A raft is any flat structure for support or transportation over water. It is the most basic type of boat design because it is characterized by the absence of a hull. Although there are cross-over boat types that blur this definition, survival rafts are usually kept afloat by using any combination of buoyant materials such as wood, sealed barrels or inflated air chambers such as pontoons. A survival raft is never powered by an engine.
A survival raft is the simplest type of boat because one can be made using low skill levels. A survival raft can hold more than one person by adding seats and it usually has two or three seats. Of course if more than one person needs to survive on a raft, they don’t necessarily need seats. But because of the low cost to make them, most people prefer to create their own seats. If you want to add more seating, then make some wooden seats and place them on your raft. A survival raft can be created by constructing a hull with two ten foot lengths of tree trunk and then lashing flatter pieces of wood together with some rope.
Traditional or primitive rafts were constructed of wood or reeds. Modern rafts may also use pontoons, drums or extruded polystyrene blocks. Inflatable survival rafts use durable multi-layered rubberized fabrics. Depending on its use and size, a survival raft may have a superstructure, masts or a rudder. Timber rafts were used by the logging industry for the transportation of logs by tying them together into rafts and then drifting or pulling them down a river. This method was very common up until the middle of the 20th century but is now used only rarely.
In biology particularly in island biogeography, non-anthropogenic rafts are an important concept. Such rafts consist of matted clumps of vegetation that has been swept off the dry land by a storm, tsunami, tide, earthquake or similar event. In modern times, a survival raft usually incorporates other kinds of flotsam and jetsam such as plastic containers. Survival rafts stay afloat because of their natural buoyancy and can travel for hundreds, even thousands of miles and be destroyed by wave action or decomposition.
Biological rafts are important means of distribution for non-flying animals such as small mammals, amphibians and reptiles and also for many invertebrates. Such rafts of vegetation are often the only means by which these life forms can reach land and if they are lucky, colonize oceanic islands before human-built vehicles provide another mode of transport.