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72
VAN NOSTRAND'S ENGINEERING MAGAZINE.
nature and to force her to give aid in con-
quering her mightiest opposing forces,
and of continuafly-occurring victories of
science and art, the one aiding the other,
over apparent impossibilities, in every
department of human activity. But we
may at least feel our way somewhat be-
yond the present limit of our advance,
and may, by careful study of the prob-
lem, and consideration of the principles
of science and methods of art known to
us, get some idea of wh^t is before us.
The speed at which a ship can be
driven through the water depends upon
many, but well-known, conditions, the
laws governing which have been, for the
purposes of the naval architect, very well
determined. Given the size and form of
any well-designed craft, it is easy to pre-
dict, with a fair degree of approximation
to accuracy, what amount of power will
be demanded to drive the vessel at any
proposed speed. This being known, it
is easy to ascertain the size and form of
the engines and boilers required, and to
calculate their weight, bulk, and fuel con-
sumption. It would thus seem that no
unknown elements enter into the prob-
lem, and that a precise answer might be
easily given to the question. That is not
the fact, however, and it will be presently
seen that there are very important factors,
the value of which, and sometimes the
nature of which, are not, and cannot as yet,
be exactly known. It is proposed in the
following paragraphs to consider the ele-
ments of the problem, and to discover
where these uncertainties lie, to what ex-
tent they obscure the subject which we
have taken up for study, and, so far as is
possible, to obtain some idea of the ex-
tent, as well as the character, of the lim<
itations which they involve.
The resistance of a steamship or other
vessel consists of two principal parts.
The effort required to overcome the fric-
tion of the water on its "wetted sur-
faces " measures the one, and the force
expended in producing the waves that
are seen arising about every ship in mo-
tion constitutes the other of these two
quantities. Of these factors, the first is
by far the greater in all well-formed
ships, and such alone can be considered
here. For every ship of a proposed size
and weight there is a certain form and
proportion of hull which is known to be
best for the intended speed, and hence
there is no great difficulty in securing al-
most exactly the best possible form, and
thus of eliminating avoidable '^ head-re-
sistance," or " wave- making " resistance,
as the smaller of the quantities is termed.
The friction of hull may be calculated,
also, very approximately, as it is found
to be very nearly proportional to the area
of wetted surfaca It is thus smaller as
the surface of the hull below the water
Une is smaller. But it is evident that
the nearer the form of the ship ap-
proaches that of a hemisphere the less
must be the resistance due to friction,
and that between the latter shape and
that elongated and graceful form which
gives minimum head resistance there
must be some intermediate form which
will give the least total resistance. The
form of minimum resistance for a given
size of ship must usually be felt out by
careful experimental work. The solu-
tion of the problem last stated is, then,
one of the elements of the problem of
larger extent, that of maximum speed on
the ocean. This solution is in process
of being effected, and may be considered
as having been already obtained with
fairly satisfactory accuracy. The Oregon,
now famous both for her speed and for
her sad fate, and even more satisfactorily,
perhaps, the *' America,*' represent very
excellent illustrations of highly success-
ful attempts at a solution.
The power demanded to propel any
vessel at ordinary speed varies as the
square of her length nearly, or as the
area of the transverse major section, and
as the cube of the speed. Thus, to
double the speed of any vessel requires
eight times the power demanded at the
lower velocity. Two vessels being of
equal speed and similar form, but the one
of twice the length of the other, the
second wUl require four times the power
of the first. The second vessel, how-
ever, carries eight times as much weight,
and the power per ton of vessel is one-
half as much as would be demanded by
the first, if driven at the higher speed.
These principles are modified by the re-
lation of form to speed and size, and the
rate of variation of increasing resistance
of a badly-formed ship is greater than
above stated ; while, on the contrary, the
well-formed ship may, at very high
speeds, meet with a resistance which in •
creases at a lower rate than the stated
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THE LIMIT OF SPEED IN OCEAN TRAVEL.
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law iDdicates. For vessels loaded to a
limit with machinery, the higher the
speed demanded, the larger mrmt be the
ship.
The impelling power of the ocean-
going steamship is supplied by engines
that have now become well fixed in their
general forms and proportions, although
signs of another revolution are already
plainly discernible. The standard form
of marine engine for merchant ships is a
machine having its steam cylinders set
vertically. It is of the "compound"
type, i, €.y so arranged that the steam
taken from the boilers is worked expans-
ively to lower pressure in one cylinder,
is then " exhausted'* into a second larger
cylinder, in which it is further expanded,
doing work, meantime, until it falls near-
ly to the pressure of the condenser, and
is then exhausted into the condenser,
where it is condensed and returned
thence into the boiler to be again evap-
orated. The condenser is called a " sur-
face condenser," because the condensa-
tion occurs on the interior surfaces of
the apparatus, which are kept cool by the
flow of watei* along the opposite side of
the metal.
The boilers supplying the steam to the
engines of ocean steamers are usually of
the Scotch type, consisting of a drum-
shaped vessel, containing the furnaces
and flues, or tubes, in which the flres are
kept burning, and through which the
flame, smoke and gases pass to the
smoke-stack, heating the water contained
in the boiler as they move over these
heating surfaces of sheet iron, which sur-
faces are, on their opposite sides, in con-
tact with the water to be made into
steam. The larger these boilers the more
economical are they, but the less power-
ful for their weight Increased economy
is always obtained at a sacrifice of power.
Increase of speed thus means decreased
efficiency.
The steam furnished to the engines
will be used with greater economy as its
pressure is greater, because it is worked
with greater expansion as the speed of
the engine is greater, and as the wastes,
some of which are more or less control-
able, are more effectively provided
against. There are two great sources of
waste — the one the unavoidable waste
which occurs in consequence of the fact
that the steam must be exhausted from
the engine at such a temperature, and
in such physical condition as to carry
away a considerable amount of heat,
partly sensible, and partly unrecognizable
to the senses, and hence called by James
Watt and Dr. Black, who discovered it,
" latent heat " ; the other is that waste
which is due to the circumstance that all
parts of the engine are made of metal,
and therefore have high conducting
power, and thus, by a process of storage
and waste which is very interesting to
the engineer, but which cannot be here
described, often cause the loss of as
much heat as is usefully applied. The
first method of waste, in good engines,
will often lead to the loss of three-fourths
of all the heat of the steam that is sup-
plied to the engine. The enormous
waste to which the steam-engine is thus
subject is reduced by steam-jacketing —
by the covering of the engine cylinder
with a jacket in which steam from the
boiler is kept, in order to sustain the
temperature of the internal surface of
the engine— by superheating, and by
high speed of the engine. The direct
means of securing economy are increas-
ing the steam pressure, with correspond-
ing increase of the range through which
the steam is expanded, and the reduction
of losses of power in the engine and its
machinery of transmission, including the
screw propeller. The extent to which
these several means of rendering the en-
gine more effective and economical and
useful, largely determines to what extent
gain of speed at sea can be secured. It
is further evident that the lighter and
stronger the engine and boilers can be
made, the higher the speed of vessel at-
tainable. It has been often proposed to
replace steam by some other fluid ; but
it is well known to men of science that
the gain to be anticipated is theoretically
ni7, and engineers famihar with the
steam-engine are well aware that not only
are there no practical advantages of im-
portance to be gained, but that many de-
cisive practical objections exist to every
other known fluid yet discovered and
used in a heat-engine, in competition
with steam.
The present state of the art may now
be perhaps understood, and the proba-
bilities 01 important advancement during
the next generation may possibly be
ganged with some degree of satisfaction.
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VAN N08TRAND'8 ENGINEERING MAGAZINE.
The steamer Oregon, of which the name
is now as familiar as as household word,
may be taken as representative of the
condition of the art at the commence-
ment of the year 1886. She was a ves-
sel of about 7,500 tons measurement, of
12,000 horse-power, and could, in a
smooth sea, make about 20 knots (24
miles) an hour. The trip across the At-
lantic was made in less than six and a-
half days. Her length was 500 feet,
breadth of beam 54 feet, and depth of
hold 38. The America, a less noteid, but
no less wonderful vessel, is of 6,500 tons
burden, 9,000 horse-power, and of very
nearly the same speed. The smaller ship
would seem to be the better illustration
of the highest success in this direction.
1'he Servia is 530 feet long, 52 feet beam,
44^ feet depth, and of 8,500 tons burden.
Her power is nearly equal to that of the
Oregon, and her speed something less.
A still later example Of the best modem
naval architecture is the Etruria, a ship
of 520 feet length, 57 feet beam, 41 feet
depth, and 8,000 tons measxurement. Her
speed is about the same as that of the
Oregon, but she is a larger, steadier, and
perhaps better ship. Ten such ships
placed stem to stem, as will be seen,
would form a line one mile long.
But the most extraordinary perform-
ances, from the point of view here taken,
are those of the steam-launches and tor-
pedo boats built in the United States
and Great Britain within the few years
covered by the construction of the ships
just described. The Herreshoflf yacht,
Stilletto,' made more than 25 miles an
hour not long since, and '* showed her
heels" to the Mary Powell, the fastest
river steamer, probably, in the world.
A torpedo boat built for the British Navy
has made 20.14 knots an hour, and an-
other 21 knots, while still another is
reported by its builder, Mr. Thomey-
croft, to the British Institution of Civil
Engineers as having made 22.01 knots
(25^ miles) an hour. These little craft
are but 80 to 100 feet long, and of but
30 or 40 tons weight, including hull,
machinery, and aU. Their performance
has excited the wonder of engineers as
being enormously beyond anything yet
attained by the larger vessels, the differ-
ence in size being considered.
Without attempting to assign a limit
to the progress of naval construction in
the coming years, we may be permitted
to ask what might be done with a ship
of a size now regarded as perfectly prac-
ticable, giving it the lines now regarded
as the best for its maximum speed, a hull
of minimum resistance to the flow of the
water past it, and driving it by engines
equal in economy, power, lightness, and
general efficiency to the best yet designed
and applied, and availing ourselves of
every known means of securing the best
result in the attempt to attain the high-
est velocity possible by these familiar
methods, while yet retaining the condi-
tions demanded of the fast transatlantic
steamer.
It was asserted by a distinguished man
of science, forty years ago, tlmt no steam-
ship could be made to cross the Atlantic,
because of the impossibility of carrying
sufficient coal to supply the engines and
boilers for the voyage. The prophecy was
proved false almost as soon as it was utter-
ed by the appearance in New York Harbor
of the Qreat Britain, the pioneer of the
Gunard Line, after a passage of 14 days
and 9 hours, and of the little Sirius be-
side her. A more credible recent pre-
diction was made by a well-known naval
architect, Mr. Robert Duncan, in 1872,
who stated that he anticipated that, be-
fore the end of the century, we should
see crossing the Atlantic the ferry-boats
of the ocean, 800 feet in length. The
Great Eastern was 680 feet long, and the
difference between that length and 800
feet is not now to be considered very
great Let us assume that such a ship
may be constructed, the question, arises,
what would be her maximum possible
speed t '
A steamer 800 feet in length, 80 feet
beam, and of 25 feet draught of water,
would weigh, complete and in sailing
trim, about 88,000 tons, if given what
may be considered as the best form to-
day known for maximum speed. The
fast ships of to-day exert about one and
a-half horse-power per ton to reach a
speed of 20 sea miles an hour. With
some little improvement, such as may be
safely anticipated before the close of the
century, this figure may be reduced some-
what, and a l^ger ship will have some
advantage. Our later Leviathan may be
expected to demand about 35,000 horse-
power at 20 knota We will, however,
aspire to 40 knots (about 47 miles), or a
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THE LIMIT OF SPEED IN OCEAN TRAVEL.
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speed of nearly one statute mile per min-
nte. At this enormous speed she would
cross the Atlantic in about 80 hours, or
less than three and a-half days. The
power requised would be calculated to
increase as the cube of the speed ; but it
is, in fact, foimd that the law often be-
comes more favorable at these higher
speeds, while a speed of 40 knots ecom-
ically corresponds, according to what are
known as "Froude's laws," to about the
speed of the torpedo-boats, which latter
are found to haye reached a velocity well
beyond the point of change of the ordi-
nary law of resistance. We may take the
probable power demanded as not far
from 260,()()0 horse-power.
The weight of the steam machinery of
vessels of various classes varies greatly,
the maximum being several himdred
pounds per horse-power, and the mini-
mum falling, in the faster torpedo-boats,
to a little above 50 pounds, while the
yacht Gitana gives a still lower figure,
43 pounds. Progress beyond the latter
point must be exceedingly slow, if we
may judge by present appearances.
These figures are partly attained by the
sacrifice of efficiency, and we may per-
haps fairly consider 60 pounds as the
minimum to be calculated upon for this
generation. Our machinery for the new
ship will thus weigh about 7,500 tons.
The fuel consumed by the most econom-
ical of known engines is much less than
by the large steam engines of the trans-
atlantic " liners ; " but we may take the
lowest figure for to-day as a fairly prob
able figure for this case. This is 1'
poimds of good fuel per horse-power ani
per hour, or a trifie less ; and our ship
will bum about 175 tons of coal an hour,
3,200 tons a day, and 10,500 tons for the
voyage. The total weight of fuel and
maclunery will then be about 18,000 tons,
leaving 20,000 tons for weight of ship
and cargo. The hull of such a steamer,
as now constructed, would weigh about
one-third the total "displacement," or
12,000 tons. The introduction of steel
and the improvements to be effected in
construction will probablv somewhat re-
duce this weight ; but it is not likely, so
far as can be seen to-day, that the reduc-
tion will be very great. Eight thousand
tons and over are left for passengers,
crew, stores, and such valuable freight as
may be taken.
It might be questioned whether the
propeller of such a steamer could take
up and usefully apply such an enormous
power; but the experiments already
made on torpedo-boats by Mr. Thomey-
croft seem, in the opinion of that author-
ity, to settle that point. He calculates
that a single screw, of less size than
those by wMch this ship would be driven,
would be capable of transmitting the
power of engines, "indicating,*' as the
engineer puts it, about 400,000 horse-
power.
Our proposed ship may be driven by
" twin " screws. It may be asked whether
economy is not to be anticipated, and to
a very great amount, by the adoption of
higher steam pressures. On this ques-
tion there is no settled opinion among
engineers. It would seem, however, that
the gain to be anticipated will be very
slight, and that a limit will probably be
reached soon. Pressures of 150 pounds
and more are already adopted in some
cases, and the introduction of the " safe-
ty" form of "water-tube" boiler will
probably soon permit still higher tension ;
but the gain of economy from this change
is now found to be very moderate, and
but little is expected from it by the ma-
jority of experienced naval engineers, ex-
cept in decrease of weight of boilers.
The boiler problem is exceedingly im-
portant ; the weight and volume of the
steam generator is a great obstacle to
further advance. Increase of piston-
speed may help us more. The maximum
reached at present is about 1,000 feet per
minute ; but steam will follow the piston
at any speed up to more than one hun-
dred times that velocity. There seems
no reason to doubt that the adoption
of familiar principles in balancing may
permit much higher speeds to be at-
tained. The gain to be expected from
increased expansion of steam is appar-
ently not likely to be rapid, or to be-
come very great, in the immediate fu-
ture. Decreased weight of parts by the
more extensive use of steel, and perhaps
by the introduction of new metals and
alloys, may prove helpful ; but nothing
positive can be said of this as yet. We
certainly are not yet in a position to ex-
pect much. The gain by improved forms
of hull, and by expedients looking to-
ward the reduction of the friction on its
exterior, cannot be expected to be im-
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VAN N08TRAND'8 ENGINEERING MAGAZINE.
portant Thus the question of increas-
ing the speed of ocean trayel seems
likely to resolve itself into one of practi-
cable size of vessel, and this means
simply a question of cost and financial
return. If higher speeds will "pay,"
higher speeds will be reached by the
construction of larger ships. The limit
is likely to prove mainly a commercial
one for generations, so far as we can now
see. To-day the fastest ships do not pay
expenses, and the limit is reached in this
direction. When more passengers and
more precious freight can be found to pay
for faster ships, faster ships will be built.
The skill and knowledge of the engineer
and shipbuilder will keep pace with the
demand, so limited, far beyond any point
that we can to-day perceive.
The wonderful effect produced by the
application of human ingenuity to the
development of inventions looking to
the subjection of the powers of nature
to the purposes of man, is well illus-
trated by these results of the introduc-
tion of steam power for the propulsion
of vessels. Some slight idea may pos-
sibly be gained of our advancement in
this direction, actual and possible, during
a single century, by considering what is
meant by the application of 250,000
horse-power to the propulsion of the
ship here schemed out. The engineer's
horse-power is the equivalent of the
work of the strongest known horses
when working at their usual rate in the
ordinary working day. But the average
horse is much less powerful, and it is
safe to say that one-horse power, in the
steam engine, is equal on the average to
at least one and a third times the power
of a horse. Then, again, the horse can-
not work up to his average full capacity
longer than about eight hours a day,
while the marine steam-engine works
continuously, day after day, the whole
twenty-four hours, without halt or slack-
ing its pace. Thus the engine horse-
power is the equivalent of the operation
of four horses, where the work is CArried
on without interruption. The 250,000
horse-power of the ship of the next
century must be taken as the equivalent
of the work of 1,000,000 horses. One
million horses would weight about 1,000,-
000,000 pounds, or nearly 500,000 tons
— over ten times the capacity of our
ship, and nearly seventy times the weight
of its machinery. The food and bed-
ding of 1,000,000 horses for a single day
would weigh probably 50,000 tons, or
more than double the weight the vessel
can float Were this great herd of horses
to be formed into a "string-team," al-
lowing ten feet for the leufith of one
horse, and for the " clearance '' between
each two in the line, its length would be
nearly 2,000 miles.
The cost of running the ship above
schemed out would be probably not less
than $75,000 for each voyage across the
ocean; and the passage money of 500
passengers, at $150 each, would be re-
quired to pay this. Each passenger
would save about four days' time, and
four days of annoyance incident to the
present method of travel ; and this must
be the equivalent to him for the increased
cost The ship could make a profit on
freight and mails.
It must not be expected that the
methods and details of construction
which must be learned aud applied prop-
perly in such a vessel are to be acquired
promptly or easily. The problem of
proper construction of the engine, or of
the propeller shaft, alone, is a serious
one which for a time may fail of solu-
tion, and may defer the realization of
this speed for many years. There are
hundreds of problems that the engineer
and the naval architect must attack and
solve before success can be attained. It
may, however, be considered as not at
all improbable that those of us who live
to the next century may see the Atlantic
crossed in less than four days.
THE ENDURANCE OF STEEL RAILS.
From "Iron.'
As a great many questions have been
asked me as to the comparative dura-
bility of iron and steel rails, I have
thought that the nineteen years* results
on the London and North- Western line
of railway, which I have been able to
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THE ENDURANCE OF 8TKEL RAILS.
77
tabulate, might be of interest to the
members of the Iron and Steel Institute,
and I be^ to submit a diagram to this
meeting showing the comparative num-
bers of tons of iron and steel rails used
for relaying purposes on the railway in
question, from 1867 to the end of this
year, the last year being, of course, the
estimated requirements. On the same
diagi'am I haye shown the quantity of
coal burned yearly in the locomotives, as
I take it that this is the only reliable
way in which we can arrive at the amount
of work done on the line in each year ;
and, as a check upon the coal consump-
tion, 1 have also shown on the diagram a
line representing the train miles along
with the engine miles, and it will be seen
at a glance that, while the coal line very
closely follows in proportion to the train
miles and the engine miles run in each
year, the quantity of rails used for re-
newals has been a constantly decreasing
amount since 1877. From 1868 to 1877,
we were putting down both iron and
steel rails on renewal account. I have
shown the iron and steel raild separately
in the diagram, and the combined iron
and steel in a double Hue. It will be
noticed tliat in 1868 the quantity of iron
and steel rails required for renewals was,
roundly, 16,400 tons, and that the larg-
est weight of rails required for renewals
was arrived at in 1876, twelve months
after which iron rails entirely disappeared
— the total number of tons used in that
year (1876) being 31,391, while the esti-
mated requirements for this year are only
11,600 tons. *
Practically, the whole of our main
lines are relaid with steel ; and while, in
past years, we have been putting down
steel rails as fast as iron ones wore out,
we are now putting down steel rails as