IMPROVE- MENTS IN SCREW PROPELLERS
Year: 1875

page_text: LETTERS PATENT to Hermann Hirsch, of Craven Street, Charing
Cross, in the City of Westminster, for the Invention of "IMPROVE-
MENTS IN SCREW PROPELLERS."
Scaled the 18th February 1876, and dated the 23rd December 1875.

page_text: By constructing the blades according to these forms I greatly increase
the efficiency of the screw propeller.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Hermann Hirsch in the Great Seal Patent Office on
the 23rd June 1876.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HERMANN
HIRSCH, of Craven Street, Charing Cross, in the City of Westminster,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-third day of December, in the
year of our Lord One thousand eight hundred and seventy-five, in the
thirty-ninth year of Her reign, did, for Herself, Her heirs and suc-
cessors, 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 PROPELLERS," upon the condition (amongst others) that I, the
said Hermann Hirsch, my executors or administrators, by an instru-
ment 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.
F
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
performed, to be particularly described and ascertained in and by the
following statement, reference being had to the Drawing hereunto
annexed, and to the letters and figures marked thereon (that is to

page_text: My Invention relates to a novel mode of forming the blades of
propellers, and consists,-
First. In giving the blade a double curve, so that seen in edge view
in a longitudinal direction, it will present the figure of an elongated S.
Second. In giving the blade two such double curves in juxtaposition,
so that the profile formed by its opposite edges will, when seen in
an oblique direction together present the figure of 8 more or less
elongated.
By using blades of either of these forms, I greatly increase the
efficiency of the propeller; thus for example,-
First. I avoid the obstructive angular resistance in the vicinity of the
boss, and utilize for more efficient propulsion the engine power ordinarily
absorbed from such cause.
Second. In imparting to the surface of the blade a radially progressive
amount of twist or angularity, I attain coincidentally with a minimum
amount of twist or angularity at and near the boss a diagonally
increasing pitch, and I thus provide that molecules of water in their
outward passage from the boss to the the periphery shall pass along a
concave surface, thereby increasing the propelling effect.
Third. The line of junction of the boss with the blade being coincident.
or nearly so with the plane of the rotary strain transmitted by the engines
instead of as is the case more or less in other propellers at right angles
or nearly so thereto, I thereby obtain a form of section best adapted to.
receive such strain, and can obtain a stronger blade with the use of less
material than is usually employed.
By referring to the accompanying Drawings, it will be seen that,―
Figures 1 and 2 show a front and side view of a four bladed propeller
constructed upon my principle, its outline in the latter view resembling
an elongated S.
Fig. 2 shows an expansion of the surface of one of the improved
blades with a number of transverse sections which illustrate the gradual
progression of the pitch from zero at the centre of the propeller to the
maximum pitch desired at the periphery.
My next form of blade which comes under the second heading of my
Specification is shewn by Figures 3 and 4. Each of its convex edges,

page_text: it will be seen have approximately the form of an elongated as already
described, and these edges seen in juxtaposition with each other,
together represent approximately a figure of 8 more or less elongated.
The material composing the blade is equally and symmetrically dis-
tributed around a normal centre line, which in this latter case passes
from the tip of one blade to the tip of the opposite one through the
centro of the boss. I thus obtain a blade whose "astern" face is
precisely identical with that of the "ahead" face.
Fig. 5 shews an expansion of the surface of a blade and sections of
the four bladed propeller illustrated in Figures 3 and 4, while Fig. 6
represents a side view taken when the shaft is at an angle of fifteen
degrees with the plane of vision, and in which view the elongated
figure 8 is represented.
Figures 7 to 16 inclusive shew on a smaller scale views of my propeller,
the angle of the shaft with respect to the plane of vision being indicated:
by a line below each Figure.
Having described the Drawings illustrative of my Invention, and the
means I employ for putting the same into execution, I would remark
that I do not limit myself to any special number of blades for any given
propeller, nor do I confine myself to the proportions of diameter, mean
pitch, nor extent of surface of blade here depicted.
I would also further remark that all screw propellers hitherto in use,
in which the formation of the blades is in conformity with the true screw
principle, viz., that of a plane wound round a cylinder, such cylinder
being represented by the boss of the propeller of necessity have that
portion of their blades which is in the vicinity of the boss parallel or
nearly so to the line of the shaft. But my propeller differs entirely
from all these in this important respect, viz., that the portion of the
blade in the vicinity of the boss is in a direction at right angles or nearly
so to the axis of the shaft instead of being parallel thereto. Thus my a
present Invention, instead of being merely an improvement in screw pro-
pellers, including my own improvements previously patented, is really a
propeller based upon an entirely new system.
Having now set forth the nature of my Invention, and explained
the manner of carrying the same into effect, I wish it to be understood;
that under the above in part recited Letters Patent, I claim the con-

page_text: struction of propeller blades as described with reference to Sheets I.
and II. of the accompanying Drawings, the pitch of which blades
ncreases from zero at or near the centre of the propeller by successive
Increments to its greatest amount at or near the periphery as illustrated
by the red lines in Figures 2 and 5, which show also an uniform pitch
hroughout each transverse section wherever taken.
In witness whereof, I, the said Hermann Hirsch, have hereunto set
my hand and seal, the Twenty-third day of June, in the year
of our Lord One thousand eight hundred and seventy-six.