234 
the cube; from 18 to 20 knots it varies as the 3°3 power. 
Then the index begins to diminish; at 22 knots it is 2°7 ; at 
25 knots it has fallen to the square, and from thence to 30 knots 
it varies, practically, as does the frictional resistance. 
The residual resistance varies as the square of the speed up 
to 11 knots, as the cube at 12} to 13 knots, as the fourth power 
about 144 knots, and at a higher rate than the fifth power at 
18 knots. Then the index begins to fall, reaching the square 
at 24 knots, and falling still lower at higher speeds. 
It will be seen, therefore, that when this small vessel has been 
driven up to 24 or 25 knots by a large relative expenditure of 
power, further increments of speed are obtained with less pro- 
portionate additions to the power. 
Passing from the destroyer to the cruiser of similar form 
but of 14,100 tons, and once more applying the ‘‘scale of 
comparison,” it will be seen that to 25 knots in the destroyer 
corresponds a speed of 474 knots in the large vessel. In other 
words, the cruiser would not reach the condition where further 
increments of speed are obtained with comparatively moderate 
additions of power until she exceeded 47 knots, which is an 
impossible speed for such a vessel under existing conditions. 
The highest speeds that could be reached by the cruiser with 
propelling apparatus of the lightest type yet fitted in large 
sea-going ships would correspond to speeds in the destroyer, 
for which the resistance is varying as the highest power of 
the speed. These are suggestive facts. 
Frictional resistance, as is well known, is a most important 
matter in all classes of ships and at all speeds. Even in the 
typical destroyer this is so. At 12 knots the friction with clean- 
painted bottom represents 80 per cent. of the total resistance ; 
at 16 knots 70 per cent ; at 20 knots a little less than 50 per 
cent. ; and at 30 knots 45 per cent. If the coefficient of friction 
were doubled and the maximum power developed with equal 
efficiency, a. loss of speed of fully 4 knots would result. 
In the cruiser of similar form the friction represents 90 per 
cent. at 12 knots, 85 per cent. at 16 knots, nearly 80 per 
cent. at 20 knots, and over 70 per cent. at 23 knots. If the 
coefficient of friction were doubled at 23 knots and the corre- 
sponding power developed with equal efficiency, the loss of 
speed would approximate to 4 knots. 
These illustrations only confirm general experience that clean 
bottoms are essential to economical propulsion and the main- 
tenance of speed, and that frequent docking is necessary in 
vessels with bare iron or steel skins, which foul in a compar- 
atively short time. 
Possibilities of further Increase tn Speed. 
From the facts above mentioned it is obvious that the increase 
in speed which has been effected is the result of many improve- 
ments, and has been accompanied by large additions to size, 
engine-power and cost. These facts do not discourage the 
“inventor,” who finds a favourite field of operation in schemes 
for attaining speeds of 50 to 60 knots at sea in vessels of 
moderate size. Sometimes the key to thisremarkable advance 
is found in devices for reducing surface-friction by the use of 
wonderful lubricants to be applied to the wetted surfaces of 
ships, or by interposing a layer of air between the skins of ships 
and the surrounding water, or other departures from ordinary 
practice. Ifthese gentlemen would ‘‘condescend to figures,” 
their estimates, or guesses, would be less sanguine. In many 
cases the proposals made would fail to produce any sensible re- 
duction in resistance ; in others they would increase resistance. 
Other proposals rest upon the idea that resistance may be 
largely reduced by adopting novel forms, departing widely from 
ordinary ship shapes. Very. often small-scale experiments, made 
in an unscientific and inaccurate manner, are adduced as proofs 
of the advantages claimed. In other instances mere assertion 
is thought sufficient. . Ordinarily no regard is had to other con- 
siderations, suchas internal capacity, structural weight and 
strength, stability and seaworthiness. Most of these proposals 
do not merit serious consideration. Any which seem worth 
investigation can be dealt with simply and effectively by the 
method of model experiments. A striking example of this 
method will be found in the unusual form of a Parliamentary 
Paper (No. 313, of 1873), containing a report made by Mr. 
William Froude to the Admiralty. Those interested in the 
subject will find therein much matter of special interest in con- | 
section with the conditions attending abnormally high speeds. 
It must suffice now to say that ship-shaped forms are not likely 
to be superseded at present. 
NO. 1561, VOL. 60] 
NATCORE 
[SEPTEMBER 28, 1899 
The most prolific ‘‘inventions” are those connected with 
supposed improvements in propellers. One constantly meets 
with schemes guaranteed by the proposers to give largely in- 
creased efficiency and corresponding additions to speed. Varia- 
tions in the numbers and forms of screws or paddles, the use of 
jets of water or air expelled by special apparatus through suit- 
able openings, the employment of explosives, imitations of the 
fins of fishes and numberless other departures from established 
practice are constantly being proposed. As a rule the ‘‘in- 
ventors”’ have no intimate knowledge of the subject they treat, 
which is confessedly one of great difficulty. When experiments 
are adduced in support of proposals they are almost always found 
to be inconclusive and inaccurate. More or less mathe- 
matical demonstrations find favour with other inventors, but 
they are not more satisfactory than the experiments. An air of 
great precision commonly pervades the statements made as to 
possible increase in efficiency or speed. I have known cases 
where probable speeds with novel propellers have been esti- 
mated (or guessed) to the third place of decimals. In one such 
instance a trial was made with the new propeller, with the 
result that instead of a gain in efficiency there was a serious loss 
of speed. Very few of the proposals made have merit enough 
to be subjected to trial. None of them can possibly give the 
benefits claimed. 
It need hardly be added that in speaking thus of so-called 
“inventors” there is no suggestion that improvement has 
reached its limit, or that further discovery is not to be made. 
On the contrary, in regard to the forms of ships and propellers, 
continuous investigation is proceeding and successive advances 
are being made. From the nature of the case, however, the 
difficulties to be surmounted increase as speeds rise; and a 
thorough mastery of the past history and present condition of 
the problems of steamship design and propulsion is required as 
a preparation for fruitful work in the nature of further advance. 
It would be idle to attempt any prediction as to the charac- 
teristic features of ocean navigation sixty years hence. Radical 
changes may well be made within that period. Confining at- 
tention to the immediate future, it seems probable that the lines 
of advance which I have endeavoured to indicate will remain in 
use. Further ‘reductions may be anticipated in the weight of 
propelling apparatus and fuel in proportion to the power de- 
veloped ; further savings in the weight of the hulls, arising from 
the use of stronger materials and improved structural arrange- 
ments ; improvementsin form; and enlargement in dimensions. 
If greater draughts of water can be made possible, so much the 
better for carrying power and speed. For merchant vessels 
commercial considerations must govern the final decision ; for 
warships the needs of naval warfare will prevail. It is certain 
that scientific methods of procedure and the use of model ex- 
periments on ships and propellers will become of increased 
importance. 
Already avenues for further progress are being opened. For 
example, the use of water-tube boilers in recent cruisers and 
battleships of the Royal Navy has resulted in saving one-third 
of the weight necessary with cylindrical boilers of the ordinary 
type to obtain the same power, with natural draught in the 
stokeholds. Differences of opinion prevail, no doubt, as to the 
policy of adopting particular types of water-tube boilers ; but 
the weight of opinion is distinctly in favour of some type of 
water-tube boiler in association with the high steam pressures 
now inuse, Greater safety, quicker steam-raising and other 
advantages, as well as economy of weight, can thus be secured. 
Some types of water-tube boilers would give greater saving in 
weight than the particular type used in the foregoing comparison 
with cylindrical boilers. 
Differences of opinion prevail also as to the upper limit of 
steam pressuré which can with advantage be used, taking into 
account all the conditions in both engines and boilers. From 
the nature of the case, increases in pressure beyond the 160 fo 
180 lbs. per square inch commonly reached with cylindrical 
boilers cannot have anything like the same effect upon economy 
of fuel as the corresponding increases have had, starting froma 
lower pressure. Some authorities do not favour any excess 
above 250 lbs. per square inch on the boilers ; others would go 
as high as 300 Ibs., and some still higher. 4 
Passing to the engine-rooms, the use of higher steam-pressures 
and greater rates of revolution may, and probably will, produce 
reductions in’ weight compared with power ©The use of 
stronger materials, improved designs, better balance of the 
moving parts, and close attention to details have tended in the 
