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" Scotch" type. In 1869 a pair of these boilers, illustrated, were fitted n
the S.S. "Mercury," a vessel 235 ft. long, 28 ft. broad, and 18-2 ft. deep.
Her engines were two-stage expansion, and indicated 434 h.p.

The shells of the boilers were semi- cylindrical with flat sides, and were
11 ft. long by 9 ft. wide, by 11 25 ft. high. Each boiler had two furnace
flues and a central flue, all oval, but with the flat sides mutually staying
each other ; these flues were 2-5 ft. wide by 3 ' 5 ft. high, and the grates
were 5 ft. long. Below these flues were three cylindrical flues, the middle
one 2 5 ft. diam. and the outer ones 1 9 ft. diam. ; at the front was a
dry uptake from the two outer of these lower flues. The flues and chambers
were strengthened by water-tubes 8 in. diam. ; these also increased the
heating surface and promoted circulation. The flames and gases from the
furnaces passed to a combustion chamber at the back and returned through
the central flue to the front, then downwards into the central circular flue,
and so to the back, finally reaching the uptake by the two other circular
flues.

The combined heating surface of the two boilers was 1,320 sq. ft., and
the grate area 42 2 sq. ft. The evaporation per Ib. of coal was 9 124 Ib. of
water from 50 deg. F., and the total evaporation per hour was 10,000 Ib. ;
the steam pressure was 45 Ib. per sq. in. The weight of the two boilers
was 25 5 tons, and they carried 17 75 tons of water when steaming.

891. Model and drawing of marine boiler. (Scale 1 : 24.)
Lent by William Gray, Esq., 1874. N. 1380.

This design was patented by Mr. Gray in 1872 ; its chief features are
the means provided_for superheating the steam and for heating the feed-
water.



296

A pair of these boilers are shown in their setting. Each boiler consists
of a main shell 20 ft. long by 8 5 ft. diam., provided with a large number
of horizontal tubes which open into a combustion chamber situated in the
middle of the length of the shell. There is a grate under each end of the
shell, and the gases from them, after passing externally beneath the boiler,
enter the combustion chamber and return to the two ends through the
tubes ; from these they are delivered into a smoke box at either end.

Above the shell is a long steam drum connected to it by numerous
vertical pipes and covered by a saddle water tank that rests on the shell,
but leaves a flue between. The funnel rises from a passage in the middle of
this tank ; the gases from the smoke boxes, in their passage to the funnel,
superheat the steam and also give off some of their heat to the feed- water
in the saddle tank.

Each furnace has a grate area of 25 sq. ft., while owing to the boiler
being externally fired each shell accommodates 239 tubes 8 ft. long by 3 in.
diam., ranged at 4'5 in. centres. The combustion chamber has 120 sq. ft.
of heating surface ; the pair of boilers represented has a total grate area of
200 sq. ft., and 7,116 sq. ft. of heating surface distributed as follows : Over
fires, 200 sq. ft. ; combustion chambers, 240 sq. ft. ; tubes, 5,736 sq. ft. ;
superheater, 520 sq. ft. ; and feed- water heater, 420 sq. ft. ; the working
pressure is 100 Ib.

Provision is made for introducing heated air beyond the bridges by
passages at the side of the grate.

892. Drawing of "Howard" marine boiler. (Scale 1:16.)
Lent by Messrs. J. and F. Howard, 1874. N. 1379.

This construction of boiler was introduced by Messrs. Howard and
Bousefield in 1869-74, and was fitted to the S.Yt. " Red Rose," a vessel of
380 tons, in which the then exceptional steam pressure of 87 Ib. was
used. The leading idea in this arrangement is to avoid the stresses in
large shells by using a number of smaller ones about 42 in. diam. In the
drawing there are three bottom shells, each containing a single furnace flue ;
above these are three shells containing return tubes, and these support three
top shells which act as water and steam drums. The combustion chamber
is water- jacketed by flat surfaces supported by screwed stays, while the
other sections of the boiler are placed in connection by large flanged necks.
The three upper shells are joined by a transverse drum above them, which
acts as a steam collector.

893. Drawing of marine boiler. (Scale 1 : 16.) Lent by
J. Dickinson, Esq., 1876. N. 1459.

This form of steam generator was patented in 1875 by Messrs.
Dickinson and Mace. It is an externally-fired boiler in a casing lined with
fire-brick. There are two horizontal cylindrical shells traversed by a large
number of ordinary boiler tubes ; these shells are arranged one above
the other and connected together by a waist, while the upper one is
surmor.nted by a steam drum. The lower shell is directly heated by the
fire, and both elements are heated by the gases traversing their tubes as
well, as by the gases in the casing.

894. Print of boilers of P.S. " Galatea." (Scale 1 : 12.)
Lent by W. Willis, Esq., 1876. N. 1460.

The " Galatea " was built and engined by Messrs. Caird & Co. at
Greenock in 1868 for the Corporation of the Trinity House. The hull was
constructed of iron, 219 5 ft. long, 26 2 ft. beam, 13 8 ft. deep, and of
507 tons register. The engines consisted of a pair of oscillating cylinders
52 in. diam. by 66 in. stroke.

In 1876 two new boilers as represented were fitted, which indicate a
transition stage between the old rectangular form and the internally fired
cylindrical construction ; the crown is cylindrical, the sides and ends are
flat, while the four furnaces have cylindrical crowns but dry bottoms, the



297

sides of the furnaces extending downwards as water legs merely. Each
"boiler is 9 -25 ft. long, 16-25 ft. wide, 12 -3 ft. high, has four furnaces
3'5 ft. wide, and 200 return tubes 3 in. diam. ; it is surmounted by a
vertical steam chest 4' 5 ft. diam. by 4 '75 ft. high. Their combined grate
area is 186 sq. ft. ; heating surface, 5,308 sq. ft. ; water space, 1,392 cub. ft. ;
and steam space, 732 cub. ft. With these boilers the vessel attained a
speed of 14 -5 knots.

895. Model of marine boiler. (Scale 1:8.) Lent by Captain
G. J. Scott, 1883. * N. 1587.

This arrangement was patented by Mr. Scott in 1876, and was fitted in
several vessels of the India General Steam Navigation Company ; the main
object of the construction was to avoid the injury commonly resulting from
the deposit of sediment, on the heating surfaces, from muddy river water.

The boiler represented consists of two cylindrical shells placed side by
side and each fitted with a large number of ordinary boiler tubes. At the
bottom of each shell, and in communication with it, is a deep water pocket
to which the feed water is supplied and from which the solids deposited can
be blown off. The grate is arranged between the two pockets, which thus
form the sides of the fire-box, while beyond the furnace bridge is a brick-
lined combustion chamber by which the gases are directed upwards through
the boiler tubes ; after passing through these to the front of the boiler they
enter the smoke-box and escape into the funnel. Above the two shells is
fitted a steam drum, the drainage from which is led back into the feed
depositing pockets.

The model represents a boiler fitted to a steam launch, and worked at
100 Ib. pressure ; in some larger vessels groups of three or four shells were
similarly fitted and worked at a pressure of 125 Ib.

896. Model of vertical marine boiler. (Scale 1 : 12.) Lent
by Messrs. Cochran & Co., 1896. N. 2083.

This is a modification of the Cochran boiler (see Mechanical
Engineering Collection) so as to adapt it better for use as a steam
generator on board ship. The vertical shell and the short horizontal
return tubes are retained, but the grates are in two short cylindrical furnace
flues opening into a water-enclosed combustion chamber as in the usual
marine tubular boiler. The top of the boiler is domed so as to avoid
stays and similarly with the bottom ; a flat front is used so as to accom-
modate the furnaces, but these act as stays. The hemispherical top serves
as a steam drum, while it is claimed that the floor space required by the
boiler is comparatively small. The furnace tubes are flanged to take the
tube plate behind and stay it. The back of the combustion chamber is
formed within the shell so as to leave a water space, and is supported by
screwed stays.

These boilers are made in sizes up to about 2,000 sq. ft. of heating
surface, and for a working pressure of 75 Ib. per sq. in. The one repre-
sented has 800 sq. ft. of heating surface, and would evaporate in ordinary
work about 4,700 Ib. of water per hour, which, with a two-stage expansion
condensing engine, would give about 200 indicated h.p.

897. Model of marine boiler with corrugated flues and
expansion ring. (Scale 1 : 12.) Lent by Samson Fox, Esq.,
1879. N. 1525.

This model shows the application of the corrugated furnace flue invented
by Mr. Fox in 1877, and of the shell expansion ring patented by Mr. G.
Hepburn in the same year.

In internally fired boilers the furnace flues, so long as they remain
cylindrical, offer great resistance to a collapsing pressure, and only fail
ultimately by a local flattening, which, however, rapidly extends. Many
means have been adopted to strengthen such flues against collapse by



298

assisting them in retaining a circular section, but for marine purposes the
corrugated flue has been the construction most extensively applied.

Upon the introduction of this flue, experiments were made to test the
relative strengths of a corrugated and a plain furnace tube. They were of
similar general dimensions and were tested by hydraulic pressure from
without; it was then found that while the corrugated flue sustained a
pressure of 1,020 Ib. per sq. in., the plain unstiffened flue failed at 225 Ib. In
addition 'to the greater strength obtained, the corrugations increase the
heating surface and also permit longitudinal expansion.

The shell expansion ring shown in the model is an application to the
shell of a boiler of the furnace ring known as the " Bowling hoop." This
hoop possesses a certain amount of elasticity and is introduced into the
boiler shell as a means of diminishing the stresses due to the unequal
expansion and contraction of the top and bottom portions.

898. Drawing of marine boiler. (Scale 1 : 16.) Lent by
Messrs. Robert Stephenson & Co., 1886. N. 1698.

This represents the boiler of the S.S. " Prometheus," built in 1886 (see
No. 855.

It is a double-ended steel boiler 16 ft. diam. by 24 ft. long, with six
Fox's furnaces 4-25 ft. diam., and 213 return tubes 4 in. outside diam. by
9 ft. long. The tube surface is 4,015 sq. ft., and the total heating surface
5,015 sq. ft.; the grate area is 153 sq.ft. The total weight of the boiler,
including water and fittings complete, is 159 tons. The working pressure
is 80 Ib.

899. Drawing of Kemp's boiler. (Scale 1 : 16.) Lent by
Messrs. Alex. Stephen and Sons, 1887. N. 1709.

The left-hand side shows one of the boilers of the S.S. " Bleville," a ship
of 3,800 tons carrying capacity, built in 1886. This construction of boiler
was patented by Mr. E. Kemp in 1885 as a combination of high and low
temperature boilers, but the arrangements are similar in principle to those
of a factory boiler when fitted with the form of feed -water heater known
as an " economiser."

The high temperature boiler is an ordinary "cylindrical boiler 10 -6 ft.
diam. by 10 ft. long, with two corrugated furnaces 3 5 ft. diam. and 108 return
tubes 3 5 in. diam. by 7 ft. long ; its grate area is 36 sq. ft. and the heating
surface 884 sq. ft.

The low temperature boiler consists of four stacks, each containing
90 tubes 2 in. diam. by 9 ft. long, arranged in the smoke-box and uptake of
the time boiler. The total surface of these secondary boilers is 1,696 sq. ft.,
and through these tubes the feed water is forced in the opposite direction to
that in which the external gases flow, so that the coldest gases are heating
the coldest water.

For increasing the draught when required, a fan 6 ft. diam., and driven
by an external engine is fitted in the uptake, above the low temperature
tubes. The boilers worked at 160 Ib. pressure, and on trial it was found that
the feed- water at 120 deg. F. was heated to 300 deg. F. before entering the
true boiler, while the gases, leaving the true boiler at 640 deg. F., had a
temperature of only 300 deg. F. when leaving the system.

The right-hand side shows a modification patented by Mr. Kemp in
1886. In it the gases pass through the tubes of the secondary boiler, which
take the form of four inultitubular cylinders ; above these is a nest of tubes
through which the air for the furnaces is forced, before it is led down to a
closed ash-pit.

900. Drawing of small marine boiler. (Scale 1 : 8.) Lent
by Messrs. Ramage and Ferguson, 1887. N. 1708.

This represents the boiler of the S.Tt. " Gladiator," built in 1886, full
particulars of which are given in No. 854.



299

The boiler is of steel, 8 5 ft. diarn. by 7 75 ft. long ; it has a single Fox's
furnace, and 98 return tubes 3 in. diam. The tube surface is 410 sq. ft.,
and the total heating surface 500 sq. ft. ; the grate area is 15 sq. ft.

The drawing also gives particulars of the joints and other details in the
construction of the boiler, which is designed for a working pressure of
150 Ib. per sq. in.

901. Sectional model of "Scotch" marine boiler. (Scale
1 : 12.) Made by the Admiralty, 1889. Setting added in
the Museum, 1902. Plate XT., No. 2. N. 183.L

The early marine boilers were of rectangular form, with slight modifica-
tions to make, them more completely fit into the vessel ; the difficulty in
obtaining sufficient strength with such shapes was not serious with the low
pressures employed. On the substitution of surface for jet condensers,,
however, the steam pressure used, which had been 20 Ib. above atmospheric,,
was increased to 35 Ib., and this alteration soon showed the unsuitability of
the large flat surfaces of the box boiler. Small cylindrical marine boilers,
working at 90 Ib. pressure had been employed on gun-boats as early as 1854,
but it was not till about 1870 that the cylindrical form of boiler was
generally adopted, and the steam pressure raised to 60 Ib. From that time
there was a steady advance to the pressure of 135 Ib., which was that used
in the Royal Navy at the date when this model was made. Since then the
cylindrical boiler has been almost completely superseded by the water-tube
boiler, but in the mercantile marine the cylindrical type is still generally
used. The boiler is shown with the interior portion removed to render the
details visible, the two portions being placed in the setting for two separate
boilers this latter portion together with the section of the vessel's bottom
were made in the Museum in 1902.

The boiler represented is one of a set of six single -ended high or
return tube " Scotch " boilers fitted in H.M.S. " Trafalgar," built at Ports-
mouth in 1887. The shell is formed of two rings of plate 1'156 in. thick,,
united longitudinally by internal and external cover straps, treble-
riveted, with rivets 1'125 in. diam. The end plates are in three pieces,,
flanged to take the furnace flues and to join the shell, and are stayed above
the tubes and combustion chamber, and below the furnaces, by long bar
stays passing through the plates, with nuts inside and nuts and washers (not
shown) outside, the washers being riveted to the plates.

The four furnace tubes are of Fox's corrugated construction, '47 in.
thick, 3 6 ft. diam. by 7 3 ft. long ; they are riveted to the front end plate,,
and to the bottom and tube plates of the combustion chambers. In the
model, however, one has been replaced by a plain tube, made in short lengths,,
and strengthened by Adamson's flanged seam ; and another by a " Farnley "
flue, in which helical corrugations are utilised to give the necessary resistance
against collapse. The fire grates are 7 ft. long, and have cast-iron fire bars
1 in. wide, with '5 in. air spaces.

There are two combustion chambers, one to each pair of furnaces,
constructed of plates 5 in. thick, and separated by a water space 5 in. wide.
The flat sides of the combustion chambers are stayed with screwed stays
1 25 in. diam., 7 in. pitch, with nuts at each end ; the roofs are each stayed
with ten girder or "dog" stays, carrying bolts 1*25 in. diam. screwed
through the combustion chamber plate from below. There are 245 return
tubes for each combustion chamber, 2 5 in. external diam., 6*6 ft. long,
pitched 3 5 in. apart, and one -fourth of the number are stay tubes fasten-
ing the front tube plate to the front of the boiler. At the fire-box end of
each tube is fitted a cap ferrule which is only in contact with the tube at
some distance from the plate, the cap thus protecting the tube-end from
the hot gases, and thereby saving much trouble from leaky tube-ends.

The smoke-box and uptake form an entirely external fitting, instead of
being partly built in the boiler as in the earlier low-pressure types, and
there are six manholes in the front plate above the furnace tubes as well as
one into the steam space. In the model the usual boiler mountings and



300

their internal connections are represented, including the surface blow-off
and bottom blow-out valves, the main feed and the auxiliary feed valves ;
the deflecting arches and separating walls of fire-brick built in the combustion
chamber are also shown.

By reference to the separate model of the forced- draught arrangements
for this ship (No. 916), it will be seen that a set of three boilers is placed in
each stokehold on opposite sides of the vessel. Each of these sets is supported
upon two continuous longitudinal plate-girders or bearers, riveted to the
inner-bottom plating of the ship and connected together by cross-bearers
placed directly under each boiler, the whole being carried upon the usual
cellular framing of the ship-structure below, of which the principal details
are here shown.

Above the longitudinal bearers are strong crutch-frames or rolling -chocks
fitted closely to the lower part of the boiler shell and forming a complete
cradle or setting for each boiler. To prevent the boilers from shifting under
the heavy rolling or pitching motions of the ship, plate straps connect the
boilers together, and angle-iron straps or lugs connect each boiler to the
fore-and-aft bulkhead at the rear. The severe stresses which would arise
from ramming or a collision are further provided for by diagonal frames or
" ramming-chocks " fitted between the end boilers in each set and the
adjacent transverse bulkheads of the ship. Portions of the main bulkheads
to the boiler-room are shown, and also of the shovelling flat which extends
from the front of the boiler furnaces to the wing coal bunkers. The " air-
lock " is shown complete, together with parts of the screen plates fitted
between and at the sides of the boilers to reduce the stokehold temperature.

The boiler represented is 16 1 ft. diam. by 10 25 ft. long, and weighs
with its water, fittings, and proportion of uptake, and funnel, 84 tons. It
lias 3,050 sq. ft. of heating surface, and 110 sq. ft. of grate area : the
working pressure is 135 Ib. per sq. in. ; and the steam it supplies is equivalent
to 1,400 indicated h.p. under natural draught, or 2,100 indicated h.p. with
forced draught, when used in three-stage expansion engines.

902. Diagram and photographs of Thorny croft boiler.
(Scale 7 : 16.) Lent by Messrs. John I. Thornycroft &
Co, 1889. N. 1834.

These show a boiler of H.M.S. " Speedy " (see No. 130), a torpedo gun-boat
built and engined at Chiswick in 1893, which was the first vessel in the
BritishNavy, with the exception of torpedo boats, to have boilers of this type.
The dimensions of the "Speedy" are: Length, 230 ft.; beam, 27 ft.;
displacement, 810 tons.

The arrangement of the boiler illustrated is very similar to No. 908, a
model of a modern type of this boiler, with the exception that the early form
had only two lower water barrels instead of the three shown in the later
form. The generating tubes are of 1-25 in. external diam., and are secured
at each end to the drums by the use of a roller expander.

The " Speedy " was fitted with eight boilers of this kind, having a total
heating surface of 14,720 sq. ft., and a total grate area of 204 sq. ft. They
supply steam, at 200 Ib. pressure, to three-stage expansion engines, which
develop 4,500 indicated h.p. under forced draught, and 2,500 indicated h.p.
under natural draught, giving a maximum speed of 29 2 knots.

903. Sectional model of Belleville boiler. (Scale 1 : 5.)
Made by Messrs. T. and C. J. Coates, from particulars
supplied by Messrs. Maudslay, Sons and Field, 1897.
Plate XI, No. 3. N. 2124.

This form of boiler was developed and introduced by Messrs. Delaunay,
Belleville & Co., of St. Denis, France, but is now constructed in this
country, and has been fitted to some of the largest ships in the Royal Navy.
In common with all water- tube boilers, its construction permits of the use
of very high pressures, and gives great steaming capacity in proportion to
the space occupied. The model shows a complete boiler ; but as four boilers



301

are usually built together, it only represents a fourth of the usual unit for
marine work.

Bach boiler consists of a set of "elements," or continuous tubes, running
to and fro ten times over the fire, always inclining upwards, and finally
opening into the "steam collector" which is common to the set; a "feed
collector " connects the lower ends of the elements. The boiler represented
has eight elements, but one of these is withdrawn so that its construction
and attachments are visible. The straight tubes are of mild steel, 4 * 5 in.
external diam. by 7 ft. long, and are screwed into malleable cast-iron bends
or " junction boxes," of which those at the front have hand-hole doors. The
junction boxes stand one on another, and the lowest row at the back rests
on a roller, so as to permit free expansion.

The feed collector is a square cast-steel pipe, into which the lower end of
each element is secured ; at each end of it is a mud-drum, with a salinometer
and a blow-out cock to give a continuous discharge. Each mud-drum is
connected to the steam collector by a vertical pipe, through which the water
carried over with the steam returns ; the steam generated in each pipe
circuit passes upward into the collector, carrying much water with it, but
the latter is separated by a complete system of baffle plates. Lime water is
introduced into the mud-drums with the feed water, in order to precipitate
the solid impurities that would otherwise be deposited in the tubes. Above
the left-hand mud-drum is the automatic feed-regulator, controlled by a
vertical cylindrical float within a vessel connected by copper pipes with the
steam and water spaces of the boiler ; to the front of this vessel the water
and pressure gauges are fitted.

Above the fire doors runs a square tube or "gas-mixer," supplied with
air under pressure which is discharged through a number of nozzles into the
furnace to complete the combustion of the gases. Deflecting plates are
placed above the tubes to promote circulation of the hot gases, and small
deflectors are also fixed to the casing. The grate bars slope considerably*
and the furnace is protected round the sides by a firebrick lining.

The doors and the whole of the external casing of the boiler are formed
of flanged plates, so arranged as to give stiffness without preventing free-
expansion. The uptake is similarly constructed, its weight being carried by
lattice girders which rest on four corner columns that constitute the vertical
framing of the structure.

The boiler, as constructed in the model, was fitted on H.M.Ss. " Powerful "
and " Terrible," but on later ships a smaller set of elements was placed
above the main set or generator, and was called the economiser. This upper
set acted as a feed- water heater, the water passing through the small tubes
before entering the lower tubes of the generator. Between the two sets of
tubes a large space was allowed, into which air was admitted from nozzles,
the space forming an efficient combustion chamber. H.M.S. " Diadem "
(see No. 134) was the first British ship fitted with this improved boiler.

The boiler represented has a grate area of 48 sq. ft. and 1,500 sq. ft. of
heating surface ; it would supply about 10,000 Ib. of steam per hour at a
pressure of 250 Ib. per square inch, or sufficient for over 500 indicated h.p.



Online LibraryScience Museum (Great Britain)Catalogue of the naval and marine engineering collection in the ... museum .. → online text (page 42 of 58)