Improvements in Screw-propellers.
Year: 1894

page_text: Date of Application, 27th Mar., 1894-Accepted, 30th June, 1894
COMPLETE SPECIFICATION.
Improvements in Screw-propellers.
1, ALFRED WELLS CASE, of Highland Park, in the Town of Manchester,
County of Hartford, State of Connecticut, United States of America, Manufacturer,
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 within invention relates more particularly to the class of screw propellers
which are adapted to be arranged on the exterior of a ship, and the object is to
provide a propeller having blades so formed and arranged that when the screw is in
motion the blades will act upon the water so as to utilize to a large extent the utmost
resistance that can be afforded by the water as the blades move through it, and by
this means obtain the greatest efficiency of the screw.
My within invention involves two features, the one relating to the particular
form and arrangement of the blade itself, and the other relating to the relative
arrangement of the blades which are set on substantially the same angle across the
axis of the screw but project outwardly at different angles as referred to that axis,
so as to thrust against the water in different lines, as more particularly hereinafter
described and pointed out in the claims.
Referring to the accompanying drawings
:-
Figure 1 is a detail view in rear elevation of a screw propeller embodying one
feature of my invention.
Figure 2 is a perspective view showing the screw propeller in position on the shaft
of a ship.
Figure 3 is a detail view in side elevation of my improved screw propeller,
the dotted lines illustrating the direction of thrust of the working surfaces.
Figure 4 is a diagram view illustrating the angular position of the blades
of a propeller of the prior art, and with dotted line indicating the inward
direction of the thrust of the working surface of the blades of such class of
propellers.
Figure 5 is a plan view of a propeller embodying my improvement with respect
of the blade and also the arrangement of a series of blades.
Figure 6 is a top view of each of the blades of the propeller, and showing also a
vertical section of the same, in order to illustrate more clearly the angle at which
the blades project from the hub.
Figure 7 is a diagram view illustrating the lines of thrust of the screw propeller
blades when in motion.
Figure 8 is a plan view of a screw propeller with four blades embodying the
invention.
Figure 9 shows sectional views of the blades of this latter propeller and the angles
at which they project from the hub.
Referring now more particularly to that feature of my invention which relates to
the particular shape and arrangement of a single blade, in the accompanying drawings
the letter a denotes my improved propeller as a whole in which the hub b is provided
with a plural number of blades c each extending radially from the hub and arranged
at regular intervals about it.
Each blade is provided with a working surface c¹ located as to its general surface
at an angle transversely of the axis of the shaft and substantially in that spiral
plane developed by the revolution and forward movement of the blade as a whole
in the rotation of the shaft. Substantially the whole extent of this working surface
from the root of the blade at the hub to the outer extremity c³ is inclined forward;

page_text: that is, a line touching the centre of the blade at the hub and extending through the
centre of the width of the blade will be inclined forward toward the direction of
forward movement of the propeller as a whole.
This working surface of the blade is not necessarily flat, that is, with all points
of the surface contained in a plane, but is essentially one developed by a straight
generatrix although it may be so shaped and curved as to conform to a spiral
plane. The working surface is, however, flat as compared with the rounded back of
a blade on which the metal is usually built out so as to provide for the necessary
strength in the structure.
It is an essential requirement of this feature of my invention, however, that this
working surface as a whole shall be so located, and forwardly inclined with reference
to the axis of the shaft or hub, that a line normal to this working surface at any
point will diverge from the axis x-y (indicated by dotted outlines in Figs. 3
and 4 of the drawings) when prolonged; and that this working surface of the
blade shall also be one developed by a substantially straight generatrix as
distinguished from a surface which is spherical and curved both lengthwise and
crosswise of the blade.
In screw-propellers as hitherto constructed, it has been an object to so construct
the blade that its working surface shall thrust against the water inwardly behind
the screw as well as rearwardly, the idea being that the water should be caused to
converge; and it was also supposed that any outward thrust was objectionable; and
means have been employed, as flanges across the ends of the blades, to prevent the
outward or centrifugal flow of water.
In carrying one feature of my improvement into effect the blade is so shaped and
located as to offer no obstacle to the outward flow or thrust, and the blade in fact
is purposely inclined at an angle with the axis of the shaft so as to obtain
an outward as well as rearward thrust against the water in the operation of
the screw.
°
It has been customary in making a screw propeller to provide the blade with a
working surface which conforms as nearly as possible with that plane which is
developed by the forward revolution of the blade about the axis of the shaft, and
is located at an angle crossing such axis. This general direction of spiral
movement of the blade and general location of the blade in such plane of move-
ment I have referred to as the angle of pitch of the screw as best descriptive of
the idea, although the pitch being a linear distance measured lengthwise of the shaft
cannot with strict accuracy be said to have either location as a line or plane, nor
angular relation to anything.
A propeller blade has two surfaces, one the face, which is carefully constructed
and shaped and is the one which directly thrusts against the water, while the other
forms the back of the blade and may be shaped and curved so as to provide the
proper thickness of material to give strength to the blade.
It is essential to that feature of my invention above described that the working
surface of the blade should be inclined substantially from the hub to the outer end
of the blade while being located also on some selected angle of pitch, both these
points of degree of forward inclination of the blade and angular location of its
surface transversely of the axis of the shaft being matters which as to their
exact degree are determined by the size of the wheel and of the character of
use of the vessel on which the wheel is to be used, that is, whether the ship
is to be built for speed alone, or for towing purposes. A. considerable forward
inclination, substantially as much as fifteen degrees (15°) at least, has been
found desirable.
A second feature of improvement that is embodied and illustrated in the propeller
shown in Figs. 5 to 9 of the accompanying drawings has for its object the production
of increased efficiency and the overcoming to a certain extent of vibration. This
feature of my invention consists in having the blades, while set on substantially
the same angle across the axis of the shaft, to also project outwardly at varying
angles and thrust against the water in different lines.

page_text: The propeller shown in Fig. 1 has three blades d, e, and f, which are set on any
desired angle across the axis of the hub and the shaft to which the propeller is
adapted to be secured. These blades may be flat or curved and are so arranged as
to project from the hub at different angles, that is, the blade d, as is shown in
plan and section in Fig. 6, projects outwardly at right angles to the axis of the
shaft; while the blade e is shown as inclining forwardly with relation to such
axis; and the blade finclines rearwardly. When a screw propeller is made in
this way the line of thrust of the working surfaces of the blade on the water may
be illustrated as in Fig. 7; the blade d which projects at right angles from the
hub and shaft, thrusts directly backward and drives the water which it enters
backward in a general direction substantially parallel with the axis of the screw
as to its line of motion; the blade e which is set on the same angle of pitch but is
inclined forwardly, will in its spiral movement forward thrust outwardly as well
as rearwardly and tends to throw the water upon which it acts centrifugally outward
or on lines diverging from the axis of the screw and shaft; the blade f which has
the same angle of pitch but is inclined rearwardly will in its movement tend to
thrust the water inward toward the axis of the screw in converging lines.
The result of this peculiar construction and arrangement of the blades in a
screw propeller is that the blade d which projects substantially at right angles to
the axis of the shaft thrusts against water which is backed by the mass of water
directly behind it, while the blade e thrusts on diverging lines outward against a
mass of water outside of the centre of disturbance created by the rotation of the
screw, and the blade f thrusts against water that is thrown in toward the centre
or converges and is compacted in prolongation rearwardly of the screw. By
combining these features of construction an arrangement of the blades and screw
propeller is produced in which the thrust of each blade is against water backed
up by a more solid mass, or water that has not already been given a motion by one
blade in the same direction of thrust that is created by a succeeding blade; and
thus a greater efficiency for the screw is obtained with a given consumption of
motive power.
The propeller shown in Fig. 8 has four blades, two of which marked g are set
diametrically opposite each other on the angle of pitch and are located at sub-
stantially right angles to the axis of the screw, as illustrated in Fig. 9, so that
the working surfate of each of these blades thrusts in lines directly backward.
The other two blades which are set on substantially the same angle of pitch are
inclined forwardly as shown in Fig. 9 and their working surfaces thrust outwardly
as well as rearwardly as they advance. By means of this construction the blades
have the same advantage with respect to the propeller last above described, the
blades being set alternately at different angles to the axis and therefore operating
in water largely undisturbed by the passage of a preceding blade.
In old types of propeller wheels where the blades drag or follow directly
behind one another the water into which any succeeding blade strikes is always in
a disturbed condition but one feature of advantage in the form of my invention
last described is that the blades cut into masses of water comparatively undisturbed
and for that reason a considerable amount of vibration incident to the use of the
older type of wheel is obviated. This reduction of vibration is due to the location
of the succeeding blades in different planes of motion with reference to each other
and as referred to the axis of the shaft.
I do not limit myself to the precise number of blades that may be used, nor to
the number that may project at the same angle of inclination; neither do I limit
myself to the exact outline or angle of pitch or inclination as they may be varied
in some degree without departing from the invention.
Having 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 :-
1. A screw-propeller comprising a hub with projecting blades, each of which has

page_text: its uninterrupted working surface described by a straight generatrix and extending
without break from the hub to the outer end of the blade, said working surface
being set on an angle across the axis of the hub and also inclined forwardly from
the hub to the outer end of the blade, whereby each blade operates to thrust
outwardly as well as rearwardly when in motion, all substantially as described.
2. A screw-propeller consisting of a hub, and a plural number of blades set on
an angle across the axis of the screw and projecting therefrom at different angles
with relation to said axis, all substantially as described and for the purpose
-specified.
3. A. screw-propeller consisting of a hub, and a plural number of blades set on
an angle across the axis of the screw, one or more of said blades projecting from
the hub at right angles to the axis, and others of the blades projecting from the
hub obliquely to the axis and at different angles with relation to each other, all
substantially as described.
Dated this 6th day of March A.D. 1894.
ALFRED WELLS CASE.
D. Young & Co.,
11 & 12, Southampton Buildings, London, W.C.,
Agents for the Applicant.