JETBOAT

A jetboat is a boat propelled by a jet of water ejected from the back of the craft. Unlike a powerboat or motorboat that uses a propeller in the water behind the boat, a jetboat draws the water from under the boat into a pump-jet inside the boat, then expels it through a nozzle at the stern.

Jetboats were originally designed by Sir William Hamilton (who invented the waterjet in 1954) for operation in the fast-flowing and shallow rivers of New Zealand, specifically to overcome the problem of propellers striking rocks in such waters.

The difference between Campini's and Hamilton's inventions is that Campini's waterjet had a very short lifetime in operation due to some unsolved material problems. Hamilton, unlike Campini, filed for a patent.

Jet boats are highly maneuverable, and many can, from full speed , be reversed and brought to a stop within their own length, in a maneuver known as a Hamilton turn.

There is no engineering limit to the size of jet boats, though the classic prop-drive is more economical than the jet-drive. Thus, the biggest jet-driven vessels are found in military use. South Africa's Valour class frigates (approximately 120m long) are the biggest jet-propelled vessels so far. Even these German-built vessels are capable of performing the Hamilton turn.

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