IMPROVEMENTS IN SCREW PROPELLERS
Year: 1866

page_text: LETTERS PATENT to Hermann Hirsch, Civil Engineer, of 24, Rue du
Mont Thabor, Paris, in the Empire of France, for the Invention of
"IMPROVEMENTS IN SCREW PROPELLERS."
Sealed the 3rd April 1866, and dated the 3rd January 1866.
PROVISIONAL SPECIFICATION left by the said Hermann Hirsch at the
Office of the Commissioners of Patents, with his Petition, on the 3rd
January 1866.
I, HERMANN HIRSCH, Civil Engineer, of 24, Rue du Mont Thabor,
Paris, in the Empire of France, do hereby declare the nature of my Inven-
tion for "IMPROVEMENTS IN SCREW PROPELLERS," to be as follows, that is to
say:-
This new propeller embodies the essential principles of a screw, with
such a modification of form in the transverse and longitudinal curvature
of the blades as secures cértain advantages and avoids certain evils.
The object of a propeller being to convert the rotatory motion of its
surface into a pressure directed in the line of its axis, that is the best
propeller which converts a given rotatory power into the greatest longi-
tudinal pressure, or which produces a given longitudinal pressure from the least
rotatory power consistently with facility of steerage and absence of vibration.

page_text: The extent to which these objects are attained by my propeller may be best
understood by comparing it with an ordinary straight-bladed screw, the form
of propeller found best until now. The pitch of a screw is always somewhat
greater than that due to the speed of the vessel, that is to say, the surface of
the blades is at every point somewhat more inclined to the axis than the line
which would at that point represent the resultant of the rotatory velocity of
the surface and its forward motion through the water. This excess of pitch,
commonly called slip, is essential because it represents the yielding of the
fluid medium in which the screw acts, the inertia of the fluid or its
resistance to this yielding being in fact a measure of the propelling force.
When all this force is applied at once, as in the common screw and in all
other propellers where the inclination of the blade is the same across its whole
breadth, not only is the resistance to rotation greater, but the water being
suddenly put in motion backwards at the very front edge is scarcely acted on
by the rest of the blade, which becomes comparatively useless, more especially
as the water suddenly put in motion at the front edge becomes much broken
and less capable of reacting on the remaining portion of the breadth.
In my improved propeller the front or entering edge is so inclined to the
axis that it cuts the unbroken water with little or no resistance, and the rest
of the blade gently curves backwards, being more and more inclined so as to
give the water a gradually increasing backward motion, thus not only avoiding
the excessive resistance caused by a sudden impulse on the water, but also
maintaining a uniform reactive pressure from unbroken water over the whole
breadth of the revolving blade. This advantage may be appreciated by those
who are aware how valuable for avoiding resistance are the hollow lines in the
run of a fast going vessel. Indeed, when it is borne in mind that all the
force expended in driving a screw round its axis is useless in propelling, except
in so far as that force by angle of surface becomes resolved into force directed
in the line of the axis, it is obvious that hollow lines in the curvature of
the blades, as in my screw propeller, are essential in order to cause the
least possible resistance to rotation consistently with the required force of
propulsion.
..
Again, the ordinary screw acts like a fan, not only driving the water, back-
wards, but also throwing it by centrifugal force outwards from the axis; and
in the oblique action resulting from these two motions it not only loses much
of its effect in propelling the vessel directly forward, but by breaking the
backwater and causing a great divergence and eddying in its streams it
deprives the rudder of much of its steering power. In my screw propeller
the blades are curved inwards, so as to dominate the centrifugal force and to

page_text: use it auxiliarly to drive the water in an unbroken column directly astern.
The reaction of the water in thus entirely expended in direct forward propul-
sion, and the influence of the rudder surrounded and acted on by the unbroken
and fast moving fluid is at once more quick and certain.
And farther, while the one blade of an ordinary screw is moving along the
upper arc of its course it displaces the water with ease, but the other blade
moving at the same instant in deep water encounters great resistance, which
tends to lift the vessel and jerk it to one side. This action being repeated
twice in every revolution of the screw puts the vessel into a stato of vibration,
which renders it impossible to work many screw steamers at full speed, and
even at moderate speed loosens and endangers the stern framing. In my
improved screw propeller the blades owing to their curvatures have their
surfaces brought gradually into action with every fresh volume of water in all
parts of their revolution, and their action on the water is thus divided and
delivered easily and gradually without vibration and with proportionally less
expenditure of power.
My improved screw propeller will thus produce very superior results,
whether an equal spead with a saving of fuel shall be required, or with
an equal expenditure of fuel a 'higher speed, in either case accompanied
by the two other advantages of absence of vibration and increase of steering
power.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Hermann Hirsch in the Great Seal Patent Office on the
2nd July 1866.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, KERMANN
HIRSCH, Civil Engineer, of 24, Rue du Mont Thabor, Paris, in the Empire
of France, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Third day of January, in the year of our Lord
One thousand eight hundred and sixty-six, in the twenty-ninth year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said Kermann Hirsch, Ier special licence that I, the said Kermann Hirsch,
my executors, administrators, and assigns, or such others as I, the said
Kermann Hirsch, my executors, administrators, and assigns, should in any
time agree with, and no others, from time to time and at all times there-
after during the term therein expressed, should and lawfully might make,

page_text: use, exercise, and vend, within the United Kingdom of Great Britain
and Ireland, the Channel Islands, and Isle of Man, an Invention for "IM-
PROVEMENTS IN SCREW PROPELLERS," upon the condition (amongst others) that I,
the said Kermann Hirsch, my executors, administrators, or assigns, 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 imme-
liately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Kermann 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:--
This new propeller embodies the essential principles of a screw, with such a
modification of form in the transverse and longitudinal curvature of the
blades as secures certain advantages and avoids certain evils. The object of a
propeller being to convert the rotatory motion of its surface into a pressure
directed in the line of its axis, that is the best propeller which converts a given
rotatory power into the greatest longitudinal pressure, or which produces a given
longitudinal pressure from the least rotatory power consistently with facility of
steerage and absence of vibration. The extent to which these objects are
attained by my propeller may be best understood by comparing it with an
ordinary strait-bladed screw, the form of propeller found best until now.
The pitch of a screw is always somewhat greater than that due to the speed
of the vessel, that is to say, the surface of the blades is at every point some-
what more inclined to the axis than the line which would at that point
represent the resultant of the rotatory velocity of the surface and its forward
motion through the water. This excess of "pitch," commonly called "slip,"
is essential because it represents the yielding of the fluid medium in which
the screw acts, the inertia of the fluid or its resistance to this yielding being
in fact a measure of the propelling force. When all this force is applied at
once, as in the common screw and in all other propellers where the inclination
of the blade is the same across its whole breadth, not only is the resistance
to rotation greater, but the water suddenly put in motion backwards at the
very front edge is scarcely acted on by the rest of the blade, which becomes
comparatively useless, more especially as the water suddenly put in motion at
the front edge becomes much broken and less capable of reacting on the
emaining portion of the breadth.
In my improved propeller the front or entering edge is so inclined to the

page_text: axis that it cuts the unbroken water with little or no resistance, and the rest
of the blade gently curves backwards, being more and more inclined so as to
give the water a gradually increasing backward motion, thus not only avoiding
the excessive resistance caused by a sudden impulse on the water, but also main-
taining a uniform reactive pressure from the unbroken water over the whole
breadth of the revolving blade. Indeed, when it is borne in mind that all the
force expended in driving a screw round its axis is useless in propelling, except
in so far as that force by angle of surface becomes resolved into force directed
in the line of the axis, it is obvious that hollow lines in the curvature of the
blades, as in my screw propeller, are essential in order to cause the least
possible resistance to rotation consistently with the required force of pro-
pulsion.
Again, the ordinary screw acts like a fan, not only driving the water
backwards, but also throwing it by centrifugal force outwards from the axis,
and in the oblique action resulting from these two motions it not only loses
much of its effect in propelling the vessel directly forward, but by breaking
the backwater and causing a great divergence and eddying in its streams, it
deprives the rudder of much of its steering power. In my screw pro-
peller the blades are curved inwards, so as to dominate the centrifugal
force and to use it auxiliarly to drive the water in an unbroken column
directly astern. The reaction of the water is thus entirely expended in direct
forward propulsion, and the influence of the rudder surrounded and acted on
by the unbroken and fast moving fluid is at once more quick and certain.
And further, while the one blade of an ordinary screw is moving along the
upper arc of its course it displaces the water with ease, but the other blade
moving at the same instant in deep water encounters great resistance, whichs
tends to lift the vessel and jerk it to one side. This action being repeated
twice in every revolution of the screw puts the vessel into a state of vibra-
tion, which renders it impossible to work many screw steamers at full
speed, and even at moderate speed loosens and endangers the stern framing.
In my improved screw propeller the blades, owing to their curvatures,
have their surfaces brought gradually into action with every fresh volume of
water in all parts of their revolution, and their action on the water is thus
divided and delivered easily and gradually without vibration and with pro-
portionally less expenditure of power.
My improved screw propeller will thus produce very superior results,
whether an equal speed with a saving of fuel shall be required, or with an
equal expenditure of fuel a higher speed, in either case accompanied by the
two other advantages of absence of vibration and increase of steering power.

page_text: After this general explanation, which sufficiently describes the innovation
for which I solicit a Patent, it is necessary for greater clearness to enter into
some developments relative to the accompanying Drawing.
Figures 1, 2, 3 represent on the scale of my improved four-bladed
screw propeller, having a diameter of 5 m. 50-18 feet 6 inches. The two
extreme lines and the whole of the intermediary lines of the surface are
spirals comprised in an angle of 60%, thus generating from the axis to the
circumference a hollow curved or spoon-shaped form of blade. The points
of the spirals may be rounded off without inconvenience, and their curvatures
may be modified towards the axis to give increased strength. This latter
practical modification, made near the centre where the propelling surface is of
small effect, does not diminish the advantage of the propeller. The projected
surface of the blades is 25% of the whole disk, which corresponds for the
surface of each blade to an angle of 22° 30', measured on its circumference.
The belicoidal directing line or directrix of increasing pitch is determined by
the development of the different cylindrical sections made from the centre to
the circumference, and represented in Figure 4 made to the scale of. In the
'accompanying Drawings will be seen the different thicknesses and modifications
required for the strength of the whole.
Up to the present time I have found that the spiral between 45° and 60°,
the latter of which is shewn in the Drawings, gives the best results, but as it
-would be possible to imitate the curved generating line of my screw propeller
I claim all those curves which from the centre to the circumference describe
a spoon-shaped blade surface, and in those curves will naturally enter spirals
of different degrees, of which I prefer those comprised between 45° and 60°.
Lastly, it is almost superfinous to add that I do not intend to confine the
application of my Invention to propellers with four blades to a projected
surface of 25° and to the degree of increasing "pitch" shewn in the Drawings,
as the number of blades, the extent of surface, and the degree of increasing
pitch" may be varied according to circumstances.
FE
.
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 by Letters Patent is,-
1°. The mode of constructing the blades of screw propellers by generating
lines forming curves from the axis to the circumference, comprising spirals of
different degrees, of which I prefer those between 45 and 60 degrees, and pro-
ducing a hollow curved or spoon-shaped form of blade, the circumferencial
arc of which I prefer not to be less than 15 or more than 45 degrees.

page_text: 2º. The combination of these generating lines with a helicoidal directrix of
increasing pitch, the increase of which I prefer not to be less than 1 or more
than.
And the whole in the manner shewn by the accompanying Sheet of
Drawings, and herein described for the purpose set forth.
In witness whereof, I, the said Kermann Hirsch, have hereunto set my
hand and seal, this Twenty-ninth day of June, in the year of our Lord
One thousand eight hundred and sixty-six.
HERMANN HIRSCH. (L.S.)