IMPROVEMENTS IN SCREW PROPELLERS
Year: 1879

page_text: PROVISIONAL SPECIFICATION left by the said James Skinner at the
Office of the Commissioners of Patents on the 3rd March 1879.
JAMES SKINNER, of South Shields. "IMPROVEMENTS IN SCREW PROPELLERS."
My Invention relating to improvements in screw propellers consists:--First. In
BO forming the propeller blades that a circumferential section at any part thereof
shall be convex on the after or propelling face in lieu of being straight as in a true
screw or concave as in what is known as Woodcroft's screw. As the convexity of
the after or propelling face is increased the convexity of the opposite face will be
reduced until they may become equal or nearly equal to each other. The result of
this will be that the pitch of the propelling face will be greatest at the forward or
leading edge, and less at the after or following edge, and the edge resistance will
be greatly diminished, and the efficiency of the propeller increased thereby.
Secondly. In so forming the leading edges of the blades that they are sharpened
partly from the after or propelling face as well as from the forward face, by which
means they will assume throughout the form of a knife edge rather than a chisel
edge, and will pass through the water with less resistance.
Thirdly. In forming the after or propelling face with circumferential ribs or cor-
rugations of suitable number and size in lieu of the same being plain and smooth,
the said ribs or corrugations preventing the water acted on by the propeller
acquiring a centrifugal motion.
Fourthly. In the application of all or any of these improvements together or
separately to what would otherwise be an ordinary screw propeller of any usual or
well known type.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said James Skinner in the Great Seal Patent Office on the 3rd
September 1879.
JAMES SKINNER, of South Shields.
"IMPROVEMENTS IN SCREW PROPELLERS."
My said Invention relates to improvements applicable separately or in any
required combination to screw propellers of any usual or well known type, the
Price AdI

page_text: object of such improvements being to diminish the resistance to the motion of the
propeller through the water, and thereby and otherwise increase its efficiency.
And in order that my said Invention may be fully understood I shall now proceed
more particularly to describe the same, and for that purpose shall refer to the
several Figures on the annexed Sheet of Drawings, the same letters of reference
indicating corresponding parts in all the Figures.
Figure 1 of the accompanying Drawings represents a front elevation of a screw
propeller constructed according to the said Invention; Figure 2 is a vertical section
of the same; Figures 3, 4, 5, 6, 7, and 8 are transverse circumferential sections of
one of the blades taken respectively along the lines 1-2, 3-4, 5 – 6, 7—8, 9—10,
and 11-12 (Figure 2).
A is the boss of the propeller; B are its blades; a is the forward face thereof;
b, the after or propelling face; c, the leading edge of the same; d, the after or
following edge; and e, the pitch line.
My said Invention consists,-
First. In so forming the propeller blades B that a transverse circumferential
section at any part thereof shall be convex on the after or propelling face b, as
shewu in Figures 3 to 8, in lieu of straight as in a true screw, or concave as in what
is known as Woodcroft's screw. As the convexity of the after or propelling face b
is increased the convexity of the opposite face a is reduced relatively to ordinary
propellers until the two faces become equal or nearly equal to each other. By
means of this arrangement the pitch of the propelling face b will be greatest at the
forward or leading edge c, and less at the after or following edge d, and the edge
resistance will be greatly diminished, and the efficiency of the propeller increased
thereby.
Second. In so forming the leading edges c of the blades B that they are sharpened
partly from the after or propelling face b as well as from the forward face a (see
Figures 3 to 8), by which means they will assume throughout the form of a knife
edge rather than a chisel edge, and will pass through the water with less
resistance.
Third. In forming the after or propelling face b with ribs f circumferentilly of
suitable numbers and size, examples of which are shown in Figures 1 and 2, in lieu
of the said face being plain and smooth, the said ribs having the effect of preventing
the water acted on by the propeller acquiring a centrifugal motion.
Having now described and particularly ascertained the nature of my said
Invention, and the manner in which the same is or may be used or carried into
effect, I would observe in conclusion that what I consider to be novel and original,
and therefore claim as the Invention secured to me by the hereinbefore in part
recited Letters Patent is,-
The employment in screw propellers of the improvements herein set forth either
separately or in combination, substantially as hereinbefore described.
In witness whereof, I, the said James Skinner, have to this my Specification
set my hand and seal, this Second day of September, One thousand eight
hundred and seventy nine.
JAMES SKINNER. (L.S.)