IMPROVEMENTS IN SCREW-PROPELLERS AND METHOD OF DRIVING
Year: 1878

page_text: LETTERS PATENT to Middleton Pratt, of 23, Rood Lane, in the City of London,
Engineer, for the Invention of "IMPROVEMENTS IN SCREW-PROPELLERS AND
METHOD OF DRIVING."
Sealed the 27th May 1879, and dated the 29th November 1878.
PROVISIONAL SPECIFICATION left by the said Middleton Pratt at the Office
of the Commissioners of Patents on the 29th November 1878.
MIDDLETON PRATT, of 23, Rood Lane, in the City of London, Engineer. "IM-
PROVEMENTS IN SCREW-PROPELLERS AND METHOD OF DRIVING."
The object of my Invention is to apply dual or multiple screw propellers to tor-
pedoes, launches, or to vessels of any description, in which a new and improved
method of driving is adopted, and also the application of dual or multiple balanced
screw propellers under an improved system of mounting and driving to facilitate
steerage, propulsion, economy, and ease of repair.
First. I apply a dual propeller with blades respectively of right and left handed
pitch to the same central axis, but of which one screw only is fixed in any suitable
manner to the driving shaft. The other screw is caused to revolve upon a support
in the same axis as the driving shaft, fixed either to the vessel or to the stern post.
The revolution of this latter screw is effected by a system of three or more bevil or
mitre wheels, of which one is fixed to or part of the first mentioned screw attached to
the driving shaft. This wheel gives motion to one or more intermediate carrier bevil
wheels fixed in a stationary position by the fixed support before referred to. These
carrier wheels thus transmit the rotation of the driving shaft, propeller, and bevil
wheel all attached together to the other or dual propeller in an opposite direction
through another bevil wheel attached thereto. All these bevil wheels, fixed support,
and carrier may be conveniently contained in and covered by an external hub or
shell.

page_text: This dual arrangement of propeller may be multiplied into as many series in the
same axis as may be found convenient.
Second. I further apply my balanced dual propeller driven from the centre by two
vertical driving shafts through another hollow, vertical, or supporting shaft by a
somewhat similar set of bevil driving gear as before described. In this case the two
outside bevil wheels are fixed to their respective propellers and the driving bevil
wheels are those between, fixed to the two vertical shafts respectively.
I may substitute for these two vertical shafts and bevil wheels either a chain,
band, or cords operated from a pulley or pulleys on the engines above, or by ap-
plying vertical engines to drive the horizontal shaft or shafts direct by connecting
rods or cranks, all or part of which may be enclosed in the vertical hollow sup-
porting shaft. In this latter case the pitch of the dual screws will be in the same
direction.
Third. I may adapt my before described balanced dual propeller, either driven by
gearing, bands, or cranks direct, to a compound pivoting frame or supporting shaft
which pivots on its vertical axis and is formed at the upper end into a circular table
upon which the engines may be fixed. The whole driving apparatus is thus capable
of turning on its vertical axis with the propeller, and is self contained. To prevent
friction the table may be supported and guided by suitable rollers or other anti-
friction appliances.
This arrangement will prevent the working strains between the engine and pro-
peller from affecting the steering gear, which may now be used to pivot the propeller
and table complete to any required angle.
By preference I use with this steering propeller one form or other of my improved
high speed motors, as applied for in my application, Numbered, 4734 on 21st
November 1878. If desired the engines operating the above steering propeller may
be made to reverse, so as to limit the angle through which the propeller would
otherwise have to rotate to reverse the vessel, or a rudder may be used in com-
bination with the action of the steering propeller in order to facilitate the handling
of the vessel.
It may be desirable to so proportion the size of the upper table or frame that the
propellers below may pass readily through the opening for the frame above, so
that the whole propelling and driving apparatus may be lifted altogether
through a hatch in the upper deck without unshipping any part except pipe
connections.
If condensing engines are used I may arrange my condensers within the vertical
pivoting frame or table, so that the admission for cold water and exit for hot water
may pass through the said vertical hollow frame or post.
In some classes of vessels which may be required to move at an angle or right
angles to their longitudinal axis or universally in any direction,-
I may apply my self contained driving and steering propellers at each end of or
in several positions on the vessel, so that motion may be easily obtained to rotate
round its own centre or to move broadside on to its longitudinal axis, or in any
possible direction.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Middleton Pratt in the Great Seal Patent Office on the 29th May
1879.
MIDDLETON PRATT, of No. 23, Rood Lane, in the City of London, Engineer.
"IMPROVEMENTS IN SCREW PROPELLORS AND METHOD OF DRIVING.",
The object of my Invention is to apply dual or multiple screw propellors to tor-
pedoes, launches, or to vessels of any description, in which a new and improved
method of driving is adopted, and also the application of dual or multiple balanced
screw propellors under an improved system of mounting and driving to facilitate
steerage, propulsion, economy, and ease of repair.
1st. I apply a dual propellor, with blades respectively of right and left handed
pitch, to the same central axis, but of which one screw only is fixed in any suitable
manner to the driving shaft. The other screw is caused to revolve upon a support
in the same axis as the driving shaft, fixed either to the vessel or to the stern post.
The revolution of this latter screw is effected by a system of three or more bevil
or mitre wheels, of which one is fixed to or part of the first mentioned screw attached
to the driving shaft. This first wheel gives motion to one or more intermediate
carrier bevil wheels fixed in a stationary position by the fixed support before referred
to. These carrier wheels thus transmit the rotation of the driving shaft, propeller,
and bevil wheel, all attached together to the other or dual propeller in an opposite
direction through another bevil wheel attached thereto. All these bevil wheels,
fixed support, and carrier, may be conveniently contained in and covered by an
external hub or shell.
This dual arrangement of propeller may be multiplied into as many series in the
same axis as may be found convenient.
2nd. I further apply my balanced dual propeller driven from the centre by
two vertical driving shafts through another hollow vertical or supporting shaft
by a somewhat similar set of bevil driving gear as before described. In this
case the two outside bevil wheels are fixed to their respective propellers, and
the driving bevil wheels are those between, fixed to the two vertical shafts
respectively.
I may substitute for these two vertical shafts and bevil wheels either a chain,
band, or cords operated from a pulley or pulleys on the engines above, or by ap-
plying vertical engines to drive the horizontal shaft or shafts direct by connecting
rods and cranks, all or part of which may be enclosed in the vertical hollow sup.
porting shaft.
In this latter case the pitch of the screws will be in the same
direction.
3rd. I may adapt my before described balanced dual propeller, either driven by
gearing, bands, or cranks direct, to a compound pivoting frame or supporting shaft
which pivots on its vertical axis and is formed at the upper end into a circular table
upon which the engines may be fixed. The whole driving apparatus is thus capable
of turning on its vertical axis with the propeller and is self contained. To prevent
friction the table may be supported and guided by suitable rollers and other anti-
friction appliances.
This arrangement will prevent the working strains between the engine and pro-
peller from affecting the steering gear, which may now be used to pivot the propeller
and table complete to any required angle.
If desired the engines operating the above steering propeller may be made to
reverse, so as to limit the angle through which the propeller would otherwise
have to rotate to reverse the vessel; or a rudder may be used in combination
with the action of the steering propeller in order to facilitate the handling of the
vessel.
It may be desirable to so proportion the size of the upper table or frame that the
propellers below may pass readily through the opening for the frame above, so
that the whole propelling and driving apparatus may be lifted altogether

page_text: through a hatch in the upper deck without unshipping any part except pipe
connections.
If condensing engines are used I may arrange my condensors within the vertical
pivoting frame or table to that the admission for cold water and exit for hot water
may pass through the said vertical hollow frame or post.
In some classes of vessels which may be required to move at an angle or right
angles to their longitudinal axis or universally in any direction I may apply
my self contained driving and steering propellers at each end of or in several
positions on the vessel, so that motion may be easily obtained to rotate round
its own centre or to move broadside on to its longitudinal axis, or in any possible
direction.
And that my Invention may be the more clearly understood I now proceed to
explain the Drawings hereunto annexed, reference being made to the figs. and letters
marked thereon.
Figs. 1 and 2 are longitudinal and transverse sections through the propeller shaft A
driving two dual propellers B and B' by means of my improved apparatus. In the
said Drawing the shaft A is shown hollow as suitable for a torpedo. In a launch or
vessel of any kind this shaft would be solid. In the arrangement as shown the
propeller B is securely screwed or fixed on to the driving shaft A and therefore
revolves with it. The cross-piece is formed of four circular pins or bosses C, C,
C, C, on which are placed four bevil wheels E, E, E, E, so that they can freely
revolve. This cross piece C is screwed or fixed to the stationary continuation
of the shaft D which does not revolve, but is securely fitted and keyed into the
propeller post F.
As the cross-piece C carrying the four bevil wheels is thus rendered immoveable
these wheels rotate by gearing into the face of the driven propeller B. There is
also a corresponding gearing on the face of the propeller B¹ into which the bevil
wheels E engage, so that by their rotation they thus drive the propeller B¹ in the
opposite direction to that of B. The bosses of the propellers B and B are
extended sufficiently to meet over the gearing and thus to enclose it in a suitable
case.
If desired this position of the driving propeller may be reversed, that is to say,
the shaft A may be carried through to drive the farthest propeller, and the cross-
piece C may then be secured to the stern post instead of the propeller post, so as to
drive the inside propeller by the gearing.
Fig. 3 is a longitudinal section through the stern of a vessel showing a pair of
balanced propellers B, B¹, revolving in opposite directions and mounted on a
pivoting frame C which carries the one, two, three, or more cylinders self-contained
upon it.
The cranked driving shaft is shown at E, which passes right down the centre of
the pivoting frame, is supported on a centre and drives the lowest bevil wheel F,
which gears into both faces of the propellers B and B¹. Upon this same crank
shaft E is keyed the highest bevil wheel G, which, gearing through an intermediate
bevil wheel H, drives, in the opposite direction, another bevil wheel K, which is fixed
to or part of another hollow shaft M which passes between the central shaft E and
the outside frame C. At the lowest end of this shaft M is fixed a bevil wheel L
which gears into both faces of the propellers B and B', and as it revolves in
the opposite direction to the central shaft E and pinion F assists the latter in driving
the said propellers.
The upper part of the pivoting frame which contains the driving engines is
capable of easy rotation round its centre pivot by travelling on a sufficient number
of the rollers N. These rollers bear on the guide plate O, and there are also hori-
zontal rollers P fitted in the frame and bearing on the same guide plate O, so as to
ensure perfect stability to the frame C.
The perfect manner in which all working strains are self contained in this frame
and the balanced action of the dual propellers, together with the roller guides, ensure

page_text: perfect ease of action to a steering gear which may be applied in any convenient form
to rotate this frame and the dual propellers.
Fig. 4 shows a general arrangement of pontoon in which, by the steering action
of the above described propellers, the said pontoon may be moved perpendicularly
to its longitudinal axis, so as to lay it easily against a wharf.
Fig. 5 shows general arrangement of a circular battery, which, by the peculiar
action of the above described steering propellers, may be rotated when in action round
its own axis.
From the apparatus herein described I wish it clearly understood that I claim
only,―
1st. The combination of a dual propeller driven in opposite directions by means of
bevil gearing, substantially as herein described.
2nd. The arranging and driving of dual propellers revolving in opposite
directions by means of two vertical shafts one inside the other and both contained in
a pivoting shaft or frame.
3rd. The combination of engines arranged on a pivoting frame for steering
purposes, and driving a pair of dual propellers by the apparatus as herein sub-
stantially described.
In witness whereof, I, the said Middleton Pratt, have hereunto set my hand
and seal, this Twenty fourth day of May, in the year of our Lord One
thousand eight hundred and seventy nine.
MIDDLETON PRATT. (L.S.)