IMPROVEMENTS IN SCREW PROPELLERS.
Year: 1878

page_text: LETTERS PATENT to Henry James Jackson, of Deptford, in the County of
Kent, Superintendent Engineer to the General Steam Navigation Company,
for the Invention of "IMPROVEMENTS IN SCREW PROPELLERS.'
.
PROVISIONAL SPECIFICATION left by the said Henry James Jackson at the
Office of the Commissioners of Patents on the 28th June 1878.
HENRY JAMES JACKSON, of Deptford, in the County of Kent, Superintendent
Engineer to the General Steam Navigation Company.
"IMPROVEMENTS IN SCREW
PROPELLERS."
My Invention has for object improvements in screw propellers, and is illustrated
in the accompanying Sheet of Drawings, Fig. 1 being a side view, partly in section,
of part of one of my improved propellers; and Figs. 2, 3, 4, 5, and 6 cross sections
of one of the blades taken respectively in the lines 1-1, 2-2, 3—3, 4—4, and
5-5 of Fig. 1.
According to my Invention the radius of the leading edge of the blade is in 'the
proportion of 33 of the diameter of the screw, and the distance of the centre of the
same radius from the axis of the screw equals 25 of the diameter of the screw.
The retiring edge of the blade has a radius equal to 8 of the diameter of the screw
struck from a point situate at a distance equal to 3 of the said diameter from the
screw axis.
The distance from the centre line to the leading edge, at the widest part of the
blade, is slightly in excess of the width from the centre line to the retiring edge, at
the widest part.

page_text: The face of the blade is straight and perpendicular to the axis of the screw. The
diameter of the boss at the centre equals 17 of the diameter of the screw.
As is obvious the width of blade and its form in other respects may be varied
to suit circumstances without departure from the essential characteristics above
mentioned.
.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Henry James Jackson in the Great Seal Patent Office on the 21st
December 1878.
HENRY JAMES JACKSON, of Deptford, in the County of Kent, Superintendent
Engineer to the General Steam Navigation Company. "IMPROVEMENTS IN SCREW
PROPELLERS."
My Invention has for object improvements in screw propellers, and is illustrated
in the accompanying Sheet of Drawings, Fig. 1 being a side view, partly in section,
of one of my improved propellers; and Figs. 2, 3, 4, 5, and 6 cross sections of one
of the blades taken respectively in the lines 1-1, 2-2, 3—3, 4-4, and 5—5, of
Fig. 1.
According to my Invention the radius of the leading edge a of the blade is in
the proportion of 33 of the diameter of the screw, and the distance of the centre of
the same radius from the axis of the screw equals 25 of the diameter of the screw.
The retiring edge of the blade has a radius equal to 8 of the diameter of the screw
struck from a point situate at a distance equal to 3 of the said diameter from the
Ecrew axis.
The distance from the centre line c to the leading edge a at the widest part of
the blade is slightly in excess of the width from the centre line to the retiring edge b
at the widest part.
The face of the blade is straight and perpendicular to the axis e of the screw.
The diameter of the boss fat the centre equals 17 of the diameter of the screw.
As is obvious the width of blade, and its form in other respects, may be varied
to suit circumstances without departure from the essential characteristics above
mentioned.
Having described the nature of my said Invention, and explained the manner in
which I prefer to carry it out in practice, I hereby declare that what I consider to
be novel and original and therefore claim as the Invention secured to me under the
Letters Patent herein-before in part recited is,
•
The constructing screw propellers substantially as herein-before described and
illustrated.
Also formning the leading edge of the blade with a curve whose radius is equal to
33 of the diameter of the screw, the distance of the centre of the same radius from
the axis of the screw being equal to 25 of the diameter of the screw.

page_text: Also forming the retiring edge of the blade with a curve whose radius is equal to
8 of the diameter of the screw struck from a point situate at a distance equal to 3
of the said diameter from the screw axis.
Also forming the blade so that the distance from the centre line to the leading
edge at the widest part of the blade is slightly in excess of the width from the
centre line to the retiring edge at the widest part.
Also making the boss of a diameter at its centre equal to 17 of the diameter of
the screw, all substantially as herein-before described.
In witness whereof, I, the said Henry James Jackson, have hereunto set my
hand and seal, this Twenty-first day of December, in the year of our Lord
One thousand eight hundred and seventy-eight.
HENRY JAMES JACKSON. (L.S.)