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 below or behind the boat, a jetboat draws the water from under the boat into a pump inside the boat, then expels it through a nozzle at the stern.
Jetboats were originally designed by Sir William Hamilton (who developed a 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.
Jetboats are highly maneuverable, and many can, from full speed, be reversed and brought to a stop within little more than their own length, in a maneuver known as a “crash stop”. The well known Hamilton turn or “jet spin” is a high-speed maneuvre where the boat’s engine throttle is cut, the steering is turned sharply and the throttle opened again, causing the boat to spin quickly around with a large spray of water.
One of the most significant breakthroughs, in the development of the waterjet, was to change the design so it expelled the jetstream above the water line, contrary to many people’s intuition. Hamilton discovered early on that this greatly improved performance, compared to expelling below the waterline, while also providing a “clean” hull bottom (i.e. nothing protruding below the hull line) to allow the boat to skim through very shallow water. It makes no difference to the amount of thrust generated whether the outlet is above or below the waterline, but having it above the waterline reduces hull resistance and draught. Hamilton’s first waterjet design had the outlet below the hull and actually in front of the inlet. This probably meant that disturbed water was entering the jet unit and reducing its performance, and the main reason why the change to above the waterline made such a difference.
Queenstown, New Zealand, where jetboats are used extensively for adventure tourism, claims to be the jetboat capital of the world, and jetboats are very common for many coastal and riverine tourism activities in the country, such as the Excitor in the Bay of Islands.
[caption id="attachment_161937" align="aligncenter" width="418"] Jakob Fugger (1459–1525) by Albrecht Dürer[/caption][responsivevoice_button voice="UK English Female" buttontext="Listen to this Post"]The Fugger family is a German family that was a historically prominent group of European bankers, members of the fifteenth and sixteenth-century mercantile patriciate of Augsburg, international mercantile bankers, and venture capitalists. Alongside the Welser family, the family controlled much of the European economy in the sixteenth century and accumulated enormous wealth. This banking family ...
