Improvements in Screw Propellers.
Year: 1893

page_text: Date of Application, 9th May, 1893-Accepted, 17th June, 1893
COMPLETE SPECIFICATION.
Improvements in Screw Propellers.
A communication from ALFRED WELLS CASE, of Highland Park, in the County
of Hartford, State of Connecticut, U.S.A., Manufacturer.
I, ALFRED JULIUS BOULT of 323 High Holborn in the County of Middlesex,
Chartered Patent Agent 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, reference being made to the accompanying
drawing, in which
Figure 1 is a view of the stern of a steamer showing the improved propeller in
perspective.
Figure 2 is a view of the propeller looking directly from the side; and
Figure 3 is a view looking directly from the stern.
The invention relates to the class of screw propellers that are adapted to be
attached to the stern of a boat for driving the same, the object of the invention
being to provide a simple propeller of this class so shaped that when in motion the
blades will act upon and throw the water in such manner that the utmost resistance
possible to the thrust of the blades is utilized to obtain the greatest power of the
screw. To this end the invention resides in a propeller having blades that, when
in motion, thrust outwardly at the same time they thrust backwardly, so as to
force the water from the blades centrifugally as well as rearwardly, as more
particularly hereinafter described.
In the views indicates the stern of a boat, the post of which supports the end
of the shaft to which the propeller 2 having any desired number of blades is
secured. In the form shown there are four blades each having a shank 3 that
projects from the hub, a throat 4 at the end of the shank, and driving wings or
lobes 5 at the outer ends. The blades are formed with their lobes on a straight
screw pitch, but may be formed, if desired, on a spiral pitch of the correct degree
to drive with the least amount of resistance for the speed required; and while the
shanks project from the hub on the desired pitch radially, each lobe is bent slightly
forward at right angles to the spirally forward line of motion of the blades, so
that the plane of each lobe is not only set on the angle of pitch across the axis of
the propeller, but also on an angle with the radii of the axis.
In the views, the dotted line a indicates the axis, radii and n the inclination of
the blades with relation to the radii; while the arrows indicate the direction of
movement.
It is well known that the water at the stern of a fast running boat is in a
disturbed state, churning, boiling and setting back toward the vessel, particularly
on the line of the axis of the propeller; and it has been the aim of most prior
inventors to so construct their screws that the blades will collect the disturbed
water and compact the same at the centre in line with the axis, thinking that
thereby the compacted water will offer a greater resistance to the thrusts of the
screw blades and increase the power of the propeller. Others have endeavoured
to not only collect the water at the centre, but utilize the force of the water thrown
centrifugally by the screw during rotation. The present invention proceeds on a
principle directly contrary to these, and the propeller herein described, with the
blades placed at the proper angle of pitch, and also inclined at an angle to the
plane of their own motion, which is spirally forward, or in a plane toward
the motion of the diametrically opposite blade, throws the water outward away
from the axis at the same time that it worms ahead and thrusts the water back-
ward. By this construction, the volume of water churned by the screw is thrown
away from the centre of disturbance outward against a more solid body of water

page_text: beyond the periphery of the blades, where the surrounding water is not as disturbed,
and the water thrown out from the centre reacts when coming in contact with the
more solid body of water beyond the centre of disturbance, against the blades of
the screw, with an energy that exerts itself forward so as to offer greater resistance
to the thrust of the screw than if the water was thrown directly astern, or gathered
toward the centre and thrown astern.
Having now particularly described and ascertained the nature of the said inven-
tion as communicated to me by my foreign correspondent and in what manner the
same is to be performed I declare that what I claim is :-
A propeller consisting of a hub with projecting blades having uninterrupted
working surfaces set upon the pitch of a screw with the working surface of each
blade forwardly inclined at an angle to the pitch of the screw so as to thrust
outwardly as well as rearwardly when in motion substantially as specified.
Dated this 9th day of May 1893.
W. P. THOMPSON & BOULT,
Agents for the Applicant.