An innovation of great interest to designers and users of high-speed boats that was introduced in the 1970s is the surface-piercing propeller, in which the propeller is mounted with its center at the water surface. It is most commonly seen in the form called the Arneson surface drive. The drive shaft projects through the stern of the boat, supported by two hydraulic cylinders that adjust the vertical position of the propeller, a feature of great importance because the angle and level of the boat change as the boat speed changes. The engine is fixed in its position, but two universal joints accommodate changing shaft angles.
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