water at the bow of the vessel may be separated and thrown to one side,
and brought to rest again at the stern and behind the vessel with the
least possible disturbance, and the measure of efficiency of form for
the maximum speed intended is inversely as the height of the waves of
disturbance. A ship that has been designed to attain a speed of 15
knots will, when moving at 12 knots, show a very slight disturbance
indeed, and in one designed for 18 knots, when moving at this lower
speed, it will be scarcely observable; but however fine the lines of a
ship may be, she must at every speed produce some disturbance, although
it may be very slight, as the water displaced by her must be raised
above the normal level and replaced at the normal level; hence, at or
near the bow of a ship there is always the crest of a wave, and at or
near the stern the hollow of one. When a vessel is going at its maximum
speed, and is properly designed for that speed, the wave should not
be very high, nor should it extend beyond the immediate neighborhood
of the bow; likewise the wave of replacement should be the same at or
near the stern of a ship, and the “wake,” or disturbance of water left
behind in the track of the ship, should be narrow.
Among naval architects and others it is usual to judge of the forms
of ships by the relation they bear to rectangular blocks of the same
dimensions; that is to say, a ship whose dimensions are—length,
100 feet; breadth, 20 feet, and draft of water, 10 feet, and whose
displacement is 12,000 cubic feet, would be said to have a coefficient
of fineness of 0.6, or that her fineness was sixty per cent., inasmuch
as that of a rectangular block[10] of the same dimensions would be
20,000 cubic feet.
Modern experience has shown that for speeds not exceeding 9 knots,
and with ships of the tonnage now common for general ocean work, the
bow may be very bluff and the stern only sufficiently fine to allow
free access of water to the propeller, so that the coefficient of such
vessels is frequently 0.78, whereas that of our fastest warships is
only 0.5, and of our large modern passenger steamers 0.55. As already
stated, in the ship whose coefficient is 0.78 any increase of power
produces very little gain in speed, and if such a ship were fitted with
engines and boilers of the same size and developing the same power as
those of a 20-knot Atlantic greyhound, the increase in speed would be
very insignificant, but the disturbance in its immediate neighborhood
would be very great; in fact, if any vessel is driven beyond a speed
for which her form is suitable, she produces waves[11] both numerous
and high, as may be seen by reference to the
illustration of H. B. M. S. Impérieuse being driven at her full speed of
17-1/4 knots when laden much deeper than the designed draft [p. 64].
As before mentioned, when speaking of the experiment with a thin sheet
of metal, the resistance to passage through the water increases very
rapidly with the increase of speed, and careful observation has shown
that _such increase is proportionate to the square of the speed_, so
that an immersed body has four times the resistance when moving at
twice the speed, and since it will travel double the distance in the
same time the power required is eight times as great; that is, _the
power needed to propel a ship varies as the cube of the speed_. It was
also discovered that the _power varied with the cube root of the square
of the displacement_; although more correct modern experiment has shown
that this variation is not strictly true, it is sufficient for the
purpose of this article to assume that it is so.
[Illustration: The Impérieuse going at Full Speed. (From an
instantaneous photograph.)]
[Illustration: The North German Lloyd Steamer Kaiser Wilhelm II.]
The indicated horse-power [called I. H.-P. for brevity], or that power
developed by the engine as registered by the indicator, is not all
usefully applied to the propulsion of a steamship. A large portion
of it is used up in overcoming the resistance of the engine itself,
as well as the necessary adjuncts of it, amounting often to thirteen
per cent. Then, again, another portion is absorbed in overcoming the
resistance of the propeller and its shafting; and as at present there
is no accurate method of determining these portions, the net effective
horse-power, or that usefully employed in propelling the vessel, can
only be guessed at, or approximated to by calculations more or less
abstruse. It is, however, the gross, or _indicated_, horse-power that
has to be obtained and paid for, and that, therefore, is the element
that has to be considered in practice; so that, from this consideration
alone, any great increase in speed has to be very dearly paid for.
Moreover, as has already been said, to admit of a higher speed the
ship must be made much finer, which means that her carrying capacity
for cargo and fuel has to be decreased; besides which the greater
engine-power will add to the dead load, thus still further diminishing
the vessel’s capability for carrying. This may be better understood by
taking a steamer of moderate dimensions, and such as for many years
was deemed sufficient for the Atlantic trade, say 300 feet long, 40
feet beam, and having a draft of water of 20 feet. Such a craft would
have a displacement of about 4,800 tons, could steam 10 knots per hour
with 1,000 I. H.-P., and carry 3,000 tons of cargo, fuel, stores, and
equipment. Taking the distance to be steamed at 3,200 knots, and the
consumption of fuel at 4 pounds per I. H.-P., it will be seen that
the net consumption of coal is 571 tons; adding to this twenty-five
per cent. for contingencies of weather, for raising steam, cooking,
heating, etc., the ship would have to leave port with 714 tons of fuel
and rather less than 2,300 tons of cargo, stores, etc., on board. If a
steamship of similar dimensions were required to do the voyage at 15
knots, her design would have to be such that the displacement would
not be more than 4,100 tons, the I. H.-P. at least 3,400, and the
amount of fuel stored at the commencement of the voyage 1,618 tons. The
machinery would probably have to be at least 400 tons heavier, so that
the capacity for cargo, stores, etc., would now be reduced to 1,000
tons. The cost, too, would be greatly increased on account of the extra
engine-power, and the expense in fuel would be more than doubled. The
engine-and boiler-room staff would likewise be materially increased,
while the earning power of the vessel would be less than half.
Seeing, however, that the power required for a certain speed varies
with the cube root of the displacement squared, the proportion of power
to tonnage will decrease considerably with the increase in the size,
so that if, instead of the steamer above referred to of 4,100 tons,
one were taken of 8,200 tons, the I. H.-P. for 15 knots—all other
things remaining the same—would be very little more than 5,000; _i.
e._, with a ship of twice the size the increase of engine-power is only
forty-seven per cent. The carrying capacity and consequent earning
power of such a boat is immeasurably more than that of the small one.
The larger ship will, moreover, make better passages, and generally be
much more economical in working, as the officers and crew will not very
largely exceed that of the smaller vessel.
* * * * *
It was, however, owing to the more economical engine that advances in
speed were rendered possible, and this is seen by referring back to the
original ship, and supposing that instead of engines burning 4 pounds
of coal per I. H.-P., it had ones consuming only 2-1/2 pounds per I.
H.-P. in which case the expenditure on the voyage would be reduced from
1,618 tons to 1,004 tons; so that 600 tons more cargo could be taken
and the cost of 600 tons of fuel per voyage saved. This was actually
the case on the substitution of compound for old-fashioned low-pressure
jet-injection engines fitted to the Cunard Company’s steamers as late
as 1862, when their largest, fastest, and most improved steamer, the
Scotia, was put on the service. But it was not until many years after
the advent of the Scotia that such economic engines were in general use
on the Atlantic, and it was only in 1874-75, when the Inman Company
and White Star Company placed steamships having these engines in
competition with the old-fashioned ones, that the day of the latter was
gone.
[Illustration: Passenger Steamer Princesse Henriette at Full
Speed—24-1/2 miles per hour.
(Built by William Denny & Co., Dumbarton.)]
The first pioneers of steamship construction were apparently satisfied
to find their efforts result in some motion, for we find exultation
rather than disappointment in the accounts extant of Patrick Miller’s
experiments with a small steamer on a Scotch canal in the year 1787;
and later, in 1789, when, with a larger and better boat and machinery,
he was able to obtain a speed of 7 miles an hour (equivalent to
6.07 knots[12]) it was deemed a great achievement; later still, in
1807, Fulton’s first attempt with the steamship Clermont, in a run
from Albany to New York and back, the average speed was only 5 miles
an hour. In those days so long as a steamer was able to face wind
and tide she was deemed a success. The competition of steamers in
early times (when there was any) was with sailing ships, or with
land conveyances whose maximum rate would be 10 miles an hour, and
that effected at considerable cost in horse-flesh. It is, however,
true that sailing ships did then, and can now, sail, under favorable
circumstances, at very much higher rates than we have just mentioned,
and even as much as 15 knots can be obtained with one of fine lines
with a favoring wind; but a sailing ship is not always free to traverse
the shortest distance from port to port, and even when wind and weather
permit of this, the _average_ speed falls far below 15 knots with the
best-designed vessels; hence if a steamer could do 9 knots she would
make shorter passages than any sailer; and from the nearer approach
to uniformity in the time occupied, passengers were attracted to
steamships, and the passenger sailing vessel, except for very long
voyages, became a thing of the past.
The Clermont, constructed by Fulton in America, and supplied by him
with engines made by Messrs. Bolton & Watt, in Birmingham, England,
was 133 feet long, 18 feet broad, and 9 feet deep; the engine had
a diameter of piston of 24 inches with 4 feet stroke; she took 32
hours performing the voyage from Albany to New York, and 30 hours in
returning—the journey can now be done in one-fourth that time. In 1815
the steamship Caledonia was placed on the service between Margate
(England) and Holland, and her speed did not exceed 7-1/2 knots per
hour. Steamships now perform the passage at double that speed, and the
most recent additions to the continental service between Dover and
Ostend are steamboats that can travel at nearly three times the pace
of the Caledonia. The Princesse Henriette is 300 feet long, 38 feet
broad, and 13 feet 6 inches deep, and has engines whose cylinders are
58 inches and 104 inches diameter, with a stroke of 6 feet, and on page
69 is shown a drawing of her, taken from a photograph when travelling
on her trial trip at a speed of 21.28 knots, or 24-1/2 statute miles
per hour.
[Illustration: Engines of the Comet.]
The first steamboat constructed and used for serviceable purposes in
Great Britain was the Comet, built by Henry Bell, on the Clyde, in
1812. She was only 40 feet long, 10 feet broad, of 24 tons measurement;
her engines were of 4 nominal horse-power, and of very curious design,
as shown by the engraving on page 70; her speed under favorable
conditions was only 5 miles an hour. She continued to ply for some
years between Glasgow and Greenock, and was doubtless a very great
convenience to the public at that time; but the advance that has been
made in the construction of river steamers for service on the Clyde and
its estuary is seen by reference to the illustration of the steamer
Duchess of Hamilton, whose dimensions are length, 250 feet; breadth, 30
feet; and depth 10 feet; her engines having cylinders 34-1/2 inches and
60 inches diameter, with a piston-stroke of 5 feet. Her speed is over
18 knots, or very nearly 21 miles per hour, at which rate she was going
when the photograph was taken.
[Illustration: Passenger Steamer Duchess of Hamilton at Full Speed—21
miles per hour. (Built for service on the Clyde.)]
The paddle steamer Puritan is another example of the very great
progress made since the days of the Clermont, and is also a marked
advance in many ways on the Bristol, which was the wonder of a few
years ago; and another noted case is the steamship Columba, built for
service on the Clyde.
The first steamships to cross the Atlantic from England were the Sirius
and Great Western,[13] names never to be forgotten. The Great Western
was built at Bristol, England, and completed in the year 1838. She was
212 feet long, 35 feet 4 inches broad, and 1,340 tons burden, and had
engines of 450 nominal horse-power. She did the voyage from Bristol
to New York in 15 days. The time of her quickest passage, given in
the table on page 80 as 10 days, 10 hours, and 15 minutes, is not
the actual passage, but is the equivalent of a passage reckoned from
Queenstown to Sandy Hook.
[Illustration: Passenger Steamer Columba at Full Speed—21 miles per
hour. (Built for Clyde passenger service.)]
In 1840 the Britannia, the first of the Cunard steamers, was put on
her station. She was a paddle boat, built of wood, and was 207 feet
long. Her speed on service was about eight and a half knots, so that
she did the passage in 15 days.
Ten years later the now renowned Inman Line commenced with an iron
screw steamer named the City of Glasgow, of 1,600 tons burden, and 350
nominal horse-power, a new departure in both ship and propeller.
It was not until 1855 that the Cunard Company built an iron steamer,
and they continued to employ paddle boats until 1862, when the
celebrated steamship Scotia was completed.
It is interesting to note, in passing, that the average length of
voyage in the Cunard Line, in 1856, from Liverpool to New York was
12.676 days, and from New York to Liverpool 11.036 days.
Thirteen years after the Scotia was built the White Star Company placed
on the station two vessels that were very great advances on anything
then existing; they were marvels of the ship-builder’s and marine
engineer’s skill, and even to-day hold their own in many respects
with the most modern ships. That these should compete successfully,
and eventually drive off the line such a ship as the Scotia is easily
seen by reference to contrasted particulars in the table on page 78.
The Britannic is a screw vessel 455 feet long; her I. H.-P. on trial
trip was 5,400, and at sea is about four thousand nine hundred, or
practically the same as that of the Scotia; but the speed on trial
was nearly two knots more, and the average of eleven voyages gives a
mean of 15.045 knots per hour; while as recently as September, 1890,
in her old age, she traversed the Atlantic from New York to Queenstown
at an average speed of 16.08 knots. She has compound engines with 4
cylinders, the two high-pressure being each 48 inches diameter, and
the two low-pressure each 83 inches diameter, with a stroke of 5
feet. Her consumption of coal will be about one hundred and thirty
tons per day, and on leaving port she will have on board, say 1,300
tons of fuel. She can carry a considerable cargo. The weight of her
machinery is 1,112 tons. She and her sister ship, the Germanic, were
in their day admitted to be all that could be desired; almost as much
as was physically possible, and certainly as much as was then possible
commercially.
Since then, however, many changes have taken place that will be alluded
to later on, so that to-day we have numerous boats running on the
Atlantic at an average speed of 19 to 20 knots, with a reputation for
being commercial successes as well as triumphs of engineering skill.
The most recent and noteworthy of these are the steamships Teutonic and
Majestic, owned by the same enterprising gentlemen, and constructed by
the same famed builders as the Britannic and Germanic; and the City
of Paris and City of New York, sailing under the same house flag as
the steamship City of Berlin, which was a worthy competitor of the
Britannic.
The Majestic is a twin-screw steamer of 9,851 tons gross, 565 feet
long (or 110 feet more than the Britannic). Each screw is driven by a
set of triple-expansion engines. Her consumption of fuel is about two
hundred and ninety tons per day, while on leaving port she will have
on board about two thousand four hundred tons of coal. Her I. H.-P. on
trial trip was 17,000. Her best speed on service is a mean of 20.18,
and taking the mean of ten voyages it is 19.72 knots. A picture of the
ship, taken while afloat on the Mersey, is shown on page 75.
The City of Paris is 10,499 tons gross register, and is 527 feet long:
she also is a twin-screw vessel. It will be observed by comparison
with the Majestic [see table, p. 78] that the City of Paris is the
larger ship, although she is 38 feet shorter, her extra beam of 5.4
feet giving her this advantage. Her speed with 20,100 I. H.-P. is
21.952 knots, her best run on service being 20.01 knots; and her daily
consumption of coal is about three hundred and twenty tons, which
necessitates her leaving port with over two thousand seven hundred tons
of fuel on board for the trip.
[Illustration: The White Star Steamer Majestic.]
Previous to the advent of these vessels the Cunard Company’s steamships
Etruria and Umbria were the fastest boats on the Atlantic, and their
performances are highly creditable to all concerned. The best voyage
from Queenstown to Sandy Hook by the Etruria was done in 6 days, 5
hours, 3 minutes, and the best from Sandy Hook to Queenstown in 6 days,
7 hours, 32 minutes, and the average in 1886 was about 6 days, 15
hours, as compared with the 11 days, 19 hours of 1856. The average of
the Britannic for ten years was 8 days, 9 hours, 36 minutes, Queenstown
to New York; and 8 days, 1 hour, 48 minutes, New York to Queenstown.
COMPARATIVE TABLE OF ATLANTIC STEAMSHIPS AND THEIR SPEEDS.
----------------+------+------+--------+--------+--------+---------+------
| | | | | | |
| | | Length | | | |
|Paddle| | on | | | |
| or | When | Water- | | | Horse- | Ton-
NAME OF SHIP. |Screw.|Built.| line. |Breadth.| Draft. | power. | nage.
----------------+------+------+--------+--------+--------+---------+------
| | |Ft. Ins.|Ft. Ins.|Ft. Ins.| Nominal.|
Sirius |Paddle| 1836 | 170 0 | | | 270 | 700
British Queen | „ | 1839 | 234 0 | 40 4 | 16 0 | 500 | 2,016
Liverpool | „ | 1839 | 210 0 | 36 0 | | 404 | 1,150
Great Western | „ | 1838 | 212 0 | 35 4 | 16 0 | 450 | 1,340
Britannia | „ | 1840 | 206 0 | 34 6 | | 450 | 1,155
Scotia | „ | 1862 | 366 0 | 47 9 | 22 0 | 1,000 | 2,358
City of Richmond|Screw.| 1873 | 440 0 | 43 6 | | 700 | 4,780
City of Berlin | „ | 1874 | 488 6 | 44 2 | | 1,000 | 5,526
| | | | | |Indicated|
Germanic | „ | 1874 | 455 0 | 45 2 | 23 7 | 5,400 | 5,008
Britannic | „ | 1874 | 455 0 | 45 2 | 23 7 | 5,400 | 5,004
Arizona | „ | 1879 | 450 0 | 45 1 | 18 9 | 6,300 | 5,164
Servia | „ | 1881 | 515 0 | 52 0 |23 3-1/2| 10,300 | 7,392
City of Rome | „ | 1881 | 542 6 | 52 0 |21 5-1/2| 11,890 | 8,144
Alaska | „ | 1881 | 500 0 | 50 0 | 21 0 | 10,000 | 6,932
America | „ | 1883 | 432 0 | 51 0 | 26 7 | 7,354 | 5,528
Oregon | „ | 1883 | 501 0 | 54 2 | 23 8 | 13,300 | 7,375
Umbria | „ | 1884 | 500 0 | 57 2 | | 14,320 | 8,128
Etruria | „ | 1884 | 500 0 | 57 2 | | 14,320 | 8,120
City of New York| „ | 1888 | 527 0 | 63 0 | | 18,400 |10,500
City of Paris | „ | 1888 | 527 0 | 63 0 | | 20,100 |10,500
Majestic | „ | 1889 | 565 0 | 57 6 | 26 0 | 17,000 | 9,861
Teutonic | „ | 1889 | 565 0 | 57 6 | 26 0 | 17,000 | 9,686
----------------+------+------+--------+--------+--------+---------+------
----------------+------+--------------------------------+---------+-----------
| | CYLINDERS. | |
| +------------------------+-------+ | Time
| | |Stroke | | occupied
|Trial | | in | Working |on Quickest
NAME OF SHIP. |Speed.| Diameter in Inches. |Inches.|Pressure.| Passage.
----------------+------+------------------------+-------+---------+-----------
|Knots.| | | Lbs. | D. H. M.
Sirius | | | | | 18 11 15
British Queen | 8.5 |Two 77-1/2 | 84 | | 13 18 10
Liverpool | |Two 75 | 84 | | 11 18 5
Great Western | |Two 73 | 84 | | 10 10 15
Britannia | |Two 72 | 82 | |
Scotia |13.9 |Two 100 | 144 | | 8 4 30
City of Richmond| |68 and 120 | 60 | | 7 18 50
City of Berlin | |41, 65, and 101 | 66 | | 7 14 12
| | | | |
Germanic |16.0 |Two 48 and two 83 | 60 | 70 | 7 11 37
Britannic |16.0 |Two 48 and two 83 | 60 | 70 | 7 10 53
Arizona |17.0 |One 62 and two 90 | 66 | 90 | 7 3 30
Servia |16.9 |One 72 and two 100 | 78 | | 6 23 50
City of Rome |18.23 |Three 46 and three 86 | 72 | 90 | 6 21 4
Alaska |18.0 |One 68 and two 100 | 72 | 100 | 6 18 37
America |17.8 |One 63 and two 91 | 66 | | 6 14 18
Oregon |18.3 |One 70 and two 104 | 72 | 110 | 6 9 51
Umbria |19.0 |One 71 and two 105 | 72 | 110 | 6 3 4
Etruria |19.5 |One 71 and two 105 | 72 | 110 | 6 1 50
City of New York|20.13 |Two sets 45, 71, and 113| 60 | 150 | 5 21 19
City of Paris |21.952|Two sets 45, 71, and 113| 60 | 150 | 5 19 18
Majestic |19.87 |Two sets 43, 68, and 110| 60 | 180 | 5 18 8
Teutonic |21.0 |Two sets 43, 68, and 110| 60 | 180 | 5 16 30
----------------+------+------------------------+-------+---------+-----------
It may well be asked how what seemed to be an impossibility in 1876
has been achieved so successfully in 1890, and it is perhaps less
interesting to note the changed conditions than the causes that have
produced them. In the very early days of steam navigation the engines
were substantially those used for pumping and other purposes on land.
Had the genius of Trevithick exerted itself in the direction of
improvements in ship propulsion as much as it did in abortive efforts
to make the locomotive a success, there is no doubt we should have
had fast passenger steamers before we had railway trains; and had
not the prejudice of Watt hung over the engineering world as a cloud
which obscured the clear light of science, some other engineer would
have accomplished the same result. It is disappointing to find that
a man of Watt’s genius and reputation should have attempted to damp
the ardor of men like Symington and Miller by predicting failure for
an engine when applied to marine propulsion, and by threatening the
pains and penalties of the law for infringement of patent should those
enterprising geniuses disprove his predictions. There can be no doubt
that the statement from a man of his position, that Trevithick and
others who were experimenting, as well as working, with steam of high
pressure deserved hanging for their diabolical inventions, would have
great effect on the engineering world, then in its infancy; and the
few accidents that in later years occurred on steamboats, through the
crass ignorance or the reckless negligence of those placed in charge,
recalled to the mind of another generation the words of Watt, and made
them doubly impressive as well as deterrent to further progress. Even
in our own days the use of steam at such pressures as have enabled
the present wonderful monuments of mechanical skill to be commercial
successes has been animadverted upon, and prophesied about, and openly
denounced, and it is only those who are engaged in this pioneer
warfare who know how depressing and discouraging such language is, or
who appreciate the great responsibility taken in advancing into the
unknown—that is, unknown to the world at large. Moreover, the body of
every nation is more or less conservative and slow to comprehend, much
less to appreciate, new inventions or new forms of old inventions.
Hence, no doubt, it was that an enterprising company like that presided
over by Sir Samuel Cunard should refrain from building its ships of
the superior material, iron, and adhere to the inferior propeller, the
paddle.
[Illustration: The Inman Line Steamer City of Paris.]