IMPROVEMENTS IN SCREW PROPELLERS
Year: 1878

page_text: LETTERS PATENT to Edward James Harland, of Belfast, in the County of
Antrim, Ireland, for the Invention of "IMPROVEMENTS IN SCREW PROPELLERS."
Sealed the 31st January 1879. and dated the 13th August 1878.
Sealed the 31st January 1879, and dated the 13th August 1878.
PROVISIONAL SPECIFICATION left by the said Edward James Harland at
the Office of the Commissioners of Patents on the 13th August 1878.
EDWARD JAMES HARLAND, of Belfast, in the County of Antrim, Ireland. "IM-
PROVEMENTS IN SCREW PROPELLERS."
My Invention consists in so constructing screw propellers that by a special form
of boss and mode of securing the blades thereto a highly elastic or flexible descrip-
tion of blade can be applied that may yield readily to any undue pressure against
the surrounding water, or when in collision with a passing obstacle, as, for instance,
wreckage, quay face, bed of channel, etc., and by such yielding to materially lessen
any sudden strain tending to derange the impelling machinery, as well as being
themselves less liable to become either fractured or disabled, at the same time
offering a minimum of resistance in cleaving the water, yet so simple and inexpensive
in character as to be easily and quickly made, and as readily secured to or removed
from the boss.
The boss is by preference cylindrical or of rather less diameter in the centre than at
the ends, so that its surface may present a straight line in the direction of the angle
that may be fixed for the root of the blade. In this direction keyways are cast or
cut, extending from end to end of the boss, with a taper longitudinally as well as
radially widening towards the centre line of shaft, and for the number of blades
desired.
The blades I make of rolled spring steel, of an equal or nearly thickness, of,
say, about of the diameter of the propeller, such blades after having been cut

page_text: to size and set to the desired pitch and form, and slightly flanged at the root end,
are tempered after the manner of a spring or sword blade.
The root ends of the blades are placed into the double tapered keyways in the
boss, and secured by suitable keys driven in, thus holding the roots of the blades
for their entire width, not only laterally, but longitudinally and radially. A split
pin cotter, or set pin, or other such safeguard either through the boss or the keys
keeps the latter from slacking back, or may be so placed that the ends of the keys.
may then be pared off flush with the ends of the boss so as to lessen the risk of
ropes fouling. Any blade can be readily removed by, simply driving the key out.
The elasticity or flexibility of the blades may be further increased by transverse
corrugations formed in it near its root end.
The propeller may be formed with any desired number of blades. The blades
are made of a uniform thinness throughout, and tapering from the root end to the
tip, so that the root is of considerable width and gives an equivalent of lateral
strength at the root, hitherto provided rather by an increase of thickness. The
uniform taper of the blade also gives a uniform elasticity or flexibility throughout
its length. The extreme thinness of this description of blade, especially towards
the root, reduces to a minimum the large per-centage of propelling power hitherto
lost in the simple passage of the blades through the water.
Spare blades of this description by reason of their extreme lightness and uniform
thickness can be more easily stowed on board, the one within the other, and their
attachment being by a simple key can the more readily be improvised in an
. emergency.
As before stated it is preferred to form the propeller blades of spring steel, but
they may be of other suitable flexible metal. Their surface may be protected by
being wholly or partially covered by any less oxidisable metal, or coated by such
well-known processes as enamelling or glazing, plating, galvanizing, electro-plating,
or with india-rubber, gutta percha, or other such gums, or be otherwise protected.