An Improved Screw for Propelling Ships, for Pumps, and for other like Purposes.
Year: 1889

page_text: Date of Application, 13th Nov., 1889
Complete Specification Left, 7th Aug., 189C-Accepted, 4th Oct., 1890
PROVISIONAL SPECIFICATION.
An Improved Screw for Propelling Ships, for Pumps, and for other
like Purposes.
GEORGE JOHN STEVENS of 95 Falmouth Road New Kent Road, in the County of
London Engineer do hereby declare the nature of this invention to be as follows:-
According to this invention in order to generate the screw surface of a screw pro-
pellor or screw to be used for pumping or forcing fluids I take a tractrix curve, that
is, a curve the length of whose tangents to a given straight line is constant, and cause
this curve to revolve uniformly around the given straight line, which is an asymptote
to the curve, and at the same time traverse along it at an uniform rate. A curved
screw surface is thus generated having the properties that any circles described in
planes at right angles to the axis, and having their centres on the axis will meet the
screw surface at a constant angle.
And any intersection of this surface in any plane at any angle if caused to revolve
and traverse as before will give me exactly the same surface, but if I cause the said
revolve at a variable rate I get n
intersection to traverse at a different rate- {and}
surface giving me different properties entirely.
Some of the variations being as follows.
1st. To be a constant angle from periphery to axis, and to vary in direction of
rotation.
2nd. To vary from periphery to axis as well as in directing of rotation.
Also the curve line used for generating the screw surface may be supplemented by
a straight continuation: that is: the root of blade being of the nature of a scroll and
the outer part of blade generated by a straight (or nearly so) line which may be at
any angle to the axis, or conversely.
Dated this 13th day of November 1889.
COMPLETE SPECIFICATION.
An Improved Screw for Propelling Ships, for Pumps, and for other
like Purposes.
GEORGE JOHN STEVENS 95 Falmouth Road New Kent Road S.E. 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 in order to generate the screw surface of a screw pro-
peller or screw to be used for pumping or forcing fluids, I take a tractrix curve, that
is, a curve the length of whose tangents to a given straight line is constant, and cause
this curve to revolve uniformly around the given straight line, which is an asymptote
to the curve, and at the same time traverse along it at an uniform rate. A curved
screw surface is thus generated having the properties that any circles described in
planes at right angles to the axis, and having the centres on the axis will meet the
screw surface at a constant angle.
Any intersection of this surface in any plane at any angle if caused to revolve and

page_text: and
or
traverse as before will give me exactly the same surface, but if I cause the said inter
section to traverse at a different rate
giving me different properties entirely. Some of the variations being as follows-
1st. To be a constant angle from periphery to axis, and to vary in direction of
rotation.
{a } revolve at a variable rate I get a surface
2nd. To vary from periphery to axis as well as in direction of rotation.
Also the curved line used for generating the screw surface may be supplemented by
a straight continuation; that is: the root of blade being of the nature of a scroll and
the outer part of blade generated by a straight (or nearly so) line which may be at
any angle to the axis, or conversely.
The tractrix curve is an envelopement of a set of lines, these lines are the traces or
joins of a plane set at a fixed angle rotating and moving upon the plane of the curve
so that the said angle shall also remain fixed in relation to all corresponding circles
about the asymptote to the curve while the plane of the curve is rotating about and
traversing along the said asymptote.
If I take a straight line as an axis and the said tractrix curve, the said straight line
will be the asymptote-I will cause this curve to rotate and traverse along the
said axis.
Now the said curve may traverse along at a variable rate while the rotation may be
at an uniform rate, I have now (so to speak) an envelopement or helical surface
generated by the one way spread of the said curve.
Now suppose I cut this envelopement or spread by a plane perpendicular to the
axis, the intersection or join will be a spiral curve lying in the said plane.
Let the said variable traverse commence at V=0 and finish at V=co I get the
complete envelopement of this particular curve.
Also if 1 cause the said plane to move from end to end of the said envelopement
the join or intersection with the said envelopement will present itself as continually
changing from {(when V=O) = circles of varying dimensions} to {(when V=∞)=
straight line in radial directions} these are the limiting values.
But any intersection between the limits will be spirals of varying dimensions.
Take any plane in which the said axis will lie, the plane so taken will intersect the
envelopement, the join between the said plane and envelopement will be the aforesaid
transcendental or tractrix curve.
Now let this plane make one complete turn about the axis, the spread or pencil of
curved lines formed in doing so will generate a close and continuous surface. Let
this spread or surface be placed in any position along the aforesaid axis so as to form
a join or intersection with the helical envelopement (as formed by the two aforesaid
motions) the angle made by the intersection or join of the two surfaces (one generated
by rotation only and the other generated by rotation and traverse) will be constant
and similar at any and every point in the aforesaid join.
For the purpose of the developement of surfaces for the propulsion of vessels and
other like purposes I will take any or all the aforesaid intersections of the before-
mentioned helical envelopement in any plano that may intersect and use one or more,
either separately or together, also in combination with a
line may be one of any set of lines that does envelope the said intersection.
straight line in part, which
1 also devolope a helical surface in the following manner; that is: by the generating
curve (while rotating and traversing as before-mentioned) to vary in dimensions,
thereby producing a conical helix which is treated in the same way as the before-
mentioned helical developement, that is to say: I will cut this conical helix by planes
and use the curves so produced to develope propeller blade as before-mentioned.
Having described how I develope these particular curves I will now proceed to
show how I apply the aforesaid curves for the developement of propeller blades.
4
50
I will take progressive sections, joins, or spirals, and place them in the position I
intend them to occupy as sections of blade, that is to say, the surface or shape shall be
generated by the successive or progressive intersections or joins of either of the 5

page_text: aforesaid cylindrical and conical helical surfaces when cut by planes as before-
mentioned.
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:
The construction and developement of screw surfaces for propelling ships, for pumps,
and for other like purposes, substantially as herein before described.
Dated this 7th day of August 1890.
GEORGE JOHN STEVENS.