(HMS Waterwitch via David S. Yetman)
During the 1860s, the Royal Navy experimented with new types of warships to replace the aging generation of screw-propelled steamships. Among them was the 1,160-ton HMS Waterwitch. This ship used a novel form of propulsion: water jets.
This system was known as the Ruthven impeller--a water turbine invented by Scottish engineer Morris West Ruthven. The impeller measured 14.5 feet across and weighed 8 tons. It rotated on a vertical axis inside a chamber 19 feet across. Two water jet nozzles opening just below the waterline fed water into the chamber. Two 160-horsepower steam engines powered the pumps which sucked water through the nozzles and into the impeller chamber.
(The water turbine on the Waterwitch, via Albert E. Seaton’s The Screw Propeller)
Because of its design, the Waterwitch could theoretically move forward or reverse at equal speed simply by reversing the jets. There was a rudder at the bow as well at the stern, so it could also control its movement in reverse. This could be helpful when attempting to ram an enemy ship, so the Waterwitch was equipped with armored rams at both ends.
The Waterwitch engaged in sea trials in 1867. Unfortunately, it proved to be slow and could reach a speed of only 9.23 knots. In reverse, it could move 7.9 knots, which was not bad, but did not live up to expectations. The Waterwitch also proved to be difficult to maneuver.
A Royal Navy panel assembled to examine the Waterwitch concluded that the design was a failure because it was difficult to draw water into the inlet of the pump and the water that was taken on board increased the weight of the ship. Also, the system experienced power losses due to bends in the water passages and friction from the water going through those passages.
Naval architect Albert E. Seaton argues that the Waterwitch might have moved faster if it had heavier boilers, larger water passages and a bigger chamber for the impeller. But this, of course, would have made the ship heavier.
Consequently, the Waterwitch’s innovations were not put to broader use. The ship was struck in 1887 and scrapped in 1890.