SEPTEMBER 28, 1899 | 
WA TU Ris 
53! 
any facts for these vessels, or to compare them with results 
obtained by similar classes of ships in the Royal Navy. 
Apart from full knowledge of the conditions under which 
speed trials are made, a mere statement of speeds attained 
is of no service. One requires to be informed accurately 
respecting the duration of the trial, the manner in which 
engines and boilers are worked, the extent to which boilers are 
“*forced,” or the proportion of heating surface to power in- 
dicated, the care taken to eliminate the influence of tide or 
current, the mode in which the observations of speed are made, 
and other details, before any fair or exact comparison is possible 
between ships. For present purposes, therefore, it is preferable 
to confine the illustrations of increase in speed in warships to 
results obtained under Admiralty conditions, and which are 
fairly comparable. 
A great increase in size has accompanied this increase in 
speed, but it has resulted from other changes in modern types, 
as well as from the rise in speed. Modern battleships are of 
13,000 to 15,000 tons, and modern cruisers of 10,000 to 14,000 
tons, not merely because they are faster than their predecessors, 
but because they have greater powers of offence and defence 
and possess greater coal endurance. Only a detailed analysis, 
which cannot now be attempted, could show what is the actual 
influence of these several changes upon size and cost, and how 
greatly the improvements made in marine engineering and ship- 
building have tended to keep down the growth in dimensions 
consequent on increase in load carried, speed attained, and 
distance traversed. 
It will be noted also that, large as are the dimensions of many 
classes of modern warships, they are all smaller in length and 
displacement than the largest mercantile steamers above de- 
scribed. There is no doubt a popular belief that the contrary is 
true, and that warships exceed merchant ships in tonnage. This 
arises from the fact that merchant ships are ordinarily described, 
not by their displacement tonnage, but by their ‘‘ registered 
tonnage,” which is far less than their displacement. As a matter 
of fact, the largest battleships are only of about two-thirds the 
displacement of the largest passenger steamers, and from 200 to 
300 feet shorter. The largest cruisers are from 100 to 200 feet 
shorter than the largest passenger steamers, and abeut 60 per 
cent. of their displacement. In breadth. the warships exceed the 
largest merchant steamers by 5 to 10 feet. This difference in 
form and proportions is the result of radical differences in the 
vertical distribution of weights carried, and is essential to the 
proper stability of the warships. Here we find an illustration 
of the general principle underlying all ship-designing. In 
selecting the forms and proportions of a new ship, consider- 
ations of economical propulsion cannot stand alone. They 
must be associated with other considerations, such as stability, 
protection and manceuvring power, and in the final result 
economy of propulsion may have to be sacrificed, to some 
extent, in order to secure other essential qualities. 
Advantages of Increased Dimensions. 
Before passing on, it may be interesting to illustrate the gain 
in economy of propulsion resulting from increase in dimensions by 
means of the following table, which gives particulars of a 
number of typical cruisers, all of comparatively recent design :— 
No.2 | No.3 | No.4 | No.5 
| ie = 
Length (feet) a PA 280) 300 | 360 | 435 | 500 
Breadth (feet) cer pale #35| Mas | 60 69 71 
Mean draught (feet) w=] 33|) TOR Meget = 2a 26} 
Displacement (tons) |II,000 14,200 
Indicated horse-power for } 
20 knots... : ... 6000) 9000 |II,000 |14,000 15,500 
Indicated horse-power per | 
ton of displacement ...| 3°33] 2°65 | 1°48 | 1°27 1°09 
The figures given are the results of actual trials, and embody 
therefore the efficiencies of propelling machinery, propellers and 
forms of the individual ships. Even so they are instructive. 
Comparing the first and last, for example, it will be seen 
that, while the displacement is increased nearly ezgh¢fold, the 
power for 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 
NO. 1561, VOL. 60] 
weights of propelling apparatus and coal fora 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 désposable werghts, after providing 
for hulls and fittings in these two vessels, might be considered 
to be proportional to their displacements. As a matter of fact, 
this assumption is distinctly in favour of the smaller ship. 
Adopting it, the larger vessel would have about ezgh¢ times the 
disposable weight of the smaller ; while the demand for pro- 
pelling apparatus and fuel would be only 2°6 ¢zes 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 attainment 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 knots. 
No. 4 | No. 5 
i= 
to knots I,500-horse-power | 1,800-horse-power 
[250 BusOO Mas 143) | "(I MBRTOOR ES MMs 
es ASOO0) %5) 1755) |) | 45,0000 1 ss 
16 ”? 6,000 +B] 2? | 73500 ”? a> 
18 2? 9,000 ” ” 11,000 99 tA 
20 ” 14,000 2” ” 15,500 > ” 
22 23,000 ;, ” | 23,000 ;, » 
| 
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 204 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, how- 
ever, 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 4o per cent. of the displacement will 
be required for the hull and fittings, so that the balance or 
‘« disposable weight”? would be about 60 per cent. ; say 6600 
tons for the smaller vessel, and $500 tons for the larger, a gain 
of nearly 2000 tons for the latter. If the speed of 22 knots 
were secured in both ships, with machinery and boilers of the 
same type, the larger ship would therefore have about 2000 
tons greater weight available for coals, armament, armour and 
equipment. its ; 
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 investiga- 
tion, will be found in text-books of naval architecture, but would 
be out of place in this Address. 
Sweft 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 construc: 
tion of the larger class, known as ‘‘torpedo-boat destroyers, 
dates from 1893. These various classes furnish some of the 
| most notable examples extant of the attainment of extraordi- 
| narily high speeds, for short periods and in smooth water, by 
vessels of small dimensions. Their qualities and performances, 
therefore, merit examination. 3 : 3 
Mr. Thornycroft may justly be considered the pioneer in this 
class of work. Greatly impressed by the combination of light- 
ness and power embodied in railway locomotives, Mr. Thorny- 
croft applied similar principles to the propulsion of small boats, 
and obtained remarkably high speeds. His work became more 
widely known when the results were published of a series of 
trials conducted in 1872 by Sir Frederick Bramwell on a small 
