Improvements in Screw-propellers.
Year: 1892

page_text: Date of Application, 9th July, 1892
Complete Specification Left, 8th Apr., 1893-Accepted, 1st July, 1893
Improvements in Screw-propellers.
I, EMMANUEL FRANÇOIS FARCOT, of 189 Rue Lafayette, Paris, in the Republic
of France, Engineer, do hereby declare the nature of this invention to be as
follows:-
My invention relates to a screw propeller based upon the employment of an
improved form of blade in the construction of the propelling screw.
Instead of arranging the blades in a plane perpendicular to the axis of rotation,
or at a certain inclination in the direction opposite to that of the motion of the
ship, the blades of the screw are inclined to the horizontal axis at an inclination
varying from 0 to 50 degrees in the direction of the motion of the ship.
The generatrix of the screw is a straight or curved line forming an angle of
from 0 to 50 degrees with the perpendicular to the axis in the direction of the
motion of the ship.
For the forward motion the direction of rotation is such that the blades cut the
water from the centre to the circumference. By this new arrangement I obtain
an important result as regards the useful effect of the screw propellers.
The parts near the extremity of the blades of the screw which are set in
rotation encounter the water before the parts of the blades which are near the
centre, and the water which serves as a point of support to the propeller is not
disturbed or interfered with by the centrifugal force as in ordinary screws.
The blade of the screw presents to the water a greater surface of action, the
By
diameters being equal, than with a straight or rearwardly inclined screw.
diminishing the action of the centrifugal force a recoil is obtained with a velocity
of outflow of the water which is approximately equal at all points, and the small
streams of water are nearly parallel with each other at the centre and at the
circumference, each part of the blade encounters at every moment water which
Thus arranged the
has not been disturbed by the central portion of the screw.
screw will worm itself into the water with a greater force, slip much less, and the
force transmitted will be greater.
A molecule encountering the surface of the blade of the screw at a point in front
will be carried away by the centrifugal force and will leave the blade at a point
at the rear after having passed over a comparatively small distance by reason of
the inclination of the blade to the horizontal axis, and the centrifugal force at the
extremity of the blade will be small.
In the case of a straight screw or a rearwardly inclined screw the centrifugal
force will be much greater, for all the molecules will push one against the other
and the distances passed over from the frout of the blade to the rear will be much
greater. At the extremity of the blade the molecules will leave in the direction
of the radius, causing counter currents and agitating the water uselessly without
assisting in the forward motion of the ship; my new arrangement will therefore be
more advantageous than the others.
My improved screw propeller may have any desired number of blades (such as
two, three, four, five or six) according to its diameter and the purpose for which it
is to be employed. I may also vary the width of the blades, which may be either
The blades of the screw
greater or smaller at the extremity than at the nave.
may be either curved or straight, and the pitch may be constant or increase or
decrease.
The nave and blades are of a section suitable for resisting the centrifugal force

page_text: and the thrust of the water which is very great. The material used in the
construction of these screws may be steel, bronze or any other appropriate metal.
If desired the blades are fixed upon the nave so that the pitch may be varied.
This screw may be placed in front of the ship or at the rear in the stern-post in
such a manner that it shall not be projecting. The screws may also be arranged
outside the keel, that is to say one placed on either side.
Dated this 9th day of July 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in Screw-propellers.
I, EMMANUEL FRANÇOIS FARCOT of 189, Rue Lafayette, Paris, in the Republic
of France, Engineer, do hereby declare the nature of this invention and in what
manner the same is to be performed to be particularly described and ascertained in
and by the following statement :-
My invention relates to a screw propeller based upon the employment of- an
improved form of blade in the construction of the propelling screw.
In the accompanying drawing I have shown how my said invention may be
conveniently and advantageously carried into practice, the figures of the said
drawing being hereinafter referred to.
Instead of arranging the blades in a plane perpendicular to the axis of rotation
as shown in Figure 1 or at a certain inclination in the direction opposite to that of
the motion of the ship as shown in Figure 2, the blades of the screw are inclined
to the horizontal axis at an inclination varying from 0 to 50 degrees in the
direction of the motion of the ship, as shown in Figure 3.
The screw is generated by a straight or curved line making an angle of
from 0 to 50 degrees with the perpendicular to the axis in the direction of the
vessel's track and changing in a direction of which the inclination corresponds to
the pitch of the screw.
For the forward motion the direction of the rotation is given so that the wings
or blades cut the water on the inside edge of the blade or wing, so that the water
is displaced from the inside edge towards the outer edge following the pitch.
The parts near the extremity of the blades of the screw which are set in rotation
encounter the water before the parts of the blades which are near the centre, and
the water which serves as a point of support to the propeller is not disturbed or
interfered with by the centrifugal force as in ordinary screws.
The blade of the screw presents to the water a greater surface of action, the
diameters being equal, than with a straight or rearwardly inclined screw as shown
in Figures 1 and 2. By diminishing the action of the centrifugal force a recoil is
obtained with a velocity of outflow of the water which is approximately equal at
all points, and the small streams of water are nearly parallel with each other at
the centre and at the circumference, each part of the blade encounters at every
moment water which has not been disturbed by the central portion of the screw.
Thus arranged the screw will worm itself into the water with a greater force, slip
much less, and the force transmitted will be greater.
A molecule e encountering the surface of the blade of the screw at a, Figure 3
will be carried away by the centrifugal force and will leave the blade at b after
having passed over the distance ab which is comparatively small by reason of the
inclination of the blade to the horizontal axis. The same is the case with the
molecules e, leaving at 616; the centrifugal force at the extremity of the blade
will be small because the centrifugal forces cannot be added together.
In the case of a straight screw (Figure 1) or a rearwardly inclined screw
(Figure 2) the centrifugal force will be much greater for all the molecules e e' es..

page_text: will push one against the other and the distances a¹ b¹ a³ 6* passed over will be
much greater. At the extremity of the blade the molecules will leave in the
direction of the radius, causing counter currents and agitating the water uselessly
without assisting in the forward motion of the ship; my new arrangement will
therefore be more advantageous than the others.
My improved screw propeller may have any desired number of blades (such as
two, three, four, five or six) according to its diameter and the purpose for which it
is to be employed. I may also vary the width of the blades, which may be either
greater or smaller at the extremity than at the nave, as shown in Figure 6. The
blades of the screw may be either curved as indicated in Figures 9 and 10 or
straight as shown in Figures 6, 7 and 8. The pitch may be constant or may
increase or decrease.
The nave and blades are of a section suitable for resisting the centrifugal force
and the thrust of the water which is very great. The material used in the
construction of these screws may be steel, bronze or any other appropriate metal.
If desired the blades are fixed upon the nave so that the pitch may be varied.
This screw may be placed in front of the ship or at the rear in the stern-post in
such a manner that it will not project; this arrangement is shown in Figure 11.
The screws may also be arranged outside the keel, that is to say, one placed on
either side, the extremity of the shaft being suitably supported as shown in
Figures 12 and 13.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
-
First. A screw having the form represented in Figures 3, 4, 6, 7, 8, 9 and 10,
that is to say a screw the blades of which are inclined to the horizontal axis an
angle varying from 0 to 50 degrees, or better, the generatrix of which is a straight
or curved line forming an angle varying from 0 to 50 degrees with the perpendicular
to the axis, the direction of rotation being such that the blades cut the water in
such a manner that the water is displaced from the centre to the circumference in
the forward movement.
Second. The application of this inclination forwards in the direction of the
movement of the vessel to any kind of screws having straight or curved blades.
Third. The application to the blades, of a pitch which is constant or varies from
the nave to the extremity.
Dated this 8th day of April 1893.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.