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pressure by the weigh-shaft, till the resulting motion, through the floating
lever, again closes the valves so that the mechanism stops and is retained
in the new position.

An air vessel is connected with the hydraulic control valve, to take up
surplus water resulting from the piston-rod being single-ended ; there is also
a small hand pump for forcing water directly into the hydraulic cylinder
and so reversing the main engine when steam is not available.

In the model of the engines of the P.S. " Princesse Henriette "
(see No. 819) is represented a later arrangement of this starting engine,
patented in 1882, in which the reduced motion for the valve is obtained by
the use of a quick-pitched screw and a slower one in place of a lever ; both
forms are, however, still made.

874. Model of marine engine governor. (Scale 1 : 8.)
Presented by T. Silver, Esq., 1869. N. 1318.

This governor, patented by Mr. Silver in 1857, for controlling the
throttle -valve of a marine engine, depends for its operation upon the
resistance offered by the air to the rotation of a fan. When the pinion-shaft
(which is independent of the fan- shaft) rotates at a sufficient speed, the
toothed segments carried by the fan- shaft are turned through a few degrees
by the pinion engaging with them, compressing to a small extent the helical
spring, and driving the fan. When the speed of driving is increased, the
balance is disturbed; the resistance of the air retarding the fan and its
shaft, the segments are turned through larger arcs, compressing the spring
to a further extent (i.e., till it again balances the resistance), and partially
closing the throttle-valve.

875. Marine engine governor. Lent by Aspinall's Patent
Governor Co, 1902. N. 2295.

This governor, patented in 1893 by Mr. H. Aspinall, belongs to that
class in which the change in the momentum, or inertia, of a reciprocating
mass, controls the regulation.

It consists of a frame bolted to any reciprocating part of an engine,
usually the air-pump lever, and carrying a swinging weight and two pawls so
connected together that when one pawl is projecting the other lies back.
The swinging weight is, by an adjustable spring, retained in its position
against the normal momentum effort at the reversals of its motion, but an
increase of about five per cent, above the intended speed of the engine
causes this effort to overcome the spring, so that the weight swings and
protrudes the other pawl.

To the engine framing is secured a bracket, carrying a lever connected
with the throttle-valve rod and so arranged that when the lower, or excess-
speed pawl is projecting it conies in contact with this lever and lifts it
throughout the whole upward travel, thus closing the throttle-valve in this



289

stroke. A detent, that has retained the swinging weight, is now released
by the throttle handle, so that, if the racing has stopped, the weight moves
the pawls into the original position and the upward pawl re -opens the
throttle-valve. An emergency gear is also provided, which comes into
operation in the case of excessive racing, such as would result from losing
a propeller ; this acts by a small additional swinging weight which, under
exceptionally rapid reversal, locks the main weight in the shut-off position,
so as to prevent the throttle -valve from re-opening automatically.

A diagrammatic working model of the governor to a scale of 1 : 8, which
was made in the Museum, is shown in its position on the engine.

876. Cylinder drain and relief valve. Lent by H. P. Holt,

Esq., 1879. N. 2518.

This arrangement of valve, patented by Mr. Holt in 1878, combines in
one fitting the drainage and relief safety valves for both ends of an engine
cylinder. Pipes from the two ends enter the casing shown, and the
discharged water from the cylinder is carried off by a central pipe. In the
casing is a valve for each end of the cylinder, and each of these valves con-
sists of a central disc or relief valve, and also of a double-seated annular
valve outside, which is the drain valve ; these annular valves are kept on
their seats by springs. The action is such that, when steam is on one side
of the cylinder, its pressure opens the drain valve of the other end or
exhaust side, while, at any time, the central or relief portion of the valve
will open should the pressure, through priming, exceed the limit determined
by the springs.



877. Model of rope-driving arrangements for screw shafts
(working). (Scale 1 : 16.) Contributed by Messrs. Maudslay,
Sons and Field, 1862. N. 440.

At the time that the screw propeller was introduced, marine engineers
had developed an arrangement of engine that was most suitable for driving
paddle-wheels. Its features were : a slow running crank-shaft high above
the keel, with large cylinders placed low down in the hull. The early
screw ships were accordingly fitted with similar engines ; the connection
between the crank-shaft and the propeller shaft being made by mechanism,
which usually increased the speed of the screw. Spur gearing was frequently
used ; but, in addition to being noisy, it was found very liable to strip.
Leather belting on smooth pulleys slipped seriously, and was unsuited to
such short centres, while pitch chain possessed similar defects to those of
spur gearing.

The arrangement shown was patented by Joseph Maudslay in 1843, and
is an early example of rope driving. It consists of a frame supporting an
extension of the engine shaft, on which is secured a six-grooved rope pulley ;
the lower part of this frame supports a similarly grooved pulley of
one-fourth of this diameter keyed to the propeller shaft. The pulleys are
connected by six independent endless ropes, which are simultaneously
tightened by a pulley carried in a swinging frame, adjustable by means of a
screw.

878. Model of link-driving arrangements for screw shafts
(working). (Scale 1 : 8.) Received 1862. N. 439.

The model shows one of the methods proposed for connecting the early
paddle-wheel type of marine engine with a screw-propeller shaft. It is a
parallel crank chain, and was probably derived from the coupling-rods of a
locomotive.

The engine would have two cylinders and overhead crank-shafts.
These shafts are connected, by overhanging cranks and a triangular
v\ G773. T



290

connecting-rod, to an overhanging crank on the screw shaft. There is no
dead point in the transmission, and this chain has been proposed for
electric locomotives as a means of raising the motors above the road dust
and mud.



879. Model of Tin-ton's crank-shaft. (Scale 1 : 12.) Made
in the Museum, 1903. N. 2302.

Owing to the difficulty of constructing large cranks from a single
forging, and the liability of such large masses of metal to contain defective
portions, many forms of crank-shaft built up from several pieces have been
adopted. The early engines usually had cast-iron shafts and crank-arms,
staked together, and a wrought-iron crank- pin cottered in, but in recent
years forged steel is the material generally used throughout for such
parts.

In the construction patented by Mr. T. Turton in 1880, the crank-pin
has one half of the web at each end forged with it, while the other halves
of the webs form solid ends to the two portions of the crank-shaft. The
two halves of each web are connected by a keyed dovetail joint and two
large through bolts.

The model represents a crank-shaft made in 1881 for the S.S. " Virginian."
which had a pair of tandem compound engines of 5 ft. stroke, indicating
3,000 h.p. The shaft was 16 5 in. diam., and there were two cranks, at
right angles, each similar to that shown.

880. Model of built-up crank-shaft. (Scale 1 : 12.) Made in
the Museum, 1903. N. 2304.

This represents one throw of the crank-shaft constructed in 1881 by
Sir J. Whitworth & Co., for the S.S. " City of Rome." The shafts, webs,
and pin were made separately of Whitworth fluid- compressed steel, and the
cylindrical portions were forged from hollow ingots ; the webs were secured
to the shafts by shrinking and keying, but the pin was retained in the webs
by shrinkage alone.

The engines for which this crank was built were of the three crank
tandem two-stage type, with a stroke of 6 ft., and indicated 10,003 h.p. ;
the crank-shaft consisted of three portions, each similar to that shown,
which were connected by flange couplings, and weighed altogether 66 tons.
Since its construction, crank-shafts of this type have been very generally
employed for large engines in the mercantile marine.

The first process in building up these crank- shafts is to shrink a web on
to each piece of the shaft, and then further secure them by pins or keys
driven into holes half in the web and half in the shaft, to nearly the full
depth of the web. The two pieces of shaft are then bolted to a vertical
plate and retained in their correct relative positions by distance pieces, so
that the crank pin can be immediately lowered into its place after the
holes in the web have been sufficiently heated, usually by internal gas jets.

When the crank- shaft for the " City of Rome " was being built numerous
experiments were carried out to determine the amount of shrinkage to be
allowed, and from these it was decided to leave the shaft and pin one-
thousandth larger in diameter than the corresponding holes in the web
when cold.

881. Model of Dickinson's crank-shaft. (Scale 1 : 12.) Made
in the Museum, 1903. N. 2303.

In this construction of built-up crank-shaft, patented in 1881 by Mr. J.
Dickinson, the crank-pin and webs are formed in one piece, of such
dimensions that flanges on the body of the shaft can fit into recesses bored
in the webs ; the parts are then held together by bolts, the nuts of which
are secured by locking plates.



291

A crank- shaft of this form was the first in which a crank-pin and its
webs were made of cast steel ; when submitted to the Board of Trade, in
1882, it was subjected to a series of tests which showed the material to be
suitable for the stresses experienced.

882. Model of Foster's crank-shaft, (Scale 1 : 12.) Made in
the Museum, 1903. N. 2305.

In this method of building up a crank-shaft, patented in 1884 by Mr.
H. F. Foster, the crank-pin and the webs are forged or cast in one piece,
which is then secured to the shaft by shrinking and keying the webs on
to the adjacent ends. These ends are made somewhat larger than the
journals so that the keys can be driven in from outside the webs. This
plan can also be used for repairing a broken crank-shaft which has been
made in one piece, since by cutting away the webs and the pin, the shaft
ends can be turned down to receive a new throw complete.

883. Models of disconnecting cranks. Contributed by Messrs.
Jackson and Watkins, 1861. N. 412 and 415.

With ocean-going paddle-steamers it was very advantageous to be able
to disconnect their paddle-wheels, as, should one wheel be seriously
damaged, the other wheel and the full engine power could be used to
complete the voyage. To readily effect this change, some form of discon-
necting crank was most generally introduced, whereby the crank-pin could
be left free of the crank web nearest the damaged wheel. These three
wooden models show some of the devices, patented by Samuel Seaward in
1840, as a means for thus releasing the outer length of the paddle-shaft.

(a) In this crank the crank-pin is secured to the nearer web, while the
outer web has a block sliding 011 it worked by a radial screw ; when the
block is forced outwards a jaw on it secures the squared end of the crank -
pin, and so completes the connection in a way that can be readily released.

(6) This arrangement resembles the above, but has the sliding jaw
working in guides arranged within the outer web.

(c) Here the outer web terminates in an eye that carries a thick sleeve,
across which is a slot through which the outer end of the crank-pin can
freely pass. This sleeve can, however, be turned through 90 deg. so as to
place the slot in a position that secures the outer end of the pin, and so
completes the connection.

S84. Models of disconnecting cranks. Presented by Messrs.
Bullivant & Co., 1902. N. 1890.

These three brass models show modifications of the connecting arrange-
ments patented by Samuel Seaward in 1840.

(a) In this construction the crank-pin, which is fixed to the inner web of
the crank, is hollow and has within it a pin which, by a central screw, can be
forced into the eye in the outer web.

(&) This plan closely resembles (a), but the closing pin is screwed into
the crank-pin from the outer web, and is fitted with a special locking device,
to prevent the screw from working back.

(c) The outer crank web has in its face a deep slot through which the
crank-pin can sweep ; contained within the web are two square bolts, which,
by means of screws, can be forced across the slot, so as to secure the
squared projecting end of the crank-pin.

885. Model of disconnecting crank. Contributed by Messrs.
Maudslay, Sons and Field, 1861. N. 441.

The outer web of the crank terminates in a heavy sleeve, in the face of
which is a slot through which the crank-pin can sweep. This sleeve can,
however, be turned in its eye through 90 deg., and be thus caused to retain
the free end of the crank-pin. The device is almost identical with (c)
in No. 883.

Note. A very large example of disconnecting cranks is represented in
the model of the " Great Eastern " paddle engines (see No. 814).

T 2



886. Clutch for propeller shaft. Lent by Henry Emanuel,

Esq., 1885. N. 1695,

This is a claw clutch intended for use in disconnecting the propellers
of launches, etc.

The clutch is loose on a sleeve keyed to the tail shaft, and when in gear
the claws engage in recesses on a flange on the engine shaft, and are
maintained in gear by a helical spring. When disconnected, the claws are
prevented from entering the jaws by an intervening masking flange, which ,
when connection is to be made, can be turned into a position in which the
claws can pass through it.

887. Model of clutch for propeller shaft. (Scale 1 : 12.) Con-
tributed by Messrs. Benjamin Hick and Sons, 1859.

N. 327.

This is a friction clutch, arranged within a large drum secured to the
tail shaft. On the engine shaft is a boss with a flange supported by four
ribs which serve as guides for four sector-pieces arranged inside the drum ;
these are forced apart by right and left-handed screws in pairs, turned by
levers attached by links to a sliding sleeve, which is forced home by a screw
independently supported.



888. Stern bush of S.S. " Royal Charter." Presented by
Messrs. Gibbs, Bright & Co, 1861. N. 465.

This bearing for the shaft of a screw propeller was made in accordance
with John Penn's patent of 1854. It consists of a gunmetal bush some-
what larger than the shaft journal ; the interior of the bush is provided with
dovetail grooves into which are inserted lignum vitse blocks so shaped as
to project above the metal. The wooden ridges are then bored to the
diameter of the journal, and form the bearing surfaces, while the inter-
vening spaces allow free passage for the water, which is an excellent
lubricant for metal sliding on lignum vitse. The screw shaft bearing had
previously given great trouble, but Penn's invention, which is now
universally adopted, has proved a perfect solution of the difficulty except
where sandy water prevails.

The bush shown was used over a distance of nearly 200,000 miles,
without suffering any material wear. It was recovered, after nearly two
years' submersion, from the S.S. " Royal Charter," an iron-built vessel of
2,719 tons and 200 nominal h.p., which was wrecked in Moelfra Bay,
Anglesea, in 1859, during a memorable gale.



MARINE STEAM BOILERS.

The earliest boilers had only to sustain the stresses due to the
weight of the water within them, the steam being at atmo-
spheric pressure, so that they were simply water tanks with
external grates and flues ; thus the boiler of the " Clermont,"
1807, was a tank set in brickwork and externally fired.

Watt's wrought iron "wagon" boiler was for many years
almost the only type of steam generator used on land, and after
it had been improved by the introduction of an internal furnace
flue, it developed into the marine "box" boiler, with internal
flat-sided flues and furnaces, which remained in almost universal
use till 1845. These boilers, even when well stayed, were not
suitable for pressures exceeding 35 Ib., but in other respects



293

they were satisfactory ; they could be made to fit the avail-
able space in the ship, had considerable heating surface, and
gave evaporative results that would even now be considered
satisfactor}^.

The vertical or modified " haystack " boiler was employed in
steamships by David Napier in 1842 ; with numerous modifica-
tions and improvements it remains a popular and compact form
for the smaller types of steamboats.

The substitution of tubes for the fiat flues in box boilers was
advocated by the 10th Earl of Dundonald about 1850, the tubes
to be about twice the diameter of those that had then been
common in locomotive practice since 1829. Small cylindrical
multi tubular boilers working at 90 Ib. pressure were in use in
1854, but there was a strong prejudice against such pressures
being used at sea, and the advance was not at the time
followed up.

The reduction in fuel consumption resulting from the use of
higher pressures, particularly after two-stage expansion engines
were adopted, caused a general increase in pressure to about
60 Ib. ; this necessitated the use of the cylindrical shell and
flues, and so led to the construction that is frequently described
its the " Scotch" boiler. This type of steam generator has been
that chiefly favoured in marine work from 1870 till the success-
ful introduction of the water-tube boiler, although with the
general use of three-stage expansion engines the working
pressure gradually increased to 155 Ib.

Where lightness and large steaming capacity were desired,
'as in torpedo craft, the locomotive type of boiler was at first
.adopted, with pressures of from 120 to 180 Ib., the exhaust
steam creating the draught. The introduction of surface-
condensing engines into such boats deprived them of their
blast, but this loss was more than counterbalanced by the
introduction of fan draught.

The use of still higher pressures led to the introduction of
the water-tube boiler composed entirely of tubes filled with
water and steam. Such boilers were fitted in the mercantile
marine on the Clyde about 1857, but owing to rapid corrosion of
the tubes they were not successful. Rowan fitted them in the
,S.S. "Propontis" in 1874, and in 1878, Loftus Perkins provided
the S.Yt. " Anthracite " with a. " pipe " boiler working at 500 Ib.
pressure consisting wholly of layers of horizontal tubes enclosed
in a lined sheet-iron case externally resembling a square vertical
boiler. In 1879, a type of water-tube boiler, the "Belleville"
(see No. 903), having tubes of large diam. placed at a slight
inclination and very closely stacked in separate elements, was
successfully used on a despatch vessel in France, where its
application was after some years extended to larger war-vessels.
This type of boiler was also adopted for the passenger steamers
-of the Messageries Maritimes.

The different types of water-tube boiler at present in use
liave been classified into groups depending on the amount and



294

freedom of the circulation of water, but the most general
division is into two groups respectively known as "large" tube
and "small" tube boilers. The former are suitable for large
ships, while the latter are suitable for small ships and short runs-
at high speed. These have also been called " express" boilers.
The " Thornycrof t " boiler (see Nos. 902 and 908) was.
patented in 1885, and first fitted on H.M. torpedo-boat " Speedy,"
It was followed by the " Yarrow " boiler in 1889, the " Reed "
boiler (see No. 906) in 1893, and many others of the small-
tube express type. The "Belleville" boiler was used in H.M.
Navy in 1893 on H.M.S. " Sharpshooter " and subsequently the
large cruisers, H.M.Ss. "Powerful" and "Terrible," each of
25,000 indicated h.p., were supplied with them. Since then
many large British warships have been fitted with these boilers r
but they are not used in the British mercantile marine. A type
of large- tube boiler which has been very successful in recent
years is the Babcock and Wilcox (see No. 905), which
Avas fitted on the S.S. " Tasso " in 1893. Many vessels of the
mercantile marine and of the British and the United States
Navies have been supplied with this type of boiler. A boiler
of the large-tube type which differs somewhat from any of the-
preceding is the " Niclausse " (see No. 907), which has double-
tubes, acting similarly to Field tubes. Great difficulties were
met with when the Belleville boiler was introduced into H.M.
Navy, in part owing to the highly skilled attention which
such boilers continually required. On the advice of an expert
committee their use was not further extended. The present
practice is to fit either the Babcock and Wilcox, the Yarrow
large- tube (see No. 904), the Niclausse, or the Diirr type to
large vessels, either as a complete installation, or in combination
with a number of Scotch boilers. For small vessels, e.g., torpedo-
boat destroyers, one of the many approved types of express boiler
is used.

Of the many advantages for marine work which the water-
tube or tubulous boiler possesses over the Scotch or tubular
type, comparative immunity from accidents, ability to stand
high pressures, lightness, and rapidity in raising steam are-
those which are most important.

A method of increasing the steaming powers of boilers, and
therefore of reducing their relative dead-weight, is by burning
more fuel per square foot of grate area. This is done either by
forced, or by induced draught. In the first case the stokehold
or else the ash-pit is air-tight and has air forced into it by a
centrifugal fan, while in the second, the waste gases are pumped
from the smoke box by a similar fan and forced up the funnel.
Both arrangements permit the use of an inferior class of fuel
and also render the stokehold cooler. Although at first only
fitted in torpedo vessels, forced-draught arrangements are now
always provided in the ships of H.M. Navy, and to a lesser extent
in those of the mercantile marine.



295

889. Model of marine boiler and funnel. (Scale 1 : 12.)
Presented by the Earl of Dundonald, 1861. N. 537.

Thomas Coclirane, 10th Earl of Dundonald (1775-1860), in his remark-
able career, did much to hasten the introduction into the Royal Navy of
propulsion by steam power, and designed a war-vessel, H.M.S. " Janus,"
which he fitted with four boilers, resembling this model, each with three
furnaces ; he also made experiments in the introduction of hot air into the
combustion chamber, and a plate on the model states that it represents
a boiler " which evaporated 785 cub. ft. of water per hour by his system of
economical firing."

The boiler is of the rectangular type, with numerous flat- stayed surfaces
and three flat- sided furnace flues ; the opposite flat surfaces were tied
together by internal stays, which, however, are not represented in the model.
The three furnaces open into a common combustion chamber, from which the
gases pass to the front through horizontal return tubes that deliver them into
the smoke-box under the uptake, just as in the modem " Scotch " boiler.
Passing the uptake through the steam space, as here shown, has now been
generally discontinued, owing to the rapid deterioration that these plates
suffered. The funnel is fitted with an air jacket, and contains a swinging
damper.

The water level is automatically maintained by a float-controlled valve ;
the safety valves have dead weights hanging within the boiler but fitted
with easing gear that can be worked from outside. The waste steam pipe
has a drain for collecting condensed water, so that it shall be returned
to the hot-well. On the front is an internally opening unloaded valve,
by which air would enter if the steam pressure was lowered, thus preventing
the boiler from collapsing under atmospheric pressure, a risk that was
greater than its bursting iinder its steam pressure.

890. Model and drawing of Hawthorn's boiler. (Scale 1 : 12.)
Lent by Messrs. R. and W. Hawthorn, 1869. N. 1316.

This construction, patented by Mr. W. Hawthorn in 1868, combines
several features of the earlier flue boilers with others of the usual marine



Online LibraryScience Museum (Great Britain)Catalogue of the naval and marine engineering collection in the ... museum .. → online text (page 41 of 58)