MARINE STEAM ENGINES AND BOILERS
Year: 1861

page_text: LETTERS PATENT to William Macnab, of Greenock, in the County of
Renfrew, North Britain, Engineer, for the Invention of
IN MARINE STEAM ENGINES AND BOILERS."
"IMPROVEMENTS
Sealed the 28th February 1862, and dated the 14th October 1861.
PROVISIONAL SPECIFICATION left by the said William Macnab at the
Office of the Commissioners of Patents, with his Petition, on the 14th
October 1861.
I, WILLIAM MACNAB, of Greenock, in the County of Renfrew, North
Britain, Engineer, do hereby declare the nature of the said Invention of
"IMPROVEMENTS IN MARINE STEAM ENGINES AND BOILERS," to be as follows, that
is to say:
This Invention relates to improvements upon marine steam engines and
boilers of the classes described in the Specification of Letters Patent granted
to the present applicant, and dated the 26th day of September 1860,
(No. 2341.)
The improvements in engines comprise, in the first place, an arrangement
in which, in place of four steam cylinders, two high-pressure cylinders and
two low-pressure cylinders, there are only two, namely, a high-pressure
cylinder which receives the steam directly from the boiler, and a low-pressure
cylinder of larger size in which the steam operates after acting in the high-

page_text: pressure cylinder. The cranks acted on by the two pistons are, by preter-
ence. situated at right angles to each other upon the shaft. The high-pressure
cylinder receives steam by a valve, by preference, of the piston class, working
in a chamber or cylinder within a larger chamber situated between the
cylinders, and into which the steam passes from the high-pressure cylinder.
In the opposite side of this chamber are the ports of the low-pressure cylinder,
which are governed by an ordinary slide valve. The cylinders and their covers
and the intermediate chamber are surrounded by steam jacket-spaces; and
to induce a slight circulation of the steam in the jacket spaces, in order that
its temperature may be maintained, provision is made for allowing it to pass
in very minute quantities from a part of the jackets farthest from the inlet
into them, the steam thus passing mingling with that which works the low-
pressure cylinders. A pair of cylinders combined in this way may be
arranged in various positionsi In one convenient design of the engines
suitable for driving the screw propeller, the cylinders are inverted, and a
surface condenser is placed against or beside the high-pressure cylinder; whilst
the air pump and current pump are placed against or beside the low-pressure
cylinder, being worked by a lever connected to the piston rod slide block. In
a convenient design of the engines suitable for driving paddle wheels, the
two cylinders are slightly inclined up towards the paddle shaft, and the surface
condenser is disposed transversely under the connecting rods, whilst the air
pump and current pump are placed nearly or directly beneath the shaft, and
may be worked by an eccentric or the shaft or by a lever connected to the
slide block of one of the piston rods. In all arrangements of the engines, the
advantages of working very expansively are obtained with very simple parts
of small cost compared with those hitherto working in that way.
In an improved boiler constructed according to the present Invention, the
lower portion is square in horizontal section, whilst the top is hemispherical
or dome-shaped. A comparatively narrow water space passes entirely round
the lower square part enclosing an internal furnace space fired, by preference,
by two doors in one of the sides. This furnace space is crossed from front to
back at a short distance above the fire-bars by a horizontal pan-shaped water
space, from which tubes, with the water inside them, pass up in directions
slightly inclined outwards to the nearly horizontal plate forming the roof of
the furnace chamber. The fire gases being made to diverge laterally by the
middle pan-shaped water space, pass inwards again across the tubes, and meet
in a central space, from whence they pass up through a series of flue tubes
traversing the dome to the funnel. A man-hole is made through one of the
side space to give access to the gas space above the middle pan to facilitate

page_text: the cleaning of the tubes; and it is also contemplated to provide jet tubes by
which jets of steam can be thrown against the tubes to clean or partially clean
them whilst the boiler is at work. To provide for the circulation of the water,
pocket-shaped casings are fixed to the sides, and communicate with the
internal spaces at the top and bottom, being rivetted to the sides throughout
their length. To enable the boiler to sustain the internal steam pressure.
vertical stay rods are connected from the top of the dome to the middle parts
of the side plates of the lower square portion, whilst the corners of the latter
are continued up within the dome, being rivetted thereto at their edges,
whereby a very strong connection is obtained. Stay rods also pass from the
top of the dome to the crown or roof of the furnace space, and a few of these
stays pass down through the innermost tubes to the lower pan space. The
narrow water spaces forming the square casing are also strengthened by.
numerous cross stays, and the middle pan space is strengthened by vertical
stays and by horizontal stays running the whole way of it.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said William Macuab in the Great Soal Patent Office on the 12th
April 1862.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, WILLIAM
MACNAB, of Greenock. in the County of Renfrew, North Britain, Engineer,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent. bearing date the Fourteenth day of October, in the year of our Lord
One thousand eight hundred and. sixty-one, in the twenty-fifth year of Her
reign, did, for Herself. Her heirs and successors, give and grant unto me,
the said William Macnab, Her special licence that I, the said William Macnab,
my executors, administrators, and assigns, or such others as I, the said
William Macnab, my executors. administrators, and assigns, should at any
time agree with, and no others, from time to time and at all times thereafter
during the term therein expressed, should and lawfully might make,
use, exercise, and vend, within the United Kingdom of Great Britain and
Ireland, the Channel Islands, and Isle of Man, an Invention for "IMPROVE-
MENTS IN MARINE STEAM ENGINES AND BOILERS," upon the condition, amongst
others. that I, the said William Macnab, my executors or administrators,
by an instrument in writing under my, or their, or one of their hands and
seals, should particularly describe and ascertain the nature of the said Inven-

page_text: to diverge laterally by the middle pan-shaped water space E, pass inwards
again across the tubes F, and meet in a central space G, from whence they pass
up through a series of flue tubes II, traversing the dome B to the funnel. A
man-hole g is made through one of the side spaces to give access to the gas
space Gabove the middle pan E, to facilitate the cleaning of the tubes F,
and it is also contemplated to provide a jet tube or tubes by which jets of
steam can be thrown against the tubes F to clean or partially clean them
whilst the boiler is at work. A man-hole e¹ is also provided at each end of
the pan-space E to give access to the ends of the tubes F. To provide for
the circulation of the water, pocket-shaped casings I are fixed to the sides,
and communicate with the internal spaces at the top and bottom, being rivetted
to the sides throughout their length. To render the boiler more able to sustain
the internal steam pressure, vertical stay rods J are connected from the top
of the dome B to the middle parts of the side plates of the lower square por-
tion A, whilst the corners K of the latter are continued up within the
dome B. being rivetted thereto at their edges, whereby a very strong connec-
tion is obtained. Stay rods may also be passed from the top of the dome to
the crown or roof of the furnace space-C, and a few of such stays may be.
made to pass down through the innermost tubes F to the lower pan space E.
The narrow water spaces a forming the square casing A, are also strengthened
by numerous cross stays, which also cross the circulating pockets I, and the
middle pan space E is strengthened by horizontal stays M running the long
way of it, and may also be strengthened by vertical stays.
Figure 12, Sheet 2, is a vertical section of a slightly modified--example of
my improved boilers: Figures 13 and 14 are quarter horizontal sections taken
respectively at the lines 5-6, and 7-8, in Figure 12, whilst Figure 15 is a
half plan of the boiler. In this example there are two pan-shaped water-
spaces E disposed across the furnace space C. the tubes F, from one being
inclined to one side, and those from the other to the opposite side. The space
between the pan spaces E is covered or closed by fire brick, and the fire gases
diverge to the side, and return across the tubes F to the middle as in the
other modification. In other respects the boilers are alike, and the description
already given applies to both.
Having thus particularly described my said Invention. and the manner
in which the same is or may be used or carried into effect. I have to state
that I do not restrict myself to the precise details herein described or
delineated but that what I consider to be novel and original, and claim as
the Invention secured to me by the herein-before in part recited Letters
Patent, is,-

page_text: may be maintained, provision is made for allowing it to pass in very minute
quantities from a part of the jackets farthest from the inlet into them. The
opening for the passage of the steam in this way out of the jackets is by pre-
ference made into the intermediate chamber H. so that the steam is not lost,
but mingles with and assists that which works the low-pressure cylinder B;
and the steam is by preference first admitted into the part of the jacket spaces
which surrounds the intermediate chamber H..
A pair of cylinders A, B, combined as described, may be arranged in various
positions. In one convenient design (represented in Figures 1. 2, and 3), the
cylinders A, B, are inverted, and a surface condenser J is placed against or
beside the high-pressure cylinder A, whilst the air-pump K and current-
pump L are placed against or beside the low-pressure cylinder B. being worked
by a lever M connected to the piston-rod slide block.
In another convenient design of the engines (represented in Figures 4, 5,
and 6). the two cylinders A, B. are slightly inclined up towards the paddle
shaft E, and the surface condenser J is disposed transversely under the con-
necting rods, whilst the air pump K and current pump L are placed nearly
or directly beneath the shaft E, and may be worked by an eccentric on the
shaft, or by a lever connected to the slide block of one of the piston rods.
In all arrangements of the engines, the advantages of working very expan-
sively are obtained with very simple parts, of less cost than those hitherto
working in that way.
The improved designs delineated on Sheet 1 of the accompanying Drawings
for the general arrangement or mode of combining the engine details are
likewise applicable with the common plan of combining and working two
cylinders.
An improved boiler constructed according to my present Invention is repre-
sented in Figures 7, 8, 9, 10, and 11, Sheet 2; Figure 7 being a half cleva-
tion; Figures 8 and 9, half vertical sections taken at right angles to each
other; and Figures 10 and 11, horizontal sections taken respectively at the
lines 1-2, and 3-4, in Figures 7 and 8. The lower portion A of the boiler
is square in horizontal section, whilst the top B is hemispherical or dome-
shaped. A comparatively narrow water space a passes entirely round the
lower square part A, enclosing an internal furnace space C, fired by preference
by two doors c in one of the sides. This furnace space C is crossed from front
to back at a little distance above the fire-bars D, by a horizontal pan-shaped
water-space E, from the top plate e of which, tubes F, with the water inside
them, pass up in directions slightly inclined outwards, to upper tube plates f
forming part of the roof of the furnace chamber. The fire gases being made

page_text: tion, and in what manner the same was to be performed, and cause the same
to be filed in the Great Seal Patent Office within six calendar months next
and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said William Macnab, do hereby declare
the nature of my said Invention, and in what manner the same is to be per-
formed, to be particularly described and ascertained in and by the following
statement in writing, reference being had to the accompanying Drawings, and
to the letters and figures marked thereon, that is to say:
My said Invention relates to improvements upon marine steam engines
and boilers of the classes described in the Specification of Letters Patent
granted to the present Patentee, and dated the 26th day of September 1860,
(No. 2341.)
And in order that my said Invention may be properly understood and
carried into effect, I have hereunto appended two Sheets of explanatory Draw-
ings, to which I will refer in the following particular description of my im-
provements, it being premised that the same reference letters mark the same
or like parts in all the Figures on the same Sheet.
Figure 1, Sheet 1, is an end elevation partly in section; Figure 2 is a
longitudinal vertical section; and Figure 3 is a horizontal section of inverted
cylinder engines as constructed with my improvements, and suitable for driving
the screw propeller; Figure 4 is a vertical section, and Figure 5 is a plan
of my improved engines as arranged for driving paddle wheels: Figure 6
being a section of the cylinders taken transversely to their axes.
The improvements in engines comprise in the first place an arrangement
in which, in place of four steam cylinders, two high-pressure cylinders and two
low-pressure cylinders, there are only two, namely, a bigh-pressure cylinder A,
which receives the steam directly from the boiler, and a low-pressure cylinder B
of larger size, in which the steam operates after acting in the high-pressure
cylinder A. The cranks C, D, acted on by the two pistons a, b, are, by pre-
ference, situated at right angles to each other upon the shaft E. The high-
pressure cylinder A receives steam by valves F, by preference of the piston
class, working in a chamber or cylinder G, within a larger chamber H, situated
between the cylinders A and B, into which chamber H the steam passes from
the high-pressure cylinder A. This chamber H also surrounds the high-
pressure cylinder A. and in the opposite side of it are the ports of the low-
pressure cylinder B, which are governed by an ordinary slide valve [. The
cylinders A, B, and their covers, and the intermediate chamber H, are sur-
rounded by steam-jacket spaces h, as shown in the Figures; and to induce a
slight circulation of the steam in the jacket spaces in order that its temperature

page_text: First, the combining of a high-pressure cylinder with a low-pressure cylinder
substantially in the manner herein described, and as delineated on Sheet I of
the accompanying Drawings, that is to say, with an intermediate chamber in
which the valves of both cylinders are situated, and into which the steam from
the high-pressure cylinder passes on its way to the low-pressure cylinder.
Second, the general designs or arrangements of marine engines represented
on Sheet of the accompanying Drawings, and herein-before described.
Third, the causing of the steam in the steam jackets to circulate substan-
tially as herein-before described.
Fourth, the constructing of marine steam boilers substantially as delineated
upon Sheet 2 of the accompanying Drawings, and herein-before described.
In witness whereof, I, the said William Macnab, have hereunto set my
hand and scal, this Eleventh day April, in the year of our Lord One
thousand eight hundred and sixty-two.
WILLIAM MACNAB. (L.s.)