TRANSACTIONS OF SECTION G. 845 
20 knots is only increased about 2°6 times. If the same types of engines and 
boilers had been adopted in these two vessels—which was not the case, of course— 
the weights of propelling apparatus and coal for a given distance would have been 
proportional to the respective powers ; that is to say, the larger vessel would have 
been equipped with only 2°6 times the weight carried by the smaller. On the 
other hand, roughly speaking, the disposable weights, after providing for hulls and 
fittings in these two vessels, might be considered to be proportional to their dis- 
placements. As a matter of fact, this assumption is distinctly in favour of the 
smaller ship. Adopting it, the larger vessel would have about eight times the 
disposable weight of the smaller; while the demand for propelling apparatus and 
fuel would be only 2°6 times that of the smaller vessel. There would therefore be 
an enormous margin of carrying power in comparison with displacement in the 
larger vessel. This might be devoted, and in fact was devoted, partly to the attain- 
ment of a speed considerably exceeding 20 knots (which was a maximum for the 
smaller vessel), partly to increased coal endurance, and partly to protection and 
armament. 
Another interesting comparison may be made between vessels Nos. 4 and 5 in 
the preceding table, by tracing the growth in power necessary to drive the vessels 
at speeds ranging from 10 knots up to 22 mots. 
_ No. 4 No. 5 
10 knots. : - : 1,500-horse-power 1,800-horse-power 
B35 : ‘ : ; 25004 f.5s o SOO 4%; 5 
10 en - : } : 4,000 ,, = 5,000 _ ,, ‘ 
‘a ae at ae tak sie! 6,000 ,, es BHOO! 45 i 
Ue ae é : : 9,000 5 a LO0ON 3 + 
Ces : : : : 14,000, i 15,500 ,, “3 
ers as : : ‘ : 23,000 ., cr 23,000 _ i, PR 
It will be noted that up to the speed of 18 knots there is a fairly constant 
ratio between the powers required to drive the two ships. As the speeds are 
increased the larger ship gains, and at 22 knots the same power is required in both 
ships. The smaller vessel, as a matter of fact, was designed for a maximum speed 
of 203 knots, and the larger for 22 knots. Unless other qualities had been 
sacrificed, neither space nor weight could have been found in the smaller vessel for 
machinery and coals corresponding to 22 knots, The figures are interesting, 
however, as illustrations of the principle that economy of propulsion is favoured 
by increase in dimensions as speeds are raised. 
Going a step further, it may be assumed that in unsheathed cruisers of this 
class about 40 per cent. of the displacement will be required for the hull and 
fittings, so that the balance or ‘disposable weight ’ would he about 60 per cent. ; 
say 6,€00 tons for the smaller vessel, and 8,500 tons for the larger, a gain of 
nearly 2,000 tons for the latter. If the speed of 22 kmots were secured in koth 
ships, with machinery and boilers of the same type, the larger ship would 
therefore have about 2,000 tons greater weight available for coals, armament, 
armour, and equipment. 
These illustrations of well-known principles have been given simply for the 
assistance of those not familiar with the subject, and they need not be carried 
further. More general treatment of the subject, based on experimental and 
theoretical investigation, will be found in text-books of naval architecture, but 
would be out of place in this Address. 
Swift Torpedo Vessels. 
Torpedo flotillas are comparatively recent additions to war fleets. The first 
torpedo boat was built by Mr. Thornycroft for the Norwegian Navy in 1873, and 
the same gentleman built the first torpedo boat for the Royal Navy in 1877. The 
construction of the larger class, known as ‘torpedo-boat destroyers,’ dates from 
1898. These various classes furnish some of the most notable examples extant of 
