An inflatable boat is a lightweight boat constructed with its sides and bow made of flexible tubes containing pressurised gas. For smaller boats, the floor and hull is often flexible, while for boats longer than 3 metres (9.8 ft), the floor typically consists of three to five rigid plywood or aluminium sheets fixed between the tubes, but not joined rigidly together. Often the transom is rigid, providing a location and structure for mounting an outboard motor.