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 16th August
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 were either worked,
altered, or feathered from the deck 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 with 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.
1.
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,
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 the
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
diameter, say, about one third the diameter of the propeller, well fitted on the
stern or propeller shaft in usual manner, and so arranged that two blades of any
form, shape, or arrangement (or any movable existing propeller blades can be
fitted to said boss if required, if formed or constructed with a flange at root of
blade, for securing same to boss of propeller). Through the centre of the boss, and
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at right angles to the centre of the propeller shaft are fitted two short journals,
with thick flanges for securing the flange of the blade to, by studs and nuts. At
the end of these journals is fixed a'double lever.
4
This double lever is placed round the propeller shaft, and givos 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 these arms being 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 oam
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 distance 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 sternpost, each actuating the lever and two of the
blades, independently of the other.
Each blade of the propeller can be so arranged and made to work from, say,
seven feet pitch 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.
The important point in this Invention is the continuous feathering action of the
blades at every revolution of the propeller,