The Propontis, built in 1864, was re-engined and fitted with tri-compounds and new boilers in 1874. The boilers (of the water-tube type) were a failure, and were replaced by cylindrical boilers in 1876, at a reduced pressure of 90 lb. With these she worked till 1884, when her boilers were renewed. Dr. Kirk declared “that the want of a proper boiler had delayed the introduction of the triple expansion.”
Plates of five tons in weight and upwards are in common use for boiler shells, yet in 1881 hardly a firm on the north-east coast would undertake to build a boiler for 150 lb. pressure.
The success of the triple engine resulted in many vessels being converted and fitted with new boilers, while others were re-engined.
Messrs. Palmer, in the James Joicey, fitted an interchangeable crank-shaft with the crank-pin on the centre engine, made with a coupling at each end to fit into a recess in the web. It was seen at quite an early stage of tri-compounds that the three-crank engine, with cranks at equal angles, from its easy turning moments, would be the most satisfactory, and its universal adoption in new engines was only the work of a very short time. The steamers Aberdeen and Claremont, both launched in 1881, were the first to have commercially successful triple-expansion engines.
As to how high steam-pressures may go, it is recorded that the yacht Salamander, with triple-expansion engines, had the valve set at 600 lb.
The invention of the turbine has been the most remarkable event in the modern history of the steam-engine. The following passages, taken from the Hon. C. A. Parsons’ paper on turbines, read at the Engineering Exhibition, 1906, give an account of its adoption for purposes of steam navigation:
“Turbines in general use may be classified under three principal types, though there are some that may be described as a mixture of the three types. The compound or multiple expansion type was the first to receive commercial application in 1884; the second was the single bucket wheel, driven by the expanding steam-jet, in 1888; and lastly a type which comprises some of the features of the other two, combined with a sinuous treatment of the steam in 1896. The compound type comprises the Parsons, Rateau, Zoelly, and other turbines, and has been chiefly adopted for the propulsion of ships. The distinctive features of these varieties of the compound type lie principally in design; nearly all adopt a line of flow of the steam generally parallel and not radial to the shaft. In the Parsons turbines there are no compartments: the blades and guides occupy nearly the whole space between the revolving drum and the fixed casing, and the characteristic action of the steam is equal impact and reaction between the fixed and moving blades. The chief object is to minimise the skin friction of the steam by reducing to a minimum the extent of moving surface in contact with the steam, and another, to reduce the percentage of leakage by the adoption of a shaft of large diameter and great rigidity, permitting small working clearances over the tops of the blades. The other varieties of turbines have all multicellular compartments in which the wheels or discs revolve.”
The first vessel to be fitted with a turbine engine was the little Turbinia, in 1894, and successful though she was it was found necessary in the two following years to make a number of experiments which resulted in radical changes in the design and arrangement of the machinery. The first engine tried was of the radial flow type, giving about 1500 horse-power to a single screw. A speed of only 18 knots was obtained. Several different propellers were tried with this engine, and the result not being satisfactory the original turbine engine was removed, and the engines finally adopted consisted of three turbines in series—high pressure, intermediate pressure, and low pressure—each driving a separate shaft with three propellers on each shaft. A reversing turbine was coupled with the low-pressure turbine to the central shaft. The utility of the turbine for fast speed having been demonstrated by the Turbinia, the destroyers Viper and Cobra were built and given Parsons turbines and propellers, and the Viper showed herself the fastest in the world with a speed of 36·86 knots per hour. These two vessels came to grief, through no fault, however, of the turbines.
Photo. G. West & Son.