Early pump jets

[ceccherini]

While searching the history of naval jet propulsion I was surprised to find that full scale experiment were conducted from mid XIX century, when mechanical propulsion itself was still a pioneering technology. An inventor named M W Ruthven proposed to employ a centrifugal pump to propel a ship and the Royal Navy built in 1867 the HMS Waterwitch, a 1280 ton gun boat, to test the concept. It resulted viable reaching a speed of 8,9 knots (against somewhat more than 9 knots of a ship with identical displacement and power but equipped with a traditional propeller) and shown impressive reverse speed, nearly equal to ahead speed and some maneuverability advantages. At the same time the full speed was inferior to that of conventional designs while complexity was far higher and the flow of water inside the hull increasing displacement was also a major concern. This failure is ascribable to two main causes: 1- turbines in general have efficiency advantages at high rotation speed, the power requirements of early steamship was just too limited to take advantage of this kind of technology; 2-the centrifugal pump is not optimal for ship propulsion. Interesting enough it was proposed to substitute the centrifugal pump with an axial one as early as the tests of were deemed a failure, never being implemented . This technology only resurfaced in the second half of the XX century. Even if interest in pump jet as a way to increase propulsion efficiency waned for about a century, in the meantime some applications of the technology were still considered potentially useful. I found some scarce notes in the D K Brown's volume "The Grand Fleet" about pre Ww1 research to employ pumpjet to provide submarines increased maneuverability and a Ww1 research to provide antisubmarine vessels whit a silent propulsion method. Has any of you any more information about these most interesting WW1 era developments?