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face. The inner face of this plate is hollowed out, and together with a
similar but fixed plate forms a ball-bearing, the balls being of brass. This
arrangement considerably reduces the friction of the gear. Between the
fixed half of the bearing and the cylinder end a spring is threaded over the
inner bush in order to give a more uniform motion. Outside this cylinder
the shaft ends in an eye .to which the hook on the end of the log line is
attached. The dial is graduated so that the inner circle gives the distance
travelled in miles, whilst the outer circle is divided into sixtieths of a mile.
By observing the number of sixtieths travelled in one minute, the speed in
miles per hour is obtained. The registering mechanism is shown separately
in section.

1114. Electric log. Presented by Miss Clough, 1876.

N. 2421-2.

This log was patented in 1876 by Tito Yisino, and consists of a recording
mechanism placed on board, together with a rotator suspended from the
side of the ship by iron bands, connection being made between the two by
an electric cable. It was also the intention to use in conjunction with the
recording mechanism an apparatus for tracing graphically the course of the
ship. The rotator is a copper tube containing bearings in which a four-
bladed propeller works. At the end of the tube, and external to it, is placed the
wheelwork connected with the propeller by a single-toothed wheel on its axis.
Water, entering the tube during the ship's motion, passes out through three
copper pipes at its end. An outer tube, acting as a shield, covers this inner
tube, and protects the wheelwork from contact with the water. The single
tooth on the propeller shaft drives a wheel train and once in every 500
rotations of the propeller contact is made between two springs by projecting
pins on the last wheel of the train, thus completing an electric circuit. The
springs are terminals from which wires pass through the end of the copper
tube, a cable being led thence to the recording mechanism on board.

This mechanism consists of a number of dials arranged in two circuits.
In one are the three first dials, recording from hundreds of fathoms to
thousands of knots. The first dial of this circuit is operated by the current
which is completed by the contact of the springs described above, An
electro-magnet controls one end of a lever, the other end rotating a ratchet-
wheel on the dial shaft. The dial operates the next two by means of spring
controlled levers and ratchet wheels. To connect the first series with the
second and thus give continuous registration there is a commutator on the
arbor of the last dial of the first series. When hundreds of knots are to be
recorded springs resting on the commutator complete the second circuit,
containing a separate electro-magnet, the mechanism being similar to that
on the first dial. A ratchet and pawl then operate the dial placed on
the top.

The advantages claimed for this log are that, as there is no towing line,
violent jerks, which would affect the record, are avoided, and that its large
size reduces the risk of its being seized by a fish, while, since it works fairly
deep in the water, it is not exposed to surface obstructions.

1115. Speed indicator for ships. Lent by the Rev. E. L.
Berthon, M.A., 1867. N. 1165.

In this instrument, which was patented by the contributor in 1849, the
velocity of the ship through the water is determined from the pressure
produced in an open tube exposed to the passing stream. The original
apparatus of this class, devised by Pitot, consisted of a tube passing



373

through the bottom of the ship and having an opening in the direction of
motion, so that the height above the sea level of the water column in the
tube gave the pressure due to the velocity ; but this height was only
obtained after correction had been made for the draught and inclination of
the vessel.

To obviate the necessity for making these allowances, Mr. Berthon
introduced the use of two tubes : one with an opening in the direction of
motion, and the other with two openings so situated that they received no
pressure from the ship's motion ; so that the difference between the pressure
in the two tubes depended upon the speed only.

In the example shown the two tubes are combined into a single " way-
tube " which passes through a stuffing-box in the bottom of the ship and
projects a few inches beyond ; the lower portion of this tube has two
circular ports, with their axes inclined at 42 deg. with the line of motion,
and a small pipe leading from it ; while the upper portion has a port with
its axis in the direction of motion. The two portions of the way- tube are
connected to air vessels, from which pipes lead to the opposite ends of a
mercury column in a bent tube. "When the ship is in motion there is a
displacement of the mercury column, by which the speed is indicated on a
graduated scale.

Secured to the bottom of the way- tube is a collapsible vane, which keeps
it in its required position, while an index on the handle of the tube indicates
the lee-way being made by the ship.



1116. Registering clinometer. Constructed at Devonport
Dockyard. Received 1897. N. 2126.

This instrument, for recording the number and the maximum amplitude
of the oscillations of a ship, was introduced by Capt. A. Gr. Edye, E/.N. In
1844 the Admiralty to some extent adopted it, and the Society of Arts
awarded the inventor a medal.

The inclination is measured by a short massive pendulum, which is
connected by spur wheels to a damping brake that prevents recoil oscilla-
tions. This brake is in the form of a pawl, which is thrown over at each
reversal ; the counting mechanism registers the reversals only, so that the
vibrations are recorded independently of their amplitude.

Two light arms are separated by the pendulum when swinging, and so
indicate the maximum swings since last closed together by the external
knobs. The instrument is hung on a hinge in the plane of the motions to
be recorded, and indicates on four decimally arranged dials.

1117. Bi-fluid clinometer. Lent by the Rev. E. L. Berthon,
M.A., 1867. N. 1164.

This instrument for measuring inclinations, or the list of a vessel, was
patented by Mr. Berthon in 1849. It consists of a glass bulb, containing
mercury, connected by a horizontal capillary tube with a similar bulb
terminating in a vertical index tube, which contain^ mercury and coloured
water. As the area of each mercury bulb is 26 times that of the index tube
a small change in level of the mercury causes 26 times as much movement
of the water index. If the density of the mercury is 13 times that of the
red water, which usually contains a little sulphuric acid, the change in level
of the mercury caused by a certain inclination is only one-half of that when
a simple y tube with legs of equal areas is employed ; but as this change is
multiplied 26 times in this instrument, it is 13 times as sensitive as the
simple tube.

The connecting capillary tube damps out oscillation and insures a steady
reading of the index scale, which in the example shown is graduated to
show the trim of the ship carrying it.



374

1118. Bi-fluid clinometer. Lent by J. Wimshurst, Esq.,
F.R.S., 1902. N. 2297.

In this clinometer, patented by Messrs. J. and H. C. Wimshurst in 1896,
two tubes containing mercury and a coloured liquid of low density, such as
water or alcohol, are connected at their upper and lower ends. The bottom
part, containing the mercury, has a greater area than the vertical index
tubes in which the light liquid moves, consequently when the instrument is
inclined the descent of the mercury on one side causes an exaggerated
motion of the light fluid, which on the other side ascends into a reservoir
situated above the zero point on the graduated scale.

In this example the lower tube has been contracted so as to check
oscillation, but in other instances a glass cock was added so as to render
the damping adjustable ; also the length of the instrument has been
reduced by bringing the index tubes close together.



DREDGING APPLIANCES.

Dredging lias been resorted to from very early times to
increase the depth of navigable channels or to remove obstruc-
tive shoals. The earliest means employed were drags or scoops
worked by hand power from a boat ; this arrangement still
survives in the bag and spoon dredger, frequently used for
cleansing locks and similar small areas. Steam power was
first applied to dredging in 1796 in Sunderland harbour, where
spoons with leather bags were in use ; the engine fitted was
supplied by Messrs. Boulton and Watt. The dipper type is
best adapted for work in sheltered positions where the depth
does not exceed 25 ft. ; it is largely used on the North
American lakes.

Ladder dredgers, in which an endless chain carrying
buckets is supported on a ladder whose lower end can be
adjusted to various depths, were first used in the Queen's
Dock, Hull, in 1783, while steam power seems to have been
first applied to drive the chain of buckets in 1811 at
Sunderland ; subsequently, additional auxiliary engines or
shafting were added to perform the work of mooring and
propelling. Ladder dredgers have at present the largest
application, and are considered the best form for general
purposes. Many are now so constructed that they can excavate
their own notation even through a solid bank, the ladder
traversing forward so far that it projects beyond the bow.
The disadvantage of bucket ladders is the height to which
the spoil has to be raised in order to shoot it into hoppers
alongside, also the great cost of repairs and the friction of the
working parts.

Hopper dredgers of the ladder type carrying their own
spoil have been largely constructed. They are ship-shaped in
form, and the propelling power is sufficient to give a speed
of about 10 knots, but they are most suited for cutting in an
estuary where the spoil has only to be carried a short distance.
In other cases the spoil is delivered into hopper barges which are



375

towed away by a tug or the barges may be made self-propelling.
If required the spoil may be delivered on adjacent land through
a long shoot or a floating tube attached to the dredger.

The bucket of the " grab " or " clam-shell " dredger imitates
the action of two spades ; the two sides being driven into the
earth have their lower edges brought together so as to lift the
intervening material when raised : an early form was patented
by John Gregory in 1744. It is most suitable for dealing with
moderate quantities of gravelly material and may be used in
confined situations, as nothing but vertical clearance is necessary.
When used for clearing heavy rock or masonry, such as the
debris of blasting operations, special buckets formed of inter-
locking bars or teeth are fitted. The orange-peel bucket, with
four spade-like sides, is a variation of this type.

A form of "sand-pump" dredger was used in 1868 by
Woodford, who placed a centrifugal pump close to the bottom,
and drove it by a vertical shaft which passed through the
discharge pipe. The water entering the pump carried the sand
with it, and upon being delivered into a hopper was allowed
to deposit the solid matter before returning into the sea. The
advantages of the sand-pump are that the vertical lift is less
than with a ladder, and that it can work, by the aid of telescopic
pipes and flexible joints, where the ground swell is 2 ' 5 ft. or
more. The sphere of usefulness of this type has been largely
extended during recent years : fitted with apparatus for cutting
or loosening the subsoil a powerful suction dredger is capable
of dealing with mud, clay and large shingle.

Owing to the rapid growth in the size of steamers during
recent years, there has been a large increase in the dimensions
and capabilities of dredging appliances.

1119. Whole model of double-ladder dredger. (Scale 1 : 24.)
Contributed by Messrs. Thos. Wingate & Co., 1877.

N. 1469.

This is typical of three dredgers built of iron by Messrs. Wingate for
the Tyne Commissioners in 1861-3, to the designs of Mr. J. T. Ure.

There are two ladders in independent wells, placed 20 ft. apart, amid-
ships. Each chain of buckets is carried upon a plate girder fitted with
bearing and guide rollers ; one chain is shown with thirty-five buckets for
working in clay with the chain tight, and the other has thirty-six buckets and
a slack chain as for excavating in sand. The buckets have a capacity of
14 cub. ft., and the total capacity of the machine is 1,000 tons per hour.
The depth to which the dredger will cut is 35 ft., and the cut is regulated
by a 6-sheave chain block suspended from A-frames and worked by a winch.
The spoil is discharged by shoots into hopper barges alongside.

The vessel is self-propelling, with capstans and winches by which it may
be moved at its moorings as required ; these appliances are also used in
working the attendant barges. Power for all purposes is obtained from a
side-lever engine of about 200 i.h.p., arranged aft, and connected by
clutches with the screws, capstans, etc. The top tumblers, or square prisms,
that drive the bucket chains are connected to the engine by gearing and
V~ grooved friction wheels, the latter being introduced to provide a slipping
drive that shall limit the stress on the ladder chain.

Length, 158 ft. ; beam, 39 ft. ; depth, 11-5 ft.



376

1120. Whole model of dipper dredger. (Scale 1 : 24.) Pre-
sented by J. K. Rennie, Esq., 1893. N. 2019.

This single-bucket dredger was constructed by Messrs. J. and G-. Rennie
at Greenwich, in 1878, for dredging at the Mauritius to a depth of 10 ft.
The capacity of each bucket is 5 to '75 ton of soil, and the vessel worked
.on trial at the rate of 43 buckets per hour, with an expenditure of 10 h.p.

Length, 40 5 ft. ; 13 5 ft. ; draught of water, 2 5 f t.

1121. Whole model of circular dredger. (Scale 1 : 32.) Lent
by W. R. Kinipple, Esq., 1881. N. 1559.

This design by Mr. Kinipple is intended to reduce the time lost in
mooring an ordinary hopper dredger, and also to secure greater accuracy in
its position and feeding.

The dredger consists of an annular hopper around which can travel a
framework carrying the machinery and two slewing bucket ladders. In the
centre of the hopper is a well, through which passes a large screw pile that
acts as a mooring post. The pile is hollow, so that when pumped out its
buoyancy shall assist in lifting it at the completion of the work. Additional
^control is giving by two revolving anchors attached to legs that reach to the
bottom, and may be used to give a circular feeding motion to the whole
machine. The two bucket ladders may be worked in opposition so as to
place the machine in equilibrium.

The dredger is provided with four screws, to enable her to steam to and
be grounded on a river bar, then dredge till loaded, and afterwards float off,
steam to sea with the flood tide, and discharge her spoil, without using any
mooring appliances. "When working alongside a quay the ladder-frame
may be fixed and the circular hopper be rotated as the sections are loaded,
or one ladder may be engaged in lifting spoil from the hopper on to the
wharf.

The dimensions of the dredger are : Outside diam., 68 ft. ; depth to deck,
17'5 ft.; draught, loaded, 14 ft.; displacement, loaded, 1,200 tons; and
carrying capacity, 1,000 tons.

1122. Models of dredger buckets. (Scale 1 : 4.) Lent by
W. R. Kinipple, Esq., 1881. N. 1559B.

These show methods of construction patented by Mr. Kinipple in 1879,
with the object of reducing the cost of the bucket repairs necessary when
dredging in hard ground.

The bucket is made of three distinct pieces ; the " back," " body," and
"lip," which are made to template, so that when any part is damaged it can
be easily replaced.

The " back " of each bucket forms part of the link of the dredger chain,
and has its rear end turned up so as to form a bottom also. Each end of
the " body " is strengthened by a metal band, and the lower end is bolted to
the turned-up end of the " back." The " lips " are made in shovel, spade,
or claw form, according to the material to be dredged.

1123. Models showing methods of mounting dredger buckets.
(Scale 1 : 8.) Lent by W. R, Kinipple, Esq., 1881.

N. 1559A.

This shows the ordinary method of mounting the buckets on the ladder
-chain, and also a plan introduced by Mr. Kinipple in 1879 with the object
of facilitating the emptying of the buckets when dealing with clayey
material.

In the former method, each bucket is attached to a pair of links, and
-occupies a position about midway between their pins, so that it passes over



377

the tumbler at the same rate as the chain. In the latter plan, the pins are
under the centre of the bucket, so that when the bucket reaches the tumbler
the front link has already cleared it, and the bucket, being pivoted on the
connecting pin, tips its contents into the hopper- shoot in a manner similar
to that of an ordinary tip-cart.

1124. Whole model of twin-screw hopper dredger. (Scale
1 : 48.) Lent by Messrs. W. Simons & Co., 1894.

N. 2035.

This represents the dredger " Gefion," built in 1885 for the Danish
Government by Messrs. Simons & Co.

It is a ladder dredger, with the chain of buckets carried over a four-
sided tumbler or drum at the top, driven by reduced gearing from the
steam engine. The returning buckets empty their contents into a large
central hold or hopper, which is provided with large flaps or doors for its
bottom. By releasing the closing- chains the doors open, and the contents
of the hopper are deposited in the position selected. Side shoots are also
arranged so that the spoil may be delivered into barges alongside when
desired.

By means of a worm and rack-and-pinion gearing, driven by power,
the ladder frame can be moved fore or aft, while the inclination and
consequent depth of the ladder is adjusted by a heavy chain pulley
attached to the dredger and to the lower frame of the ladder. The buckets
will excavate 350 tons of spoil per hour, and the capacity of the hopper
is 300 tons. The dredger works to a depth of 26 ft., and is so con-
structed that it can excavate in advance of itself, and thus clear its own
channel.

Twin screws are provided by which the dredger propels itself to and fro
the excavating and depositing grounds. Each screw is driven by a separate
set of two-stage expansion engines, with cylinders 16 in. and 29 in. diam.
by 21 in. stroke.

Length, 154-7 ft. ; breadth, 29 -6 ft. ; depth, 13 '4 ft.

1125. Whole model and photographs of sand-pump hopper
dredger. (Scale 1 : 48.) Lent by Messrs. Lobnitz & Co.,
1898. N. 2013.

This type of dredger is used for forming or deepening a channel when
the bottom is of a loose sandy nature. The sand is carried up with the
water lifted by a centrifugal pump, and quickly settles in a hopper, from
the top of which the superfluous water is continuously overflowing. Such
machines have been in use many years, and were employed in forming the
Suez Canal.

The dredger represented, named the " Thyboron," was built by Messrs.
Lobnitz for the Danish Government in 1892. She is constructed with raised
fore-deck and quarter-deck; when loaded she carries 700 tons on a draught of
10 ft., and has been engaged in making a channel through a sand bar upon
which there is only 7 ft. of water. She is propelled by twin screws, which are
driven by two -stage surface condensing engines, with cylinders 16 in. and
30 in. diam. by 24 in. stroke ; steam at 100 Ib. pressure is supplied by two
boilers 11 ft. diam. ; her speed is 9 knots.

The dredger has two suction pipes, which may be used separately or
together ; they are connected to the centrifugal pumps which deliver into
a discharge pipe placed over the hopper. Settling troughs are set below
the discharge pipe to assist the precipitation of the sand, but the water
carried into the hopper overflows along the coamings. The pumps are
driven by the propelling engines.

On arriving at the scene of operations it is usual to drop anchor and
pay out chain cable, so as to allow the dredger to drift with the wind or
current until the cable is taut ; if necessary one of the screws is kept



378

running reversed; the cable then keeps the dredger sufficiently steady
without the use of side or stern moorings. While the cable is being paid
out a suction pipe is lowered, and as soon as the vessel is steady the
pumping is commenced.

Directly the mouth of the suction pipe touches the bottom the vacuum,
which when pumping water only is 6 in., increases to more than 12 in., and
the fluid delivered is a mixture of sand and water.

The mixture is sampled from time to time in test tubes, 2 in. diani.
and 12 in. long, graduated in percentages. The sample taken immediately
the suction pipe touches the bottom will show from 5 to 10 per cent, of
sand ; after being at work five minutes the sample will probably show 15 to
20 per cent, of sand in the test tube, and during this time the man in
charge of the winch to the suction pipe will have been gradually lowering
the mouthpiece into the large hole excavated. As the hole deepens the
vacuum increases, and the percentage of sand rises to 30, 40, and even
50 per cent.

A sand- dredger may be worked either by making a large hole in the
sand each time she loads the surface of the sand being levelled by the
subsequent scour of the tide or she can dredge to a given depth,
leaving a level surface as she trails the suction pipe lowered to that
depth.

Before leaving for Denmark, the " Thyboron " was tested on the
Mersey bar, and after pumping for 20 mins. the hopper was filled to within
2 ft. of the top of the coaming, the quantity of sand deposited in the
hopper being between 500 and 600 tons, at an expenditure of about 2 5 cwt.
of coal. A feature in this dredger is her light draught, enabling her to
work on an even keel at an immersion of 6 25 ft.

Length, 165 ft. ; breadth, 34 ft. ; depth, 12 ft. ; carrying capacity,
700 tons.

1126. Rigged model of suction liopper dredger " Poulton."
(Scale 1 : 48.) Lent by Messrs. Fleming and Ferguson,
Ltd., 1905. N. 2372.

This twin-screw suction or sand-pump dredger was built of steel, and
engined at Paisley in 1899, by Messrs. Fleming and Ferguson, to the joint
order of the Lancashire and Yorkshire, and London and North Western
Railway Companies, for the purpose of clearing the Fleetwood Bar.

The vessel is schooner-rigged, and has one steel deck, sheathed with
wood. Her quarter-deck is 79 ft. long, and her forecastle 53 ft. She has
a flat keel, and her hold is subdivided by seven bulkheads. There is a deep
water ballast tank forward, which is 22 ft. long, and has a capacity of 200
tons.

The engines are of the three- stage expansion type, with six cylinders, of
13 in., 21 in., and 34 in. diam. by 24 in. stroke. Steam at 160 Ib. pressure
is supplied by two single-ended boilers, with four corrugated furnaces
having a grate surface of 84 sq. ft., and a heating surface of 2,125 sq. ft.
The speed of the vessel is 9 knots.

There is one suction pipe which is fitted with a flexible joint, and is
connected to the centrifugal pump ; the latter was made by Messrs. J. and
H. Gwynne, and is capable of lifting 1,500 tons per hour. It delivers into
two horizontal pipes running the full length of the hopper, these have
adjustable apertures placed at intervals along their lower sides through
which the mixture of sand and water passes into perforated troughs below,
from which it is discharged into the hopper. This arrangement allows the
spoil to be directed into any particular part of the hopper, and the water
overflows over double coamings.

Auxiliary steam-driven machinery is provided for raising and lowering
the suction pipe, and for opening and closing the hopper doors. On her
load draught the vessel carries 1,250 tons.

Length, 204ft. ; breadth, 38 -2 ft. ; depth, 14 -5 ft.



379



1127. Rigged model of steam hopper-barge. (Scale 1 : 48.)
Lent by Messrs. Fleming and Ferguson, Ltd., 1908.

N. 2490.

When the dumping ground is at a considerable distance from the locality
where the dredging operations are being carried out, it is usual for the
dredger to deliver its spoil into hopper-barges which, when filled, are taken
by a tug to the dumping ground. By this course the dredging machinery
can be kept at work for the maximum number of hours and the difficulty of
recovering the moorings after each tide is avoided. For continuous and
extensive operations of this nature, large self-propelled hopper-barges are
frequently employed ; they possess good speed and sea-going qualities.



Online LibraryScience Museum (Great Britain)Catalogue of the naval and marine engineering collection in the ... museum .. → online text (page 53 of 58)