IMPROVE- MENTS IN SCREW PROPELLERS
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by the said Henry Hardy at the Office
of the Commissioners of Patents on the 1st August 1882.
HENRY HARDY of 43 North Pitt Street Edinburgh, Cabinet Maker. " IMPROVE-
MENTS IN SCREW PROPELLERS"
The object of my said invention is to provide screw propellers for propelling
ships & other floating vessels which shall be more efficient than those at present
in use; giving a larger per centage of useful effect; being also simple in construction
of great strength and easy to repair if damaged.
I construct my said improved propellers (by preference) with four blades
or propelling surfaces. Each blade is supported and held in position by two
radial arms
or spokes, one forward & one aft which spokes are attached to
the central boss by being cast therewith, keyed rivetted bolted or otherwise
attached thereto. The blades are annular plates keyed rivetted bolted or cast in,
one with the spokes & such blades are as nearly as practicable annular portions
of a true helice. The boss is made of a length suitable to the pitch of the propeller
in order that 4 spokes may be attached to, & radiate from the fore end of such boss,
and 4 other spokes may be in like manner attached to the after end thereof. The
distance of the forward spokes from the after spokes being governed by the angle
or pitch which the blades are required to take with respect to the line of motion of
the vessel.
I prefer to make the length of each blade such that each one considerably
overlaps the other that is to say the lengths of the 4 blades when added together
would exceed the circumference of the circle of which they severally form a part.
The inner portion of the screw area is purposely left free from any screw surface
in order that the water may have free access to and egress from the propeller.
The several parts of the propeller may be constructed of wrought or cast metal

page_text: and are severally made as thin and light as may be consistent with the requisite
strength in order that the friction with the water may be reduced to a minimum.
Propellers constructed in accordance with my said invention, act with great
efficiency, by utilizing the propelling force upon the outer portion of the screw
area where the effect is greater than that of the more central portion and the
reaction of the water is more direct.
.
Although I have described my said improved propeller as consisting of four
blades, I do not confine myself to that number as a greater or less number may be
used and it may not in all cases be necessary to construct the blades to overlap
each other, as the length and surface of each blade is made to suit the particular
requirements of the vessel to be driven, heavy and slow vessels and towing vessels
requiring a larger proportion of propelling blade or "blade area" than light and
swift vessels.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent and
of an Order of the Lord Chancellor filed by the said Henry Hardy in the
Great Seal Patent Office on the 12th February 1883.
HENRY HARDY of 43 North Pitt Street, Edinburgh, Cabinet Maker,
MENTS IN SCREW PROPELLERS
"
"IMPROVE
The object of my invention is to provide screw propellers for propelling ships
and other floating vessels which shall be more efficient than those at present in use,
giving a larger per centage of useful effect; being also simple in construction; of
great strength easy to repair if damaged.
I construct my said improved propellers (by preference) with 'four blades or
propelling surfaces, each blade is supported and held in position by two radial arms
or spokes, one forward and one aft, which spokes are attached to the central boss:
by being cast therewith, keyed, rivetted bolted or otherwise attached thereto.-...
The blades are annular plates, keyed, rivetted, bolted, or cast in one, with the
spokes; and such blades are as nearly as practicable annular portions of a true
helice. The boss is made of a length suitable to the pitch of the propeller in order
that 4 spokes may be attached to and radiate from the fore end of such boss and 4
other spokes may be in like manner attached to the after end thereof.--The
distance of the forward spokes from the after spokes and the length of the boss is
governed by the angle or pitch together with the number of blades; a large number
of blades requiring a shorter boss than a small number....
I prefer to make the length of each blade such that each one considerably over-
laps the other, that is to say, the lengths of the 4 blades when added together
would exceed the circumference of the circle of which they severally-form a part.
The inner portion of the screw area is purposely left free from any screw surface
in order that the water may have free access to, and egress from, the propeller.
The several parts of the propeller may be constructed of wrought or cast metal,
and are severally made as thin and light as may be consistent with the requisite
strength in order that, the friction with the water may be reduced to a minimum.
Propellers constructed in accordance with my said invention act with great
efficiency by utilising the propelling force upon the outer portion of the screw
area, where the effect is greater than that of the more central portion, and the
reaction of the water is more direct.
Although I have described my said improved propeller as consisting of four
blades, I do not confine myself to that number, as a greater or less number may be
used, and it may not in all cases be necessary to construct the blades to overlap
each other, as the length and surface of each blade is made to suit the particular
requirements of the vessel to be driven; heavy and slow vessels, and towing
vessels, requiring a larger proportion of propelling blade, or "blade area” than
light and swift vessels.
In some cases I construct the spokes and blades in such a manner that they are
readily detachable, the spokes being in some cases screwed into the boss and bolted
to the blades with bolts and nuts. In other cases the spokes are made detachable
by means of a central ring or collar to which they are fixed by forging or other
suitable means such collars with the spokes attached thereto being fitted to the
boss and fixed thereto by gibs and cotters.
I also prefer to construct the boss of malleable iron, and of a spherical or barrel
form in order to reduce the resistance as much as possible; but the same may be
otherwise formed.
And in order that my said Invention may be fully understood, reference is

page_text: hereby made to the accompanying drawings, wherein similar letters of reference
indicate corresponding parts in the several figures.
Fig 1 is an elevation of the driving face of a four bladed screw propeller, con-
structed in accordance with my said invention, and Fig 2. is a side view of the
same. The pairs of spokes are preferably in line with each other, as shewn A
propeller with 4 blades requires 8 spokes, and I prefer, in some cases, that the
blades should overlap each other, as shewn; but in other cases it may be advan-
tageous to shorten the length of the blades. Also the position and number of the
spokes may be varied to suit the varied lengths of the blades, a is the axle, b is
the boss, keyed or otherwise securely fixed to the axle. The boss b is enlarged at
its centre in order to reduce the friction, and this boss may be otherwise formed,
in some cases a globular form being adopted.
The mode of securing the spokes to the boss may be varied as herein-before
mentioned In Figs 1. 23 and 4 they are represented as screwed into the boss.
In Figs 5 and 6 the mode of attachment by means of rings or collars is shewn ;
ccare the arms or spokes, a is the axle, 6 is the boss and e e the rings or collars,
held in position by the gib or cotter ff.
The spokes are fixed to the back of the blades, in order that the driving face of
each blade may be smooth and fair, and present no external obstruction to the
water.
Fig 3 is an elevation of a 3 bladed propeller, having 6 spokes and Fig 4 is an
elevation of a two bladed propeller If the blades of Fig 4 are made sufficiently
strong and stiff 4 spokes will be sufficient and an economy will ensue from there
being less friction, but if the blades are thin intermediate spokes may be fitted to
strengthen them and prevent bending from the pressure of the water.
Having thus particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I claim.
The manufacture and use of screw propellers with segmental or peripheral
driving blades in the manner substantially as hereinbefore described and shown on
the drawings, or any mere modification thereof.
In witness whereof I the said Henry Hardy have hereunto set my hand and
seal this twenty ninth day of January in the year of our Lord One thousand
eight hundred and eighty three.