These vessels are of approximately the same dimensions as the thirty-knot destroyers now in her Majesty’s service, but have slightly more displacement. The boilers are about twelve per cent larger, and it is estimated that upward of ten thousand horse power will be realized under the usual conditions, as against sixty-five hundred with reciprocating engines.
The engines of these vessels are in duplicate. Two screw shafts are placed on each side of the vessel, driven respectively by a high- and a low-pressure turbine; to each of the low-pressure turbine shafts a small reversing turbine is permanently coupled for going astern, the estimated speed astern being fifteen knots and a half, and ahead thirty-five knots; two propellers are placed on each shaft.[G]
[G] On her second trial trip the Viper attained a mean speed of 34.8 knots, her fastest trial being over 35 knots, or about 41 statute miles per hour, with an indicated horse power of 11,000. This vessel is of about 350 tons displacement.
The latter of these two vessels has commenced her preliminary trials, and has already reached a speed of thirty-two knots. The manipulation of the engines is a comparatively simple matter, as to reverse it is only necessary to close one valve and open another, and, owing to there being no dead centers, small graduations of speed can be easily made.
In regard to the general application of turbine machinery to large ships, the conditions appear to be more favorable in the case of the faster class of vessels such as cross-Channel boats, faster passenger vessels, cruisers, and liners; in such vessels the reduction in weight of machinery, as well as economy in the consumption of coal per horse power, are important factors in the case, and in some vessels the absence of vibration, both as regards the comfort of passengers, and in the case of ships of war permitting greater accuracy in sighting of the guns, is a question of first importance.
As regards cross-Channel boats, the turbine system presents advantages in speed, absence of vibration, and, owing to the smaller diameter of the propellers, reduced draught.
As an instance, a boat of two hundred and seventy feet length, thirty-three feet beam, one thousand tons displacement, and eight feet six inches draught of water could be constructed with spacious accommodation for six hundred passengers, and with machinery developing eighteen thousand horse power; she will have a sea speed of about thirty knots, as compared with the speed of nineteen to twenty-two knots of the present vessels of similar size and accommodation.
It is, perhaps, interesting to examine the possibilities of speed that might be attained in a special unarmored cruiser, a magnified torpedo-boat destroyer of light build, with scanty accommodation for her large crew, but equipped with an armament of light guns and torpedoes. Let us assume that her dimensions are about double those of the thirty-knot destroyers, with plates of double the thickness and specially strengthened to correspond with the increased size—length, four hundred and twenty feet; beam, forty-two feet; maximum draught, fourteen feet; displacement, twenty-eight hundred tons; indicated horse power, eighty thousand; there would be two tiers of water-tube boilers; these, with the engine space, coal bunkers, etc., would occupy the whole of the lower portion of the vessel; the crew’s quarters and guns would be on the upper decks. There would be eight propellers of nine feet in diameter revolving at about four hundred revolutions per minute, and her speed would be about forty-four knots.
She could carry coal at this speed for about eight hours, but she would be able to steam at from ten to fourteen knots with a small section of the boilers more economically than other vessels of ordinary type and power, and, when required, all the boilers could be used, and full power exerted in about half an hour.
In the case of an Atlantic liner or a cruiser of large size, turbine engines would appear to present some considerable advantages. In the first place they would effect a reduction in weight of machinery and some increase in economy of fuel per horse power developed, both thus tending either to a saving in coal on the one hand, or, if preferred, some increase in speed.