IMPROVEMENTS IN SCREW-PROPELLERS
Year: 1879

page_text: PROVISIONAL SPECIFICATION left by James Newall and George William
Newall at the Office of the Commissioners of Patents on the 31st December
1879.
"
JAMES NEWALL and GEORGE WILLIAM NEWALL, both of Canning Town, in the
County of Essex. ་་ IMPROVEMENTS IN SCREW-PROPELLERS."
This Invention has reference to improved arrangements of construction of screw
propellers on the fish tail principle, which are provided with new and simple
means of feathering and altering the pitch of propeller blades.
Previous feathering screw propeller blades when altered or set to a given pitch
remained at this set pitch during the will of the operator, and where either worked,
altered, or feathered from the dock of the vessel where fitted, by means of the rack
and pinion, screw and hand wheel, or by any motion whatever, being under control
of the operator apart from the screw propeller itself.
Now our arrangements for feathering or altering the pitch of the blades are not
under the control of anything or anyone beyond the altering of the blades and
feathering of the same by the mechanism arranged in the boss of the propeller, the
feathering and pitching of the blades being self acting. More or less pitch can be
given to the blades by the elongevity of the holes in the flange at the root of the
blade. At each revolution of the propeller the blades alternately move from a
fine pitch while turning the top centre or through the water above the centre of
the shaft, and increasing the pitch while turning the bottom centre, or working
through the useful water below the centre line of the shaft, operated by levers fixed
on the lower end of the blades in connection with connecting-arms and rollers,
which said rollers run on a smooth eccentric faced cam fixed to the stern post of the
ship. Our Invention further consists in combining the arrangements we employ
with a lifting frame, by means of which the propeller may be raised to the deck of
he vessel when required.
The means of carrying out our Invention mainly consist of,-
First. In the case of a propeller having two blades a large globe or boss in
liametor, say, about one third the diameter of the propeller, well fitted on the stern
r propeller shaft in usual manner, and so arranged that two blades of any form,
hape, or arrangement (or any movable existing propeller blades can be fitted to
aid boss if required, if formed or constructed with a flange at root of blade for
ecuring same to boss of propeller). Through the centre of the boss, and at right
IPrica 201

page_text: angles to the centre of the propeller shaft, aro fitted two short journals with thick
flanges for securing the flange of the blade to by studs or nuts. At the end of
these journals is fixed a double lever; this double lever is placed round the propeller
shaft and gives motion to the two journals, so altering the angle the surface of the
blades makes with the line of shafting. Attached to this double lever are two
short arms, with at the end of each a roller or wheel, the opposite ends of the arms
boing jointed by a suitable pin to each end of the double lever working the blades.
To the stern post of the ship and fitted round the propeller shaft is bolted on and
firmly secured an eccentric faced cam with a turned face. This face may be angled
or flat, or the rolling face may be at right angles to the centre line of two arms
that project out of the boss through two holes. This eccentric faced cam fitted to
the stern post actuates the two arms which project out of the end of the boss,
causing the double lever to oscillate fore and aft of the propeller shaft through a
distanco equal to the eccentricity of the cam. By this mechanism as the propeller
revolves the blade turning the bottom centre into deep water increases its pitch to
a maximum, and on rising again over the shaft into shallow or water that is moving
with the ship the blade on the top reaches a minimum pitch and cuts or feathers
the water instead of lifting it like a scoop, as in the present arrangement of
the screw propeller. With a screw propeller having four blades the boss is slightly
elongated, and consists of three separate parts fitted with four journals similar to
those for two blades at right angles to each other, and at right angles to the centre
of the propeller shaft. Two double levers are fitted in the boss with their similar
arms and rollers as in the two-bladed propeller with an eccentric faced cam fitted
at each end of the boss, one on the stern post, and one fitted to the rudder or false
stern post, each actuating the lover and two of the blades independently of the
other. Each blade of the propeller can be arranged and made to work from, say,
seven feet pitch, more or less, when the blade is on the top centre to, say, twenty
six feet pitch, or even more, when the blade reaches the bottom centre or lowest
point in its revolution, and so on at each revolution, the blade feathering from seven
to twenty six feet pitch, cutting the water at the top or near the surface while the
greater pitch is taking place in the more solid and useful water below the centre of
the shaft.
By this arrangement of the double levers and arms a thrusting back or lashing
motion twice every revolution of the two-bladed propeller, and four times every
revolution of the four bladed screw propeller is given to the water as 'each blade
moves from a fine to a coarse pitch on every downward stroke of the blades while
it feathers from a coarse to a fine pitch on the upward stroke, the motion of the
propeller blades resembling the motion of the thrust or lash on the back water by
the tail of a fish when moving forward.
Sometimes we cast a shank or journal to the flange of each blade; this shank is
fitted and keyed into the double lever. A. set screw also secures the shank of the
blade working in the journals of the boss to the double levor.
To each short arm may be fitted at the back of the roller before described other
roller or rollers, each roller revolving and touching the other. As the outer roller
working on the cam turns on the pin it actuates the next similar roller diminishing
the friction and wear on one pin to two or more pins.
The important point in this Invention is the continuous feathering action of the
blades at every revolution of the propeller.