BOAT AND SHIP RAISING LIFTS
In modern locomotion, whether by land or water, it becomes increasingly
necessary to keep the way unobstructed where traffic is confined to the
narrow limits of a pair of rails, a road, or a canal channel. We widen
our roads; we double and quadruple our rails. Canals are, as a rule,
not alterable except at immense cost; and if, in the first instance,
they were not built broad enough for the work that they are afterwards
called upon to do, much of their business must pass to rival methods of
transportation. Modern canals, such as the Manchester and Kiel canals,
were given generous proportions to start with, as their purpose was to
pass ocean-going ships, and for many years it will not be necessary to
enlarge them. The Suez Canal has been widened in recent years, by means
of dredgers, which easily scoop out the sandy soil through which it
runs and deposit it on the banks. But the Corinth Canal, cut through
solid rock, cannot be thus economically expanded, and as a result it
has proved a commercial failure.
Even if a canal be of full capacity in its channel-way there are
points at which its traffic is throttled. However gently the country
it traverses may slope, there must occur at intervals the necessity of
making a lock for transferring vessels from one level to the other.
Sometimes the ascent or descent is effected by a series of steps,
or flight of locks, on account of the magnitude of the fall; and in
such cases the loss of time becomes a serious addition to the cost of
transport.
In several instances engineers have got over the difficulty by
ingenious hydraulic lifts, which in a few minutes pass a boat through
a perpendicular distance of many feet. At Anderton, where the Trent
and Mersey Canal meets the Weaver Navigation, barges up to 100 tons
displacement are raised fifty feet. Two troughs, each weighing with
their contents 240 tons, are carried by two cast-iron rams placed
under their centres, the cylinders of which are connected by piping.
When both troughs are full the pressure on the rams is equal, and
no movement results; but if six inches of water be transferred from
the one to the other, the heavier at once forces up the lighter. At
Fontinettes, on the Neufosse Canal, in France, at La Louvière, in
Belgium, and at Peterborough, in Canada, similar installations are
found; the last handling vessels of 400 tons through a rise of 65 feet.
Fine engineering feats as these are, they do not equal the canal-lift
on the Dortmund-Ems Canal, which puts Dortmund in direct water
communication with the Elbe, and opens the coal and iron deposits
of the Rhine and Upper Silesia to the busy manufacturing district
lying between these two localities. About ten miles from its eastern
extremity the main reach of the canal forks off at Heinrichenburg,
from the northward branch running to Dortmund, its level being on
the average some 49 feet lower than the branch. For the transference
of boats an "up" and "down" line of four locks each would have been
needed; and apart from the inevitable two hours' delay for locking,
this method would have entailed the loss of a great quantity of
precious water.
Mr. R. Gerdau, a prominent engineer of Düsseldorf-Grafenburg, therefore
suggested an hydraulic lift, which should accommodate boats of 700
tons, and pass them from the one level to the other in five minutes.
This scheme was approved, and has recently been completed. The
principle of the lift is as follows:--A trough, 233 feet long, rests
on five vertical supports, themselves carried by as many hollow
cylindrical floats moving up and down in deep wells full of water. The
buoyancy of the five floats is just equal to the combined weight of
the trough and its load, so that a comparatively small force causes
the latter to rise or fall, as required. By letting off water from the
trough--which is, of course, furnished with doors to seal its ends--it
would be made to ascend; while the addition of a few tons would cause a
descent. But this would mean waste of water; and, were the trough not
otherwise governed, a serious accident might happen if a float sprang a
leak. Motion is therefore imparted to the trough by four huge vertical
screws, resting on solid masonry piers, and turning in large collars
attached to the trough near its corners. All the screws work in unison
through gearing, as they are sufficiently stout to bear the whole load;
even were the floats removed, no tilting or sudden fall is possible.
The screws are driven by an electric motor of 150 horse-power, perched
on the girders joining the tops of four steel towers which act as
guides for the trough to move in, while they absorb all wind-pressure.
Under normal circumstances the trough rises or sinks at a speed of
four inches per second. The total mass in motion--trough, water, boat,
and floats--is 3,100 tons. Our ideas of a float do not ordinarily rise
above the small cork which we take with us when we go a-fishing, or
at the most above the buoy which bobs up and down to mark a fair-way.
These five "floats"--so called--belong to a very much larger class of
creations. Each is 30 feet across inside and 46-1/2 feet high. Their
wells, 138 feet deep, are lined with concrete nearly a yard thick, to
ensure absolute water-tightness, inside the stout iron casings, which
rise 82 feet above the bottom.
In view of the immense weight which they have to carry, the piers under
the screw-spindles are extremely solid. At its base each measures 14
feet by 12 feet 4 inches, and tapers upwards for 36 feet till these
dimensions have contracted to 8 feet 10 inches by 6 feet 6 inches. The
spindles, 80 feet long and 11 inches in diameter, must be four of the
largest screws in existence. To make it absolutely certain that they
contained no flaws, a 4-inch central hole was drilled through them
longitudinally--another considerable workshop feat. If shafts of such
length were left unsupported when the trough was at its highest point,
there would be danger of their bending and breaking; and they are,
therefore, provided with four sliding collars each, connected each to
its fellow by a rod. When the trough has risen a fifth of its travel
the first rod lifts the first collar, which moves in the guide-pillars.
This in turn raises the second; the second the third; and so on. So
that by the time the trough is fully raised each spindle is kept in
line by four intermediate supports.
The trough, 233 feet long by 34-1/2 feet wide, will receive a vessel
223 feet long between perpendiculars. It has a rectangular section, and
is built up of stout plates laid on strong cross-girders, all carried
by a single huge longitudinal girder resting on the float columns.
One of the most difficult problems inseparable from a structure of
this kind is the provision of a water-tight joint between the trough
and the upper and lower reaches of the canal. At each end of the
trough is a sliding door faced on its outer edges with indiarubber,
which the pressure of the water inside holds tightly against flanges
when pressure on the outside is removed. The termination of the
canal reaches have similar doors; but as it would be impossible to
arrange things so accurately that the two sets of flanges should be
water-tight, a wedge, shaped like a big U, and faced on both sides with
rubber, is interposed. The wedge at the lower reach gate is thickest
at the bottom; the upper wedge the reverse; so that the trough in both
cases jams it tight as it comes to rest. The wedges can be raised or
lowered in accordance with the fluctuations of the canals.
After thus briefly outlining the main constructional features of the
lift, let us watch a boat pass through from the lower to the upper
level. It is a steamer of 600 tons burden, quite a formidable craft
to meet so far inland; while some distance away it blows a warning
whistle, and the motor-man at his post moves a lever which sets the
screw in motion. The trough sinks until it has reached the proper
level, when the current is automatically broken, and it sinks no
further. Its travel is thus controllable to within 3/16 of an inch.
An interlocking arrangement makes it impossible to open the trough
or reach gates until the trough has settled or risen to the level of
the water outside. On the other hand, the motor driving the lifting
screws cannot be started until the gates have been closed, so that an
accidental flooding of the countryside is amply provided against.
A man now turns the crank of a winch on the canal bank and unlocks the
canal gate. A second twist couples the gates between the canal and the
trough together and starts the lifting-motors overhead, which raise the
twenty-eight ton mass twenty-three feet clear of the water-level. The
boat enters; the doors are lowered and uncoupled; the reach gate is
locked. The spindle-motor now starts; up "she" goes, and the process
of coupling and raising gates is repeated before she is released into
the upper reach. From start to finish the transfer occupies about five
minutes.
If a boat is not self-propelled, electric capstans help it to enter and
leave the trough. Such a vessel could not be passed through in less
than twenty minutes.
Putting on one side the ship dry docks, which can raise a 15,000 ton
vessel clear of the sea, the Dortmund hydraulic lift is the largest
lift in the world, and the novelty of its design will, it is hoped,
render the above account acceptable to the reader. Before leaving the
subject another canal lift may be noticed--that on the Grand Junction
Canal at Foxton, Leicestershire--which has replaced a system of ten
locks, to raise barges through a height of 75 feet.
The new method is the invention of Messrs. G. and C. B. J. Thomas.
In principle it consists of an inclined railway, having eight rails,
four for the "up" and as many for the "down" traffic. On each set of
four rails runs a tank mounted on eight wheels, which is connected with
a similar tank on the other set by 7-inch steel-wire ropes passing
round winding drums at the top of the incline. The tanks are thus
balanced. At the foot of the incline a barge which has to ascend is
floated into whichever tank may be ready to receive it, and the end
gate is closed. An engine is then started, and the laden tank slides
"broadside on" up the 300-foot slope. The summit being reached, the
tank gates are brought into register with those of the upper reach,
and as soon as they have been opened the boat floats out into the
upper canal. Boats of 70 tons can be thus transferred in about twelve
minutes, at a cost of but a few pence each. On a busy day 6,000 tons
are handled.
[Illustration:
_By permission of_]
[_Mr. Gordon Thomas._
A BOAT LIFT
A canal barge lift which has superseded ten locks at Foxton,
Leicestershire. Two tanks, balancing one another, run on separate
tracks up and down an incline. At the bottom and top of the incline the
tank is submerged so that a barge may float in or out.]
A SHIP-RAISING LIFT
The writer has treated one form of lift for raising ships out of the
water--the floating dry dock--elsewhere,[21] so his remarks in this
place will be confined to mechanism which, having its foundations on
Mother Earth, heaves mighty vessels out of their proper element by
the force of hydraulic pressure. Looking round for a good example of
an hydraulic ship-lift, we select that of the Union Ironworks, San
Francisco.
Some years ago the works were moved from the heart of the city to the
edge of Mission Bay, with the object of carrying on a large business
in marine engineering and shipbuilding. For such a purpose a dry
dock, which in a short time will lift a vessel clear of the water for
cleaning or repairs, is of great importance to both owners and workmen.
By the courtesy of the proprietors of _Cassier's Magazine_ we are
allowed to append the following account of this interesting lift.
The site available for a dock at the Union Ironworks was a mud-flat.
The depth of soft mud being from 80 to 90 feet, would render the
working of a graving dock (_i.e._ one dug out of the ground and pumped
dry when the entrance doors have been closed) very disagreeable; as
such docks, where much mud is carried in with the water, require a long
time to be cleaned and to dry out. Plans were therefore prepared by Mr.
George W. Dickie for an hydraulic dock, including an automatic control,
which the designer felt confident would meet all the requirements
of the situation, and which, after careful consideration, the Union
Ironworks decided to build. Work was begun in January, 1886, and the
dock was opened for business on June 15th, 1887--a very fine record.
This dock consists of a platform built of cross and longitudinal steel
girders, 62 feet wide and 440 feet long, having keel blocks and sliding
bilge blocks upon which the ship to be lifted rests. The lifting power
is generated by a set of four steam-driven, single-acting horizontal
plunger pumps, the diameter of the plungers being 3-1/2 inches and the
stroke 36 inches. Forty strokes per minute is the regular speed.
There is a weighted accumulator, or regulator, connected with the
pumps, the throttle valve of the engines being controlled by the
accumulator.[22] The load on the accumulator consists of a number of
flat discs of metal, the first one about 14 inches thick and the others
about 4 inches thick, the diameter being about 4 feet. The first disc
gives a pressure of 300 lbs. per square inch. This is sufficient to
lift the dock platform without a ship, and is always kept on.
In lifting a ship, as she comes out of the water and gets heavier on
the platform, additional discs are taken on by the accumulator ram as
required. The discs are suspended by pins on the side catching into
links of a chain. The engineer, to take on another disc, unhooks the
throttle from the accumulator rod, runs the engine a little above
the normal speed, the accumulator rises and takes the weight of the
disc to be added; the link carrying that disc is thus relieved and is
withdrawn. The engineer again hooks the accumulator rod to the engine
throttle, and the whole is self-acting again until another weight is
required. When all the discs are on the ram the full pressure of 1,100
lbs. per square inch is reached, which enables a ship of 4,000 tons
weight to be raised.
There are eighteen hydraulic rams on each side of the dock. These rams
are each 30 inches in diameter and have a stroke of 16 feet; and as
the platform rises 2 feet for 1 foot movement of the rams, the total
vertical movement of the platform is 32 feet. When lowered to the
lowest limit there are 22 feet of water over the keel blocks at high
tide.
The foundations consist of seventy-two cylinders of iron, which
extend from the top girders to several feet below the mud line.
These cylinders are driven full of piles, no pile being shorter than
90 feet. The cylinders are to protect the piles from the _teredo_
(the timber-boring worm), which is very destructive in San Francisco
Harbour. A heavy cast-iron cap completes each of the foundation
piers, and two heavy steel girders extend the full length of the dock
on each side, resting on the foundation piers and uniting them all
longitudinally. The hydraulic cylinders are carried by large castings
resting on the girders, each having a central opening to receive a
cylinder, which passes down between the piers. There are thirty-six
foundation piers, and eighteen hydraulic cylinders on each side of the
dock.
On the top of each hydraulic ram is a heavy sheave or pulley, 6 feet
in diameter, over which pass eight steel cables, 2 inches in diameter,
making in all 288 cables. One end of each cable is anchored in the
bed-plates supporting the hydraulic cylinders, while the other end is
secured to the side girders of the platform. Each of the cables has
been tested with a load of 80 tons, so that the total test load for the
ropes has been 21,000 tons.
In lifting a ship the load is never evenly distributed on the platform.
There is, in fact, often more than one ship on the platform at once.
Some rams, therefore, may have a full load and others much less. Under
these conditions, to keep the platform a true plane, irrespective of
the irregular distribution of the load, Mr. Dickie designed a special
valve gear to make the action of the dock perfectly automatic. Down
each side of the dock a shaft is carried, operated by a special engine
in the power house. At each hydraulic ram this shaft carries a worm,
gearing with a worm-wheel on a vertical screw extending the full height
reached by the stroke of the ram. This screw works in a nut on the end
of a lever, the other end of which is attached to the ram. Between the
two points of support a rod, working the valves--also carried by the
ram--engages with the lever. If at a given moment the screw-end is
raised, say, six inches, the lever opens the valve. As the ram rises,
the lever, having its other end similarly lifted by the rise, gradually
assumes a horizontal position, and the valve closes.
To lift the dock the engine working the valve shaft is started, and
with it the operating screws. These, through the levers, open the inlet
valves. The rams now begin to move up: if any one has a light load it
will move up ahead of the other, but in doing so it lifts the other end
of the lever and closes the valve. In fact, the screws are continually
opening the valves, while the motion of the rams is continually closing
them, so that no ram can move ahead of its screw, and the speed of the
screw determines the rate of movement of the lifting platform.
To lower the dock, the engine operating the valve shaft is reversed,
and the screws and levers then control the outlet valves as they
controlled the inlet valves in raising. When the platform has reached
the limit of its movement, a line of locks on top of the foundation
girders, thirty-six on each side, are pushed under the platform by an
hydraulic cylinder, and the platform is lowered on to them, where it
rests until the work is done on the ship; then the platform is again
lifted, the locks are drawn back, and the platform with its load is
lowered until the ship floats out. All the operations are automatic.
Since the dock was opened well over a thousand ships have been lifted
in it without any accident whatever; the total register tonnage
approaching 2,000,000. The great favour in which the dock is held by
shipowners and captains is partly due to the fact already mentioned,
that the ship is lifted above the level of tide water, where the air
can circulate freely under the bottom, thus quickly taking up all the
moisture, and where the workmen can carry on operations with greater
comfort.
When extensive repairs have to be undertaken on iron or steel vessels,
the fact that this dock forms part of an extensive shipbuilding plant,
and is located right in the yard, enables such repairs to be executed
with despatch and economy. Several large steamships have had the
under-water portions of their hulls practically rebuilt in this dock.
The steamship _Columbia_, of the Oregon Line, had practically a new
bottom, including the whole of the keel, completed in twenty-six days.
This is possible, because every facility is alongside the dock and the
bottom of the vessel is on a level with the yard.
This being the only hydraulic dock controlled automatically (in 1897),
it has attracted a large amount of attention from engineering experts
in this class of work. English, French, German, and Russian engineers
have visited the Union Iron Works to study its working, and their
reports have done much to bring the facilities offered to shipping for
repairs by the Union Iron Works to the notice of shipowners all the
world over.
FOOTNOTES:
[21] _The Romance of Modern Engineering_, pp. 383 foll.
[22] For explanation of the "accumulator," see the chapter on Hydraulic
Tools (p. 81).