Improvements relating to Screw Propellers.
Year: 1889

page_text: Date of Application, 18th Dec., 1889
Complete Specification Left, 18th Sept., 1890-Accepted, 1st Nov., 1890
PROVISIONAL SPECIFICATION.
Improvements relating to Screw Propellers.
We, SAMUEL CAWSTON, of Bromley Hill, Bromley, in the County of Kent, Gentle-
man, and THOMAS WILLIAM SCOTT, of Highland Road, Shortlands, in the County of
Kent, Engineer, do hereby declare the nature of this invention to be as follows:-
This invention relates to the construction of screw propellers especially adapted for
use in vessels constructed according to the Specification of Letters Patent No. 474
dated 11th January 1888.
According to our invention we form the blades of screw propellers of circular discs
which are flat or without any twist and approximately equal in thickness from the
tip to the root, and we find it advantageous to make each blade to fit or be screwed
independently or directly upon the shaft instead of forming the blades with a con-
necting boss as usual.
Dated the 18th day of December 1884.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicants.
COMPLETE SPECIFICATION.
Improvements relating to Screw Propellers.
We, SAMUEL CAWSTON, of Bromley Hill, Bromley, in the County of Kent, Gentle-
man, and THOMAS WILLIAM SCOTT, of Highland Road. Shortlands, in the County
of Kent, Engineer, do hereby declare the nature of this invention and in what
manner the same is to he performed to be particularly described and ascertained in
and by the following statement:-
This invention relates to the construction of screw propellers especially adapted for
use in vessels constructed according to the Specification of Letters Patent No. 474
dated 11th January 1888.
According to our invention we form the blades of screw propellers of circular or
diamond shaped discs which are flat or without any twist and approximately equal in
thickness from the tip to the root, and we find it advantageous to make each blade to
fit or be screwed independently or directly upon the shaft instead of forming the blades
with a connecting boss as usual.
In order to enable our invention to be fully understood we will describe how it can
be carried into practice by reference to the accompanying drawing in which,
Figure 1 is an elevation of a screw propeller constructed according to our
invention.
Figure 2 is a plan of Figure 1 and,
Figure 3 is an elevation taken at an angle of 45 degrees to Figure 1.
a, a are the blades of our propeller which we form of circular discs as shewn (or of
diamond shaped discs) which are flat or without any twist and approximately equal
in thickness from the tip b to the root c as clearly illustrated in Figure 3.
The blades a are advantageously made separate from one another and with flanges c, c
whereby they can be bolted directly to the propeller shaft d. e, e indicate the bolts
for this purpose.
The circular or disc shape of our propeller blades enables us to reduce the leverage
of the blades from the tip to the centre thus increasing the power of the engine over
that portion of the blades, and thereby reducing the amount of engine power required
to exert a given thrust from the propeller. By making the blades flat the whole of
the blades from the tip to the root is caused to exert an equal degree of thrust, as the
root of the blade being at the same angle to the propeller axis as the tip, instead of
Price 6d1

page_text: almost in a line therewith does not strike the water so flat as do the blades of existing
propellers and the usual rotation or churning of the waters so detrimental to the
thrust of a propeller is therefore considerably reduced or entirely avoided.
The blades of our propeller will not displace such a large quantity of water as those
of propellers at present in use as they can be made much lighter and are of uniform
thickness from tip to root. Moreover the blades having no actual twist given to them
the centrifugal action of the water on their surfaces is reduced.
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 what we
claim is:
1. A screw propeller having blades formed of circular or diamond shapod discs
which are flat or without any twist and approximately equal in thickness from the tip
to the root, substantially as herein before described.
2. The improved screw propeller herein before described and illustrated in the
companying drawing.
Dated the 17th day of September 1890.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicants.