IMPROVEMENTS IN SCREW OR OBLIQUE-BLADED PROPELLERS
Year: 1878

page_text: LETTERS PATENT to William Glass Wrench, of Glasgow, in the County of
Lanark, North Britain, Engineer, for the Invention of "IMPROVEMENTS IN
SCREW OR OBLIQUE-BLADED PROPELLERS.”
Sealed the 20th August 1878, and dated the 1st March 1878.
PROVISIONAL SPECIFICATION left by the said William Glass Wrench at the
Office of the Commissioners of Patents on the 1st March 1878.
WILLIAM GLASS WRENCH, of Glasgow, in the County of Lanark, North Britain,
Engineer. "IMPROVEMENTS IN SCREW OR OBLIQUE-BLADED PROPELLERS."
This Invention has for its object to improve the form of screw or oblique-bladed
propellers with the view of obtaining increased efficiency.
The improved propeller is by preference made with three blades, although the
improved construction is applicable with other numbers of blades. The boss or
hub is of a spherical, or spheroidal, or ellipsoidal, or pear-like form, but when the
blades are not cast in the same piece with the boss flat facets are formed on the
boss, parallel, or nearly parallel, to planes passing through the axis.
A strong stud
projects from the centre of each facet, and on this stud the root of the blade is
secured by a screw nut or otherwise, other smaller studs or bolts being employed
to fix the blade in the proper position angularly on the centre stud. Each blade
is on its acting face in the form of a quadrant or less part of a cylindrical or
approximately cylindrical band having on the back a graduated thickening, giving
the necessary strength, but with sharp edges, the root of the blade having on its
inner side a flat surface, which is tangential to its cylindrical surface, and which
fits on the facet of the boss. Each blade is set on its stud, so as to lie aft there-
from at an angle between the fore-and-aft position and the position at right angles
to the shaft, the effective pitch depending on the angle at which the blade is set,
and which may be varied in different cases; or the angle of the blades of the same
propeller may be altered until the best position is found by trial.

page_text: The propeller with the blades shaped in the manner herein-before described may
be cast or otherwise formed all in one piece, and instead of each blade being a
cylindrical quadrant it may be otherwise curved; or it may have a flat or straight
form, making an angle with the root part.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said William Glass Wrench in the Great Seal Patent Office on the 30th
August 1878.
WILLIAM GLASS WRENCH, of Glasgow, in the County of Lanark, North Britain,
Engineer. "IMPROVEMENTS IN SCREW OR OBLIQUE-BLADED PROPELLERS."
My said Invention has for its object to improve the form of screw or oblique-
bladed propellers with the view of obtaining increased efficiency.
My improved propeller is by preference made with three blades, although the
improved construction is applicable with other numbers of blades. The boss or
hub is of a spherical, or spheroidal, or ellipsoidal, or pear-like form, but when the
blades are not cast in the same piece with the boss flat facets are formed on the
boss, parallel, or nearly parallel, to planes passing through the axis. Each blade
is on its acting face in the form of a quadrant or less part of a cylindrical or
approximately cylindrical band, having on the back a graduated thickening, giving
the necessary strength, but with sharp edges, the root of the blade having on its
inner side a flat surface, which is tangential to its cylindrical surface, and which
fits on the facet of the boss. Each blade is set on its stud, so as to lie aft there-
from at an angle between the fore-and-aft position and the position at right angles
to the shaft, the effective pitch depending on the angle at which the blade is set,
and which may be varied in different cases; or the angle of the blades of the same
propeller may be altered until the best position is found by trial.
The propeller with the blades shaped in the manner herein-before described may
be cast or otherwise formed all in one piece, and instead of each blade being a
cylindrical quadrant it may be otherwise curved; or it may have a flat or straight
form, making an angle with the root part.
And in order that my said Invention and the manner of performing the same
may be properly understood, I hereunto append a Sheet of explanatory Drawings
to be herein-after referred to, and representing a screw or oblique-bladed propeller
as made with my improvements. In these Drawings the same reference numerals
are used to mark the same or like parts wherever they are repeated.
Figures 1 and 2 on the accompanying Sheet of Drawings are side and front or
forward elevations of my improved propeller.
Figure 3 comprises several sections of one of the blades at different distances
from the boss.
Figure 4 is a cross section of the boss.

page_text: And Figures 5 and 6 are elevations of one of the blades as at right angles to
each other.
The dotted lines in Figure 6 indicate the parts at which the sections in Figure 3
are supposed to be taken. In this example the propeller is fitted with three blades,
to receive which the boss 7 is formed with three facets, which are equally inclined
to each other, and each parallel to a plane passing through the axis of the shaft 8.
Each facet on the boss is formed with a small central projection or boss 9, on which
the root 10 of the blade is fitted, so that it can turn so as to be set in a suitable
angular position.
The best angular position for the blades may be found by trial, and each blade
may then be fixed by its root 10 on a facet of the boss 7 by means of a central
screw pin or bolt 11, and a number of smaller screw pins or bolts 12, the latter
being applied, as shown, round the main screw pin or bolt 11. Each blade 13 is of
a curved form, its propelling face (for driving the ship ahead) having the form of a
quadrantal cylindrical band, whilst the necessary strength is imparted by making
the different parts of the blade of the sections indicated in Figure 3.
The blades may be cast or otherwise formed of the sections shown entirely of
metal; or they may consist of comparatively thin blades of metal with strengthening
ribs on the forward non-propelling surface, the cavities formed by the ribs being
filled up flush with wood or other light material.
If the blades were set on the boss facets in fore-and-aft positions the propeller
would, in rotating, carry them edgeways through the water, and if they were set
at right angles to the fore-and-aft position they would, in rotating, act like fan
blades. In neither position would any appreciable propelling effect be produced,
but on the blades being set intermediately between the two positions their after
surfaces assume oblique attitudes, which cause a very efficient propelling action to
be attained with extremely little, if any, divergency of the water driven aft.
The propeller can be made right-handed or left-handed with the same blades by
suitably setting these on the boss.
Having thus particularly described my said Invention and the manner of per-
forming the same, I have to state that I do not restrict myself to the precise details
herein described or delineated, but that what I believe to be novel and original, and
claim as the Invention secured to me by the herein-before in part recited Letters
Patent is, the constructing of screw or oblique-bladed propellers with blades shaped
and placed substantially as herein-before described.
In witness whereof, I, the said William Glass Wrench, have hereunto set my
hand and seal, this Fifteenth day of May, in the year of our Lord One
thousand eight hundred and seventy-eight
▸ Witness,
EDMUND HUNT,
Patent Agent,
Glasgow.
W. G. WRENCH. (L.B.)