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the disc rocks on the conical ends of the chamber. There is a port on each
side of the partition, one being for steam and the other for the exhaust.

To obtain better contact between the disc and the conical ends of the
chamber, so as to reduce leakages, the cones and the faces of the disc are
made with radial teeth gearing into each other.

In 1845 several improvements in this type of engine were patented by
Mr. G P. Bishopp, with whose name it is frequently associated.



263

822. Model of engines of S.S. "Simla." (Scale 1 : 4.) Lent
by G. F. G. Des Vignes, Esq., 1908. N. 2455.

With the practical introduction of screw propulsion for ships in 1836,
the established type of slow-running paddle engine with its overhead crank -
shaf t was adapted to the new conditions, and the necessary speed of the
propeller shaft was obtained by the use of multiplying mechanism, such as
ropes, belts, pitch chain, or toothed wheels.

The model shows the application of the last of these and is a steeple
engine of the type patented by Mr. David Napier in 1842 (see also No. 803).
It represents the engines of S.S. " Simla," one of the first Peninsular and
Oriental boats fitted with a screw propeller. The vessel was built of iron,
in 1854, and appears to have been subsequently converted into a sailing
vessel. Her dimensions were : Displacement, about 2,600 tons ; length,
330 ft. ; breadth, 38 ft. ; depth, 27 ft. The vessel, her engines, and the
model shown were built by Messrs. Tod and McGregor, Glasgow ; the model
was exhibited in the Paris Exhibition of 1855.

The engines, which are. very compact, consist of two cylinders 90 in. diam.
by 78 in. stroke, each with 4 piston rods and a return connecting-rod, driving
cranks at right angles. The main slide valves are worked from a weigh-
shaft by loose eccentrics on the crank-shaft. Connected with the main
eccentric straps are diagonal rods which operate rocker shafts working four
gunmetal bilge pumps with clack valves. These pumps are arranged to
throw out of gear in pairs, as the upper portions of the diagonal rods are
capable of either being locked to, or disengaged from sheaves attached to
the lower portions. The expansion valves are driven in a similar manner to
the main valves, but they have separate weigh-shafts. Disengaging gear,
resembling that on the diagonal rods driving the bilge pumps, allows these
expansion valves to be thrown out of action at will. The reversing gear is
of the balanced slip sheave kind and reversal is effected for each engine
separately by throwing over the loose eccentrics by a hand-wheel and geared
quadrant.

The hot-well and jet condenser are formed in the bed plate of the engine,
and the latter is cleared by two diagonal air-pumps, one port and one
starboard. They are driven from the main crank-shaft by connecting-rods
working in trunks. A crosshead attached to the trunk of the starboard air
pump drives two plunger feed pumps.

The gearing, in the ratio of 2 75 to 1, is in four steps and consists of a
mortise wheel and pinion, the latter, which is a casting, directly driving
the propeller. The nominal h.p. was 640, and the boiler pressure 17 Ib.
per sq. in.

823. Diagram model of four-cylinder condensing engine.
(Scale 1 : 8.) Contributed by R. Bodmer, Esq., 1857.

N. 57.

This arrangement of balanced engine was patented by Mr. J. G. Bodmer
in 1844, and appears to have been intended for driving a screw propeller.

There are two cylinders with trunk pistons, acting downwards upon the
crank-shaft at an angle of 35 deg. with the horizontal, and outside each is a
larger cylinder with an annular piston of equal area to the inner one ; these
annular pistons are connected to a crank immediately opposite the crank of
the inner cylinder, so that the two sets of pistons move in opposite directions
and thus balance their inertia stresses as well as their thrusts on the crank-
shaft. The inner pistons were to have elongated trunks, while the annular
ones were to be each fitted with two such trunks. The condenser is arranged
below and is fitted with two trunk air pumps, driven from the two crank
pins ; the piston of each pump is without valves, ports in the side of its
}}arrel being periodically covered by the air pump piston, while the water
and air which enter the space above the piston are expelled through similar
ports at the top, suitably controlled by the cover of the air pump, which has
a slight amount of vertical travel.



264

824. Drawing of Bisliopp's disc engine. (Scales 1 : 12 and
1 : 48.) Presented by J. K. Rennie, Esq., 1876. N. 1415.

This arrangement of disc engine has the improvements, patented by
Mr. D. G. Bishopp in 1845, on the earlier form patented by Messrs. W.
Taylor and H. Davies in 1836.

In this class of engine the steam chamber serving as a cylinder is a
portion of a sphere, while the end covers are cones. Inside the chamber is
a piston in the form of a circular disc provided with a central boss that fits
in spherical seats formed in the covers, while a projecting arm at right
angles to the disc engages with a crank-arm on the screw shaft. A fixed
radial partition, which intersects the disc, completes the division of the
chamber into four cells of varying capacity, and amongst these the steam is
suitably distributed by a slide valve.

The disc engine was applied by Messrs. G. and J. Bennie in various mills
and factories, and in 1842 was applied to marine propulsion in the " Geyser"
pinnace, which at 200 revs, per min. attained a speed of 6 knots. In 184-9 a
disc engine of 27 in. chamber diam. was so fitted in H.M.S. " Minx " that it
could be coupled to the propeller shaft without removing her horizontal
high pressure engines ; the disc, engine gave a speed 11 per cent, higher
than that with the ordinary engines.

The larger drawing shows a design, prepared in 1853, for a 60 h.p.
condensing engine, while the smaller one shows the proposed application to
H.M. wooden sloop " Cruiser " ; in the latter case, however, horizontal
geared engines were ultimately fitted by Messrs. Bennie.

825. Model of proposed screw engine (working). (Scale 1 : 12.)
Maudslay Collection, 1900. N. 2219.

This is a modification of the twin cylinder paddle-wheel engine (see
Nos. 807 and 808) to suit the requirements of screw propulsion. As
the model has only a single crank, however, it probably represents but half
of the engine, the great fore-and-aft length of which doubtless led to its
abandonment.

There are two vertical cylinders arranged over the crank-shaft with their
piston-rods connected by a crosshead, moving in overhead guides, from which
a connecting-rod passes downwards between the cylinders to the crank in the
screw shaft below. The steam chest is common to the two cylinders and
contains a long piston valve driven through a rocking shaft by a single
eccentric on the crank-shaft. The jet condenser is arranged in the bedplate,
and the air, feed, and bilge pumps are driven from the crosshead by rocking
levers.

826. Model of engines of H.M.S. "Ajax" (working). (Scale
1 : 12.) Maudslay Collection, 1900. Plate IX., No. 4.

N. 2221.

The "Ajax "was originally a 74-gun line -of -battle sailing ship of the
following dimensions : B.o.m. 1,761 tons ; length (b.p.), 176 ft. ; breadth,
(extreme) 48 54 ft. ; draught, forward, 21 5 ft. ; aft, 22 9 ft. ; in 1848 she was
converted into a steam block- ship of 60 guns without being lengthened or
seriously altered in dimensions.

Her engines, by Messrs. Maudslay, Sons and Field, were the first horizontal
direct-acting screw-engines fitted in the British Navy. They had two
horizontal cylinders, 55 in. diam. by 30 in. stroke, on the same side of the
crank-shaft which had cranks at right angles ; the guides were utilised to
tie the cylinders to the crank bearings, and the connecting-rods were four
times the crank radius in length. To shorten the steam passages and reduce
the size of the slide valves, each cylinder had two valves inclined to each
other in a single chest ; each pair was driven through a single rocking shaft
from link motion reversing gear. The jet condensers (not shown) were in
the engine bed, and the two vertical ah* pumps employed were each driven
by a pair of eccentrics on the crank- shaft.



265

Steam was supplied at a pressure of 6 Ib. and the engines made 48 revs,
per min., indicated 846 h.p. and drove a screw 16 ft. diam., by 17 '9 ft. pitch,
and 3 16 ft. long, which gave the vessel a speed of 7 1 knots with a slip of
15 7 per cent. These results were obtained on a draught of 22 54 ft. with
an immersed midship section of 807 sq. ft. and a displacement of 3,090 tons.

827. Model of engines of S.S. "Harbinger" (working).
(Scale 1 : 12.) Maudslay Collection, 1900. N. 2222.

The " Harbinger " was a screw steamer, built of iron in 1851 by Messrs.
C. J. Mare & Co., Blackwall, for the East Indian and Cape mail service.
Her dimensions were: Register, 599 tons, gross, 848 tons; length (b.p.),
186-5 ft. ; breadth (extreme), 31 ft. ; depth of hold, 19-2 ft.

Her engines, by Messrs. Maudslay, Sons and Field, were of the diagonal
direct-acting type and had two cylinders 41 * 5 in. diam. by 27 in. stroke, acting
in an upward direction on a single crank. There were two slide valves for each
cylinder, moved by rocking shafts driven by two eccentrics. The condenser
was beneath the crank-shaft and formed in the engine framing or bed, while
the vertical air-pump was driven by an outside crank, which also drove the
feed and bilge pumps, but had a shorter throw than the main crank.

Steam was supplied at a pressure of 15 Ib. by tubular boilers, and the
engines made 26 5 revs, per min. with a coal consumption of 16 tons in
24 hours ; several other vessels were fitted with similar engines between the
years 1848-52.

828. Model of engines of H.M.S. "Wanderer" (working).
(Scale 1 : 12.) Maudslay Collection, 1900. Plate IX., No. 5.

N. 2224.

The " Wanderer " was a gun- vessel designed by the Admiralty and built
in 1855 by Messrs. Wigrain and Green, in about nine months, during the
Crimean War.

Her dimensions were : Displacement, 745 tons ; length, 180 ft. ; breadth,
28 3 ft. ; mean draught, 10 5 f t. ; area of midship section, 281 sq. ft.

Her engines, by Messrs. Maudslay, Sons and Field, were of the return
connecting-rod type with two cylinders 45 in. diam. by 24 in. stroke. The
condenser was of the jet type and arranged centrally opposite the cylinders ;
it had two horizontal air-pumps driven by an additional rod from each
piston while the other pumps were driven directly from the crosshead ; the
link motions were counterbalanced and were reversed by rack and pinion.

On trial, with steam at 20 Ib. pressure, the engines made 83 25 revs, per
min. and indicated 706 '8 h.p., which gave the ship a speed of 10 '7 knots.
The screw was 11 ft. diam., 16 ft. pitch, and 2' 5 ft. long, while the slip was
18 '3 per cent. Besides the "Wanderer," which was broken up in 1866,
13 other despatch vessels were fitted with this arrangement of ecrew
engine.

829. Drawing of engines of S.S. " Candia." (Scale 1 : 12.)
Lent Toy the Peninsular and Oriental Steam Navigation Co.,
1878. ' N. 1502.

The " Candia " was built of iron at Blackwall in 1854. Her dimensions
were : Displacement, 2,436 tons ; length (between perps.), 281 ft. ; breadth
(moulded), 39 ft. ; depth of hold, 26 '2 ft. ; area of immersed midship section,
527 sq. ft. (see No. 203).

The engines, by Messrs. G. E-ennie & Co., consisted of vertical trunk
cylinders, 71 in. mean diam. and 4 ft. stroke, arranged fore-and-aft. The
trunks were on the upper side of the pistons only, but the resulting
inequality in piston area was neutralised by the weight of the moving parts,
while the trunks greatly reduced the height of the engines.

The condensers were of the jet type, and arranged between the cylinders,
with the air-pumps worked from an intermediate crank ; the feed and bilge
pumps were worked by sway beams from an eccentric.



266

The crank-shaft was connected to the propeller- shaft by spur gearing,
which doubled the speed of the screw, and so avoided running the engines at
what, at the time, would have been considered a dangerous speed.

Steam at 22 Ib. pressure was supplied by four Lamb and Summers' sheet-
flue boilers, with 16 fires, and a total heating surface of 7,905 sq. ft. The
engines made 36' 5 revs, per min., indicated 1,672 h.p., and drove a two-
bladed screw, 15'5 ft. diam., 20 ft. pitch, which gave a speed of 12 -6 knots.

830. Diagram model of compound trunk engine (working).
(Scale 1 : 12.) Presented by Vaughan Peiidred, Esq., 1903.

N. 2331.

The construction of a compound, or two-stage expansion engine with a
single cylinder, in which by the use of a trunk at one end, the equivalent of
two single-acting cylinders of different volumes is obtained, was first carried
out in 1830 by Mr. "W. Whitham. In such an engine the boiler steam is
admitted to the annular or high-pressure cylinder surrounding the trunk
and on the return stroke passes to the low-pressure chamber on the other
side of the piston, while in the next stroke it is discharged.

The compact modification of this arrangement shown by the model was
patented as a marine engine in 1855 by Mr. E. E. Allen. In it there are
two cylinders in line, with the crank-shaft between them and the trunks
secured together by rods, while from the bottom of one cylinder is a con-
necting-rod to the crank-pin. The engine-bed forms two jet condensers,
which are cleared by inclined trunk air-pumps driven by a single eccentric,
and the top of the condensers is used as a hot-well. By the use of opposite
cylinders both strokes are maintained of equal power, and to insure uniform
turning the crank- shaft has a second crank, at right angles, driven by a
similar pair of cylinders.

In 1888, this type of cylinder was tried on a portable compound engine,
but the steam consumption was found to be about the same as that with a
simple engine ; probably because the arrangement, in addition to introducing
the cooling action of a trunk, does not limit the cylinder temperature range
so well as do separate cylinders.

831. Model of screw engines of the " Great Eastern " (working).
(Scale 1 : 12.) Presented by Messrs. James Watt & Co.,
i860. Plate IX., No. 6. N. 322.

The steamship " Great Eastern," built at Millwall in 1858, was an iron
ship of the following dimensions: Displacement, 27,384 tons; length.
680 ft. ; breadth, 82 -5 ft. ; depth at side, 58 feet (see No. 213). The vessel
was propelled by paddle-wheels and a screw propeller ; this model represents
the engines for driving the screw.

They were designed and constructed by Messrs. James Watt & Co., and
were of the horizontal direct-acting type, of 1,600 nominal h.p., but indi-
cated 4,886 h.p. ; the weight of the engines was 500 tons. There were four
steam cylinders, each 84 in. diam. by 48 in. stroke, driving two cranks at
right angles on the shaft, and the mean number of revolutions per min.
was 38 8. Each cylinder had two piston rods and a crosshead which moved
in guides ; from the crosshead of each of the starboard engines proceeded
one connecting-rod to a crank-pin, while from the crosshead of each of the
port engines two connecting-rods proceeded, so that there were three con-
necting-rods to each of the cranks. Between the cranks a balance weight
in the form of a disc was introduced.

There were four jet condensers arranged between the cylinders, with
horizontal air pumps worked from the crossheads. Circular doors were
placed on the ends of the condensers opposite to each air pump, through
which access to the air pump valves could be obtained or the buckets be
withdrawn. The delivery from the air pumps was discharged into the hot-
wells and overboard by square pipes that proceeded from the ends of the
condensers. The vacuum maintained was 25 5 in,



267

The slide valves of opposite cylinders were directly connected by a frame,
to which motion was imparted by the usual link motion reversing gear.
The weight of the link was counterbalanced by a chain, and it could be
moved either by a hand-power screw- gear or by a steam reversing gear
which had vertical trunk cylinders. The slide valves were of the gridiron
type, and on account of their great weight were borne on rollers. The
pressure on the valve faces was reduced by a circular relief frame and ring,
formed on the back of each valve, and sliding on the inside surface of the
steam chest cover.

Steam to these screw engines was supplied at 25 Ib. pressure by six
double-ended tubular boilers of the rectangular or box type, each 18 5 ft.
long, 17 '5 ffc. wide, and 14 ft. high, giving a total of 72 furnaces and a heat-
ing surface of 5,000 sq. ft. Each boiler weighed 55 tons and contained
about 45 tons of water.

The propeller was a four-bladed cast iron screw 24 ft. diam., 44 ft. pitch,
and weighed 36 tons. The propeller shafting was 150 ft. in length and
weighed 60 tons.

In order that the speed of the ship might not be retarded by the screw
propeller when under way with paddles alone or paddles and sails, two
auxiliary engines of 20 h.p. each were placed abaft the screw engine-room
to keep the screw shaft revolving when disconnected from the main engines.

The calculated speed of the vessel with both screw and paddle working
was 15 knots ; a trial trip of the ship under the screw alone gave a speed of
9 knots. It is now considered that the resistances of both the paddle-wheels
and the screw were too great for their respective engines, so that the latter
never attained the speeds at which their full powers would have been
exerted.

For a description of the paddle engines of this vessel see No. 814.

832. Water-colour drawing showing the longitudinal section
of the " Great Eastern." (Scale 1 : 96.) Contributed by
John Scott Russell, F.R.S., 1868. N. 1262.

This indicates the relative positions of the paddle and screw engines with
their boilers ; also the general arrangement of the screw shaft and the other
machinery. Full particulars of the vessel's hull are given elsewhere (see
No. 213).

833. Model of engines of S.Yt. "Hebe" (working).
Maudslay Collection, 1900. Plate IX., No. 7. N. 2225.

These screw engines were built by Messrs. Maudslay, Sons and Field in
1856, under a patent granted to Joseph Maudslay in that year ; the
arrangement is, however, an adaptation of the annular engine patented by
him in 1841 for driving paddle-wheels (see No. 809) to suit the requirements
of the screw propeller.

The engine consists of two vertical annular cylinders arranged above the
screw shaft, each with its connecting-rod passing from a guided crosshead
on the top of the cylinder through the central passage to its crank. The
air-pump crossheads, which serve also for the feed and bilge pumps, are
worked by levers directly attached to the connecting-rods, and carried on
swinging fulcrums ; these pumps are all arranged above the jet condensers,
which are at the sides.

834. Model of engines of H.M.S. " MaiTborough " (working).
(Scale 1 : 18.) Maudslay Collection, 1900. N. 2223.

The " Marlborough " was designed a sailing line-of -battle ship of 131 guns
and laid down at Portsmouth in 1850, but in 1852 was altered so that
when launched in 1855 she was fitted for screw propulsion (see No. 82).
Her dimensions were: Displacement, 6,050 tons; length, 245' 5 ft.;
breadth, 61 2 ft. ; depth, 25 8 ft. Her draught on trial was 26 3 ft, with
an immersed midship section of 1,190 sq. ft.



268

The engines, by Messrs. Maudslay, Sons and Field, were of the return
connecting-rod type with a pair of cylinders 82 in. diam. by 48 in. stroke ;
there were two valve chests to each cylinder, and the usual link-motion
reversing gear, worked by a screw. The screw propeller was 19 ft. diam.,
3 ' 6 ft. long, by about 26 ft. pitch, and the slip was nearly 22 per cent.

Steam was supplied at 20 Ib. pressure ; the engines made 56 revs, per
inin. and indicated 3,054 h.p., which gave the vessel a speed of 11 -2 knots.

835. Model of engines of U.S. turret ship "Monitor"
(working). (Scale 1 : 24.) Presented by J. Ericsson, Esq.,
1865. N. 1089.

This construction of screw engine, patented by Mr. Ericsson in 1858,
is an improvement on the vibrating piston engine of the U.S. frigate
" Princeton," built in 1842. The leading features of these designs is that
a single overhanging crank is used, and that two cylinders exert their power
upon it in directions at right angles. The arrangement places the machinery
below the water line and reduces the length of the space required, but it is
probably less efficient than one giving a more direct connection.

The " Monitor " was designed and built of iron by Mr. Erics son in 1862
for the Federal Government. Her dimensions were : Tonnage, 614 tons ;
length on deck, 173 ft. ; breadth (extreme), 41 -5 ft. ; draught, 10 ft. She
was protected by iron armour 4 5 in. thick on 21 in. of wood backing. Her
principal armament consisted of two heavy guns placed parallel with each
other and contained in a revolving turret.

The engines indicated 400 h.p. and had two cylinders of 40 in. diam.
by 22 in. stroke, arranged back to back athwartship and separated by a
plate which formed a bottom to both. Each piston had a trunk piston-rod,
within which swung a connecting-rod that joined the piston to an arm
forged on a rocking shaft. From a longer arm on each of these two rocking
shafts a connecting-rod proceeded to the crank on the propeller shaft ; to
reduce frictional losses the throw of this crank was made as long as possible.

The valve chests were placed on the forward side of the cylinders and
contained balanced slides with independent cut-off valves : the valves were
worked by eccentrics on a small shaft driven by the screw shaft, and the
engine was reversed by a hand gear that rotated this small shaft.

There was a single jet condenser and one air pump for both cylinders ;
this air pump was horizontal and double-acting, and was worked from one
of the rocking shafts.

The screw propeller was 9 ft. diam., 16 ft. pitch, and had four blades.

836. Model of engines of H.M.S. "Conqueror" (working).
(Scale 1 : 8.) Lent by Messrs. Ravenhill, Hodgson & Co.,
1869. N. 1308.

The " Conqueror " was a wooden ship built in 1833, and altered into a
screw steamship in 1859. Her first engines were of the horizontal irunk
type, but in 1863 these were replaced by the return connecting-rod set
represented in the model.

The dimensions of the ship were : Displacement, 4,300 tons ; length
(b.p.), 218 ft. ; breadth, 55 '3 ft. ; immersed midship section, 963 sq. ft. ;
draught, 24 ft. The propeller was 18 ft. diam., 20 ft. pitch, and 3 ft. in
length. On the trial runs in 1863 the engines, with 20 Ib. boiler pressure,
made 61' 3 revs, per min., and gave a speed of 9 '93 knots.

It is stated that the first engines of the type shown were constructed in
1844 for H.M. frigate " Amphion," with cylinders 48 in. diam. by 48 in.
stroke, and that the design was the joint production of Joseph Miller and
John Ericsson. Between 1845 and 1863 the makers fitted similar engines
to 42 vessels, including H.M.S. " Nelson " and the troopship " Tamar."
The horizontal arrangement was adopted, as it placed the machinery below
the water-line, and, therefore, out of the reach of shot, while the return
connecting-rod permitted the use of a long stroke in ships of only moderate
beam.



269

The engines of the "Conqueror" consist of two horizontal cylinders,
71 in. diam. by 36 in. stroke, each having two piston-rods and a return
connecting-rod, driving cranks at right angles on the main shaft. The
connecting-rod guides are supported above the bed of the condensers, which
are of the jet type, and the air pumps are directly driven from the pistons
by rods passing through the glands in the front of the cylinders. The feed
and bilge pumps are of the plunger type and are directly driven from the
crossheads. The slide valves are moved by the usual reversing link motion
controlled from a driving platform above the condensers.

837. Model of horizontal screw engines (working). (Scale
I : 16.) Contributed by W. Smith, Esq., 1860. N. 325.

This model shows an arrangement of marine engine patented by Mr. J. A.
Limbert, B.N., in 1857 ; the leading features of the design do not, however,
differ from those of the return connecting-rod engines then in use, and
which are more clearly seen in some of the larger models.

The engine represented was to have two simple cylinders 68 in. diam. by
3 25 ft. stroke, with connecting rods 2 5 times the length of the stroke.



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