Improvements in Screw-propellers.
Year: 1896

page_text: Date of Application, 4th Feb., 1896-Accepted, 27th June, 1896
COMPLETE SPECIFICATION.
Improvements in Screw-propellers.
I, ALFRED WELLS CASE, of Highland Park, in the Town of Manchester,
County of Hartford, State of Connecticut, United States of America, Manu-
facturer, 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 :-
The object of my invention is to provide a screw-propeller of such construction
as to secure a more efficient thrust upon the water in the rotation of the screw, to
secure a smoothly running screw which shall tend to reduce vibration, and also to
provide one in which the outward and rearward thrust of the blades can be
obtained without requiring the blade to be inclined so far forward as to encounter
the stern-post, bracket or web of the ship or boat to which the screw is fitted.
To this end my invention consists in the details of the several parts making up
the screw-propeller as a whole and including the disposition, location and arrange-
ment of each blade as more particularly hereinafter described and pointed out in
the claims.
Referring to the accompanying drawings:
Figure 1 is a front view, in elevation, of a four-bladed screw constructed in
accordance with my invention.
Figure 2 is a detail side view of the screw of the improved form.
Figure 3 is a perspective view of my improved screw propeller as applied to a
vessel.
In the accompanying drawings the letter a denotes a screw-propeller comprising
a hub and a number of blades c projecting therefrom, each blade having its
working surface located in such position with reference to the hub b and the axis
of the screw that a straight line, 1, touching the working surface of the blade at its
centre and following along said surface to the root will not pass through the axis of
the bub; and as a result of this substantially the whole of the working surface of
the blade will be located at an angle with any radius, 3, which extends from the
axis, 2, of the hub and passes through the root of the blade. Each blade prefer-
ably has its working surface formed by a straight generatrix and conforming to any
desired pitch.
The working surface of the blade at the leading edge, c', and for a distance
backward therefrom extending beyond the centre line, rakes backward from a
radial line, 3, drawn through a point as at the root of the blade, and this
angular location of the blade, as described, so places it with reference to the hub
as to enable an outward and rearward thrust upon the surrounding mass of water
to be obtained.
The blade is also forwardly inclined although the leading edge does not
necessarily overhang the front end of the hub. This feature of forward inclination
is illustrated by the location of the centre line, 4, in Fig. 2 of the drawings, which
extends from the centre of the working surface at the root of the blade outward
through the centre of the surface to the tip of the blade. The angle which this
line 4 makes with the axis 2 is the angle of forward inclination.
When so constructed the wheel will easily fit within a narrow space at the stern
of a boat with no danger of the leading edge e' of the blade striking the stern-
post, bracket or web; the blade in a prior wheel of this class described in the
Specification of former Letters Patent granted to me and dated 27th March 1894
No. 6182 which has an extreme inclination forward having in some instances been

page_text: a detriment to the ready fitting of a wheel which embodies the features of
improvement residing in that location of the blade which produces a backward
and outward thrust, when an attempt has been made to fit such a prior wheel to a
boat in replacing an old type of propeller wheel.
The main feature of my invention resides in the peculiar iocation of the working
surface of the blade on a line at an angle with a radius of the wheel, as herein
described, the working surface of the screw being preferably formed as stated by a
straight generatrix and conforming to any desired pitch.
The working surface of my improved blade as I have constructed wheels is
formed on an expanding pitch, substantially straight from root to tip, and with the
backward rake, and forward inclination at the ratio of two inches to each foot in
length of the blade. The back of the blade is curved or made full to an extent
sufficient to give proper strength by thickening the centre when the leading and
following edges are worked fine to produce the proper impact and avoid drag.
My invention is not limited to a wheel in which the blade shall have its working
surface formed by a straight generatrix, nor is an expanding pitch and the exact
ratio of compound inclination important, these features as stated being variable at
will and depending upon the size of the wheel and work to be performed.
Each blade is offset at the roots so that the generatrix does not extend through
the axis of the hub when the centre line of the blade is prolonged inward and this
particular location of the working surface with reference to a radial line and
including the compound slope, that is, the backward rake and forward inclination
referred to distinguish the improvement from prior blades.
In the accompanying drawings a propeller has been shown with four blades, but
this particular number of the blades and the precise proportions of each blade are
not essential features of the improvement, which resides, as stated, in the peculiar
construction and location of each blade as a whole whereby as a result of the
compound inclination the advantages of the outward and rearward thrust and the
arrangement of the blade within a limited space lengthwise of the propeller are
obtained.
From tests which have been made with a screw-propeller constructed in
accordance with the within invention, it has been found that there is an almost
entire absence of vibration, a gain in speed over wheels of other types, and a
reduction of the amount of coal consumed; and further that the blade constructed
as described is particularly efiective in stopping a boat promptly and in backing.
The tests have shown that a vessel under a certain headway could be brought to a
complete stop and backed quicker in a less distance when going at a given rate of
speed than with screws of the forms heretofore made.
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:
A screw-propeller having a hub and a series of blades arranged about and
projecting from it, each blade inclined forward in the direction of forward motion
of the vessel as described, aud also having its working surface at its centre line
offset and located in a plane raking backward at an angle from a radius passing
through the root of the blade and in the plane of rotation of the screw, whereby a
rearward and outward thrust upon the water is obtained in a forward rotary
movement of the wheel, all substantially as described.
Dated this 16th day of December AD 1805
ALFRED WELLS CASE.
D. Young & Co.,
11 & 12 Southampton Buildings, London, W.C.,
Agents for the Applicant.