In a recent impression we gave some particulars of the trial trip of a
boat built for the Italian government by Messrs. Yarrow & Co., which
attained the highest speed known, namely, as nearly as possible, 28 miles
an hour. On the 14th April the sister boat made her trial trip in the
Lower Hope, beating all previous performances, and attaining a mean speed
of 25.101 knots, or over 28 miles an hour. The quickest run made with the
tide was at the rate of 27.272 knots, or 31.44 miles per hour, past the
shore. This is a wonderful performance.
In the following table we give the precise results:
+-------+---------+-------+-----+-------+-------+-------+
| | | | | | | Second|
|Boiler.|Receiver.|Vacuum.|Revs.| Speed.| Means.| Means.|
+-------+---------+-------+-----+-------+-------+-------+
| | | | per | Knots | Knots | Knots |
| lb. | lb. | in. | min.|per hr.|per hr.|per hr.|
+-------+---------+-------+-----+-------+-------+-------+
1 | 130 | 32 | 28 |373 | 22.641| 24.956| |
2 | 130 | 32 | 28 |372.7| 27.272| 25.028| 24.992|
3 | 130 | 32 | 28 |372 | 22.784| 25.028| 25.028|
4 | 130 | 32 | 28 |377 | 27.272| 25.248| 25.138|
5 | 130 | 32 | 28 |375 | 23.225| 25.248| 25.248|
6 | 130 | 32 | 28 |377 | 27.272| | |
------+-------+---------+-------+-----+-------+-------+-------+
Means | 130 | 32 | 28 |374.5| | | 25.101|
------+-------+---------+-------+-----+-------+-------+-------+
The boat is 140 ft. long, and fitted with twin screws driven by compound
engines, one pair to each propeller. These engines are of the usual type,
constructed by Messrs. Yarrow. Each has two cylinders with cranks at 90°.
The framing, and, indeed, every portion not of phosphor-bronze or gun
metal, is of steel, extraordinary precautions being taken to secure
lightness. Thus the connecting rods have holes drilled through them from
end to end. The low pressure cylinders are fitted with slide valves. The
high pressure valves are of the piston type, all being worked by the
ordinary link motion and eccentrics. The engine room is not far from the
mid length of the boat, and one boiler is placed ahead and the other
astern of it. Each boiler is so arranged that it will supply either
engine or both at pleasure. The boat has therefore two funnels, one
forward and the other aft, and air is supplied to the furnaces by two
fans, one fixed on the forward and the other on the aft bulkhead of the
engine room.
The fan engines have cylinders 5½ in. diameter and 3½ in. stroke, and
make about 1,100 revolutions per minute when at full speed, causing a
plenum in the stokeholes of about 6 in. water pressure. Double steam
steering gear is fitted, for the forward and aft rudder respectively, and
safety from foundering is provided to an unusual degree by the
subdivision of the hull into numerous compartments, each of which is
fitted with a huge ejector, capable of throwing overboard a great body of
water. A body of water equal to the whole displacement of the boat can be
discharged in less than seven minutes. There is also a centrifugal pump
provided, which can draw from any compartment. The circulating pump is
not available, because it has virtually no existence, a very small pump
on the same shaft as the centrifugal being used merely to drain the
condensers. These last are of copper, cylindrical, and fitted with pipes
through which a tremendous current of water is set up by the passage of
the boat through the sea. Thus the space and weight due to a circulating
pump is saved and complication avoided. The air and feed pumps are
combined in one casting let into the engine room floor, quite out of the
way, and worked by a crank pin in a small disk on the forward end of the
propeller shaft. This is an admirable arrangement, and works to
perfection.
The armament of the boat consists of two torpedo tubes in her bows, and a
second pair set at a small angle to each--Yarrow's patent--carried aft on
a turntable for broadside firing. There are also two quick firing 3 lb.
guns on her deck. The conning tower forward is rifle proof, and beneath
it and further forward is fixed the steering engine, and a compressing
engine, by which air is compressed for starting the torpedoes overboard
and for charging their reservoirs. A small dynamo and engine are also
provided for working a search light, if necessary. The accommodation
provided for the officers and crew is far in advance of anything hitherto
found on board a torpedo boat.
The weather on the morning of Thursday, April 14, was anything rather
than that which would be selected for a trial, or indeed any, trip on the
Thames. At 11 A.M., the hour at which the boat was to leave Messrs.
Yarrow's yard, Isle of Dogs, the wind was blowing in heavy squalls from
the northeast, accompanied by showers of snow and hail. The Italian
government was represented by Count Gandiani and several officers and
engineers. In all there were about thirty-three persons on board. The
displacement of the vessel was as nearly as might be 97 tons. A start was
made down the river at 11:15 A.M., the engines making about 180
revolutions per minute, and the boat running at some 11½ or 12 knots.
During this time the stokehole hatches were open, but the fans were kept
running at slow speed to maintain a moderate draught. The fuel used
throughout the trip was briquettes made of the best Welsh anthracite
worked up with a little tar. The briquettes were broken up to convenient
sizes before being put in the bunkers. This fuel is not of so high
evaporative efficiency as Nixon's navigation coal, but it is more
suitable for torpedo boat work, because it gives out Very little dust,
while the coal in closed stokeholes half smothers the firemen. Watering
only partially mitigates the evil. Besides this, the patent fuel does not
clinker the tube ends--a matter of vital importance.
During the run down to Gravesend, the small quantity of smoke given out
was borne down and away from the tops of the funnels by the fierce head
wind, and now and then a heavy spray broke on the bows, wetting
everything forward. In the engine room preparations were made for taking
indicator diagrams. No attempt was made to drive the boat fast, because
high speeds are prohibited by the river authorities on account of the
heavy swell set up.
The measured mile on the Lower Hope is on the southern bank of the river,
about three miles below Gravesend. Just as the boat passed the town, in
the midst of a heavy rain squall, the stokehole hatches in the deck were
shut, and the dull humming roar of the fans showed that the fires were
being got up. The smoke no longer rose leisurely from the funnels. It
came up now with a rush and violence which showed the powerful agency at
work below. A rapid vibrating motion beneath the feet was the first
evidence that the engines were away full speed. As the boat gathered way
she seemed to settle down to her work, and the vibration almost ceased.
The measured mile was soon reached, and then in the teeth of the
northeaster she tore through the water. The tide and wind were both
against her. Had the tide and wind been opposed, there would have been a
heavy sea on. As it was, there was quite enough; the water, breaking on
her port bow, came on board in sheets, sparkling in the sun, which, the
rain squall having passed, shone out for the moment. As the wind was
blowing at least thirty miles an hour, and the boat was going at some
twenty-six miles an hour against it, the result was a moderate hurricane
on board. It was next to impossible to stand up against the fury of the
blast without holding on. The mile was traversed in less than 2½ minutes,
however; but the boat had to continue her course down the river for
nearly another mile to avoid some barges which lay in the way, and
prevented her from turning. Then the helm was put over, and she came
round. There was no slacking of the engines, and astern of her the water
leaped from her rudder in a great upheaved, foaming mass, some 7 ft. or 8
ft. high. Brought round, she once more lay her course. This time the wind
was on her starboard quarter, or still more nearly aft. The boat went
literally as fast as the wind, and on deck it was nearly calm. The light
smoke from the funnels, no longer beaten down by wind, leaped up high
into the air. Looking over the side, it was difficult to imagine that the
boat was passing through water at all. The enormous velocity gave the
surface of the river the appearance of a sheet of steel for 1 ft. or more
outside the boat. Standing right aft, the sight was yet more remarkable.
Although two 6 ft. screws were revolving at nearly 400 revolutions per
minute almost under foot, not a bubble of air came up to break the
surface. There was no wave in her wake; about 70 ft. behind her rose a
gentle swelling hill.
Her wake was a broad smooth brown path, cut right through the rough
surface of the river. On each side of this path rose and broke the angry
little seas lashed up by the scourging wind. Along the very center of the
brown track ran a thin ridge of sparkling foam, some 2 ft. high and some
20 ft. long, caused by the rudder being dragged through the water. There
was scarcely any vibration. The noise was not excessive. A rapid whirr
due to the engines, and a rythmical clatter due to the relief valve on
one of the port engine cylinders not being screwed down hard enough, and
therefore lifting a little in its seat at each stroke, made the most of
it. The most prominent noise perhaps was the hum of the fans. Standing
forward, the deck seems to slope away downward aft, as indeed it does,
for it is to be noted that at these high speeds the forefoot of the boat
is always thrown up clean out of the water--and the whole aspect of the
boat: the funnels vomiting thin brown smoke, and occasionally, when a
fire door is opened, a lurid pillar of flame for a moment; the whirr in
the engine room; the dull thunder of the fans, produce an impression on
the mind not easily expressed, and due in some measure no doubt to the
exhilaration caused by the rapid motion through the air.
The best way to convey what we mean is to say that the whole craft seems
to be alive, and a perfect demon of energy and strength. Many persons
hold that a torpedo boat is likely to be more useful in terrifying an
enemy than in doing him real harm, and we can safely say that the captain
of an ironclad who saw half a dozen of these vessels bearing down on him,
and did not wish himself well out of a scrape, has more nerve than most
men.
The second mile was run in far less time than that in which what we have
written concerning it can be read, and then the boat turned again, and
once more the head wind with all its discomforts was encountered. Events
repeated themselves, and so at last the sixth trip was completed, and the
boat proceeded at a leisurely pace back again to Poplar. Mr. Crohn,
representing Messrs. Yarrow on board, and all concerned, might well feel
satisfied. We had traveled at a greater speed than had ever before been
reached by anything that floats, and there was no hitch or impediment or
trouble of any kind.
The Italian government may be congratulated on possessing the two fastest
and most powerful torpedo boats in the world. We believe, however, that
Messrs. Yarrow are quite confident that, with twin screw triple expansion
engines, they can attain a speed of 26 knots an hour, and we have no
reason to doubt this.--_The Engineer._
* * * * *