Improvements in Ships' Propellers.
Year: 1893

page_text: Date of Application, 19th Apr., 1893-Accepted, 10th June, 1893
COMPLETE SPECIFICATION.
Improvements in Ships' Propellers.
I ALFRED TOWNSEND ELFORD, of No. 134 Sutter Street in the City and
County of San Francisco, State of California, United States of America,
Engineer, 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 invention relates to that class of propellers connected to an axis or axle
parallel with the keel of the vessel and revolving beneath the surface of the water
at the stern of the vessel.
The objects of my invention is to produce a propeller wherein the vibration slip
and friction is considerably reduced and the actual advance or rate of the ship
augmented.
The improvements constituting my said invention comprise a novel construction
and arrangement of blades connected to arms spirally arranged around a common
axis or hub suitably sustained by annular bands so that each blade forming the
screw will stand perpendicular to the axis of the hub and cross the same diagonally
at an angle of about 45°.
The accompanying drawings which form part of this Specification are referred to
therein by figures and letters, represent a propeller constructed according to my
invention.
Figure 1 is a front elevation.
Figure 2 is a side view.
Figure 3 is a side view of one of the blades and Figure 4 a cross section.
The hub A of my propeller is cast solid with the exception of the usual pipe.
slots for feathers and bolt-holes for keying to the driving shaft, and a series of
arms B, B, B, are arranged spirally from front to rear around the hub the radii
of which form the diameter of a true circle in each series.
The first of the arms 1, in each series stands at a true tangent to the hub,
the third is truly radial thereto and the second 2, is located about midway between
the first and third all as seen in Figure 1.
Taken diagonally across or spirally around the hub the ends of each series
form a support for the diagonal blades of the propeller.
Each of the spirally arranged arms B, B, passes through a circular collar or
band C, C, before entering the blades and thus the arms are strengthened and
much vibration prevented, each band being independent of the other.
By arranging the first of the series of arms B at a tangent to the hub A it
will be seen that when the latter revolves this arm is drawn forward, and the
resistance of the water against the blade is more strongly overcome than if the
arm were truly radial to the hub. At the same time by having the other
arms 2 and 3 respectively truly and nearly radial to the hub, the tendency of the
first arm 1 to incline to the rear is resisted and the tendency of the outer ends
is overcome by the band C which holds such outer ends always at the same
distance from the hub.
The blades D, D, are set at an angle about 45° with the longitudinal axis of
the hub perpendicular and spirally to it by which a screw is formed in segments
that will be free from back-flow or dead-water.
The edges and ends of each blade are gothic in form or oval with a sharp
line drawn in the center of the oval from all points and smoothly finished to
present as little friction to the water as possible and each blade is slightly arched
as at DX DX so as to be in cross-section nearly like an ellipse bisected on its
shorter diameter; the spokes or arms bands and blades are also set and arranged

page_text: in a true geometrical order to give the greatest
slip."
66
rate
and the least possible
As thus constructed it will be seen that in operation the forward and backward
thrust of the propeller will be the same.
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 :-
:―
1. The herein described propeller comprising a hub A, a number of series of
aims seated therein, each series having three arms arranged in different eirules
around the length of the hub, the first of the series standing at a tangent to the
hub, the third truly radial thereto, and the second at an angle between the other
two, a band C surrounding the hub in a plane with each of said circles and through
which band said arms pass, and a blade D secured to the outer ends of the arms of
each series and set spirally around the hub, as and for the purpose set forth.
2. The herein described propeller comprising hub A, a number of series of
arms B seated therein, each series having three arms arranged in different circles
around the length of the hub, the first of the series standing at a tangent to the hub
and inclining to the rear in the direction of rotation of the hub, the third standing
truly radial to the hub and the second standing between and parallel with the
other two and a blade D secured to the outer ends of the arms of each series, as
and for the purpose set forth.
3. In a propeller the combination with a hub, and arms projecting therefrom;
of a series of blades secured to the arms, each blade forming a segment of a circle
and standing spirally around the hub and the edges and ends of the blade being
rounded in cross section to less than the smallest curve of an ellipse with a sharp
corner along its transverse center as and for the purpose set forth.
Dated this 19th day of April 1893.
HASELTINE, LAKE & Co,
45, Southampton Buildings, London, W.C., Agents for the Applicant.