An Improved Screw Propeller.
Year: 1894

page_text: Date of Application, 15th Jan., 1894
Complete Specification Left, 15th Oct., 1894-Accepted, 22nd Dec., 1894
PROVISIONAL SPECIFICATION.
An Improved Screw Propeller.
I, JAMES WILSON, of 8, Stanley Street, Fairfield, Liverpool, in the County of
Lancaster, Engineer, do hereby declare the nature of this invention to be as
follows:-
According to this invention I provide an improved propeller, wherein the pitch
is of such a nature as to reduce "slip," and at the same time obviates and prevents
non-useful action of the blades, or such action as detracts from the full efficiency of
propellers, at that part of the blades where the most useful effect should be had.
The form of construction of my propeller is as follows:-
The outer parts of the blades, say about the outer half thereof, are constructed of
a decreasing pitch, the rate of decrease being regular throughout this portion from
the tip inwards, this total decrease of pitch being in proportion to the amount of
assumed "slip" which an ordinary propeller of a true pitch would have; whilst the
rest of the blade, that is from the part where this proportional decreasing pitch
ceases to the boss, the blades are made of or provided with an irregularly decreasing
pitch, the rate of irregularity of decrease increasing as it approaches the boss; as
for instance, the rate, for each unit of successive distance towards the boss, may be
two to one.
By the above construction, that part of the blade nearest the boss acts upon the
water in such a manner as to diminish churning or carrying round of water by the
propeller, or to cause any negative action as regards the passage of the ship through
the water, and at the same time enables the parts of the blades further from the
boss to have a more effective action upon the water, and so providing a more
effective propelling force aft.
Dated thin 12th dow of Jonu 1801
An improved Screw
1, JAMES WILSON of 8 Stanley Street, Fairfield, Liverpool, in the County of
Lancaster, 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 :-
According to this invention I provide an improved propeller, wherein the pitch
is of such a nature as to reduce "slip," and at the same time obviates or prevents
actions which detract from the full efficiency of propellers at any part of the blade,
taking place. The form of construction of my propeller is as follows:-
The outer parts of the blades, say about the outer half thereof, are constructed of
a decreasing pitch, the rate of decrease being regular throughout this portion from
the top inwards, this total decrease of pitch being a proportion of the amount of
estimated "slip” which an ordinary propeller of a true pitch would have; whilst

page_text: the rest of the blade, that is from the part where this proportional decreasing pitch
ceases, to the boss, the blades are made of or provided with an irregularly decreasing
pitch, the rate of irregularity of decrease increasing as it approaches the boss; as
for instance, the rate, for each unit of successive distance towards the boss, may be
two or three to one.
By the above construction, that part of the blade nearest the boss acts upon the
water in such a manner as to diminish churning or carrying round of water by the
propeller, and does not act as to cause any negative action as regards the passage
of the ship through the water, and at the same time enables the parts of the blades
further from the boss to have a more effective action upon the water, and so
providing a more effective propelling force aft.
The drawings hereto annexed illustrate my invention diagrammatically.
In Figure 1 there is illustrated the first stage or step of the mode of setting out
of the propeller. In this diagram c, c, is the centre of the propeller, and the
distance p on it represents the pitch of a propeller, wherein it is assumed that such
pitch is equal to the actual distance the ship, to which the propeller is to be fitted,
is to travel in one revolution thereof,-i.c., where the propeller is assumed to be
capable of working without any slip. On one end of this distance on the line c, c,
the vertical line is erected, the length of which represents the radius of the
propeller blade. The line is marked off with the ordinates 1. 2. 3. 4. 5. 6.
dividing the blades radially into a number of sections of equal length; and
aa aa a³ are lines representing the pitch angles of the blade at these points.
In the outer part of the blade,i.e. the part to be of the regularly decreasing
pitch (which in the case given is taken between the ordinates 6 and 3) the pitch
angle lines as a a a³ are, in the ordinary manner of setting out propellers, carried
between the points of intersection of the ordinates 6, 5, 4, and 3, with the vertical
line r, and the central point_x. As regards the inner part of the blade, viz. the
part having the irregular decreasing rate of pitch, the decrease of pitch at
ordinate 2 is taken at one third of the assumed slip of the propeller (referred to
hereafter with reference to Figure 2) and this is marked off by the vertical line
between ce and ordinate 2 giving the horizontal p, and the pitch angle line a³
drawn from the point of intersection of this vertical with ordinate 2, to z.
decrease at ordinate 1 equals 13 the slip, this is marked off by the line between cc
and ordinate 1 giving the horizontal &, the pitch angle line a being drawn from
the point of intersection of the line with ordinate 1, to x. Therefore the rate of
decrease of pitch between ordinates 2 and 1 is three times that of from 3 to 2. This
completes the actual setting out of the pitch as regards its formation or contour, but
not its position as regards the pitch angles or inclinations in relation to the centre
line cc, when on the boss, this being represented in Figure 2.
The
In this Figure 2, to the pitch p is added the amount of assumed slip represented
by the distance p², the distance p* therefore representing the sum of the pitch p
and slip p; and from the centre line, at this distance px, the second vertical radius
line is drawn: the actual position of the blade and its position as regards pitch
angles, in relation to the centre line or axis of the propeller, is determined by this line;
namely, by turning the blade angularly about the point, the pitch angle lines-if
prolonged in passing from the liner will cut the line, and where the pitch
angle line a (that is, the ordinates, on either side of which the two different kinds
of pitches of the blade exist), prolonged as described, meets the point of intersection
of ordinate 3 and the vertical, there the turning of the blade stops, and will
constitute the position of the blade. By this turning of the blade about, the pitches
of the parts of the blade represented by ordinates 4, 5 and 6 will by their being
prolonged until intersecting such ordinates, have become greater than that repre-
sented by ordinate 3, being greatest at the tip of the blade; and the rate of
decrease from the tip to the point represented by ordinate 3 will be a regular
decrease as shewn by the straight dotted line. And, as regards the portion of the
blade between ordinate 3 and the boss, the effect of turning the blade in this
manner, on this part is, that the relative rate of decrease will not be materially

page_text: affected or altered, the joining of the points of intersection being a curve as shewn
by the broken dotted line. Thus as regards the whole propeller, the decrease, as
will be seen by Figure 2 of each blade, is, that from the tip to the point where the
two different rates of change of pitch meet, the rate of decrease is regular, and
from this point inwards, it is irregular and increasing, for each unit of distance
inwards.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
:-
1. The herein described improved propeller, that is to say, a propeller having at
the outer part, a decreasing pitch, the rate of decrease of which is regular per unit
of distance inwards, and at the inner part a decreasing pitch, the rate of decrease of
which per unit of distance towards the boss, is an increasing irregular one;
substantially as herein set forth.
2. A screw propeller wherein the pitches or formations of the blades are arranged
and combined as herein set forth with reference to the drawings.
Dated this 13th day of October 1894.
CHEESBROUGH & ROYSTON, Fels. Chart. Inst. P.A.,
15, Water Street, Liverpool.