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external hand-wheel ; the position of this sleeve determines the level at
which the water will be maintained; the sleeve can moreover be so far
withdrawn if required, as to leave a free passage for the feed water.



932. Drawing of Kirk's evaporator. (Scales 1 : 24 and 1 : 8.)
Presented by Messrs. R. Napier and Sons, 1891. N. 1859.

This is an arrangement introduced by Dr. A. C. Kirk for distilling sea
water and so obtaining suflicient pure water for making up the boiler feed,
etc., without using additional fuel.

The evaporator is simply a cylindrical drum or low-pressure boiler
placed in the uptake of the main boilers of the ship. This drum has a few
necessary fittings and is fed with sea water, from which it generates steam
at a low pressure but in suflicient quantity to make up for the losses of
fresh water from the working of the engines, etc. The steam generated is
taken either into the receiver of the main engines to help in propulsion or
direct to the condenser ; the salt accumulating in the evaporator is removed
by systematic blowing out, as usual in marine boilers working with sea
water.

The drawing shows the evaporator fitted in the S.S. " Damascus," a vessel
of 3,700 tons register, built and engined in 1887 by Messrs. Napier. The
evaporator is 4ft. diam. by 26 -5 ft. long, weighs 3' 5 tons, and contains
4' 5 tons of water. In practice it was found that when the main engines
were developing 2,000 h.p. the pressure in the evaporator was from
13-5 to 14 lb., and the production 3 tons of fresh water per 24 hours.
After 40 days' work a scale 125 in. thick was formed, but it was easily
removable.

933. Automatic evaporator. Lent by Messrs. Caird and
Rayner, 1902. N. 2296.

This apparatus, which is used in conjunction with a special condenser,
prepares drinkable fresh water from sea water by distillation, and also



315

provides suitable water for making up the loss in boiler water resulting from
the various small leakages existing in engines, boilers, and condensers. As
originally practised, boiler steam was directly cooled in a special condenser,
but owing to the grease and other impurities earned over with the priming
water in this steam, the distilled water obtained was most unsatisfactory,
while the whole of the impurities removed from it were deposited as scale in
the main boiler. To overcome these defects the steam or vapour for the
special condenser is now usually generated by evaporating sea water in a
vessel heated by a coil of pipes supplied with steam from the main boiler,
the vapour thus obtained for condensation being practically pure, while the
deposited solids remain in an apparatus from which they can be easily
removed. The primary steam from the main boiler by its condensation in '
the coils of the evaporator generates secondary steam, which when condensed
gives practically pure distilled water, a plant acting in this way being
accordingly known as a " double distiller."

The evaporator shown was patented by Mr. T. J. Rayner in 1888, and it
also embodies seA T eral later improvements introduced by Mr. E. B. Caird.
It consists of a vertical cylindrical vessel in the lower part of which is fitted
a series of spiral coils of solid drawn copper pipe, the two ends of which are
rigidly fixed to the door in such a way that they can expand and contract
with the variations of the temperature and pressure to which they are
subjected. Sea water is admitted and maintained at a constant level within
the vessel by an automatic valve, while boiler steam is admitted within the
pipes so that it transmits much of its latent and sensible heat to the sea
water, thus boiling it off while the water from the boiler steam is again
returned to the boiler. The solids from the sea water deposit chiefly on the
heating pipes, from which, however, they are continually flaking off owing
to the slight movement that takes place in the coils, so that the deposit can
be removed by washing out and occasional scraping. The secondary steam
or vapour from the evaporator passes off from the top of the vessel, where
is fitted a series of baifle plates for the purpose of preventing water being
carried over.

In the example shown the surface of the heating coils is 10 sq. ft., and
their evaporating capacity 300 Ib. of pure water per hour. The steam from
the evaporator is conveyed to a condenser (not shown), which is of vertical
tubular construction and has vapour inside the tubes and sea water outside
them ; with the object of reducing the amount of heat carried away by the
process, the cooling water from the hottest portion of the condenser is used
for feeding the evaporator. The distilled water drained from this condenser
is sprayed into fresh air to aerate it somewhat, and then passed through the
test tank into the storage tanks of the ship.



PROPELLERS.
PADDLE-WHEELS.

The radial float paddle-wheel, suggested possibly by the
water-wheel, is recorded to have been tried spasmodically as a
ship propeller, rotated of course by muscular power, from the
loth century onwards, but it never seems to have threatened
seriously the simpler reciprocating oar. With the application
of the steam engine to marine propulsion the paddle-wheel,
along with many other apparatus (see p. 341), was tried, but the
former, connoting as it does a rotative movement, proved most
convenient, so that it alone survived. It was independently
decided upon by the pioneers in steam navigation : Symington
for the " Charlotte Dundas," 1801 ; Fulton for the " Clermont, 1 ":
1807 ; and Bell for the " Comet," 1812.



316

The paddle-wheel has been placed in many positions ; in
the " Comet," two wheels, one abaft the other on each side, were
used, but this quickly gave way to the modern single wheel. It
has also been placed in a casing amidships or in the space
between twin hulls ; as recently as 1877 the P.S. " Calais
Douvres," a vessel of the latter type, was so fitted. The stern
wheel was used in the " Charlotte Dundas," and at the present
day it is preferred for exceptionally shallow draught as it is less
influenced by rolling, besides occupying less width than side
wheels.

The modifications of the wheel that have been tried are very
numerous. When used as an auxiliary power or with the
varjang draught incident to an ocean voyage, it was proposed
to raise the wheel bodily, but the usual plan was to reef the
floats by moving them radially along the arms. To reduce
splashing, floats have been given a sinuous form with right and
left hand inclination on opposite sides. They have also been
divided into separate slats or provided with holes and valves
to let out entangled air. Galloway in 1835 introduced the
" cycloidal " wheel in which a float is made up of horizontal
slats arranged on a cycloidal curve and several such wheels were
successfully used.

As speeds increased, the defects of the radial float became
more apparent and attempts have been made, in two directions,
to reduce loss of power by " feathering." In one, the resistance
of the air to the float when out of the water has been reduced
just as is done by a rower feathering his oar, by arranging the
float to turn on a radial axis ; numerous paddle- wheels were
invented with this object in view, but the practice has not
survived. In another direction the loss of power arising from
the oblique blow with which a radial float strikes the water and
the splashing it occasions when leaving have been minimised
by turning the float on an axis parallel to that of the shaft.
Robertson Buchanan in 1813 patented a wheel in which the
floats always remained vertical (see No. 944), but this solution,
although frequently repatented, is only correct at the moment
the vessel starts ; when under weigh it may be as imperfect,
although in the opposite direction, as the radial float. John
Oldham's wheel of 1827 (see No. 948) gave a true action but
involved the use of spur gearing. Elijah Galloway in 1829
patented what was subsequently known as Morgan's wheel ; in
this there is, within the wheel, a fixed eccentric pin to which
the floats are connected by rods and brackets. By varying the
eccentricity of the pin any inclination, for a predetermined slip
ratio, can be given to the floats. With the exception that the
fixed pin is outside the wheel an improvement introduced by
John Seaward Morgan's wheel still represents the latest practice
{see No. 955). The floats now used in conjunction with this
feathering mechanism are curved and present a concave face to
the water ; they were brought out in 1877 by A. C. Kirk and
fitted to boats on Continental and other routes.



317

Paddle-wheels have, for many reasons, long been displaced,
for ocean steamers, by the screw propeller ; the " Scotia " of
1861 was the last Cunarder so fitted. They are, however, still
retained for river traffic where the available draught is limited.

934. Paddle-wheel with radial floats. (Diam. 10 in.) Contri-
tributed by William Morgan, Esq., 1860. N. 410.

This is a wheel with a single ring, the floats being supported by back
struts ; the ring is feather-edged.

The usual construction of the common radial float paddle-wheel is shown
in the side-lever engine model No. 797, while the largest examples ever
bnilt are represented in the model of the engines of the " Great Eastern/'
No. 814.

935. Rennie's paddle-wheels. (Diam. 9 ' 5 in. and 12 in.) Pre-
sented by George Rennie, Esq., 1857. N. 144-5.

These four models represent various forms of fixed-float paddle-wheel
patented by Mr. Rennie in 1839, and practically applied at the time with
some success. The floats are trapezoidal in form, generally with the
diagonals in the ratio of 2 : 3 and with the longer one radial, while the
surfaces were to be plain, convex, or concave. The shape of the float
reduced the suddenness of the shock on entering and leaving the water,
and was considered to give increased thrust with a diminished water-lifting
action.

Two of the models have rhomboidal floats, and in one wheel the shorter
diagonals are radial ; the third model has trapezoidal floats. In the fourth
model the floats are triangular in shape, and this wheel was known as the
" duck-foot " propeller from its resemblance to the webbed foot of a bird ;
a small model of a steamer fitted with this form of paddle-wheel is also
shown.

In 1840 the trapezium form of paddle-wheel float, when tried on a
Thames steamboat, gave an increase of 14 per cent, in speed over that with
ordinary floats ; Mr. Rennie considered that his construction halved the
weight and width of the paddle-wheels required for attaining similar speeds
under like conditions, when compared with those with rectangular floats.

936. Paddle-wheel with radial floats. (Diam. 8' 7 in.) Con-
tributed by W. H. Muntz, Esq., 1862. N. 786.

This fixed-float paddle-wheel was patented by Mr. Muntz in 1862.

The floats in outline resemble a canoe paddle and are arranged three in a
row, on three rings. They were intended to dip deeper than common floats
and to cause less shock on entering.

937. Model of "cycloidal" paddle-wheel. (Scale 1:32.)
Made in the Museum, 1898. N. 2170.

This form of fixed float wheel was introduced in 1833 by Joshua Field,
F.R.S. In 1835 Elijah Galloway re-invented the arrangement, and it is
from his patent specification that this model has been made.

Each float, instead of being in a single piece, is divided into several
naiTOw widths set stepwise in advance of one another, as the circumference
is approached, approximately along a cycloidal curve. In this way the shock
on entering was reduced and distributed, while the discharge of water and
air from the floats was facilitated.

Galloway's wheels were first tried on the City of Dublin steam packets,
and they were in considerable use by about 1845 (see Nos. 182 and 807) ;
many modern steamers have each float in two pieces arranged in this
manner.



318

938. Model of " cycloidal " paddle-wheel. (Scale 1 : 20.)
Maudslay Collection, 1900. N. 2233.

This represents Field's construction of the cycloidal paddle-wheel (see
No. 937), as fitted in 1838 to the " Great Western," a vessel 1,320 tons
register, 236 ft. long, 35 3 ft. broad, and 23 25 ft. deep, which was one of the
pioneer steamships crossing the Atlantic (see No. 182).

Each float is in four separate parts stepped one behind the other from
the circumference towards the centre, approximately on cycloidal curves ;
the parts of the float nearest the centre are wider than those further away.
The arms of the wheel are not quite radial, being tangential to a circle
somewhat larger than the boss ; in this way the faces of the float, being
parallel with the arms, are more favourably placed for quietly entering the
water. Each float is of wrought iron, and is secured to the stepped framing
at each end by hooked bolts.

By thus dividing the area of the float into horizontal sections the escape
of air is facilitated, while by the arrangement of the sections, an action on
entering is secured that somewhat resembles feathering.

939. Model of wooden paddle-wheel (1843). (Scale 1:24.)
Presented by D. Lapraike, Esq., 1868. N. 1201.

This represents one of the paddle-wheels of the American river steamer
" Empire " (see No. 189). At that period wood was the material almost
exclusively used in the construction of American vessels and their paddle-
wheels, as it compared favourably with iron in being both light and cheap,
while the frequent repairs, necessited by the presence of floating ice and
timber, were easily made locally.

In the wheel represented there were four sets of arms, and the arms of
each set were bolted alternately into recesses in each side of a cast-iron boss
or " centre " keyed to the wrought-iron paddle shaft. Each set of arms was
consolidated by a concentric ring, and the sets were tied together at the
circumference by the floats without any cross bracing. Divided floats were
adopted (see No. 938), which diminished the loss arising from there being
no feathering motion. The wheel was 32 '5 ft. diam., and had 26 floats,
12 5 ft. wide by 2 ft. deep (in two parts).

940. Paddle-wheel with oblique floats. (Diam. 12 in.)
Contributed by Messrs. Jackson and Watkins, 1860. N. 413.

This is a wooden model of a paddle-wheel with radial floats fixed
obliquely, and probably represents the wheel patented in 1829 by Archibald
Robertson ; the construction was patented subsequently by many others.

Each float is a portion of a left-handed helix with an angle of about
45 deg. ; to neutralise the side thrust the other paddle-wheel was to
have its floats oppositely inclined. This oblique setting was probably
introduced to reduce the blow given by a common float on entering the
water.

941. Paddle - wheel with oblique floats. (Diam. 7 in.)
Woodcraft Bequest, 1903. N. 1338.

This wheel was designed by Mr. Bennet Woodcroft in 1850, and is a
modification of No. 940. Each float is V-shaped, being formed by the
meeting of a right-handed and a left-handed helical surface, so that side
thrust is avoided while gradual immersion is secured.

942. Paddle-wheel with sinuous floats. (Diam. 8 in.) Lent
by Messrs. McClennan and Owen, 1883. N. 1599.

This paddle-wheel was patented by Messrs. J. McClennan and B. Owen
in 1 880. It is intended to diminish the noise and swell usually created by
paddle-wheels.

Instead of float boards, a continuous sinuous blade is employed which
acts like a series of oblique floats ; enclosing side discs are added to prevent
lateral escape of the water.



319

943. Paddle-wheel with reefing floats. (Diam. 18 "7 in.)
Contributed by J. J. Brunet, Esq., 1860. N. 406-7.

When paddle steamers were used for ocean voyages considerable loss of
efficiency was experienced owing to the change in the immersion of the
floats that resulted from the consumption of the coal on board.

The wheel shown was patented in 1843 by Mr. Brunet as a means for
correcting this. It has arrangements by which the floats can be quicfldy
and simultaneously moved further from the centre as the vessel becomes
lighter. On the paddle-shaft is a wheel connected by a separate rod to each
float in such a way that a partial rotation of the wheel relatively to the shaft
slides the floats along the radial arms of the paddle-wheel. This relative
motion is given by a train of gearing worked by a winch handle. The floats
are in two parts, one being in front and the other behind the wheel arm ;
they are united by brackets which clamp them to the arms when canted by
a second set of rods and a wheel worked similarly to the first.

A second model shows a simplified form of the arrangement in which
gearing is omitted, the float arms being secured by lashing.

944. Buchanan's feathering paddle-wheels (working). (Diam.
12 '5 in. and 7 '5 in.) Presented by Messrs. Bullivant
& Co., 1902. N. 1887-8.

Very soon after the practical introduction of marine propulsion by
paddle-wheels the loss of power resulting from the oblique action of the
entering and leaving floats of a radial wheel was realised, with the result
that many modifications were proposed. The model represents the wheel
patented .by Robertson Buchanan, of Glasgow, in 1813, which, although a
failure, introduced the four-bar mechanism that subsequently led to the now
universal construction known as Morgan's wheel.

In the Buchanan wheel each float has through its centre a horizontal
spindle, which keeps the side rings together and also carries a crank-arm
which is attached to a ring that turns freely on a sheave fixed to the ship,
but not concentric with the paddle-wheel. The eccentricity of the sheave is
equal to the radius of the cranks, and as the wheel revolves the floats remain
vertical, thus entering and leaving the water edgeways, provided the ship is
not moving. When the ship is in motion, however, its velocity so alters the
conditions that this constantly vertical position of the floats is as unsatisfac-
tory as the radial position in the simple wheel.

In the later model of Buchanan's wheel shown, the floats are smaller
but more numerous ; they have cranks at both sides controlled by rings
revolving on eccentrics.

945. Model of Napier's feathering paddle-wheel (working).
(Scale 1 : 24.) Made in the Museum, 1898. N. 2171.

This feathering arrangement, patented in 1841 by David Napier, of
Millwall, resembles Buchanan's wheel in principle, but instead of the ring
which moves the crank-arms being controlled by an internal eccentric, it is
made massive, so that gravity supplies the restraining force without other
assistance.

Wheels of this construction were successfully fitted in 1842 to the
celebrated London and Margate iron-built passenger steamers " Eclipse "
and " Isle of Thanet," driven by Napier's steeple engines and haystack
boilers. The " Eclipse " was of 278 tons b.m., 156 ft. long, 19 ft. beam,
and 9 '5 ft. deep. Her paddle-wheels were 16' 5 ft. diam., and her load
draught 5 ft.

946. Feathering paddle-wheel (working). (Diam. 21 in.)
Contributed by Richard Sheward, Esq., 1866. N. 1090.

This modification of Buchanan's wheel (see No. 944) was proposed in 1865.
The guiding ring is fitted with rollers to reduce the friction between it and
the fixed sheave.



320

947. Feathering paddle-wheel (working). (Diam. 11 in.)
Presented by Messrs. Bullivant & Co., 1902. N. 1885.

This represents the automatic feathering arrangement patented by
W. H. Hill in 1825.

Each of the four floats is free to move on its horizontal axis ; but to its
back is fixed a rod connected by links to the float behind and to that in
frpnt, the intention being that the resistance of the water should secure the
feathering action. By lashing the floats to the arms it could be converted
into a fixed float wheel.



948. Oldham's feathering paddle-wheel (working). (Diam.
13 in.) Presented by Messrs. Bullivant & Co., 1902.

N. 1886.

This arrangement, patented by John Oldhain in 1820-7, is an interesting
expansion of the linkage introduced by Buchanan for the same purpose.

The floats turn on horizontal axes, and are connected by short outside
cranks to the feathering rods, which are the arms of a frame embracing an
eccentric attached to a loose sleeve on the main shaft. This sleeve is so
geared to the shaft that the eccentric makes one revolution for every two
revolutions of the paddle-shaft, the result being, that instead of the floats
remaining constantly vertical, as in Buchanan's wheel, they revolve at half
the speed of the wheel, so that, while vertical at the bottom of their path,
they become horizontal at the top, and vertical when again at the bottom ;
but they are then presenting the other face to the water. The gearing and
the reversal of the floats are objectionable features, but the feathering action
appears to be perfect.

Oldham's paddle-wheels were, in 1822, fitted to the " Aaron Manby," an
iron boat, constructed at Horseiey, near Birmingham (see No. 811).

949. Poole's feathering paddle-wheels (working). (Diam.
9 in.) Presented by Messrs. Bullivant & Co., 1902.

N. 1883-4.

This feathering arrangement, patented in 1829 by William Poole, of
Lincoln, was fitted to numerous paddle- steamers by Messrs. Seaward and
Capel.

The floats are secured to horizontal shafts, each of which terminates in
an arm carrying a friction roller that travels in a groove, formed in a circular
ring, secured to the vessel, but not concentric with the paddle-wheel.

Such wheels, fitted to several river packets plying between Lincoln and
Boston, showed an increase of 20*7 per cent, in speed and a decrease of 19
per cent, in fuel consumption, when compared with the plain wheels that
they replaced. To obviate the noise made by the friction rollers, they were
subsequently made of sole leather.

A modification of Poole's wheel, introduced by Messrs. Seaward, is shown ;
the race for the rollers, instead of being circular, has two semi-circular ends
joined by straight portions.

950. Model of feathering paddle-wheel (working). (Diam.
10'7 in.) Maudslay Collection, 1900. N. 2234.

This is a greatly improved form of Poole's wheel (No. 949) and is pro-
bably of much later date, the paddles resembling those of the early Gallo-
way wheel (ISTo. 951), to which its action is equivalent. Each float has a
shaft carried between the two main rings of the wheel and provided with an
external crank- arm, the pin of which is controlled by a circular groove in a
large ring, free to turn on a pin secured to the outer sponson beam. Through
the rotation of the ring, the wear and resistance of the circular race are
almost entirely eliminated.



321

951. Galloway's feathering paddle-wheel (working). (Diam.
17 in.) Contributed by J. J. Brunet, Esq., 1860. N. 408.

This model represents the original form of the wheel patented by Elijah
Galloway in 1829.

Each float turns on an axis along one edge, and has a short arm projecting
from its centre connected by a long rod to a ring which turns on a crank-pin
held stationary within the wheel near the centre. The mechanism gives a
practically perfect feathering action, but the construction is unsatisfactory
on account of the severe stress on the feathering rods ; also because the
wheel is only driven at one side, as provision had to be made for supporting
the internal crank-pin.

The patent was purchased by William Morgan, of New Cross, who brought
the invention to a practical success, and in 1838 patented improvements in
the wheel, so that it is generally known as Morgan's. (See No. 953.)

952. Galloway's feathering paddle-wheel (working). (Diam.
14 in.) Presented by Messrs. Bullivant & Co., 1902.

N. 1882.

This model of Galloway's wheel closely resembles the adjoining example,
but renders the construction more clearly visible, since the crank-pin which
moves the feathering rods has no bearing in the end of the paddle-shaft
The rods are strengthened by struts.

953. Model of Morgan's feathering paddle-wheel (working).
(Scale 1 : 24.) Contributed by William Morgan, Esq.,
1861. N. 409.

Morgan's improvements upon the Galloway wheel consisted chiefly in
increasing the number of floats ; turning them on central spindles ; altering
the arms connecting the feathering rods with the floats, and strengthening
the wheel by cross-bracing a matter of great importance, owing to one side
only being directly driven.

This improved construction was fitted in 1830 to H.M. gun-brig
" Confiance." When tried against her sister ship, the " Echo," which had
simple radial floats, the Morgan wheel showed an increase in speed of from
28 to 55 per cent., according to the state of the sea. In consequence of these



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