APPLICATION TO VARIOUS CLASSES OF VESSELS. 201 
At the present time, two fast destroyers are nearing completion in 
England having geared turbine machinery driving two shafts. Two Channel 
steamers for the London and South Western Railway Company are also 
under construction. These ships will have two shafts, each shaft being 
driven by two fast running turbines in series connected to a double helical 
gear-wheel through pinions. (Plate 106.) 
With regard to the question of multiple shafts, the present tendency 
among certain naval authorities is to cut down the number of shafts and 
turbines in vessels of the destroyer classes. A difference of opinion appears 
to exist as to whether two, three or four shafts, are most suitable from an 
economical and a practical point of view. 
The builders of the Curtis, the Zoelly and similar types of turbines favor 
two-shaft installations, although in three large warships which have Curtis 
turbine machinery, three shafts have been adopted. 
In a two-shaft arrangement of turbine machinery, a slightly better 
propeller efficiency may be obtained as compared with three or four-shaft 
installations, but the fact should not be lost sight of that propeller efficiency 
has to go hand in hand with turbine efficiency, and increased propeller 
efficiency can only be obtained by reducing the revolutions with a certain 
sacrifice in turbine efficiency. 
There is a great deal to be said in favor of the distribution of the total 
power over several shafts, and the system of placing the turbines in series 
not only reduces the weight of the machinery and increases the propulsive 
efficiency of the steam, but improves the conditions for examination and 
overhaul carried out on board ship. 
Further, by this subdivision of power over three or four shafts the 
turbines are much smaller, the weights to be dealt with are considerably less, 
and the work of opening out is greatly facilitated. 
Contracts have recently been awarded for eight destroyers in this 
country, which are to be fitted with twin screws driven by turbines. In 
addition, all these vessels are being installed with two sets of reciprocating 
engines for cruising speeds up to 153 knots. These engines are arranged 
to exhaust into the turbines up to this speed, above which they will be 
disconnected. 
Two of these ships have turbines of the Parsons type, similar to the 
atrangement in the steam yacht Narcissus (Fig 9, Plate 103); with the 
addition of a compound reciprocating engine at the forward end of low 
pressure turbine shaft for cruising speeds up to 16 knots. 
At the present time there are only two battleships being constructed 
with twin sets of reciprocating engines, namely the U. S. S. New York and 
U.S. S. Texas. 
