HMS Waterwitch (1866)

Waterwitch was an armoured gunboat of the breastwork type, with a hull constructed of iron.[1] Her 4+1⁄2-inch (11 cm) armour plating was backed by 10 inches (25 cm) of teak and extended for about 60 feet (18 m) amidships.

A contemporary cut-away diagram of Waterwitch

The bottom of the armoured box extended 3 to 4 feet (0.9 to 1.2 m) below the waterline and up to the upperdeck. The forward and aft ends of the box were similarly armoured, although the front end also extended upwards by a further 5 feet 6 inches (1.7 m).[2] In addition, a waterline armoured belt extended for the whole length of the vessel. She and her two sisters were the only armoured gunboats ever built for the Royal Navy. Unlike her sisters, she was fitted with a bow rudder as well as the traditional stern rudder.[1]

She was equipped with a barquentine rig.[1]

Waterwitch was armed with two 7-inch (6½-ton) muzzle-loading rifled guns and two 20-pounder breech-loading rifled guns.[1]

Waterwitch's unique propulsion system was essentially a vast centrifugal steam-powered pump which drew water from sluices in the centre of the vessel and ejected it in jets from adjustable nozzles.[3] Two sets of nozzles were provided, one for ahead propulsion and one for astern propulsion.[2] Steam was provided by two Maudslay iron fire-tube boilers fed from six furnaces. The horizontal Ruthven "hydraulic reaction engine" was manufactured by J & W Dudgeon and comprised a wheel 14 feet 6 inches (4.4 m) in diameter weighing 8 long tons (8,100 kg) and contained within a case 19 feet (5.8 m) across.[3] The wheel was rotated by three steam cylinders and developed 780 indicated horsepower (580 kW).[1] The hopes of safety, performance and control that were expected from this propulsion were summed up by Mr. M. W Ruthven:

My efforts to make a ship safe, from an engineer's point of view, lie in the method of propulsion. My plans are to apply all the engine-power of the ship to pumps for propulsion, and which can be used for pumping out leakage and propelling at the same time. In the largest pump I have made, 800 indicated horsepower discharged 350 tons of water a minute, and propelled the vessel faster than her sister ships with twin screws. The hydraulic propeller is of greatest value for the highest speeds, and has the greatest power of control. As the hydraulic is capable of subdivision to a great degree, the greatest amount of safety is possible. After an experience of sixty years of hydraulic propulsion, I am still of opinion that it is the means by which greater safety can be obtained at sea, and by which the highest speeds can be obtained with safety and economy

— Mr M W Ruthven, son of the inventor[3]