532 
NATURE 
[SEPTEMBER 28, 1899 
vessel named the J/zvanda. She was only 45 feet long and 
weighed 4 tons, yet she exceeded 16 knots on trial. The Nor- 
wegian torpedo boat built in 1873 was 57 feet long, 74 tons, 
and of 15 knots ; the first English torpedo boat of 1877 was 81 
feet long, 29 tons and attained 184 knots. 
Mr. Yarrow also undertook the construction of small swift 
vessels at a very early date, and has greatly distinguished him- 
self throughout the development of the torpedo flotilla. Messrs. 
White, of Cowes, previously well known as builders of steam- 
boats for use on board ships, extended their operations to the 
construction of torpedo boats. These three firms for a consider- 
able time practically monopolised this special class of work in 
this country. Abroad they had able competitors in Normand 
in France, Schichau in Germany, and Herreshoff in the United 
States. Keen competition led to successive improvements and 
rapid rise in speed. During the last six years the demand for 
a fleet of about 100 destroyers, to be built in the shortest possible 
time, involved the necessity for increasing the sources of supply. 
At the invitation of the Admiralty, a considerable number of 
the leading shipbuilding and engineering firms have undertaken 
and successfully carried through the construction of destroyers 
varying from 26 to 33 knots in speed, although the work was 
necessarily of a novel character, involving many difficulties. 
As the speeds of torpedo vessels have risen, so have their 
dimensions increased. Within the class the law shown to hold 
good in larger vessels applies equally. In 1877 a first-class 
torpedo boat was 81 feet long, under 30 tons weight, developed 
400-horse-power, and steamed 184 knots. Ten years later the 
corresponding class of boat was 135 feet long, 125 tons weight, 
developed 1500 horse-power and steamed 23 knots. In 1897 
it had grown to 150 feet in length, 140 to 150 tons, 2000 horse- 
power and 26 knots. 
Destroyers are not yet of seven years’ standing, but they come 
under the rule. The first examples (1893) were 180 feet long, 
240 tons, 4000 horse-power and 26 to 27 knots. They were 
followed by 30-knot vessels, 200 to 210 feet long, 280 to 300 
tons, 5500 to 6000 horse-power. Vessels now in construction 
are to attain 32 to 33 knots, their lengths being about 230 feet, 
displacements 360 to 380 tons and engine-power S000 to 10,000 
horse: power. 
Cost has gone up with size and power, and the limit of pro- 
gress in this direction will probably be fixed by financial con- 
siderations, rather than by constructive difficulties, great as these 
become as speeds rise. 
It may be interesting to summarise the distinctive features of 
torpedo-vessel design. 
(1) The propelling apparatus is excessively light in proportion 
to the maximum power developed. Water-tube boilers are now 
universally adopted, and on speed trials they are ‘‘ forced” toa 
considerable extent. High steam pressures are used. The engines 
are run at a high rate of revolution—often at 400 revolutions per 
minute. Great care is taken in every detail to economise weight. 
Speed trials at maximum power only extend over three hours. 
On such trials in a destroyer each ton weight of propelling 
apparatus produces about 45 indicated horse-power. Some idea 
of the relative lightness of the destroyer’s machinery and boilers 
will be obtained when it is stated that in a large modern cruiser 
with water-tube boilers, high steam pressure, and quick-running 
engines, the maximum power obtained on an eight hours’ trial 
corresponds to about 12 indicated horse-power per ton of 
engines, boilers, &c. That is to say, the proportion of power 
to weight of propelling apparatus is from three and a half to four 
times as great in the destroyer as it is in the cruiser. 
(2) A very large percentage of the total weight (or displace- 
ment) of a torpedo vessel is assigned to propelling apparatus. 
In a destroyer of 30 knots trial-speed, nearly one-half the 
total weight is devoted to machinery, boilers, &c. In the 
swiltest cruisers of large size the corresponding allocation of 
weight is less than 20 per cent. of the displacement, and in the 
largest and fastest mail steamers it is about 20 to 25 per cent. 
(3) The torpedo vessel carries a relatively small load of fuel, 
equipment, &c. Taking a 30-knot destroyer, for example, the 
speed trials are made with a load not exceeding 12 to 14 per 
cent. of the displacement. In a swift cruiser the corresponding 
load would be from 40 to 45 per cent., or proportionately more 
than three times as great. What this difference means may be 
illustrated by two statements. If the load in a destroyer were 
trebled and the vessel correspondingly increased in draught and 
weight, the speed attained with the same maximum power 
would be about three knots less. If, on the other hand, the 
NO. 1561, VOL. 60] 
vessel were designed to attain 30 knots on trial with the heavier 
load, her displacement would probably be increased about 70 
to 80 per cent. 
(4) The hull and fittings of the torpedo vessel are exceedingly 
light in relation to the dimensions and engine-power. For 
many parts of the structure steel of high: tensile strength is 
used. Throughout, the utmost care is taken to economise 
weight. In small vessels, for special service, many conditions 
can be accepted which would be inadmissible in larger sea- 
going vessels. The result of all this care is the production of 
hull-structures having ample geveva/ strength for their special 
service. Lightness of scantling, of course, involves small /ocal 
strength against collision, grounding and other accident. Ex- 
perience proves, however, that this involves no serious risk or 
difficulty. 
These conditions are essential to the attainment of very high 
speeds for short periods. They resemble the conditions ruling 
the design of cross-Channel steamers, so far as relative lightness 
of propelling apparatus, small load and light scantlings are con- 
cerned. The essential differences lie in the requirements for 
passenger accommodation as compared with the requirements 
for armament of the torpedo vessel. No one has yet proposed 
to extend the torpedo-vessel system to sea-going ships of large 
dimensions. Very similar conditions for the propelling appar- 
atus have been accepted ina few cruisers of considerable dimen- 
sions, wherein high speeds for short periods were required. It 
is, however, unquestionable that in many ways, and particularly 
in regard to machinery design, the construction of torpedo 
vessels has greatly influenced that of larger ships. 
One important consideration must not be overlooked. For 
short-distance steaming at high speeds economy in coal con- 
sumption is of little practical importance, and it is all-important 
to secure lightness of propelling apparatus in relation to power. 
For long-distance steaming, on the contrary, economy in coat 
consumption is of primary importance ; and savings in weight of 
propelling apparatus, even of considerable amount, may be un- 
desirable if they involve increased coal consumption. Differ- 
ences of opinion prevail as to the real economy of fuel obtainable 
with boilers and engines such as are fitted in torpedo vessels. 
Claims aresmade for some vessels which represent remarkable 
economy. Only enlarged experience can settle these questions. 
Endurance is also an important quality in sea-going ships of 
large size, not merely in structures, but in propelling apparatus. 
The extreme lightness essential in torpedo vessels obviously does 
not favour endurance if high powers are frequently or con- 
tinuously required. Still, it cannot be denied that the results 
obtained in torpedo vessels show such a wide departure from 
those usual in sea-going ships as to suggest the possibility of 
some intermediate type of propelling apparatus applicable to 
large sea-going ships and securing sufficient durability and 
economy of fuel in association with further savings of weight. 
The Parsons Turbo-Motor. 
The steam turbo-motor introduced by Mr. Charles Parsons 
is to be described by the inventor during these meetings ; 
but it is impossible for me to pass it over in this review 
without a brief notice. This rotary engine, with its very high 
rate of revolution, reduces the weights of machinery, shafting 
and propellers greatly below the weight required in the quickest- 
running engines of the reciprocating type. This reduction in 
the proportion of weight to power carries with it, of course, 
the possibility of higher speed in a vessel of given dimensions ; 
and when large powers are employed the absolute gain is very 
great. An illustration of this has been given by Mr. Parsons 
in the 7z7dzzza. That remarkable vessel is 100 feet long and 
of 444 tons displacement, but she has attained 33 to 34 knots 
in short runs. Thereare three shafts, each carrying three screw 
propellers, each shaft driven by a steam turbine making over 
2000 revolutions at full speed, when more than 2000-horse- 
power is developed. A water-tube boiler of special design 
supplies steam of 175 lbs. pressure, and is exceptionally light 
for the steam produced, being highly forced. The whole weight 
of machinery and boilers is 22 tons; in other words, about 100 
horse-power (indicated) is produced for each ton weight of 
propelling apparatus. This is rather more than twice the pro- 
portion of power to weight as compared with the lightest 
machinery and boilers fitted in torpedo boats and destroyers. 
It will be noted that in the Zw7denza, asin the destroyers, about 
half the total weight is devoted to propelling apparatus ; and im 
both instances the load carried is relatively small. The secret 
