Improvements in Screw Propeller Blades.
Year: 1895

page_text: Date of Application, 5th Apr., 1895
Complete Specification Left, 5th Nov., 1895-Accepted, 7th Dec., 1895
PROVISIONAL SEMNALLA.
Improvements in Screw Propeller Blades.
I, ROBERT CLUCAS residing at 16 Claughton Road Birkenhead Cheshire
Joiner do hereby declare the nature of this invention to be as follows:-
:―
My invention relates to screw propellers, and its object is to propel & vessel
through the water at a greater speed with the same amount of motive power. My
invention consists, in making a triangular portion of my propeller blade extending
from the boss and following edge to one third of its length along its leading edge,
finer in its pitch than the rest of the blade, for the purpose of, and as herein
afterwards explained.
Fig. 1, represents an ordinary propeller.
Figs. 2 and 3, are elevations of my improved propeller seen from different points,
A, and. B, are parts of the blade herein afterwards explained, and C is the boss.
Figs. 1, and 2, are placed so that the face of one of the blades in each elevation
is presented to the eye almost in its true development.
That my invention may be perfectly understood, it is necessary to explain the flow
of water over the face of an ordinary propeller blade when it is fully engaged in
propelling a vessel.
Fig. 1, represents an ordinary propeller with blades standing perpendicular to
the direction of propeller shaft, the pitch of the propeller being one and a half
times its diameter. The direction of the water across the face of the blade is
shown at A, by the lines drawn from the leading to the following edge inclining in
their direction towards the periphery.
This oblique direction of the water is owing to it being projected astern perpen-
dicular to the blade's surface, therefore as the blade's angles get coarser towards
the root, the flow of water towards the periphery increases, (the said flow is very
little affected when the blade is made with the usual decreasing pitch towards the
boss, because the propeller is not rotating in still water, but is rotating in water
strongly inclined to flow in the same direction as the vessel).
The water is therefore forced over the face of the blade in the direction already
described, and away from the triangular portion at its root represented by the
blank space B. A vacuum in consequence forms at B, and the said vacuum sucks
the water in its vicinity around with the propeller as it revolves, thereby wasting
a great amount of power. My improved blade is developed and pitched in the
manner herewith explained and shown at B Figs. 2, and 3, to prevent the aforesaid
vacuum from forming. B should extend from C at the following edge of the blade,
to about one third the length of the blade along its leading edge as shown. The
rest of the blade A. may be made with any suitable pitch (regular or otherwise)
coarser than B. But to explain my invention the pitch of A is made similar to A
Fig. 1.
As the real slip of a propeller is the difference in the speed of its screw to the
speed of the water fed to it, the pitch of B should be decreased equal to the real
slip of the screw. As the real slip of A increases as its surface decreases towards C,
the pitch of B should be decreased so much per cent. equal to the percentage of real
slip A has following in the same line of rotation. The pitch of B is thus made
equal to the speed of the water fed to it over its entire surface, making, it cut
edgewise through the water it traverses, thereby allowing the water to flow over
the entire face of the blade in the direction of the lines drawn from the leading to

page_text: the following edge, thus preventing the vacuum herein before described from
forming. The separate pitches of A, and B, may join abruptly or be eased into
each other. As the real slip of a screw propeller increases with the fulness of the
vessel's lines astern and many other causes too numerous to mention, it is
impossible to make B with a standard pitch to perfectly suit all vessels. A.
suitable pitch for some vessels is to make B fifty per cent. less than A at C, then
gradually increase its pitch to twenty per cent. less than A at its furthest extremity
from C, but to ensure the perfect working of B, the speed of the water fed to it
should be taken over its entire length, and its pitch regulated as herein before
described. By making B similar in development to B Fig. 1, the propelling surface
of the blade is maintained.
My improved propeller may be constructed in numerous ways different to that
hereinbefore described. B may be made with a regular pitch finer than A equal
to the general real slip of the propeller, or it may be made to extend some distance
from C along the following edge of the blade, or extend from the leading edge some
distance along C. My propeller may have any desirable number of blades, which
may be made of any suitable material. The propeller may be cast in a piece, or
the blades fixed on to the boss separately. The pitch of A, the development of the
blades, and their angles of inclination either fore or aft may be altered at the
discretion of those interested. My invention relates only to a triangular portion
of a screw propeller blade (hereinbefore described at B Figs. 2, and 3,) being made
finer in its pitch than the rest of the blade, for the purpose of preventing the
vacuum from forming at the blade's root..
Dated on the 4th day of April 1895.
Improvements in Screw Propeller Blades.
I, ROBERT CLUCAS, residing at 16 Claughton Road Birkenhead Cheshire
Joiner 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 screw propellers for navigable vessels. My object being
to propel a vessel at a greater speed without increasing the motive power. My
invention consists in pitching a particular portion of my propeller blade finer than
the remaining portion. The said particular portion should extend from the boss
about one third the length of the leading edge of the blade and then recede
obliquely towards the blade's following edge and boss or thereabout, for the
purpose of and as berein afterwards explained with reference to the drawings filed
with my Provisional Specification. Figs. 2, and 3, are respective elevations of my
improved propeller. A, and B, are parts of the blade herein afterwards explained
and C is the boss. Fig's. 1, and 2, are placed so that the face of one of the blades-
in each elevation is presented to the eye almost in its true development.
That my invention may be perfectly understood it is necessary to explain the
flow of water over the face of an ordinary propeller blade when it is fully engaged
in propelling a vessel. Fig. 1 represents an ordinary propeller with blades standing
perpendicular to the direction of propeller shaft and with pitch one and a half
times its diameter. The direction of the water across the blade's face is shown at A
represented by the lines drawn from the blade's leading to following edge and is
caused by the water being projected astern perpendicular to the blades surface
thereby causing the oblique flow towards the periphery as the propeller revolves.
The said oblique flow increases with the coarsenes of the blades' angles and is
therefore very little affected when the blade is made with the usual ten per cent.

page_text: decreased pitch at the boss, because the propeller is not rotating in still water but
is rotating in water strongly inclined to flow in the same direction and at the same
velocity as the vessel, but is prevented from so flowing by the action of the
propeller.
The water is therefore forced over the face of the blade in the direction already
described and away from the portion at its root represented by the blank space B,
thus causing a vacuum to form at B which sucks the water in its vicinity around
with the blade as the propeller revolves, thereby wasting a great amount of power
by causing a continual suction sternwards, and in rough weather the propeller
being lifted frequently out of the water and the consequent racing which ensues.
followed by the terrible shock on the propeller-shaft-engine-and vessel—when.
the blades again strike the water are defects which require no further comment.
My improved blade is pitched in the manner herewith explained and shown at B,.
Fig's. 2, and 3, to prevent the aforesaid vacuum from forming and to decrease the
propeller's impact with the water when racing, in rough weather. B should extend
about one third of the blades length along its leading edge from C and recede back
to C in an oblique direction to the following edge of the blade as shown, and
should be pitched much finer than the remaining portion of the blade A as herein.
afterwards explained. For the purpose of comparison in explaining my invention
A is made with a similar pitch to Fig. 1. B's pitch should be made equal to the
speed of the water as fed to it so that it may cut edgewise through the water it
traverses and thus constitute A the sole propelling portion of the blade. The real
slip of a screw propeller being the difference in the speed of its screw to the speed
of the water fed to it, the pitch of B should be decreased equal to the real slip of
the screw.
As the real slip of A increases as its surface decreases towards C, the pitch
of B should proportionately be decreased equal to the percentage of real slip A
has following in the same line of rotation. B's pitch is thus made equal to the
speed of the water as fed to it over its entire surface, and is thus made to cut
edgewise through the water it traverses, thereby allowing the water to flow over
the entire face of the blade in the direction of the lines drawn from the blade's
leading to following edge as shown, thus preventing the vacuum herein before
described from forming. The separate pitches of A, and B, may join each other.
abruptly, or be eased gradually into each other.
As the real slip of the propeller will vary with the build of the vessel and other
numerous causes B's pitch should vary to suit the respective vessel. A useful
pitch and one which gives a fair increase in speed is to make B fifty per cent. less
pitch than A at C then gradually increase its pitch to ten per cent. less than A at
its further extremity from C. But to ensure the perfect working of the propeller.
the speed of the water as fed to B should be taken and B's pitch regulated as
herein before described. By making the developinent of B similar to "B, Fig. 1,"
the propelling surface of the blade "A" is maintained.
My improved propeller may be constructed in numerous ways different to that
hereinbefore described. B may be made with a regular pitch finer thau A equal
to the general real slip of the propeller-or extend to some distance from C along
the following edge of the blade-or extend from the leading edge some distance
along C-or extend to any desirable distance from C along the blade's leading
edge. My propeller may have any desirable number of blades-may be made of
any suitable material-and may be cast in a piece or the blades fixed on the boss
separately. The pitch of A-the development of the blades-and their angles of
inclination either fore or aft-may be altered at the discretion of those interested,
as my invention relates only to the portion at the blade's root hereinbefore
described at B, Fig's. 2, and 3, being made finer in its pitch than the remainder of
the blade, for the purpose of preventing the vacuum hereinbefore described from
forming and for decreasing the shock to the propeller when racing in rough.
weather.

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 I
claim is :
An improvement in screw propeller blades.
The said improvement to consist in pitching a "portion" of my propeller blade
finer than the remaining portion-preferably as hereinbefore described at B,
Fig's. 2, and 3.
The said "portion" to extend from the boss at or near to the following edge of
the blade in an oblique direction towards the periphery across the blades surface
to about one third or two fifths or any reasonable distance along the length of the
blade's leading edge, for the purpose of preventing the vacuum from forming at
the blade's root and for decreasing the shock consequent on the propeller's racing,
in rough weather.
Dated on this 2nd day of November 1895.
ROBERT CLUCAS,
Applicant.