TRANSACTIONS OF SECTION G, 55] 
essential to economical propulsion and the maintenance of speed, and that frequent 
docking is necessary in yessels with bare iron or steel skins, which foul in a com-~ 
paratively short time. 
Possibilities of further Increase in Speed. 
From the facts above mentioned it is obvious that the increase in speed which 
has been effected is the result of many improvements, 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 
this remarkable 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 inter- 
posing a layer of air between the skins of ships and the surrounding water, or 
other departures from ordinary practice. If these 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 reduction 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 considerations, such as internal 
capacity, structural weight and strength, stability and seaworthiness. Most of 
these proposals do not merit serious consideration. Any which seem worth inves- 
tigation can be dealt with simply and effectively by the method of model experi- 
ments. 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 connection with the conditions attending abnormally 
high speeds. It must sutlice now to say that ship-shaped forms are not likely to 
be superseded at present. 
The most prolific ‘ inventions’ are those connected with supposed improvements 
in propellers. One constantly meets with schemes guaranteed by the proposers to 
give largely increased efficiency and corresponding additions to speed. Variations 
in the numbers and forms of screws or paddles, the use of jets of water or air 
expelled by special apparatus through suitable openings, the employment of explo- 
sives, imitations of the fins of fishes, and numberless other departures from esta- 
blished practice are constantly being proposed. As a rule the ‘inventors’ 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 iwaccurate. More or less mathematical 
demonstrations find favour with other inventors, but they are not more satisfactory 
than theexperiments. 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 estimated (or guessed) to the 
third place of decimals. In one such instance a trial was made with the new pro- 
peller, 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 characteristic features of 
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