death is widely considered to be a matter of great luck or extreme skill)
Reference: Wikipedia White Water Rafting