IMPROVEMENTS IN SCREW PROPELLERS
Year: 1874

page_text: LETTERS PATENT to James Howden, of the City of Glasgow, in the
County of Lanark, North Britain, Engineer, for the Invention. of
56
IMPROVEMENTS IN SCREW PROPELLERS."
PROVISIONAL SPECIFICATION left by the said James Howden at the
Office of the Commissioners of Patents, with his Petition, on the
22nd September 1874.
I, JAMES HOWDEN, of the City of Glasgow, in the County of Lanark,
North Britain, Engineer, do hereby declare the nature of the said In-
vention for "IMPROVEMENTS IN SCREW PROPELLERS," to be as follows:-
This Invention relates to improved modes of constructing screw
propellers which have their blades made separately from the central boss,
by which great strength combined with lightness is obtained, also greater
facility and simplicity in fixing, removing, replacing, and altering the
pitch of the blades, and also giving more efficient propelling action than
in and by the screw propellers heretofore in use.

page_text: The nature and novelty of this Invention under one modification
consist all as follows:-In making the central boss of a spherical or
other convenient shape, with as many plain cylindrical holes at right
angles to its axis as there are blades in the propeller, these holes being
bored or otherwise made truly cylindrical to receive the stocks of the
blades. Each of these blades by these improvements consists of three
principal parts, viz., the stock or central piece of a wrought iron or steel
forging, and the two plates or sheets of wrought iron, steel, or other
metal, one forming the propelling face, and the other the back surface
of the blade. These two plates or sheets are rivetted or otherwise
sufficiently fastened to each other at the sides and outer end to the
stock through the centre and inner end of the blades. The stock is
made truly cylindrical in the part which fits into the holes in the boss,
while the outer part is flattened into a bar and carried up the middle
or radial centre of the blade between the two plates. Near to the
cylindrical part of the stock the flattened bar has a cross piece, on which
the inner end of the blade is rivetted or otherwise secured. This cross
piece is made of the same outline on its outer edge, or that nearest the
boss, as the blade itself; and the thickness of the flattened central bar
and cross piece is greater at the centre and inner end than at the sides
and outer end.
When the propeller is of considerable diameter there may be one or
more additional cross pieces forged on the central bar of the stock for
the purpose of stiffening the plates which are rivetted to these cross
pieces, so as thus to strengthen these large blades. In the construction
of the blades the plates and also the central bar and cross piece or pieces
of the stock are bent to the required curves before being rivetted or
otherwise fastened together. It is preferred to fill up the space between
the plates forming the blade, not taken up by the stock, with Portland
cement in a fluid state after the plates and stock are fastened together.
The cement when hardened stiffens the blades and preserves the material
by preventing the sea water from obtaining access between the plates.
Another modification consists in rivetting or otherwise securely
fastening a single plate or sheet of wrought iron, steel, or other metal
for the propelling face of the blade on the stock, with its central bar and
one or more cross pieces, as described. Filling pieces are fitted and
rivetted to the plate on each side of the central bar, and between the
cross pieces if there are more than one. These filling pieces are of the

page_text: same thickness as the edge of the central bar against which they lie, but
taper as they approach the sides of the blade; and they may be of cast
iron or other metal, or forgings, and may be partially hollowed on their
under side at their thicker part, their purposes being to make with the
stock a smooth back for the blade, and to assist in stiffening it. The
propelling face of the blade may also have one or more parallel bars of
a limited width rivetted or otherwise securely fastened through the plate,
stock, and filling pieces, so as to further stiffen the blade, these bars
being curved and fixed on the circle of the revolution of the propeller.
The central bar of the stock may also be increased in breadth across
the back of the plate or sheet, so as to take the place of the filling
pieces.
Another modification of this Invention consists in making the part
of the stock of the blade which is secured in the central boss square or
rectangular, or other polygonal shape, in cross section instead of circular,
the holes in the boss being shaped to fit the stock. The blades by this
Invention are so shaped at their inner ends or part nearest to the
central boss, that instead of curving inwards round the circle of the
boss, as is usual in propeller blades, the blades increase in their distance
from the boss as they branch outward from the part of the stock fixed
in the boss.
It is preferred to have the blades curving or tending upwards from
the boss on either side of the central part of the stock in order to reducc
the great resistance edgeways, and inefficient action of the blades of the
usual form at the boss when slip occurs in the working of the propeller.
The blades beyond the part described may be of any usual shape, and
they may be curved on their face or have any variation of pitch; but
it is preferred in most cases to make them somewhat narrower towards
their outer end.
In this Invention the blades are secured in the boss in the desired
position by a single pin passing through the boss and the stock within
the boss; the pin is by preference made of steel, and to prevent its
shaking out it has a small gun metal stud screwed into the boss and
bearing against the head of the pin, but any other usual method of fixing
the same may be adopted.
This Invention also provides for altering the pitch of the blades when
required in a very simple manner. This is effected by making the hole

page_text: in the stock through which the holding pin passes somewhat larger than
the diameter of the pin, and filling this hole entirely with a piece of
steel or other suitable material. The hole for the holding pin is then
bored through this filling, so that the axis of the pin hole may be at an
angle with the axis of the filling piece, these axes intersecting each
other in the axis of the stock. If the blade be fixed in the boss by the
pin passing through the filling piece placed to give the greatest pitch
a lesser pitch will be obtained by simply turning the fitting piece 180°
on its axis, and again securing the blade by the pin. An intermediate
pitch between the greater and lesser pitch will be obtained by using a
filling piece having its axis coinciding with the axis of the pin hole. The
filling pieces may be in the boss instead of the stock, one being on each
side of the stock. For convenience of shifting it is preferred to make
the filling pieces oval in section. When the part of the stock in the
boss is square or rectangular the pitch is altered by fitting thin inter-
changeable wedge pieces one on each side between the boss and the
stock. When the pitch is altered these wedge pieces change places, the
whole being secured by the holding pin, and to obtain an intermediate.
pitch parallel pieces are used.
Another improvement under this Invention consists in making the.
central boss of one or two principal pieces of iron or steel forgings,
though castings of steel, or malleable cast iron, or gun metal may be
used. When the boss is made of one principal piece the body, through
which the shaft passes, is cylindrical, with a thick flange part about the
centre, lengthways, into which the holes for the stock of the blades are
made. This flange part may not be of equal thickness all round but
swelled out at intervals to receive the stocks of the blades. When two
principal pieces are used in the construction of the boss cach piece
consists of a cylindrical part and comparatively thin flange. The two
pieces are bolted or rivetted together, with distance pieces between the
flanges, arranged so as to form the holes cither for the cylindrical or
rectangular stocks of the blades. The pins for holding the blades in
the boss pass through these flanges and the stocks of the blades, as before
described. The two pieces of the boss may also be made to be bolted
directly together without distance pieces, and the holes for the blade
stocks may be wholly in one piece, or one half in each. The boss may
also be made spherical on the outer surface by a thin shell piece over the
boss here described.

page_text: Blades made in the manner before described with the stock pieces, and
methods of fastening and altering the pitch, may have their inner ends
curving towards the boss; and may also, when desired, be forged solid
with the stock piece. The holes in the boss and the stocks of the
blades may be slightly tapered instead of parallel.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said James Howden in the Great Seal Patent Office on
the 20th March 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JAMES
HOWDEN, of the City of Glasgow, in the County of Lanark, North Britain,
Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-second day of September, in the year of
our Lord One thousand eight hundred and seventy-four, in the thirty-
eighth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said James Howden, Her special licence
that I, the said James Howden, my executors, administrators, and
assigns, or such others as I, the said. James Howden, 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 "IMPROVEMENTS IN
SCREW PROPELLERS," upon the condition (amongst others) that I, the
said James Howden, 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 Invention, 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 James Howden, do hereby declare
the nature of my said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by
the following statement, reference being had to the several Figures on;

page_text: the accompanying Sheet of Drawings, and to the letters and figures
marked thereon, that is to say :—
My said Invention relates to improved modes of constructing screw
propellers which have their blades made separately from the central boss,
by which great strength combined with great lightness is obtained, also
greater simplicity in fixing, removing, and replacing the blades, and in
altering the pitch thereof, besides a more efficient propelling action
than is obtained by the screw propellers heretofore in use.
And in order that my said Invention and the manner of performing
the same may be more clearly understood, I append hereunto a Sheet of
explanatory Drawings to be herein-after referred to, on which various
modifications of my improved arrangements are represented.
C
One modification of my said Invention consists in making the central
boss of a spherical or other conveniently shaped. casting A, A, as shown
in Figures 1 and 2 of the Sheet of Drawings, having as many plain
cylindrical or slightly tapered circular holes B, B, at right angles to the
axis or shaft C, as there are blades in the propellers, these holes being
bored or otherwise made truly circular to receive the correspondingly
shaped stocks D, D, of the blades E, E.
Figure 1 represents a propeller with one blade developed on its "flat":
with the central boss in section; and Figure 2 is a section of the blade
and boss at right angles to Figure 1, but with part of the blade shown
in its actual position. Each of the blades E in this modification of my
Invention consists of three principal parts, namely, the stock D, D, or
central part of a wrought iron or steel forging, and the two plates or
sheets of wrought iron, steel, or other metal, one forming the propelling
face F, and the other G the back surface of the blade. These two plates
or sheets F and G are rivetted or otherwise sufficiently fastened to each
other at the sides or outer end, and to the stock D through the centre
and inner end of the blade. While the stock D is made truly circular 3
in the part which fits into the holes B in the boss A, the outer part D' is
flattened into a bar and carried up the middle or radial centre of the
blade between the two plates. Near to the cylindrical part D of the
stock the flattened bar has a cross piece a, a, (shown in dotted lines in
Figure 1, and in full lines in Figure 3), on which the inner ends of the a
plates are rivetted or otherwise secured. This cross piece a is made of
the same outline on its outer edge, or that nearest the boss as the blade

page_text: itself, and the thickness of the flattened central bar D¹ and cross piece is
greater at the centre and inner end than at the sides and outer
end.
When the propeller is of considerable diameter there may be one
or more additional cross pieces forged on the central bar of the stock,
as at b, b, Figure 3, for the purpose of stiffening the plates which are
rivetted to these cross pieces. In the construction of the blades the
plates and also the central bar and cross piece or pieces of the stocks are
bent to the required curves before being rivetted or otherwise fastened
together. It is preferred to fill up the spaces between the plates not
taken up by the stock with Portland cement in a fluid state after the
plates and stock are fastened together. The cement when hardened
stiffens the blades and preserves the material by preventing the sea
water from obtaining access between the plates.
Another modification of these improvements consists in rivetting or
otherwise securely fastening a single plate or sheet of wrought iron,
steel, or other suitable material for the propelling face of the blade on
the stock with its central bar and cross piece or pieces as previously
described. To make a smooth back surface on the blade thus con-
structed filling pieces I are fitted and rivetted or otherwise fastened to
the plate on each side of the central bar D¹, and between the cross
pieces a, b, if there are more than one. These filling pieces are of the
same thickness as the edge of the central bar against which they lic but
taper as they approach the sides of the blade as they may be of cast
iron or other metal, and they may be partially hollowed on their under
side at their thicker parts.
In Figures 3 and 4, a blade according to this modification is shown
(Figure 3 showing a back view of the blade on the "flat," and Figure 4,
a transverse vertical section), and in which D, D*, is the stock, and H, H,
the plate forming the propelling face fastened to the stock, and I, I, are the
filling pieces on the back of the blade. The propelling face of the blade
may also have one or more parallel bars of a limited width rivetted or
otherwise fastened through the plate, stock, and filling pieces, so as to
further stiffen the blades, these bars being curved and fixed on the face
of the blades to the circle of the revolution of the propeller. The
central bar of the stock may also be increased across the back of the
plate or sheet forming the face of the blade so as to take the place of

page_text: the filling pieces, as shown in Figure 5, where K, K, represents the
stock flattened out and attached to the plate L, L, as described.
Another modification of my said Invention consists in making the
part of the stock of the blade which is secured to the central boss square
or rectangular or other polygonal shape in cross section instead of
circular, the holes in the boss being shaped to fit the stock ends. In
Figure 11 a rectangular shaped stock end M is shown fitted into a
similarly shaped hole in the boss R, R, and in Figure 13 a flat sided
stock end N is shown. The blades by this Invention are so shaped at
their inner ends or part nearest the central boss that instead of curving
inwards round the circle of the boss, as propeller blades are usually
made the blades E increase in their distance from the boss at E' as they
branch outwards from the part of the stock fixed in the boss.
•
It is preferred to have the blades curving or tending upwards from
the boss on either side of the central part of the stock, as shown in the
Figures on the Sheet of Drawings representing the blades. This mode
of forming the blades greatly reduces the inefficient action and great
resistance of the blades when working, especially when slip occurs. The
blades beyond the part described may be of any usual outline, and they
may be curved on their face or have any variation of pitch, but it is
preferred in most cases to make them somewhat narrower towards their
outer ends.
In this Invention the blades are secured in the boss in the desired
position by a single pin c passing through the boss A and stock ends D
within the boss, as shown in the Drawings. These pins c arc by pre- a
ference made of steel, and they are prevented from shaking out by a
small gun metal stud screwed into the boss, and shown at d, d, in
Figures 1, 3, and 10, when the central bosses are shaped as in these
Figures. These pins c may be secured by a small locking pin, as at e in
Figure 11, or by a nut screwed on their smaller ends, as at fin Figures 6,
7, and 13, 14.
My said Invention also provides for altering the pitch of the blades
when required in a very simple manner. This is effected by making the
hole in the stock through which the holding pin c passes somewhat
larger than the diameter of the pin, and filling this hole entirely with a
-piece-of-steel / or other suitable material through which the hole for

page_text: the holding pin c is bored, with its axis at an angle to the axis of the
filling piece, these axes intersecting each other in the axial line of the
stock, as shown (at g and h) in Figures 9 and 10. If the blade be fixed
in the boss by the holding pin c passing through the filling pieces, so as
to give the greatest pitch, a lesser pitch will be obtained by simply'
turning the filling piece 180° on its axis, and again securing the blade
by the holding pin. An intermediate pitch between the greater and
lesser pitches will be obtained by using a filling piece having its axis
coinciding with the axis of the pin hole. The filling pieces may be in
the boss instead of the stock of the blades, one being on each side of the
stock, as shown at i, i, in Figures 6, 7, and 8. For the convenience of
shifting it is preferred to make the filling pieces h, i, described oval in
section. When the part of the stock fitting into the boss is rectangular or
flat sided the pitch is altered by fitting thin interchangeable wedge-shaped
pieces, one on each side, between the boss and the stock, as shown at
k, k, in Figures 11 and 13. When the pitch is altered these pieces.
change places or are reversed in position, the whole being again secured.
by the holding pin c. When an intermediate pitch is wanted parallel
filling pieces are used.
Another improvement under my said Invention consists in making.
the central boss of one or two principal pieces of forged iron or steel,
though castings of steel or malleable cast iron may be used. When the
boss is made of one principal piece the body through which the shaft.
passes is cylindrical, with a thick flanged part about the centre length-
ways, into which the holes for the stock of the blades are made. The
flange part of the boss may not be of equal thickness all round, but
swelled out where the holes for the stocks of the blades are bored. A
boss, as just described, is shown in Figures 6, 7, and 8, in which O, O,
is the cylindrical body, and P, P, the flanged part swelled at Q to receive
the stock ends of the blades. When two principal pieces are used in
the construction of the boss cach piece consists in one modification of a
cylindrical part and a comparatively thin flange. The two pieces are
after being properly turned or machined bolted together with distance
pieces between the flanges, and arranged so as to form the holes for the.
cylindrical, rectangular, or otherwise shaped ends of the stocks of the
blades, as in Figures 11 and 12, where a boss of this construction is.
shown, R, R, being the two principal pieces, and S, S, the distance pieces
between, with the holes for the ends of the stocks of the blades at T, T.

page_text: The holding pins pass through these flanges and the stocks of the blades,
as before described. The two pieces of the boss may also be made to be
bolted directly together without distance pieces, and the holes for the
blade stock ends may be wholly in one of the pieces, as in Figures 13
and 14; while they may also be formed partly in each piece, as shown t
in Figure 15. In central bosses made in the manner thus described it
is preferred to give them a spherical outer surface by thin shell pieces
being fastened to the bosses, as shown in Figures 6, 7, 8, 11, 12, 13, 14,
and 15. It is preferred also to fill up the interior spaces under these
thin shell pieces with Portland cement, and also all the holes for the 1
holding pins in the cast spherical bosses.
Blades made in the manner before described with the stock pieces
and methods of fastening and altering the pitch, may have their inner
ends curving towards the boss, and blades of the shape described in this
Specification and shown in the Drawings, may also when desired (say 1
for small blades) be forged solid with the stock piece. The holes in the
boss and the stocks of the blades may be slightly tapered instead of
parallel.
In order to prevent corrosion from immersion in water, and to
facilitate the removal of the blades when required, it is preferred to have 2
the holes in the central boss of the propellers, and the stock ends which
fit into the holes plated with copper, and also when desired to have the
whole surface of the blades so coppered.
Having thus particularly described and ascertained the nature of my
said Invention, and the manner in which the same is to be performed, 2
I have to state that I do not restrict myself to the precise details or
proportions of parts I have herein described or delineated, and further,
I do not claim the exclusive use of wrought iron, steel, or other metal
plates or sheets, either double or single, in the construction of screw
propeller blades in connection with pieces for attaching the plates to a 3
central boss, otherwise than in the manner and by the means or mode of
construction herein specified and constituting my said improvements,
but what I consider to be novel and original, and therefore claim as the
Invention secured to me by the herein-before in part recited Letters
Patent is,―
3

page_text: inner ends described and delineated in the accompanying Sheet of
Drawings, with two plates or sheets of wrought iron, steel, or other
metal, and a central stock of wrought iron or steel forging, all
substantially as herein-before described and delineated in the Drawings.
Second. The construction of screw propeller blades of the form at
their inner ends, and with one plate or sheet of wrought iron, steel, or
other metal forming the face of the blades, and a stock of wrought iron
or steel forging and filling pieces forming the back, the ends of the
stocks being fitted into the central boss, all substantially as herein-before
described and delineated in the accompanying Sheet of Drawings..
Third. The construction of propeller blades of the form herein-before
described and delineated, with one plate of wrought iron, steel, or other
metal forming the propelling face of the blade, and a stock of wrought
iron or steel forging flattened out on the part attached to the plate or
sheet, so as to form a back without filling pieces, all substantially as
herein-before described and shown in Figure 5 of the accompanying
Drawings.
Fourth. The several modes of constructing the ends of the stocks of
the blades, and the manner of fixing the same in the central boss of the
propeller and the modes of altering the pitch of a blade, all as herein-
before described and delineated in the accompanying Drawings.
Fifth. The construction of the central bosses of screw propellers with
a flange piece in the centre for receiving the stocks of the blades, all
substantially as described in reference to Figures 6, 7, and S of the
accompanying Drawings.
Sixth. The construction of the central bosses of screw propellers in
two principal pieces and distance pieces, substantially as herein-before
described in reference to Figures 11 and 12, and without distance pieces
as herein-before described in reference to Figures 13, 14, and 15 of the
accompanying Drawings.
Seventh. The construction of propellers with the stocks of similar
materials and shapes, and the methods of securing the same in the
bosses, and of altering the pitch, as herein-before described and
delineated, with the inner ends of the blades curved towards or lying
against the central bosses of the propeller.

page_text: Eighth. The construction of propellers where the blades are of the
shape herein-before described and delineated, with the stock and face of
the blade in one forging of iron or steel, and the stock ends fitted
and secured in the central boss, all substantially as herein-before
described.
described.
In witness whereof, I, the said James Howden, have hereunto set
my hand and seal, this Nineteenth day of March, in the
year of our Lord One thousand eight hundred and seventy-
five.