Some raft manufacturers use urethane for the construction of inflatable boats. Skis and inflatable floats may be fitted. Balloon tanks are not true monocoques but act in the same way as inflatable shells. Inflatable life rafts provide for additional passengers and crew. Attendees gather on rafts and inflatable tubes. Harry completed an insertion training exercise using a rigid-hull inflatable boat. The wall is inflated, and looks similar to other inflatable structures. The training made use of inflatable boats and included some swimming. The alternative is a tender such as an inflatable boat. These led to the modern Zodiac inflatable boat. USN inflatable life rafts are serviced every five years. Officials resorted to using inflatable rafts to access affected areas. Lifeboats may be rigid, inflatable or rigid-inflatable combination hulled vessels. It is also an air pump such as the one used for inflatable mattresses. Koons started creating sculptures using inflatable toys in the 1970s.