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pair of caissons was rigidly connected by 11 lattice and plate girders,
which retained them at a distance apart of 32 5 ft., and on the top of the
girders were four 12-in. square timber blocks supporting 20 wrought iron
lattice columns, the caps of which formed nuts and capstan heads for lifting
screws.

These camels were floated into position over the vessel and sunk till the
tops were awash ; a hook attached by a wire rope to each of the lifting
screws was then passed into the side-lights of the vessel, or into holes 5 in.
diameter cut under the doubling plate by divers, and the whole of the cables
screwed taut ; the water was then pumped out from the caissons by centri-
fugal pumps and the vessel raised, beached, and towed into dry dock. It
was found that though submerged for more than two years the engines were
but little injured, and the vessel subsequently resumed her station. The
caissons were afterwards utilised as water tanks at Holyhead.

743. Whole model of wreck-raising lighter. (Scale 1 : 48.)
Made in the Museum from drawings supplied by the
Conservators*of the River Thames, 1908. Plate VII., No. 6.

N. 2468.

This wreck-lifting vessel was built of iron at Greenwich in 1882 by
Messrs. J. and G-. Rennie for the use of the Thames Conservancy Board.

The hull is vertical sided and flat-bottomed ; for the purpose of lifting
operations, a narrow " well " or opening 60 ft. in length, is provided along
the centre line of the vessel. Throughout this central portion the design is
of the " double-hulled " type, each half-body being subdivided into six water-
tight compartments, while before and abaft this portion there are strongly
constructed holds or living-spaces of ordinary form. The starboard side is
sectioned to show the general character of the constructional work in the
vessel.

Steel- wire lifting ropes, 7 in. to 9 in. circumference, are here used in
conjunction with eight Bullivant's automatic nippers or cable compressors
(see No. 1104), each capable of sustaining a pull of 100 tons. A series of cast-
iron fair- leads secured to the edges of the well keep the ropes in position,
and the adjacent bollards give them a direct lead to the nippers.

When in use the ropes pass down the well and are fastened to slings
placed around the submerged wreck. At low tide the slack rope is taken ill
and secured ; the subsequent rise of tide lifts both lighter and wreck which
are then towed into shallower water. Several lighters, some of which are
provided with steam pumps, winches, and other appliances, are used when
large vessels have to be raised. With a freeboard of 1-5 ft., this lighter
will carry 400 tons.

Length, 105 ft. ; breadth, moulded, 28 ft. ; depth of side, 9 -5 ft.

744. Fixed masting sheers. (Scale 1 : 20.) Presented by the
Admiralty, 1864. N. 1014.

This shows the jetty and sheers for erecting the masts of battleships,
originally used at Sheerness Dockyard which was opened in 1823.

The sheers consist of three compression members connected at the top
by extensive lashings and considerably spreading at the feet, where they fit
into cast-iron sockets. These members are of built-up timber, hooped with
iron bands : at intervals the three legs are tied together by iron rods. This
compound jib is tied back by four chains which, after being led through an
independent mast at the back, are secured to anchorages in the masonry ;
on the jib side this mast is separately stayed by two inclined struts. The
mast is also fitted with crosstrees and a topmast for signalling purposes, etc.

The lifting tackle consists of blocks and falls worked by capstans.

p 2



228

745. Model of a float for discharging cargo. (Scale 1 : 64.)
Contributed by Messrs. Wm. Cory and Sons, 1862.

N. 829.

This represents a design patented by Mr. Wm. Cory, junr., in 1861,
for a floating pontoon for discharging cargo. With tapering ends it has
considerable beam, to minimise listing.

It is provided with a gantry on which are narrow- gauge rails for coal
tubs, and there are six hydraulic jib cranes of 20*5 ft. radius, for unloading
coal from vessels and discharging it by screens and shoots into barges lying
alongside. The pontoon shown is intended for discharging vessels up to
900 tons burden.

Length, 250ft. ; breadth, 90 ft. ; depth, 14 -5 ft.

746. Model of Turnbull's derrick. (Scale 1 : 8.) Lent by
Messrs. G. S. Yuill & Co., 1894. N. 2039.

This represents an arrangement of derrick introduced by Mr. J. Tumbull
for taking in or discharging cargo. There are four derricks arranged round
the mast, each having a steam winch on the deck. When the load is lifted
by any derrick its jib swings round automatically, either towards the centre
line of the ship or from there to the side, according to which of two sockets
the pin forming the heel of the derrick is placed in. The jibs are each
supported by an outrigger fixed to a clamp on the mast, the extremities of
the outriggers being so held by guys that the eye to which the jib is tied is
almost vertically over the centre of the line joining the two socket-holes,
but slightly forward of the holes in the fore- socket plate and aft of the
holes in the after plate. The result is that the pull of the chain acts in a
direction passing between the two sockets, and thus there is a tendency for
the loaded jib to turn round one way or the other according to the hole into
which its heel is put.

The two hatchways and the positions of the four winches are marked
upon the deck.



747. Model of diving bell. (Scale 1: 12.) Presented by
Prof. John Taylor, M.D., 1874. N. 1346.

The diving bell in its modern form was introduced by Smeaton in 1788,
although many attempts in a similar direction had previously been made.
As now generally constructed it consists of a chamber built of plates about
4 in. thick, open below, but with the bottom edge turned up so as to carry
ballast and also to stiffen it. The air is supplied through a flexible pipe
entering the chamber at the top.

In the modification represented the air is introduced in an upward jet
near the mouth, so that should the supply pipe burst the water would not
rise within the bell. The same result is usually secured by fitting the supply
orifice with a non-return valve, generally made of leather.

748. The original closed diving helmet. Presented by W. A.
Gorman, Esq., 1881, N. 1543.

Augustus Siebe had in 1829 invented the open helmet, which was a
small diving bell surrounding the head only, and was therefore of only
somewhat limited application. In 1839, however, he constructed the closed
helmet shown, which enabled the diver to work in any position and to a
depth of about 100 ft. ; with modern apparatus of the same type the present
working limit is about 200 ft., or 87 Ib. pressure.

The helmet and breastplate shown are made of sheet copper, and they
are connected together by a relieved screw joint. The breastplate is secured



229

to the diving dress of waterproof material by screws and washers fitted with
wing nuts. There are two windows in the helmet, and at the back is the
attachment for the air supply pipe, fitted with a non-return valve. The
vitiated air is discharged directly into the water through an adjustable valve,
by closing which the diver can increase his buoyancy and so rise, while a
small two-way valve in front allows the pressure inside to fall when reaching
the surface.



749. Model of cofferdam to screw aperture. (Scale 1 : 48.)
Lent by the Royal United Service Institution, 1903.

N. 2323.

This represents the stern body of H.M.S. " Royal Alfred," 1864 (see
No. 81), and the details of a temporary wooden cofferdam used to facilitate
repairs to the propeller shaft without the vessel being dry- docked.

Two strong wooden frames were first made, which fitted closely against
the stern and rudder-posts respectively, on each side of the screw-aperture.
These formed watertight shields, and when lowered into position became
the sides and bottom of the cofferdam, access to the interior of which was
obtained through the screw " well " on the main deck a lifting propeller
being usually fitted to ships-of-war at this date. Internal struts, stays and
clamps, with a few external bolts and chains, placed in position by a diver,
held the sides of the cofferdam to one another and to the adjacent portions
of the ship. After the contained water was pumped out a clear space,
8 ft. long, 4 ft. wide, and 18 ft. high, was obtained in the vicinity of the
propeller- shaft.

750. Model of plates for stopping holes in ships. (Scale
1 : 12.) Lent by John McCool, Esq., 1872. N. 1333.

These devices, for stopping leaks, shot holes, etc., in iron ships while at
sea, were patented by Mr. McCool in 1871. .

In one method a weighted line is dropped through the hole, grappled for,
brought on deck, and a washer plate attached, which is then drawn back by
the line so as to cover the hole ; it is finally secured by a bolt.

The other arrangement consists of a rubber-faced metal plate, provided
with a hinged bar which is pushed through the hole and then turned so as to
form a bridge against which the plate can be screwed.

751. Model of mat for stopping holes in ships. (Scale 1 : 3.)
Lent by Messrs. Creswell & Co., 187(5. N. 1401.

This extensively-adopted mat for covering shot-holes and leaks in ships
was patented in 1875 by Lieut, (afterwards Admiral) S. Makaroff, of the
Russian Navy, but is only an adaptation of an old device.

It consists of two similar pieces of canvas, from 5 ft. to 20 ft. square,
sewn together on a matting made of plaited -rope ; on one side of this is
oakum or cocoanut fibre. The whole resembles a door mat bordered with
rope, and is drawn over the damaged portion of the hull by lines.



LIGHTHOUSES, ETC.

Lighthouses, to serve as landmarks both by day and night,
have been generally erected on conspicuous or dangerous
positions in the vicinity of important navigable routes since



230

B.C. 331, when the famous Pharos of Alexandria was built.
The Romans were particularly energetic in this matter, and the
remains of one of their lighthouses still exists at Dover. The
early lighthouse was a tower or beacon, carrying a brazier in
which wood or coal was burnt at night so as to give an all-round
illumination, which was, however, fitful and unreliable ; the
arrangement survived, however, till 1822 in England, and to an
even later period abroad.

The modern construction of lighthouse varies according to
the site. In the most exposed positions, and where founded on
a tidal rock, the foundation is quarried out of the solid, and the
masonry of the base is built in blocks joggled together ; this
solid structure rises to a height of from 20 to 30 ft., when the
rooms begin and the masonry is carried up hollow to the lantern.
In an estuary, a braced structure erected on screw piles of
wrought iron is usually adopted, while for the top of a cliff
beyond the reach of waves, a brick or stone tower is sufficiently
stable.

Lightships are usually established to indicate the position of
dangerous shoals and in similar situations where the foundation
for a permanent structure would present exceptional difficulties.
During the day, their colour and a large ball on the masthead
indicate their meaning, while at night they display a light
similar to that of a lighthouse, although not of the same high
order. Recently the value of lightships has been further in-
creased by placing them in telegraphic communication with the
shore, by which means they are enabled to convey information
of disasters that woiild not otherwise be known by those on
shore. A lightship was placed at the Nore as early as 1731.

Considerable development has taken place in the illumina-
tion of lighthouses. The early beacons, which were estimated
to have burnt about one ton of fuel per night, were followed
in the 16th century by oil lamps which, with a flat torch-
like wick, gave a better but still very unsatisfactory light ;
Smeaton, in his " Eddystone " lighthouse of 1759, lighted it by
24 candles, each weighing 4 Ib. Argand invented his annular
wick in 1789, and Rumford increased the illuminating power of
the arrangement by placing several of these wicks concentric
with each other ; seven, eight, or nine wicks are thus used in
some modern oil lamps for this purpose. The commercial
introduction of mineral oils in 1860, and their adoption in
lighthouses in 1870, considerably improved the general illu-
mination, and also reduced the cost of oil lighting. Coal gas,
when readily available, has proved itself more convenient and
economical than oil. Since the close of the 19th century the
use of incandescent mantles with oil or gas burners has greatly
added to the efficiency of these illuminants. Acetylene gas
has also been successfully adapted for lighthouse use. The
electric light has, however, some of the advantages possessed
by gas and far greater power, but as it is considered to have



231

but little more penetrative effect during foggy weather and
is certainly more expensive, its application has but slowly
extended ; it was so long ago as 1858 that the lighthouse at
the South Foreland was first lit by electricity.

To concentrate the rays from the illuminant, so as to avoid
loss due to all-round dispersion, reflectors built up of small
pieces of mirror-glass were first used ; these were replaced by
spherical reflectors, and subsequently by parabolic reflectors in
metal, in which the reflected rays were discharged as parallel
beams : these systems, relying on reflection only, are known as
" catoptric." In 1849, Thomas Stevenson reduced both the
direct and reflected rays into one parallel beam, by placing a
lens in front of the light and a hemispherical reflector behind
it ; being a combination of a refractor and a reflector, the
arrangement belongs to the " catadioptric " class. In 1822,
Augustus Fresnel introduced the " dioptric " system, in which
refraction only is used. To avoid the losses and other defects
connected with the use of large thick lenses he substituted a
small one in the centre and surrounded it with annular prisms
set in frames ; in the original arrangement portions of the
light escape above and below, but this defect has since been
remedied.

The three classes of light now shown are (a) " fixed," the
earliest and still more widely used form, but one which is
hardly distinctive enough for much frequented routes ; (b)
u flashing," showing flashes or groups of flashes at short
intervals, and thus telegraphing its name, also concentrating
the whole energy of the light into two or three comparatively
narrow beams ; (c) " occulting," or " eclipsing " lights, which,
although resembling fixed lights most of the time, have one,
two, or three short eclipses, by which their identity is established
without any considerable interval of darkness occurring.

For use during fog, when lighthouses would cease to be of
value either by day or night, some form of acoustic apparatus is
always fitted to both lighthouses and light-vessels. Bells, guns,
steam or compressed air whistles, reed trumpets and sirens have
all been adopted, but for the most exposed situations the com-
pressed-air siren is resorted to, on account of the penetrating
and distinctive notes it gives. Submerged bells as fog-signals
have been widely adopted on lightships, shore-stations arid large
seagoing A^essels since 1905 ; when fitted with suitable receiving
apparatus, vessels are enabled to hear such submarine signals
at far greater distances than aerial signals and also to locate
them with sufficient accuracy for safe navigation.

Buoys and beacons are small signals used to define the
limits of a navigable channel in a river or estuary. They vary
from a bunch of brushwood on a pole to the can-buoy of boiler-
plate which is often fitted with a gas light and bell ; but such
arrangements are only of very local value.



232

All of these provisions in England and Wales are arranged
and controlled by the Corporation of the Trinity House,
originally a semi-religious body established at Deptford, but
incorporated in 1514, and which has carried out its present
important duties since 1680. The corresponding department,
in Scotland is the Northern Lighthouse Board, constituted in
1786, while the Irish Lighthouse Board, of about the same date,
performs similar duties for the Irish coast. A special tax or
toll upon shipping, known as " light dues," is levied for the
support of these departments.



752. Model of the Smalls lighthouse. (Scale 1 : 48.) Lent
by Capt. F. C. Pickering Clarke, R.N., 1862. N. 780.

The Smalls rocks are about 17 miles off the coast of Pembrokeshire,
near the entrance to Milford Haven. This model, made out of one of the
oaken piles of the original lighthouse, represents the first lighthouse on
these rocks, erected in 1776. It was designed and the construction super-
intended by Mr. Whiteside, a musical instrument maker, assisted by Cornish
miners, the expense being borne by a Mr. Phillips. The lighthouse was
replaced in 1861 by a granite structure.



753. Model of Maplin lighthouse. \ Scale 1:24.) Received
1899. N. 2199.

This lighthouse is situated on the Maplin Sand at the mouth of the
Thames, near Shoeburyness. It was constructed in 1837 on Alexander
Mitchell's screw-pile system, patented in 1833, and was the second lighthouse
erected in this way.

It is octagonal in plan with a central wrought- iron pile and eight exterior
ones 5 in. diam. and 26 ft. long, each with a cast-iron screw 4 ft. diam.
These piles were screwed-in about 22 ft. and then the upper lengths added,
which were slightly bent so as to give a pyramidal form to the structure.
The piles are braced to the central one and to one another by horizontal and
diagonal tie-rods riveted to clamps on the piles.

The lantern is above the platform, and the dwelling-rooms, stores, etc.,
arranged below it. Beneath these is an inverted pyramidal deck provided
as a wave deflector. The model shows also the sliding ladder, boat, davits
and fog bell.



754. Lithograph of Fleetwood lighthouse (1840). Wood-
croft Bequest, 1903. N. 2319.

This lighthouse was erected in 1839-40 on a submerged sandbank at the
entrance of Morecambe Bay. It was designed and built by Mr. A. Mitchell
and was the first lighthouse completely carried on screw piles.

The substructure consists of seven wrought-iron piles, 16 ft. long and
5 in. diam., with screws 3 ft. diam. driven 12 ft. below the surface, forming
a hexagonal pyramid with a slope of 1 in 5. To the tops of these piles are
attached wooden baulks 12 in. diam. which reach to the height of the upper
platform, while diagonal tie-rods connect the outside supports with one
another and with the central one. A layer of clay and stones, several feet
in thickness, was placed upon the loose sandy bottom around the structure.
The lantern is 10 ft. diam. and has 12 sides, while its height above the
sea level is 45 ft.



233

755. Model of Gunfleet lighthouse. (Scale 1 : 24.) Lent by
the Corporation of the Trinity House, 1874. N. 1385.

This lighthouse on the Gunfleet Sands, at the entrance to the Thames,
31 miles from the Nore Lighthouse, is erected on Mitchell's patent screw
piles, of which a separate model is shown. There are one central and six
exterior piles inclining inwards, supporting columns of about 12 in. diam.,
strongly braced ; the piles are screwed 40 ft. into the sand, and have screws
4 ft. in diain. The sockets for the columns are secured to the face of the
piles by bolts.

The accommodation for the two keepers is under the lantern floor, one
storey in height and divided into a living room, bed room, and oil room.
Below this floor is a store room in the shape of an inverted pyramid, to
which access is obtained by a ladder from the gallery. The sides and roof
of the structure are of corrugated iron, with wrought iron angle plates.

The lantern contains a revolving catoptric apparatus, with fifteen
reflectors and Argand burners in sets of five, placed on a frame of three
sides, glazed with red glass.

756. Model of the Great Basses lighthouse. (Scale 1 : 48.)
Lent by the Corporation of the Trinity House, 1874.

N. 1386.

This lighthouse was erected on the Great Basses rocks, Ceylon, from the
design of Sir James N. Douglass. It was commenced in 1870 and completed
in 1872.

The lighthouse has a cylindrical base 30 ft. high and 32 ft. diam., on
which is a tower 67 '5 ft. high, 23 ft. diam. at the base, and 17 ft. at the
springing of the curve of the cavetto. The thickness of the wall at the
base of the shaft is 5 ft., and at the top 2 ft. The accommodation within
consists of six circular chambers each 13 ft. diam. There is also a room in
the basement 12 ft. diam. for coals a,nd water, and a rain-water tank below
7*5 ft. diam. From the floor of the tank to the rock, a depth of 11 -5 ft.,
the base is solid. The stones forming the wall of the tower are dovetailed,
both horizontally and vertically, and set in cement ; the tower is of Scotch
granite, and the stones were fitted before being sent out.

The lantern is 110 ft. above high water, and shows a revolving red
flashing light at 45 seconds intervals. The illuminant is Ceylon cocoa-nut
oil. There is also a 5 cwt. fog bell.

757. Model of Malacca lighthouse. (Scale 1 : 32.) Received
1899. Plate VII., No. 7. N. 2200.

This lighthouse in the Straits of Malacca was erected by Messrs. G.
Wells & Co. in 1874 on Mitchell's screw-pile system. The design is light,
as the situation is well sheltered, and there is a depth of 15 ft. at low water
and a tidal rise of 12 ft. ; the bottom is muddy.

The structure is hexagonal in plan, with one central and six exterior
wrought-iron piles 6 in. diam., screwed 15 ft. into the ground at a batter of
1 in 5. The lower lengths of the piles are coupled with socket joints formed
on the pile itself, while the upper lengths have cast iron sockets. The
structure is braced together with 5-in. by -625-in. T-irons at high water
level, and by 4-in. by 5-in. ones above. The tie rods are from 1 5 to 2 5 in.
diam., adjustable by right and left-handed screw couplings. The- platform
is 28-3 ft. above high water level, and at this height the distance between
the pile centres is 13 ft.

The dwelling-house has four rooms, with a kitchen and lavatory which, on
account of the climate, are in a detached overhanging structure ; for the
the same reason, the lean-to roof is extended over the gallery. The building
is of angle-bars, covered with galvanised sheets and lined with matchboarding,
grooved and tongued.



234

The lantern surmounts the dwelling, and is 9 6 ft. diam. by 7 53 ft.
high : it contains a third order holophotal light with 8 sides, giving 1 min.
intervals.

758. Model of Hino-Misaki lighthouse. (Scale 1 : 50.) Pre-
sented by the Board of Lighthouses, Japan, 1910. N. 2585.

This stone structure was built in 1903 on Cape Hino in the province of
Izunio (S.W. Japan). It is fitted with dioptric group-flashing apparatus
of the first order, giving double white flashes and a single white flash
alternately every 20 seconds ; three keepers are in attendance.

It is the highest stone lighthouse in Japan ; the centre of the lantern is
128 ft. above the base, and the diameter of the structure varies from 15 ft.
to 25 ft.

759. Model of Tsutsu-Zaki beacon. (Scale 1 : 25.^ Presented
by the Board of Lighthouses, Japan, 1910. N. 2586.

This lighted beacon was erected in 1909 on a sunken rock situated on the
north side of the Eastern Channel of Tsushima Strait (Southern Japan). It
is fitted with dioptric illuminating apparatus of the fifth order, flashing a
white light every 15 seconds ; this requires attention once a fortnight.

Great difficulty was experienced in the erection of this structure owing
to the rough seas in the vicinity, only 82 actual working days being possible
out of a total of 735 days in progress. A native visiting -boat, fitted with a
special weather- screen at the bow, is shown near the beacon.

The centre of the lantern is 76 ft. above high water, and the diameter of
the structure varies from 10 ft. to 32 ft.

760. Whole model of early lightship. (Scale 1 : 36.) Lent
by the Corporation of the Trinity House, 1897. N. 2158.

The first lightship was established by Robert Hamblyn and David Avery
in 1731 at the Nore, to mark the entrance to the Thames and Medway.
The light was maintained by a species of toll, but ultimately the Trinity
Brethren paid an annuity of 100Z. for 61 years to purchase the ship and any
rights that might have been secured. The "Dudgeon" lightship off the



Online LibraryScience Museum (Great Britain)Catalogue of the naval and marine engineering collection in the ... museum .. → online text (page 32 of 58)