An Improved Screw Propeller.
Year: 1888

page_text: Date of Application, 4th Sept., 1888
Complete Specification Left, 3rd June, 1889-Accepted, 13th July, 1889
PROVISIONAL SPECIFICATION.
An Improved Screw Propeller.
CAMPBELL FORREST Engineer 95 Grey Mare Lane Bradford Manchester & CHARLES
MYERS Designer 22 Park Terrace Beswick Manchester both in the County of
Lancaster do hereby declare the nature of this invention to be as follows:-
The object of our invention is to construct or arrange a new shape of a screw
propeller in one casting or built in segments of iron or steel plates. Our improve-
ments consists in utilising the space between the ordinary propeller blades by
connecting the same blades with a segmental circular blade extending from one
to the other thus giving a new & novel circular propelling power in addition to the
ordinary blade. We join the circular segments nearly at the points of the blades leaving
a space between the boss of each blade & the inner circumference of the circular
segments. We do not confine ourselves to any given pitch.
Dated this 3rd day of Santamber 1888
CAMPBELL FORREST.
CHARLES MYERS.
COMPLETE SPECIFICATION.
An Improved Screw Propeller.
We CAMPBELL FORREST Engineer of 95 Grey Mare Lane Bradford, Manchester and
CHARLES MYERS, Designer of 22 Park Terrace Beswick Manchester both in the
County of Lancaster 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 our invention is to construct a new form of screw propeller, either in
one casting or built in segments of iron or steel or other metal plates attached to a
cast iron or other metal boss whereby we are enabled to obtain an increased amount of
propelling surface, a free passage for the water in a direction parallel with the centre
line of the axis together with a reduction in the amount of "slip," and in the vacuum
formed in the rear of the propeller.
The nature of our said invention and the manner in which the same is to be
performed or carried into practical effect will be readily understood on reference to
the annexed sheet of drawings and the following explanation thereof.
-
Fig. 1 on the drawings is a face view and Fig. 2 an edge view of a screw propeller
constructed according to our invention.
The most ordinary form of screw propeller at present in use consists of two, three, or
more blades standing out in a radial direction (or nearly so) from a central boss
situated on the axis of rotation of the propeller these blades being placed in different
positions round the axis, and so twisted as each to form a portion of the thread, or
threads of a screw, and are attached by the inner edge to the central boss, as shown on
the drawing at Fig. 3 wherein a is the central boss and the twisted blades which
form the screw.
Our improvements consist principally in utilizing the space between the ordinary
radial propeller blades to obtain an increased propelling surface by connecting the
ends of the said radial portion b of the blades (see Figs. 1 and 2) with a segmental
circular continuation c of such blade extending from one radial portion a to the
other b' and thus causing the blade to return in one single sweep back again to the
boss as seen at Fig. 1. each blade of the propeller thus forms a complete loop by
the combination of two twisted quasi-radial portions 6 and 6' with a segmental
continuation c joining the two.

page_text: The return portion a¹ of the blade is joined to the boss nearly at the back of the
portion 6 of the next blade leaving a space between the radial portions of the two
adjoining blades.
Thus it will be seen that each complete blade is equal to two of the ordinary radial blades
plus the circular portion c that the propelling surface is thus increased, at the same
time that there is a perfectly free passage through the three openings d for the escape
of the water through the propeller close to and in a direct line with the axis, and by
the same means the vacuum at the back of the propeller is reduced to a minimum and
it has been found in practise that a great increase in propelling power and speed is
obtained thereby; the blades also being attached to the boss at both ends are stronger
and much less liable to fracture, than when attached only by one end, and with the
other end free as in the usual arrangement.
In some cases instead of constructing the blades so that their outer circumference
forms a portion of a circle struck from the centre of the axis (see Fig. 1.) we propose
to increase the width of the central portion so as to gain additional propelling surface
as shown by the dotted lines e.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed, we declare that we do
not wish to confine ourselves to any particular number of blades nor to any precise
angle or pitch of the same but we claim :-
1. The construction of screw propellers with spiral or twisted blades in the form of
loops attached to the boss at each end substantially as hereinbefore described and
illustrated by the drawings annexed.
2. Constructing screw propellers with a series of blades each of the form of a
severed loop helically disposed relatively to the axis of its centre opening, and angularly
arranged relatively to the axis of the boss of the propeller, to which both ends of the
loop are connected substantially as hereinbefore described with reference to the
accompanying drawings.
Dated this 1st day of June 1889.
GEORGE DAVIES,
4, St. Ann's Square, Manchester, Agent for the Applicants.