Improvements in Marine Propellers.
Year: 1892

page_text: Date of Application, 25th Aug., 1892-Accepted, 19th Aug., 1893
COMPLETE SPECIFICATION.
Improvements in Marine Propellers.
I, GEORGE JOHN STEVENS, of No. 95 Falmouth Road, West Newington, in
the County of Surrey, 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 a construction of marine propeller whereby I obtain
great efficiency and lessen vibration. In a previous Specification No. 18124 of
1889 I have described in general terms a construction of somewhat the same
character as that which I shall now describe referring to the accompanying
drawings which illustrate diagrammatically the mode of shaping one blade of a
propeller according to my invention.
I select a curve A Fig. 1 which has an asymptote B, preferring the curve which
is such that tangents to it a, b, a, b at any points as a meeting the asymptote
at b, b, are all of the same length as a b₁. I divide the asymptote in any number
of equal divisions and draw ordinates from the points of division to meet the
curve at the points a, a, as a &c. As the curve A is to determine the profile of a
radial section of the propeller blade, this curve being supposed to revolve round
the asymptote B as an axis, and at the same time to advance along the axis more
or less rapidly according as the pitch is greater or less, I obtain this profile as
shewn in Fig. 2 by drawing parallels to the axis from the points a₁ a₂ &c. to meet
a radius C at points eg ca &c. respectively. With radius C c₁ I describe a
circular arc which I divide equally at d₂ dad, and each of these divisions being such
as to represent the partial revolution of a radius while it advances through one
division of the asymptote B representing the corresponding portion of the pitch.
From the centre with radii Cc, Ce, &c. I describe arcs meeting the correlated
radii Cd Cd, &c. at e₂ ez е, &c., through which points I trace the curve E
representing the profile of a section of the blade made by a plane perpendicular to
the axis. In order to determine the outline of the blade, I proceed as shewn in
Figs. 3 and 4, this outline being the result of assuming the helical surface to be
intersected by a cone. FG represents the oblique side of a cone which practically
I find should make an angle with the axis of from 45° to 60°, and which should
touch one edge of the boss S. Another line H K drawn from the other edge of
the boss, preferably at a somewhat greater inclination to the axis, represents the
oblique side of another coue. I divide the length of axis L M into a number of
equal parts and draw ordinates such as & cutting the two lines H K and F G at
points such as kg, and I draw from these points, parallels to the axis meeting a
perpendicular radius C N at points such as respectively. From the centre C
I describe through these points circular arcs such as k³ ³ g² g³N P. On each
side of N I set off equal arcs such as NP, NP, PP, P2 P, &c. corresponding with
the arcs c, d, d, d, &c. in Fig. 2. I then apply the curve E determined in Fig. 2
to meet these points of division as E' E' &c. and through the points where the
ares k²² &c. are intersected by the curve E, as for instance at 3 I trace a
curve T defining the outline of one edge of the blade, and through the other
intersections as for instance at g, 1 trace another curve V defining the outline of
the other edge of the blade I prefer to cut off the sharp part W of the blade to
prevent it from catching chains or the like when it revolves with the part W
forwards, and another part between V and the dotted line may be cut off when it
is desired to narrow the blade. Thus for example the outline V may be adopted
for a propeller with two blades, and the outline for a propeller with three blades.

page_text: 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 1.
claim is :-
A marine propeller the blade of which has its helical surface generated by
the simultaneous revolution round and advance along an asymptote as an axis, of
an asymptotic curve such as A Fig. 1, the general outline of the edges of the blade
being determined by the intersections of two cones with this helical surface,
substantially as herein described.
1 Anaut 100D
t
ABEL & IMRAY,
Agents for the Applicant.