Improvements in Screw Propellers."
Year: 1897

page_text: 66
PROVISIONAL SPECIFICATION.
Improvements in Screw Propellers."
We, ALEXANDER WALLACE DAVIDSON, of Clifton, Craigmore, Rothesay, Bute-
shire, North Britain, Commission Agent, and ANDREW DUTHIE of 4, Hillfoot
Terrace, Bearsden, in the County of Dumbarton, North Britain, Cashier, and
ROBERT BROWN STEWART, Violet Grove House, St. Georges Road, Glasgow,
Commission Agent, do hereby declare the nature of this Invention to be as
follows:-
This Invention relates to Improvements in screw propellers.
According to our Invention the blades are built or cast upon a central boss, and
in outline may be of any convenient shape and number. In thickness from the
boss to the outer edge of the blades they are wedges, and from the leading edge to
the trailing edge across the thrusting face they are also wedges, and those wedges
across the thrusting face and from boss to the outer edge may be either formed
of straight lines or may be cycloidal either of full or hollow lines as may be
most suitable for strength and effect. The leading edge of the back of each blade
is in one plane and this plane commences from the leading edge of the thrusting
face of blade at an acute angle and continues in that plane across the back of each
blade for such distance as shall allow the blade to have sufficient strength when
the plane takes the direction of a retreating plane until it meets the trailing thrust-
ing edge. This retreating plane on the trailing part of the backs of the blades
may be formed of straight lines, or may take the form of a cycloidal curve, full
or hollow, as may be found desirable for strength, free run for water, grace of form,
and such like. The wedge forms of the blades may be taken out of solids which
are sharp or blunt wedges, or parallelograms, or other solids, or have right angles
at their bases, or have equal angles or unequal angles at their bases according to
the range or variety of pitches wanted in the blades. To give range, variety, and
effect to pitches, the blades may be built, or cast on the bosses concentric, or more
or less eccentric, with a point at right angles to the axis of driving shaft, and may
have a rake aft, stand perpendicular, or a forward inclination.
Dated this 13th. day of January, 1897.
We, ALEXANDER WALLACE DAVIDSON, of Clifton, Craigmore, Rothesay, Bute-
5 shire, North Britain, Commission Agent, and ANDREW DUTHIE, of 4, Hillfoot
Terrace, Bearsden, in the County of Dumbarton, North Britain, Cashier, and
[Price 8d

page_text: ROBERT BROWN STEWART, Violet Grove House, St. George's Road, Glasgow,
Commission Agent, 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: —
This Invention relates to improvements in screw propellers.
According to our Invention the blades are built or cast upon a central boss, and
in outline may be of any convenient shape and number. In thickness from the
boss to the outer edge of the blades they are wedges, and from the leading edge to
the trailing edge across the thrusting face they are also wedges, and those wedges
across the thrusting face and from boss to the outer edge may be either formed of
straight lines or may be cycloidal either of full or hollow lines as may be most
suitable for strength and effect. The leading edge of the lack of each blade is
in one plane and this plane commences from the leading edge of the thrusting face
of blade at an acute angle and continues in that plane across the back of each blade
for such distance as shall allow the blade to have sufficient strength when the
plane takes the direction of a retreating plane until it meets the trailing thrusting
edge. This retreating plane on the trailing part of the backs of the blades may be
formed of straight lines, or may take the form of a cycloidal curve, full or hollow,
as may be found desirable for strength free run for water, grace of form, and such
like. The wedge forms of the blades may be taken out of solids which are sharp
or blunt wedges, or parallelograms, or other solids, or have right angles at their
bases, or have equal angles or unequal angles at their bases according to the range
or variety of pitches wanted in the blades. To give range, variety, and effect to
pitches the blades may be built, or cast on the bosses concentric, or more or less
eccentric, with a point at right angles to the axis of driving shaft, and may havo
a rake aft, stand perpendicular, or a forward inclination.
On account of the form and position of the leading edge and back of any modern
propeller blade the thrust got from it is only a compromise between the action of
its back and thrusting side; or, in other words, there is in all modern propeller
blades thrust by the back of the blade in the contrary direction to that of the
thrusting side which amounts to a dragging effort and to power being wasted in
at least two ways.
We propose, so that this compromise or dragging effort and waste of power may
be done away with and an easier driven and more perfect thrusting form of pro-
peller introduced, to form the leading edge of our blade in plane with the back
of the blade and this plane to extend across the back of blade so far as is necessary
for strength when it takes direction till it meets the trailing edge of thrusting
side. With the exception of the actual join of blade to boss where it would be
better for strength that there should be a fillet, we propose to keep the leading edge
in plane with leading part of back of blade from root to tip. The thrusting, side
springs from the leading .edge at as fine an angle as is compatible with strength;
necessarily being of greatest angle at root of blade and growing finer as it reaches
the tip and this can be done in such ratio as will assist to modify the difference
between root and tip speed of blade.
We propose to form our propeller blades out of such solids as will give the most
desirable ratio of pitch between root and tip for any given propeller and also that
we may take a portion, or all, of the desired pitch for any given propeller out of
the wedge form of the blade and the remainder of the pitch desired, if any, by
setting the blade upon the boss with the leading edge and plane of leading part
of back of blade at any desired angle thereby getting a propeller with a fine entrance
and a progressively increasing pressure of the water without undue shock until
the fullest effect of pitch is attained.
To enable us to get improved thrust from our propeller, we propose to form
propellers with blades either concentric or more or less eccentric from a point at
right angles to axis of driving shaft and to do so to any point of eccentricity on
either or both sides of perpendicular to axis of shaft, or angle therefrom, and the
blades may either stand perpendicular to axis of shaft or have rake fore or aft.

page_text: In order that our Invention may be properly understood and readily carried
into effect we have hereunto appended one sheet of Drawings of which
Figure 1 is an end view of one blade of our improved propeller attached to the
boss with sections shaded at various distances from the boss to the tip.
Figure 2 is a similar view of one blade of an ordinary propeller.
A is the shaft and B the boss, C is the leading edge. From the leading edge a
plane is formed extending across the back of the blade so far as is necessary for
strength. The back is then brought round so as to meet the trailing edge D.
One edge of the plane is indicated by the dotted line. E which is carried from root
to tip. By forming the back of the blade with this plane the propeller cuts the
water in such a manner as to cause as little thrust on the back of the blade in the
contrary direction as possible. In the ordinary propeller as shewn in Figure 2
the water at the back of the blade has to force its way round the curve of the back,
and thus a considerable back thrust in the contrary direction is caused.
In order to produce an increased thrust with our improved propeller we may
form our blades so that when attached to the boss they will be more or less
eccentric as shewn in Figure 1.
Having now particularly described and ascertained the nature of our said
Invention and in what manner the same is to be performed, we declare that what
we claim is:-
1. The improved propeller constructed substantially as described.
2. A propeller having the leading edge and leading part of the back of the
blade in a plane so as to cut the water in one line and direction.
3. A propeller having the blades placed eccentrically upon the boss so as to
give a combined lateral and transverse thrust.
Dated this 12th day of Navramhan 1907
BOTTOMLEY & LIDDLE,
154, St. Vincent Street, Glasgow, Applicants' Patent Agents.