Experimental Jet-Propelled Ironclad Gunboat (1866)
Waterwitch was said to handle wretchedly under sail; here heroically depicted in the Illustrated London News of Nov. 17, 1866. The water jet can be seen foaming out its discharge pipe below the mainmast. Enlarge
The Waterwitch was part of Britain's 1860s experimental trio, the Viper, the Vixen, and the Waterwitch. These were all experimental vessels of one kind or another, and all made to trial different forms of propulsion. The Vixen and Viper were the first twin-screw ships in the Royal Navy, but the Waterwitch was a different proposition altogether. She was equipped with the Ruthven impeller -- water turbines fed by a set of powerful hydraulic pumps that would shoot high-pressure jets of seawater from her hull, making her an early jet-propelled ship; Ruthven had patented the idea in 1849. The jets were called hydraulic propellers in their day, and were controlled by adjustable nozzles (see description below).
Waterwitch's hull and fittings were constructed at Thames Iron Works; her great water turbines at Dudgeon's. The hydraulic system worked well within limitations; the ship moved. Her maximum speed was 9.25 kts, however, making her not really suitable as a warship in a time when a great speed was 14-15 knots; her sisters were half a knot slower with conventional screws alone, but not as neatly maneuverable as Waterwitch. Once the ship was tried, improvements immediately suggested themselves in the placement of her jets. It was seen that full power to get her to high speed would take up all the remaining space; the amount of space occupied by the propulsion plant was one issue with this motive power scheme. Additional features trialed included turning radius at different speeds; the three ships worked Stokes Bay on the Solent through the late 1860s trying different rigs and tweaks of their machinery. In 1869, Vixen and Viper were dispatched to Bermuda, bringing a large floating dock across for the naval station there; they served as harbor work vessels, ending as accommodation hulks in the 1890s. After 25 years as a test bed, Waterwitch was sold out of the service in 1890; her two sisters followed her in 1895. The Vixen was sunk as a blockship at Hamilton's Channel, where she can still be seeen today. Glass-bottom boats and divers visit her wreck to delight in the rich marine life living in her sheathed-iron remains. One of her 7-in guns is still displayed in St. George's. Waterwitch gave up her name to a famous survey ship, the wooden hydrographic ship Waterwitch of 1892 (left), a familiar sight in Australian and Asian ports for several decades.
Although the steam-powered equipment of the 1860s was not sufficiently powerful to make a competitive powerplant, jet propulsion's feasibility was proven by the Waterwitch. Many years later, with the advent of high-speed electric pumps, it became a practical propulsion system and is now in use particularly on tugs. Water jets can be aimed and shot in different directions, making the boats extremely maneuverable in tight spots. For this reason, pressure jets have been installed on a number of large screw-propelled cruise liners to assist in docking.
How the Propulsion Worked
A contemporary account of how the propulsion system worked:
She was flat-bottomed, broad in proportion to her length, and double-ended and had a rudder at each end. Her armour consisted of a belt of plating 4½ inches in thickness at the water-line and centrally on her broadside, with armour-plated bulkheads across her upper deck, the object of the latter arrangement being to enable her to fight her guns over her deck in line with her keel, through gunports in the thwartship bulkheads as well as through broadside ports. For the machinery, and in the bottom of the vessel near the centre, was a long and shallow iron box with its length in the direction of the vessel. The lower side of this box had an immense number of small rectangular orifices, admitting water from outside and under the ship's bottom, the passage of the water being controlled by valves which were only opened when the engines were at work. The turbine wheel drew the water in through the bottom of the vessel and ejected it through copper proulsion pipes and nozzles, through an aperture on each side of the ship, a little below the water-line.
The propelling power of the hydraulic wheel is obtained from the force and volume of the column of water ejected by the wheel from the discharge pipes, on a principle that a gun recoils on being discharged, but with this difference, that the recoil from the water-wheel is continuous. If the column of water were discharged towards the stern the vessel moved forward, and if towards the stem it moved in the other direction; if discharged in both directions the vessel remained stationary, and if discharged forward on one side and towards the stern on the other, the vessel turned either on her centre as on a pivot, or if the pressure were greater in one direction than in the other, in a circle the size of which depended on the pressure of the discharge from either set of nozzles. No reversing of the engines or of the hydraulic wheel was required under any circumstances, the direction and force of the discharge being regulated by a series of valves.
The hydraulic wheel was fixed immediately over the sluice valves and water-box, and revolved in a cast-iron circular case 19 feet in diameter. The wheel was itself 14 feet 6 inches in diameter and weighed eight tons, and was fitted with eleven vertical or radial arms and blades. The engines were of 160 nominal horse-power, and steam was supplied by two ordinary tubular boilers. At her trial the Waterwitch covered the measured mile in Long Reach in 6 minutes 20 seconds. At other trials later in the day she averaged 9 knots.
The shape of the vessel and the fact that she could be steered in either direction with equal facility were of undoubted advantage from the point of view of manoeuvring, but the trials can hardly be called successful so much as experimental, as it was ascertained that she would probably have done better had her nozzles been differently placed and provision made for altering the size of the nozzles according to the speed at which the vessel was required to travel. The machinery itself, however, worked beautifully.
The Government ordered a number of comparative tests to be made in which the efficacy of the Waterwitch method could be judged against that of the double-screw system installed in the gunboats Viper and Vixen, all three vessels being of the same size. The two gunboats were not the best of their kind as they had double sternposts with a cavernous recess between them and flat overhanging sterns.
Mr. M.W. Ruthven, son of the inventor of the system, it being under his father's patent that the Waterwitch machine was built, in addressing the Institute of Marine Engineers a few years ago, said:
"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."
Plan and Specifications
Green areas indicate armor protection. Dotted outlines at ends indicate rudders.
Specifications for the Waterwitch:
Dimensions: 162' x 32' x 13'9" Displacement: 780 tons. Armament: (2) 7" 6½-ton RML, (2) 20-pdr BLR. Hull: Composite. Iron hull with 5½" teak sheathing over entire hull. Armor: Wrought-iron type. 4.5" belt and bulkheads, backed by 10" teak. Propulsion: Steam power provided to pumps by two Maudslay iron fire-tube boilers with six furnaces. Sail plan: 3-mast barquentine rig. Crew: 80. Speed: 9.25 kts. Cost: £67,000 at 1866 valuation.
Dimensions: 49m x 9.8m x 3.4m Displacement: 780 tons. Armament: (2) 7" 6½-ton RML, (2) 20-pdr BLR. Hull: Composite. Iron hull with 5½" teak sheathing over entire hull. Armor: Wrought-iron type. 11 cm belt and bulkheads, backed by 25 cm of teak. Propulsion: Steam power provided to pumps by two Maudslay iron fire-tube boilers with six furnaces. Sail plan: 3-mast barquentine rig. Crew: 80. Speed: 17.13 km/hr Cost: £67,000 at 1866 valuation.
Pictures of Ruthven's Witchcraft
Waterwitch at anchor, c. 1867.
Detailed plans of Waterwitch's hydraulic pumps, from the Illustrated London News. Enlarge
Waterwitch tied up at Greenwich in 1870. All her yards are crossed.
A rare view on deck.