AN IMPROVED MODE OF AND APPARATUS FOR ASCERTAINING THE EFFECTIVE PRESSURE OF SCREW PROPELLERS
Year: 1880

page_text: LETTERS PATENT to George Wilhelm Cabjolsky, of Charlottenburg, near
Berlin, Engineer, for the Invention of "AN IMPROVED MODE OF AND
APPARATUS FOR ASCERTAINING THE EFFECTIVE PRESSURE OF SCREW
PROPELLERS."
PROVISIONAL SPECIFICATION left by the said George Wilhelm Cabjolsky
"AN
at the Office of the Commissioners of Patents on the 28th May 1880.
GEORGE WILHELM CABJOLSKY, of Charlottenburg, near Berlin, Engineer.
IMPROVED MODE OF AND APPARATUS FOR ASCERTAINING THE EFFECTIVE PRESSURE
OF SCREW PROPELLERS."
The object of this Invention is to provide a means for ascertaining under
varying conditions the effective pressure exerted by screw propellers.
To attain this end I avail myself of the tendency which the screw shaft has
when driven to move forward in its bearings, and by interposing a yielding
resistance to such motion I obtain a means of indicating the amount of that motion.
A convenient mode of carrying out this principle is to mount the screw shaft in a
thrust block, which is fitted to the bed plate in such a manner that it may move
freely with the propeller shaft in the line of its axis, and by such movement work
an indicator, from the indications of which the total resistance overcome by the
screw may be calculated, as hereinafter described. The bed plate is formed with
an abutment at its forward end to receive a pair of hydraulic cylinders which are
fitted between the thrust block and the abutment. These cylinders are connected
together by a coupling pipe, and are supplied with liquid from a force pump which
serves to hold the plungers of the hydraulic cylinders against the thrust block, and
thereby enable that block to offer a suitable resistance to the forward endway
movement of the propeller shaft. Rising from the coupling pipe is a pipe which
leads to a pressure gauge or recording indicator that marks the pressure of the
liquid within the cylinders. In connection with one of the cylinders is a small
chamber which is closed by a screw plug. The use of this chamber is to provide a
vent for the liquid under pressure, and thereby to reduce the indication made by
the indicator under certain circumstances. By turning the plug by a handle
provided for the purpose, the chamber may be gradually opened to the compressed
Ping G71

page_text: liquid or in place of this contrivance the liquid may be discharged by a valve into
the tank which supplies the force pump.
In working with this apparatus the hydraulic cylinders are first filled by the
force pump, and in the act of filling, the thrust block is forced rearwards to its
normal position. When the screw shaft is set in action it will move forward in
its fixed bearings and carry with it the thrust block, thereby putting pressure upon
the liquid within the cylinders, and causing the liquid to rise in the indicating
tube, and shew by the gauge or other indicator the pressure of the liquid within
the cylinders. If now the pump is again put in action and liquid is driven into
the cylinders sufficient to force back the thrust block, and with it the screw shaft,
to their normal position, a second and higher indication will be marked.
The mean
of the two readings thus obtained will give the proportional effective force of the
screw expended in propelling the ship. A comparison of readings thus obtained,
when the vessel is driven at different speeds, will shew the rate of increase of
resistance due to the increased speed of the vessel. Again, by subtracting from
the mean of the two indications above mentioned the first indication, we obtain as
a result an indication of the amount of power absorbed by the friction of the
screw shaft in its bearings, and by the moving parts used in obtaining the
indications.
It will also be understood that by comparing the results of tests taken at
different periods by this indicating apparatus, any increase in the resistance to the
propelling power due to the straining of the vessel may be readily determined.
Another advantage derivable from this indicating apparatus is, that it provides a
sure test of the efficient mounting of the propeller shaft.
So also by changing the propellers, their relative efficiency may be compared, and
a comparison of the indications of the apparatus applied to ships of various forms
will serve to determine the lines of least resistance.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said George Wilhelm Cabjolsky in the Great Seal Patent Office on the
27th November 1880.
" AN
GEORGE WILHELM CABJOLSKY, of Charlottenburg, near Berlin, Engineer.
JMPROVED MODE OF AND APPARATUS FOR ASCERTAINING THE EFFECTIVE PRESSURE
OF SCREW PROPELLERS."
The object of this Invention is to provide a means for ascertaining under various
conditions the effective pressure exerted by screw propellers.
To attain this end I avail myself of the tendency which the screw shaft has
when driven to move forward in its bearings, and by interposing a yielding
resistance to such motion I obtain a means of indicating the amount of that motion.
A convenient mode of carrying out this principle is to mount the screw shaft in a
thrust block which is fitted to the bed plate in such a manner that it may move
freely with the propeller shaft in the line of its axis, and by such movement work
an indicator, from the indications of which the total resistance overcome by the
screw may be calculated, as hereinafter described.
The thrust block transmits the pressure it receives from the screw propeller to
two hydraulic cylinders arranged at the sides of the screw shaft and the amount
of the pressure of the fluid in the cylinders registered by the indicator.
It is necessary that the thrust of the screw propellor shall be received only by
the thrust block, and that the thrust ring on the stern post, if such be fitted, be
entirely relieved from this thrust. It is also necessary to compensate for and to
ascertain exactly the resistance to friction of the screw shaft when moved in a
fore and aft direction and contrary to that of the thrust of the screw propeller.
This is done by pushing the screw shaft with the thrust block back a small
distance by means of the bydraulic cylinders and a hand pump, and registering the
pressure while this backward motion of the screw shaft is made slowly and steadily,
and also registering the pressure when the screw shaft is allowed to move forward
again.
The thrust ring will of course be relieved of the pressure as soon as the screw
shaft with the thrust block is pushed backwards.
Let P be the effective thrust of the screw propeller; R, the resistance to the
sliding friction of the screw shaft in a fore and aft direction; then is P + R the
pressure that must be exercised by the hydraulic presses to push the screw shaft
with the thrust block in an aft direction; and P R, the pressure which still
remains in the hydraulic cylinders when the screw shaft has been allowed to move
in a forward direction.
-
The arithmetical mean of these two pressures which have been registered by the
indicator is to P, the effective thrust of the screw propeller.
=
It is necessary that the shaft should be free from ridges near the bearings and
the stuffing box Should these however have been formed by long running of the
shaft, they must in that case be removed to enable the screw shaft with the thrust
block to be moved freely about 10 to 15 / (millimetres) in an aft direction.
In the accompanying Drawing, Figures 1 to 4 represent an indicating apparatus
constructed according to my Invention for an engine of 2,800 I. EP.; Fig. 1 being
a side view; Fig. 2, a plan; Fig. 3, a section through the bydraulic cylinder; and
Fig. 4. a section through the thrust block.
A is the plumber block containing the annular bearing as usual; it is fitted with
two longitudinal flanges B and rests on the bed plate C, on which it will be free
to move a short distance in a fore and aft direction as soon as the wedges D, that
can be tightened by the screws E, are removed.

page_text: Wrought iron bars F keep the plumber block from rising on its bed plate.
The fore and aft motion of the screw shaft and thrust block is limited by the
projections G on the bed plate, against which the flanges B press when the
apparatus is not in use, and thus transmit the pressure immediately to the ship in
the ordinary way.
The ends of the flanges B press against the pistons of the hydraulic cylinders H
which are secured by four screw bolts H2 to the abutments I formed on the bed
plate.
The cylinders are of phosphor bronze or of gun metal; they communicate by the
tube F and have therefore to bear equal fluid pressures; they are of equal diameters
and are placed equidistant from the centre of the screw shaft.
"
The pistons H' are shewn in the Drawing it will be understood are "ground in
air tight, but they may be kept airtight by means of the ordinary leather collar
without influencing the correctness of the registered pressure.
The friction of the
leather collars being included in the total resistance to friction of the screw shaft
when moved in a fore and aft direction is eliminated in the above described
manner.
One of the two cylinders is fitted with an indicator O; P is a piston which is
ground airtight into the steel tube O, and is free to compress the helical spring Q
in proportion to the pressure imparted to it from the fluid. The tube O is screwed
airtight in the hydraulic cylinder and receives the fluid pressure through a hole
in the bottom of the cylinder. The spring presses with its base against a flange
fixed to the indicator piston rod and with its top against a cover screwed into a
case formed on the hydraulic cylinder. The upper end of the indicator spindle
passes through the cover and acts on the lever R which works a pencil T sliding
in the prismatic guide arrangement U by means of the guide rod S.
The prismatic guide arrangement is fixed to the bed plate of the thrust block by
two screws.
The area of the indicator piston is of the total area of the two pistons in the
hydraulic cylinders, and the lever R is so constructed that a height of ordinate
of 10 m/m in the diagram represents an effective pressure of one thousand
kilograms.
The drum V which carries the paper for receiving the indications is driven by a
worm a which consists of two halves screwed together and placed on the screw
shaft. This worm gears into the worm wheel a¹ on the drum spindle c.
The drum spindle with the drum can be put out of gear by means of the slide
rest arrangement d formed on the bed plate of the thrust block.
The tightening screw e which moves in a slot of the guide bar limits the length
of the disconnecting movement and permits of the drum spindle being fixed in the
required place.
The drum is loose on the spindle and can be fixed to the latter by a butterfly
nut. When the drum has to be taken off its spindle for the purpose of putting on
or removing a strip of paper the butterfly nut has to be turned one quarter of a
circle.
A wooden lath W is let into the drum for the purpose of fixing the strips of
paper by means of drawing pins.
The number of teeth in the worm wheel and worm are so arranged that the
drum will complete one rotation in about one minute.
A hydraulic pump is fitted to the left hydraulic cylinder for forcing the screw
shaft backwards and forwards in a fore and aft direction. The plunger M of this
pump is hollow, and can be screwed in and out of the tube formed on the cylinder
by the screw N, and it is moreover kept airtight by means of a leather collar.
The screw spindle N is fitted with the handle f, and the plunger has two
projections which work in the uprights g to prevent the plunger from rotating
with the screw while leaving it free to work up and down (see Fig. 3).
The hydraulic pump communicates with the cylinder by means of the opening h,
the plunger moves downwards when the screw is turned to the right and forces the

page_text: screw shaft with the thrust block aft. When the screw is turned to the left, the
plunger moves upwards and permits the screw shaft with the thrust block to
move in a forward direction under the pressure of the screw propeller.
The plunger screw permits the two above described motions to be performed'
steadily and in a perfect manner, and this ensures correctness in the determination
of the various pressures.
The plunger M may be taken out entirely to permit of the cylinders being filled
with fluid directly through the plunger tube. The air can escape through the
communicating tube F1 and through the aperture in the right hydraulic
cylinder.
The aperture i can be closed by the screw plug k.
From the foregoing it will be understood that on a 'comparison of readings
obtained from the indicator when the vessel is driven at different speeds, the
rate of increase of resistance due to the increased speed of the vessel will be
found.
It will also be understood that by comparing the results of tests taken at
different periods by this indicating apparatus, any increase in the resistance to the
propelling power due to the straining of the vessel may be readily determined.
Again by changing the propellers their relative deficiency may be compared, and
a comparison of the indications of the apparatus applied to ships of various forms
will serve to determine the lines of least resistance.
Having now set forth the nature of the said Invention of "An Improved Mode
of and Apparatus for Ascertaining the Effective Pressure of Screw Propellers," and
explained the manner of carrying the same into effect, I wish it to be understood
that under the above in part recited Letters Patent I claim,-
First. The mode above described of utilizing the thrust of screw propeller shafts
and obtaining therefrom indications of the effective pressure of screw propellers.
Secondly. The apparatus for ascertaining the effective pressure exerted by screw
propellers, substantially as herein shewn and described.
In witness whereof, I, the said George Wilhelm Cabjolsky, have hereunto set
my hand and seal, the Twenty second day of November, in the year of our
Lord One thousand eight hundred and eighty.
GEORGE WILHELM CABJULSKY. (L.S.)