Im- PROVEMENTS IN SCREW PROPELLERS
Year: 1875

page_text: LETTERS PATENT to Joseph Hirsch, of No. 27, Norfolk Street,
Strand, in the County of Middlesex, for the Invention of "Im-
PROVEMENTS IN SCREW PROPELLERS."-A communication from abroad
PROVISIONAL SPECIFICATION left by the said Joseph Hirsch at the
Office of the Commissioners of Patents, with his Petition, on the
17th February 1875.
I, JOSEPH HIRSCH, of No. 27, Norfolk Street, Strand, in the County
of Middlesex, do hereby declare the nature of the said Invention
of "IMPROVEMENTS IN SCREW PROPELLERS," to be as follows:
-
In the Specifications of Patents granted to Hermann Hirsch, on the
29th November 1860, No. 2930, and on the 3rd January 1866, No. 17,
were described screw propellers the blades of which were made with a
curvature forwards in the direction of their rotation combined with a
pitch increasing backwards.

page_text: The present Invention relates to improvements in the construction of
propeller blades of this character, the chief object of such improvements
being to secure an efficient action of the outer part of the blade which
moves with the greatest velocity and strength in the inner part of the
blade which serves chiefly as a spoke or arm to carry the outer part.
In order that the nature of these improvements may be more clearly
understood the blade may be supposed to be intersected by a number of
successive planes perpendicular to the axis of the propeller, presenting
lines of intersection on the face of the blade. The foremost of these
intersections constituting the entering edge of the blade is a line, not
radial, but curving gently forwards from the root of the blade to its tip.
The hindmost of the intersections constituting the leaving edge of the
blade has a forward curvature of the same character but considerably
greatly than that of the entering edge. The intermediate intersections
present curvatures of like kind but of degrees intermediate between
those of the front and the back edges, that is to say, the blade becomes
the more curved forwards the further it is from the entering edge. This
increase of forward curvature is determined in such a manner that the
blade has a pitch increasing from the front edge backwards, but this
increase of pitch is greatest at the tip of the blade and becomes less and
less towards the root. It is preferred that the pitch along the entering
edge should be that due to the forward motion of the vessel, so that the
blado has there an obliquity to the axis determined by compounding
the velocity of rotation with the velocity of advance, and the increase of
pitch at the tip of the blade may be from 20 to 30 per cent.
The forward curvature, as was described in the Specifications above
referred to, counteracts to a certain extent the lateral effect of centrifugal
force impressed on the water, and when at the same time the pitch is
made to increase, as was also described, the blade, instead of striking the
water, glides through it, accelerating it backwards and sustaining a
corresponding pressure forwards. This is generally true of blades so
constructed, but by adopting for such curved blades the construction
above set forth, the increase of pitch as well as the forward curvature is
rendered greatest where most required and most deficient, that is to say,
towards the tip of the blade, which moving with the greatest velocity
has the greatest action on the water, and both these features diminish
towards the root of the blade where the velocity is least.

page_text: The curved surface formed as above described may be supposed to be
a thin sheet occupying the middle of the blade, on each side of which is
to be provided a thickness of material to give the necessary strength.
The edges of the blade so thickened are curved off like the bow of a
vessel so as to diminish the resistance of the water to the passage of the
blade through it. As the thickness is necessarily increased towards the
root of the blade where the increase of pitch is least, the inner part of the
blade becomes almost a mere spoke or arm fined off at the edges and
propelled through the water in the direction of its width with compara-
tively little resistance, and proportionately little propelling efficacy, its
chief function being to carry the outer part of the blade in which the
principal portion of the propulsive energy resides.
.
.
Although the blade has been described above as being included
between two planes perpendicular to the axis, and therefore as presenting
in side view a uniform width from the root to the tip, it may be readily
understood that a blade of similar character can be made to taper in
width from the root outwards, the intersections on its face being in that
case not planes perpendicular to the axis but conical or conoidal
surfaces having an obliquity to the axis which becomes less towards the
middle of the blade's width. For large propellers this modification is
generally to be preferred as the strength of the blade towards its root
can thus be obtained with less thickness of material, the width being
greater, and thus the inner portion of the blade has a form of less
resistance.
5 SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Joseph Hirsch in the Great Seal Patent Office
on the 16th August 1875:
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOSEPH
HIRSCH, of 27, Norfolk Street, Strand, in the County of Middlesex, send
0 greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
-Letters Patent, bearing date the Seventeenth day of February, in the year
of our Lord One thousand eight hundred and seventy-five, in the thirty-
´eighth year of Her reign, did, for Herself, Her heirs and successors, give
5 and grant unto me, the said Joseph Hirsch, Her special license, that I
L

page_text: the said Joseph Hirsh, my executors, administrators, and assigns, or
such others as I, the said Joseph 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," a
communication to me from abroad by Max Hirsch, of Cologne, in the
German Empire, upon the condition (amongst others) that I, the said
Joseph Hirsch, my executors or administrators, by an instrument in
writing under my, or their, or one of their hands and seals, should par-
ticularly 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 Joseph Hirsch, do hereby declare
the nature of the said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by
the following statement thereof, reference being had to the accompanying
Sheet of Drawings and to the figures and letters marked thereon, that
is to say :-
In the Specifications of Patents granted to Hermann Hirsch on the
29th November 1860, No. 2930, and on the 3rd January 1866, No. 17,
were described screw propellers the blades of which were made with a
curvature forward in the direction of their rotation, combined with a
pitch increasing backwards.
The present Invention relates to improvements in the construction
of propeller blades of this character, the chief objects of such improve-
ments being to secure an efficient action of the outer part of the blade
which moves with the greatest velocity and strength in the inner part
of the blade, which serves chiefly as a spoke or arm to carry the inner
part.
In order that the nature of these improvements may be more clearly
understood the blade may be supposed to be intersected by a number
of successive planes perpendicular to the axis of the propeller, presenting
lines of intersection on the face of the blade. The foremost of these
intersections constituting the entering edge of the blade is a line not

page_text: radial, but curving gently forward from the root of the blade to its tip.
The hindmost of the intersections constituting the leaving edge of the
blade has a forward curvature of the same character, but considerably
greater than that of the entering edge. The intermediate intersections
present curvatures of like kind, but of degrees intermediate between
those of the front and back edge; that is to say, the blade becomes the
more curved forwards the farther it is from the entering edge. This
increase in forward curvature is determined in such a manner that the
blade has a pitch increasing from the front edge backwards; but this
increase of pitch is greatest at the tip of the blade, and becomes less
and less towards the root. It is preferred that the pitch along the
entering edge should be that due to the forward motion of the vessel,
so that the blade has there an obliquity to the axis determined by
compounding the velocity of rotation with the velocity of advance, and
the increase of pitch at the tip of the blade may be from 20 to 30 per
cent.
The forward curvature, as was described in the Specifications above
referred to, counteracts to some extent the lateral effect of centrifugal
force impressed on the water, and when at the same time the pitch is
O made to increase, as was also described, the blade instead of striking
the water glides through it, accelerating it backwards, and sustaining
a corresponding pressure forwards. This is generally true of blades
so constructed, but by adopting for such curved blades the construction
above set forth the increase of pitch as well as the forward curvature is
5 rendered greatest where most required and most efficient, that is to say,
towards the tip of the blade, which moving with the greatest velocity
has the greatest action on the water, and both these features diminish
towards the root of the blade where the velocity is least.
0
5
The curved surface formed as above described may be supposed to be
a thin sheet occupying the middle of the blade, on each side of which
is to be provided a thickness of material to give the necessary strength.
The edges of the blade so thickened are curved off like the bow of a
vessel so as to diminish the resistance of the water to the passage of the
blade through it. As the thickness is necessarily increased towards the
root of the blade where the increase of pitch is least, the inner part of
the blade becomes almost a mere spoke or arm, fined off at the edges
and propelled through the water in the direction of its width, with
comparatively little resistance, and proportionately little propelling

page_text: .efficiency, its chief function being to carry the outer part of the
blade in which the principal portion of the propelling energy resides.
Although the blade has been described above as being included
between two planes perpendicular to the axis, and therefore as pre-
senting in side view a uniform width from the root to the tip, it may be
readily understood that a blade of similar character can be made to
taper in width from the root outwards, the intersections on its face being
in that case not planes perpendicular to the axis but conical or conoidal
surfaces having an obliquity to the axis which becomes less towards the
middle of the blade's width. For large propellers this modification is
generally to be preferred, as the strength of the blade towards its root
can thus be obtained with less thickness of material, the width being
greater, and thus the inner portion of the blade has a form of less
resistance.
Fig. 1 represents a face view of a propeller blade constructed according
to this Invention, and Fig. 2 represents sections across it at the various
distances from the axis marked by the circular arcs A B, CD, E F, G H,
¡on Fig. 1.
It will be seen from Fig. 1 that the entering edge of the blade B FX:
is slightly curved, and the leaving edge A EX has a considerably greater
curvature, the intermediate section lines LOX, KNX, and IMX,
formed by planes transverse to the axis being more and more curved as
· they are nearer to the leaving edge. In Fig. 2 it will be seen that the
pitch of the outermost section AB increases from the entering edge B
towards the leaving edge A by a quantity VA which is determined in
the following manner:-The line YB being taken to represent the
velocity of the blade, and YV the velocity of the vessel, the entering
edge at B is tangential to the line B V. The increase of pitch VA (which
may be as above stated from 20 to 30 per cent.) being added to YV,
and a line A N drawn to the middle of BV, the leaving edge at A is
tangential to AN. The other sections in Fig. 2 are constructed in a
similar manner, the increase of pitch represented by the lines V C, V E,
and V G, respectively becoming less and less towards the axis of the
propeller.
Having thus described the nature of this Invention and in what
manner the same is to be performed, as communicated, to me by my
3

page_text: foreign correspondent, I hereby declare that I make no general claim
to the combination in the blade of a screw propeller of a forward curva-
ture with an increase of pitch, such combination of curvature having
been described in the Specifications above referred to. Further, I am
aware that propellers have been heretofore constructed by and are
described in the Specification of Letters Patent granted to Hermann
Hirsch, dated 28th August 1871, No. 2257, known as Hirsch's propellers,
and I make no claim to such propellers, but I claim, the combination in
the blade of a screw propeller of a forward curvature increasing from
the entering edge to the leaving edge with an increasing pitch, the
increase whereof diminishes from the tip towards the root of the blade,
substantially in the manner and for the purposes herein set forth.
In witness whereof, I, the said Joseph Hirsch, have hereunto set
my hand and seal, this Ninth day of August, in the year of our
Lord One thousand eight hundred and seventy-five.