IMPROVEMENTS IN SCREW PROPELLERS
Year: 1860

page_text: LETTERS PATENT to Hermann Hirsch, of Berlin, in the Kingdom of Prussia,
and of Bridge Road, Lambeth, in the County of Surrey, Civil Engineer,
for the Invention of "IMPROVEMENTS IN SCREW PROPELLERS."
Sealed the 28th May 1861, and dated the 29th November 1860.
PROVISIONAL SPECIFICATION left by the said Hermann Hirsch at the
Office of the Commissioners of Patents, with his Petition, on the 29th
November 1860.
I, HERMANN HIRSCH, of Berlin, in the Kingdom of Prussia, and of Bridge
Road, Lambeth, in the County of Surrey, Civil Engineer, do hereby declare
the nature of the said Invention for "IMPROVEMENTS IN SCREW PROPELLERS," to
be as follows:-
My improvements apply to the form of the blades of propellers for vessels,
the surfaces of which I make of such a curvature that if sections were made
by cylindrical surfaces concentric with the axis of the propeller, the profiles of
the sections on these cylindrical surfaces would shew a pitch gradually
increasing from the entering edge, in such a manner that every successive
portion of the surface, reckoned from the entering edge, gives the water an
additional impulse backwards as it revolves through it, and if sections were
made by planes perpendicular to the axis of the propeller the profiles of tho
surfaces on these planes would be spiral lines concave towards the water, acted
on in such a manner that every portion of the surface in revolving through the

page_text: water impels it to some extent towards the axis, and thus overcomes a portion
of its centrifugal tondency. That surface of the blade which acts on the water
is therefore made of such a curvature as to combine the two curvatures above
described, namely, the curvature of increasing pitch as projected on cylindrical
sections, and the spiral curvature as projected on planes perpendicular to the
ατία
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Hermann Hirsch in the Great Seal Patent Office on the
29th May 1861.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HERMANN
HIRSCH, of Berlin, in the Kingdom of Prussia, and of Bridge Road, Lambeth,
in the County of Surrey, Civil Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Twenty-ninth day of November, in the year of our Lord
One thousand eight hundred and sixty, in the twenty-fourth year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said
Hermann Hirsch, Her special licence that I, the said Hermann Hirsch, my
executors, administrators, and assigns, or such others as I, the said Hermann
Hirsch, 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 PRO-
PELLERS," upon the condition (amongst others) that I, the said Hermann
Hirsch, my executors or administrators, by an instrument in writing under
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 Hermann Hirsch, 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, that is to say:-
My improvements apply to the form of the blades of screw propellers for
vessels.

page_text: In order that my Invention may be fully comprehended; I now proceed to
describe the manner of performing the same, reference being had to the
illustrative Sheet of Drawings hereto annexed, and to the numeral figures and
letters of reference marked thereon, as follows:-
DESCRIPTION OF THE DRAWINGS.
Fig. 1 represents an elevation of a double-bladed propeller constructedl
according to my Invention, and Fig. 2 represents several developed sections
of the propelling surface of one of the blades; each blade has a curvature in
elevation and also a curvature in section, which I will now describe.
I take an arc of the circumference a, a, which I prefer to be not less than
.45° nor more than 75°, and divide it into equal parts at, the points a', a³, a³,
and through these points draw radii to the centre c. I divide the radius a, c,
into the same number of equal parts at the points c¹, c, c, and through them
describe circular arcs cutting the radii successively in the points b', b³, bs,
through which I trace a spiral line a, 61, 62, 63, c, for the outline of the front
or entering.edge of the blade, and I repeat the same curve a, e, e, e³, c, for
the outline of the back edge of the blade. I provide a suitable cylindrical or
spherical boss, and sweep the curved surface of the blade into the boss, as
indicated at d and e, and I round off the extremities of the blade at land m.
The sectional curvature of the blade is determined by the construction
represented in Fig. 2. I draw f, f', of the same length as the arc a, a, and
divide it at the points f',ƒ³, ƒ³, into the same number of equal parts as the
radius a, c, and consequently the lengths of the lines f¹ƒ^‚ƒ`ƒˆ‚ƒ³ƒ*, in
Fig. 2, correspond with the lengths of the circular arcs b¹¹, be, b³ ³, in
Fig. 1. I draw f, g, perpendicular to f,f*, and of such a length that it bears
to f.f, the same proportion as the velocity of the vessel through the water
bears to the rotary velocity of the propeller at its circumference, and I extend
ƒ*, g, to h such that g, h, is a section at f, g, which I prefer to be not less
than th nor more than th, and I draw lines from the points ffff, to g.
I bisect f, g, in k, and draw a line parallel to f.f, cutting these lines in the
points k, k, l, k³, and I join these points to h. I then describe a curve
touching the line f, k, at f, and the line h, k, at h, which gives the developed
section of the propelling face of the blade at the circumference from a to a',
and another curve touching f, k, at f, and h; k, at h, which is the developed
section at 6, e, another curve touching f, l, at fs, and h, k, at h, which is
the developed section at 6, e, and another curve touching f³, k, at f³, and
h,, at h, for the developed section at &, . The propelling face of the blade
is thus a curved surface, determined by the spiral line a, 61, 62, 63, which is the

page_text: outline of a section made by a plane perpendicular to the axis of the propeller,
combined with the curves f, fb, fs, fh, which are the developments of
the outlines produced by cylindrical surfaces concentric with the axis of the
propeller, intersecting the blade at different distances from the centre, and the
object of these two curvatures combined is to overcome a portion of the centri-
fugal tendency of the water acted on by the revolution of the blade in the
"direction of the arrow, and thereby increase the directness of the reaction in
propelling the vessel, and at the same time to render each successive portion of
the blade, from the entering edge backwards, available in giving additional
impetus to the water by means of the gradually increasing pitch.
Having now described the nature of my said Invention of "Improvements
in Screw Propellers," and the manner in which the same is to be performed,
I would remark in conclusion that what I claim as my Invention intended to
be secured to me by the herein in part recited Letters Patent is, the mode of
constructing the blades of screw propellers so as to combine these two curvatures
in the form of their acting surfaces, in the manner shown by the accompanying
Sheet of Drawings, and herein described for the purposes set forth.
In witness whereof, I, the said Hermann Hirsch, have hereunto set my
hand and seal, this Twenty-ninth day of May, in the year of our
Lord One thousand eight hundred and sixty-one.
Witness,
ALEX, PRINCE,
Agent for Patents,
4, Trafalgar Square,
Charing Cross.
HERMANN HIRSCH. (L.B.)