A raft is any kind of structure that is able to float. The raft is the simplest boat design that was used by several cultures and ancient societies. This embarkation does not have a hull but not all of them, the only characteristic that all of them have is that they use a floating material, such as: wood or inflated air chambers, that allows it to float.
Rafts are not supposed to have an engine but as said before people use the embarkation as they like, so some of this do use an engine, like the life guard boats (inflatable).
The raft in the history was made of different basic materials, such as: reeds and wood. These days rafts are no longer made from basic materials, instead of that they are now made of several modern materials such as: drums, pontoons or extruded polystyrene blocks. They also can be built with durable materials, can have a mast or have rudders depending of the use that the raft is going to have.
You can also search a boat at any part of it.