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etc. and would prevent the escape of the valve should its spindle break. To
avoid the galvanic action which takes place when brass and steel in metallic
contact are immersed in sea- water, a renewable protective ring of zinc is
fitted round the hole through the plating where the steel would otherwise
rapidly corrode.

732. Model of large sea-inlet valve. (Scale 1 : 4.) Made in
the Museum from drawings supplied by the Admiralty,
1903. Plate VII., No. 4. N. 2333.

The valve represented is of 20 in. diam. and is shown as arranged for
closing the sea-inlet to the circulating pumps of the main engine condensers ;
it is, however, typical of the class of valve fitted to the larger inlets
throughout the hull of a modern vessel. The valve-box, in addition to its
connection with the sea and the circulating pumps, has usually an extra
flange, as shown, for a pipe by which the circulating water may be taken
from the bilge should a serious leak occur.

The valve is of the screw-down type, opens inwards and has four wings ;
it is loosely attached to its spindle by an undercut lug of horse-shoe shape
cast on the crown of the valve, while the spindle has a solid collar formed
on its end, so that there are no loose pieces in the connection. The spindle
passes through a stuffing-box in the cover of the valve-box, and then
terminates in a left-handed, square-threaded end which engages in a long
nut capable of being rotated by a box key ; this key is extended to any
convenient position and is there supported by a bracket containing an
indicator showing the extent to which the valve is open.

Rotation of the spindle is prevented by its inner end being square and
fitting between guides secured to the cover, while the square-ended nut
through which it works is held in position by a bracket made in halves and
secured to the cover.

The valve is shown fitted to a vessel having a double bottom, the inlets
through the two skins being connected by a conical steel tube riveted to
both the inner and outer plating ; the hole through the outer skin is fitted
with a gun-metal grating, to prevent the entrance of sea-weed, etc., and it is
chiefly to reduce the obstruction the grid occasions that the outer hole is
made so much larger than the valve orifice.

The valve-box is directly attached, by studs and nuts of naval brass, to
a steel facing-ring riveted to the inner skin of the ship, and there is a
similar facing-ring on the inside of the outer skin. To prevent the steel
plate suffering through galvanic action, where the brass castings are in
contact with it and at the same time immersed in sea water, protective
rings of zinc are inserted as indicated in the model.



SLIPWAYS, DOCKS, ETC.

The first requisites of a modern shipbuilding yard are : a
slipway upon which the hull can be built, and a dock to accom-
modate the vessel while it is being completed and fitted, after
launching. In the early days of shipbiiilding, the hard, gently-
rising bank of a tidal river sufficed for the former, and a small
sheltered cove, with yielding bottom, for the latter. Even now
it is very customary to " beach " a small vessel at high water and
execute repairs during the ebbing and flowing of a tide. The



221

increase in the size and weight of vessels, however, led to the
introduction of specially-constructed inclines of wood, stone or
concrete, provided with powerful hauling appliances, and upon
such " slipways " most of our ships are now louilt and repaired.

The first Royal Dockyards were at Deptford, Woolwich and
Portsmouth, all established or greatly developed early in the
16th century, while the oldest commercial docks are those at
London, 1660, Liverpool, 1710, and Hull, 1778.

A "building" slip is usually provided with a row of wood
blocks upon which the various portions of the ship's structure
are gradually built up and secured together ; shores, guys,
ribbands, etc., being used temporarily to hold the parts in their
correct relative positions. When complete, or in a sufficiently
advanced stage, the vessel is launched by being permitted to
slide with its " cradle," down the slipway into the water. The
cradle is a strong wood and iron framework, built under the
vessel, to carry the total weight after the building blocks are
removed, just prior to launching. It is supported on each side
by narrow, well-greased planes, or " ground ways," iipon which
the whole slides when the restraining blocks are removed.

A "repairing" slip is generally fitted with lines of rails,
upon which long trolleys or carriages, fitted with a large
number of wheels and shaped to fit the under-water body
of the vessel, are run ; when deposited on this carriage any
vessel of moderate size can be quickly hauled up high and
dry beyond the reach of the tide.

" Dry " or " graving " docks are used in examining and
repairing the largest vessels and occasionally to retain a hull
during construction. Such docks may be placed with advan-
tage on low-lying lands where there is a considerable rise and
fall of tide. They are formed by excavating a cutting to
suitable dimensions and then lining it with a thick body of
brick, stone, or concrete ; this is provided with a number of
steps or ledges, to receive the heels of the shores or props which
keep the vessel upright when unsupported by the water and
resting upon the blocks arranged under its keel. If the dock
opens into a tidal river or basin, the vessel enters at high
tide, then the entrance is closed and the water pumped out,
or drained by sluices at low tide ; when the repairs are
completed, water is readmitted and the vessel is floated out.

" Floating " docks are employed when excavated docks are
impracticable, or present great engineering difficulties ; they
likewise possess the advantages of rapid construction and
mobility and may be adapted for lifting the largest Atlantic
liners or battleships. They usually consist of floating pon-
toons, enclosing a space fitted similarly to an ordinary dry
dock and provided with large water chambers which when
filled will sink the structure sufficiently to permit of the entry
of a vessel at ordinary draught ; by subsequently emptying
these chambers the buoyancy necessary to raise the vessel above
water-level is exerted.



222

The entrances to docks or basins are closed by means of
gates or caissons. Gates are of wood or iron, pivoted on each
side of the entrance and generally arranged so as to offer, when
closed, a curved or V-shaped surface to the external water.
When a strong movable roadway is necessary at such openings,
or when not to be frequently opened, a caisson takes the place
of gates. It may be either floating or sliding ; the floating
construction is a large hollow chamber of somewhat ship-shape
form with the ends and bottom formed so as to fit into recesses
at the dock entrance ; by admitting water into the caisson it
sinks into position and closes the entrance. Sliding caissons
are moved horizontally along rails or grooves, by means of
machinery, and when opened slide back into covered spaces on
one side of the dock entrance, the top-sides of the caisson being
mechanically lowered to permit of this movement.

A diving-bell, or more generally a close-fitting diving dress
comprising a metal helmet attached to a waterproof jacket, is
used for the survey of the submerged portions of slipways,
docks, caissons, etc., as well as for the inspection of ships'
bottoms while afloat ; complete diving dresses, together with
the necessary tubing and air pumps are for this purpose carried
on all of H.M. ships.

Wood and iron derricks, stationary cranes driven by steam,
air, or water power, together with locomotive and floating cranes,
do the bulk of the heavy lifting work of a shipyard. For
articles of considerable weight or dimensions, such as engines,
boilers, masts, etc., " tripod sheers " are employed. These are
formed of three inclined " legs " or supportSj of circular or rect-
angular section, widely spaced at the base but connected
together at the head, from which a block-pxirchase worked
by a steam winch is suspended. Two of the legs are pivoted
near the edge of the dock or wharf, the third being adjusted
by means of a horizontal screw so as to give the required over-
hang. The legs of the largest sheers are built up of steel
plates and stiffening bars, and take the usual parabolic form
applied to crane jibs, etc. In some cases the legs are given a
permanent overhang by means of guys and backstays attached
to a strong vertical upright at the rear ; this method was also
adopted on the old-fashioned floating "sheer-hulks" used for
the masting of ships.

Note. Several of the ship models are shown with launching ways
(see Nos. 17, 40, 62 and 166), whilst others are represented
on the keel blocks upon which they rest while in dry dock
(see Nos. 64, 96, 98, 103, 105, 237 and 293).

733. Model of the floating dock at St. Thomas. (Scale
1 : 48.) Lent by E. Hodges, Esq., 1878. N. 1486.

This iron structure was built at Cardiff in 1867, from the designs of
Sir F. J. Bramwell, F.R.S., for use at the island of St. Thomas in the West
Indies, where it has proved of great value.



223

The upper portion of the deck is formed of continuous lattice girders
supporting a wide roadway on each side ; the necessary buoyancy is given by
a number of submerged pontoons, which are made portable to facilitate
their overhaul and repair. To lower the dock preparatory to receiving a
ship, water is admitted into these pontoons until they sink sufficiently, and
this is subsequently pumped out so as to cause the structure to rise
under its burden.

Alteration in the immersion or the trim is provided for by six " floats "
or rectangular tanks on each side, which can be independently raised or
lowered by means of vertical screws fixed to the structure and working
in nuts attached to the floats. A single float is shown in its raised
position at one end of the model. A coloured drawing of this dock is
also shown.

Length, 300 ft. breadth, extreme, 100 ft. ; breadth at entrance, 70 ft. ;
height, 42 ft. ; carrying capacity, 3,000 tons.

734. Model and photographs of Bermuda floating dock.
(Scale 1 : 64.) Presented by A. J. Campbell, Esq., 1880.
Plate VII., No. 5. N. 1468 and 1528.

In consequence of the great need of a graving dock, capable of
receiving large vessels on the North American and West Indian station,
it was decided to provide such accommodation at Bermuda ; but, owing to
the porous nature of the rock of which the island is composed, the con-
struction of a stone dock was considered to be impracticable, and it was
decided to adopt one of the floating type patented by Messrs. Campbell,
Johnstone & Co. This iron structure was accordingly built at Silvertown
on the Thames in 1868 and afterwards towed to Madeira by H.M. ships
" Northumberland " and " Agincourt," and from thence to its destination by
H.M. ships " Warrior " and " Black Prince."

The dock is of cellular construction and has nine main transverse water-
tight bulkheads, intersected by seven continuous longitudinal watertight
frames, making a total of forty-eight watertight compartments, each of
which is fitted with valves for admitting or discharging water. Several
smaller additional compartments contain the pumps, mooring cables, and
the steam-driven machinery for working the capstans and cranes.

When employed to dry-dock a vessel of moderate dimensions, water is
first let into the lower compartments of the dock and pumped from thence
to the upper chambers, the whole structure meanwhile sinking until the
valves on the floor of the dock are awash ; these latter are then opened and
the dock sunk sufficiently to enable the vessel to enter. When the vessel is
in position over the blocks, the upper chambers of the dock are gradually
emptied while " breast-shores " are being placed to support the ship, water
is then let out of the intermediate chambers until the bottom of the dock is
dry. For vessels of larger tonnage an increased lifting power is obtained
by using the caissons with which each end of the dock is fitted, the water
contained in them being partly discharged through sluices and partly into
the lower chambers of the dock, as shown in the accompanying diagrams.
The undocking process consists in refilling the spaces in the dock until the
vessel is afloat. By admitting water into compartments on one side only,
the dock can be heeled over sufficiently for all necessary cleaning or repairs
on the opposite side, and in this way the whole of the surface is rendered
accessible for cleaning, etc.

At its station the dock floated in a specially excavated basin, and
was connected to the shore by three long brows or bridges whose free
ends rose and fell with the tidal or other movement of the dock. During
stormy weather the safety of the dock was insured by grounding it, the
structure being then almost submerged. This model was originally con-
structed as a working one for experimental and lecture purposes, but was
finished in detail and the external fittings added at this Museum in 1902.

The leading particulars of the dock were : Total weight of materials,
8,200 tons ; length, overall, 381 ft. ; length, between caissons, 330 ft. ;



224

breadth, between sides, 84 ft.; depth, overall, 74 -4 ft.;- depth, inside,
53-4 ft.; thickness of plates, '31 to -62 in.; and the maximum lifting
power, 10,000 tons. The draught of water when light is 11-17 ft. and
when sunk for docking a large ironclad 50 ft.

Owing to the increased size of warships a new floating dock was built
for Bermuda in 1902 of the following dimensions : Length, overall, 545 ft. ;
breadth, between sides, 100 ft. ; maximum lifting power, 17,500 tons.

735. Lithograph of a tubular floating dock. Presented by
Messrs. (Mark and Standfield, 1878. N. 1511.

This construction of floating dock was patented by Messrs. Clark and
Standfield in 1874.

The floor of the structure is formed of iron cylinders laid horizontally,
and the sides of similar tubes placed vertically. By this arrangement the
side and shape of the dock can be modified to suit special requirements.

736. Model of double-power floating dock. (Scale 1:96.)
I'xMit by Messrs. Clark and Standfield, 1878. N. lf)l 1.

This invention of Messrs. Clark and Standfield uses the buoyancy of
the sides of the dock as well as that of the bottom, the inventors consider-
ing that the high sides of the usual construction form so much unnecessary
weight which has to be lifted with each ship docked. The independent
sides are also used for lifting the rest of the dock when it is being cleaned
or repaired.

The lower pontoon or bottom of the dock has four fixed corner towers,
between which the sides can rise and fall as if in guides ; provision is also
made for locking these sections together in any position.

To place a vessel in such a dock, if the sides are in. the usual elevating
position water is admitted into them and to the body of the dock until the
whole sinks to the lowest level necessary for docking the vessel, the vessel
is then floated in and secured ; the water is now pumped from the main
pontoon, which accordingly rises, while the sides still remain at the lower
level. The sides are then secured to the main pontoon and emptied, thus
raising the whole structure to a still higher level and completing the
operation. The model shows a vessel in position in the dock, supported by
keel blocks and shores.

This general principle has been successfully applied to the largest
modern floating docks.

737. Lithographs and photographs of depositing docks.
(Scale 1 : 240.) Lent by Messrs. Clark and Standfield, 1878.

N. 1511.

This type of dock was introduced by Messrs. Clark and Standfield, who
in 1877 constructed a large dock on this system at Nicolaieff for the Russian
Government, its leading feature enabling it to accommodate vessels of the
exceptional beam found in the circular ironclads.

The dock consists of a number of horizontal pontoons projecting, as
cantilevers, from one side of a long horizontal pontoon resembling a box
girder. This girder, or " side," as it is termed, is of such a depth that it
is never completely submerged, while the cantilever pontoons attached to it
are sufficiently low to allow the vessel to float over them when the arrange-
ment is at its maximum immersion, through water having been admitted to
some of the pontoons.

When a vessel is to be docked she is brought over the submerged
cantilevers and secured in position by ropes and shores ; water is then
pumped out of the pontoons until the dock rises and the vessel bears firmly
on the keel blocks. Sliding bilge blocks are then hauled under the bilges
of the vessel, eo as to form a suitable cradle, and the pumping is proceeded
with until the dock rises to such a height that the vessel is completely above
water level.



225

As the dock has only one side, a special arrangement is employed to
keep the pontoons level at all immersions and with varying loads. This
consists of a large outrigger in the form of a broad shallow pontoon,
projecting from the outside of the main pontoon and capable of sliding in
grooves attached to the side, so that while free to rise or fall it exerts a
constant righting movement on the dock.

The arrangement is thus far equivalent to a floating dock, but its chief
merits consist in the means by which it is enabled to deposit the vessel
raised on a suitable staging, so that the number of ships that can be simul-
taneously docked depends simply upon the number of stages provided.
These stagings are formed of iron or timber piles, braced together and
forming narrow piers, each about 5 ft. broad, and usually from 10 ft. to
15 ft. apart. The cantilevers of the floating dock are arranged at corre-
sponding distances, so that they can pass between these piers, and thus when
the pontoon is lowered will deposit the vessel on the piers. Keel and bilge
blocks are used as before ; in one drawing air cushions are shown fitted in
the position of the bilges to facilitate the operation of docking by reducing
the shoring required.

The Nicolaieit' dock, of which three photographs are shown, has ten
cantilever pontoons projecting from the "side," which is made in three
separate lengths, which can be used independently for small vessels. The
side is subdivided longitudinally into compartments, 15 ft. and 5 ft. wide
alternately ; in the upper portion of each length there is a 25 h.p. semi-
portable steam engine driving a vertical centrifugal pump 2*3 ft. diam. for
emptying it. The cantilever pontoons are divided into watertight compart-
ments, a number of which are permanently sealed, so that it is impossible to
entirely sink the dock by any mistake.

738. Model of dock entrance and caisson. (Scale 1 : 48.)
Presented by A. J. Campbell, Esq., 1880. N. 1528.

This represents a dock entrance closed by a caisson instead of the
more usual dock gates ; it is sometimes from its shape called a ship-
caisson.

The caisson is formed of iron plating, stiffened internally with angle
irons, diagonal braces, and horizontal decks ; these decks and bulkheads
also divide it into several watertight compartments, some of which form air
chambers which provide the necessary flotation, while others are ballasted.
When the dock entrance is to be closed the caisson is floated into its place
between the entrance walls, and water is admitted into the air chambers
until the keel of the caisson sinks into a recess in the sill. The ends of the
caisson are also provided with ribs which enter recesses in the side walls, so
that when any subsequent alteration is made in the water level on either
side of it the side pressure tends to keep the sill and side joints tight ;
wooden facings also assist in securing a good joint. The upper deck of the
caisson when in position forms a wide and strong bridge ; but the arrange-
ment, being less convenient than dock gates, is not generally used for
entrances that have to be frequently opened.

739. Model of apparatus for repairing dock gates. (Scale
1 : 12.) Contributed by W. Smith, Esq., 1860. N. 369.

This is an apparatus patented by Mr. B. Hockin in 1858 for enabling
repairs to be done to the submerged portions of dock gates without removing
the gates or interfering with their working. It consists of a three-sided
chamber, the open side of which is intended to fit against the face of the
gate with a watertight indiarubber joint. The bottom of the chamber has
a projecting flange to be passed under the bottom edge of the gate ; for
this purpose the gate may be slightly lifted by means of the vertical timbers
provided with yokes or cross bars and lifting screws. When the chamber
is in position the water is pumped out of it, and the workman is able to
descend and execute the necessary repairs.

u 0773. P



226

740. Models of combined floating dock and wreck-raising
apparatus. (Scales 1 : 384, 1 : 96 and 1 : 24.) Presented by
Druitt Halpin, Esq., 1901. N. 1521.

These models were used to illustrate a paper read by Mr. Halpin before
the United Service Institution in 1870, explaining an expansion of a scheme
he had prepared in detail for raising H.M.S. " Yanguard," sunk by collision,
1875.

The dock consists of two ship-shaped self-propelled iron hulls, sub-
divided by bulkheads and joined together by cross girders so as to form a
pontoon capable of lifting and transporting the largest vessels, either above
or below the surface of the water. The vessel was to be raised by means of
numerous 100-ton wire cables attached to its side and secured to the floating
dock, by which the wreck could be raised and carried to shallow water
where, after the hull had been repaired and floated off, the dock could be
sufficiently immersed to receive the vessel and then lift it for completing
the repairs.

A detailed model is shown of the means proposed for attaching the wire
ropes to the sunken ship without the use of divers. The scheme depended
upon the use of a long tube, which could be towed to the scene of the wreck
and there weighted by the admission of water till it floated vertically ; it was
then to be sunk till its foot bedded upon the sea bottom while the upper
end remained above water. From the side of the tube projects a drilling
post, carrying a wire brush for cleaning the side of the ship and also a large
drilling cutter driven by an air motor, and this mechanism was to be con-
trolled by a man within the open tube who, after drilling a hole could by
apparatus provided pass through it a stretcher attached to one end of a
lifting cable. The vertical open shaft was then to be sufficiently floated to
enable it to be taken to a fresh position ready for the attachment of another
cable and so on, the depth at which the apparatus could be worked
depending upon the length of shaft that could be manipulated and not upon
the hydrostatic pressure as when divers are employed.



741. Lithograph of a wreck-raising pontoon. Presented by
Messrs. T. Christy & Co., 1873. N. 1358.

This shows a device patented in 1871 by Messrs. Siebe, Gorman, and
Christy. The pontoon consists of twin hulls, self-propelled, and is provided
with a number of continuous chains led over pulleys fitted to the inner deck
edges. These chains are passed, by divers, under the submerged vessel and
then by means of steam-hauling gear are drawn in from each side simul-
taneously till the wreck is lifted above the water level and supported between
the twin hulls ; in this position the hull may be either repaired and pumped
out, or be carried into shallower waters. Exceptional lifting power may be
obtained by emptying water spaces in the pontoon itself.

742. Model of wreck-raising apparatus. (Scale 1 : 48.)
Presented by Druitt Halpin, Esq., 1901. N. 2264.

This shows the method successfully adopted in raising the iron paddle-
ship " Edith " belonging to the London and North Western Railway Co.,
which in 1875 sank after collision in Holyhead harbour to a depth of 36 ft.
Her registered dimensions were : Length, 250 -6 ft. ; depth, 14 '4 ft. ;
breadth, 30*1 ft.; gross tonnage, 758 tons; displacement, 1,180 tons.
Submerged the total weight to be lifted was 800 tons.

Owing to the presence of paddle-boxes it was decided to use camels at
the bow and stern, calculation having shown that the vessel was strong
enough as a girder to be lifted in this way. The lifting apparatus employed
consisted of four rectangular caissons each 59 ft. long, 15 ft. wide, and



227

15 ft. deep, constructed of '375-in. plate, with three bulkheads in each
caisson and the flat surfaces supported by internal timber struts. Each



Online LibraryScience Museum (Great Britain)Catalogue of the naval and marine engineering collection in the ... museum .. → online text (page 31 of 58)