IMPROVEMENTS IN SCREW PROPELLERS
Year: 1885

page_text: I JOHN HENRY JOHNSON of 47 Lincolns Inn Fields in the County of Middlesex
Gentleman do hereby declare the nature of said Invention for "IMPROVEMENTS IN
SCREW PROPELLERS" which Invention has been communicated to me from abroad
by Nicholas Yagn of Spasskaya Oulitpa N 13-42 St Petersburg in the Empire of
Russi Mechanical Engineer to be as follows:-
In devising Screw Propellers they are commonly supposed to act in quiet
undisturbed water. For this reason the angle of inclination of the blades of the
Propeller is calculated according to the desired speed of the vessel and the number
of revolutions of the Engine. Of course however when the vessel is moving, the
water wherein the Propeller is revolving never remains quiet and independently
of its being stirred up by the Propeller the water behind the stern even before the
Propeller enters in it receives a certain velocity in the direction followed by
the vessel (dead water current). This velocity is different in different parts of the
current formed: it is greatest at the surface of the water in the middle of
the current and gradually decreases on either side and below the surface. Therefore
the blades of the Propeller in order to be fit for regular action ought to be con-
structed in such manner as to have a different inclination at different moments of
the propellers revolution which of course is impossible to obtain with Screw
propellers immoveably fixed to their shafts. In practice it has been the custom to
give the blades of the Propeller a certain medium inclination.
It is evident that from such medium inclination of the Propellers blades not only
results a loss of power, but besides the screw and the hull of the vessel at different
moments of the Propellers revolution undergo very strong and irregular pressures.
whose resultant does not coincide with the axis of the shaft and which are:
accompanied by shocks tending to shake loose the shaft in its bearings and doing
great injury to all the joints of the vessel.
+
To the action of the dead water current are added the alterations in the relative
velocity and direction of motion of the water surrounding the Propeller caused
by the vessel's pitching and rolling. These alterations also are causes of shocks
and commotions and diminish the useful effect of the Propeller where the same is.

page_text: immovably fixed to the shaft and provided with blades of an Invariable
inclination.
My foreign correspondent has found that all the aforementioned defects can be
overcome by making the angle of inclination of the blades of the Screw Propeller
to change automatically in accordance with the alterations in the relative velocity
and direction of the motion of the water wherein the propeller is working.
"
This end is attained either by making the blades so that they are springy or
elastic blades or yield to pressure, or by fixing the Screw Propeller to the shaft-in
a manner permitting an oscillation of the Propeller in a perpendicular direction to
the plane of its revolution and consequently permitting alterations in the angle of
inclination of its blades.
The last mentioned way is considered the most practical and may be effected as
follows:-
The propelling shaft is provided at the place where the propelling screw is fixed
to it with a spherical collar provided with two pivots on which are square or rect-
angular muffs or bearings adjusted to the sides of a cavity or chamber and bearing
against projections compelling the propeller to rotate simultaneously with the
shaft.
The blades of the screw-Propeller form, one with the muffs or bearings held by
a cover provided with an aperture for the shaft.
The outside end of the muff or bearing is limited by a spherical or cylindrical
surface which is concentric with the surface of the spherical collar-In the body of
the muff or bearing is a cavity or recess having in end elevation a rectangular
shape and provided with inclined sides narrowing towards the inner part of the
muff or bearing-In this recess is placed the end of the propelling shaft, for the
better guidance of which a bearing is provided having flanges and tightly sliding
in the recess in the muff or bearing.
It is to be observed that the blades of the Propeller are not placed in one plane
with the pivots but somewhat deviate backwards so that the resultants of the
pressures exercised on the blades by the water do not pass through the continuation
of the axles of the pivots, since only under this condition can be obtained a
momentum of rotation-i.e., the aforesaid resultants of the pressures compel the
Propeller to rotate on the pivots and to alter accordingly the angle of inclination
of the blades. It is easily conceived that disposing the blades not behind but at
the side of the axis of revolution of the pivots, there can be obtained a momentum
of rotation even when placing the blades in one plane with the pivots, which
sometimes may be found necessary, as for instance in cases where the space for the
shaft between the stern and the rudder is not sufficiently large.
With, the construction of the Propeller just explained its blades when meeting
in their motion an increased resistance, from the water will deviate in the. direction
in which the angle of their meeting with the water decreases, diminishing in. pro-
portion as the resistance met by them is greater. It is precisely by this means
that an equalizing of the thrust-power of two opposite blades is obtained..
But when the propeller is revolving in the opposite direction the same cause--
that is, the increased resistance will turn the blade to the opposite side, the
moveableness of the blade contributing not to diminish but on the contrary to more
increase, the aforesaid angle of meeting-Therefore when the Propeller is revolving
in the opposite direction (backwards) it must not remain moveable (in regard to
the shaft) but automatically fix itself firmly on the shaft; therefore as soon as the
shaft begins to revolve in the opposite direction the pivots leave the projections
with which their muffs or bearings were in contact, and gliding in the cavity or
recess pass to the opposite sides of the projections. But at this position of the
pivots the muff or bearing of the screw can no longer oscillate on these pivots, hence
the screw remains fast or-immovably fixed on the shaft.
With a four bladed Propeller it is useful to dispose the recess or cavity in the
body of the muff or bearing at an angle of 45° to the direction of one of the opposite
pairs of blades.

page_text: When the blades are arranged to spring or yield, the muff or, bearing is fixed
immovably on the shaft and is provided with solid ribs or spokes whereon are
fixed flexible or spring-plates corresponding to the outlines of the screw Propeller.
It is easily understood that when during the action of such a Propeller the
water opposes an exceedingly strong pressure to the blade, flexible plates yielding
to that pressure will bend and the angle of inclination of the blade diminish of
itself, and on the contrary when the resistance offered to the blade by the water
diminishes the angle of inclination of the blade grows larger.
Owing to the moveableness of the muff or bearing on the pivots two opposite
blades will always automatically take a position in which the pressures undergone
by the one blade as well as by the other are exactly alike, and consequently the
resultant of these pressures will pass near the axis of the shaft-ie., it will be
observed the condition necessary for preventing shocks and that both blades meet
the water at equal angles, whereby a very efficacious action of the Propeller is
secured.

page_text: COMPLETE SPECIFICATION.
Improvements in Screw Propellers.
I JOHN HENRY JOHNSON of 47 Lincoln's Inn Fields in the County of Middlesex
Gentleman do hereby declare the nature of this Invention for "IMPROVEMENTS IN
- SCREW PROPELLERS" which Invention has been communicated to me from abroad
by Nicholas Yagn of Spasskaya Oulitpa N° 13-42 St Petersburg in the Empire
of Russia Mechanical Engineer and in what manner the same is to be performed
to be particularly described and ascertained in and by the following statement:-
Screw propellers have hitherto been designed as though they were only to act
in quiet undisturbed water and the angle of inclination of the blades of the
propeller is calculated merely according to the desired speed of the vessel and
the number of revolutions of the engine. Of course however when the vessel is
moving the water wherein the propeller is revolving never remains quiet, and
independently of its being stirred up by the propeller the water behind the stern
even before the propeller enters it receives a certain velocity in the direction
followed by the vessel (dead water current). This velocity is different in different
parts of the current formed, being greatest at the surface of the water in the
middle of the current and gradually decreasing on either side and below the
surface, therefore the blades of the propeller in order to give a regular action,
ought to be constructed in such manner as to have a different inclination at
different moments of the propellers revolution, which it is impossible to obtain
with screw propellers immovably fixed to their shafts in the ordinary way. In
practice it has been the custom to give the blades of the propeller a certain medium
inclination.
It is evident that from such medium inclination of the propeller's blades not
only does a loss of power result but also the screw and the hull of the vessel, at
different moments of the propeller's revolution undergo very strong and irregular
pressures whose resultant does not coincide with the axis of the shaft and give rise
to shocks tending to shake loose the shaft in its bearings and to do great injury to
all the joints of the vessel.
To the action of the dead water current are added the alterations in the relative
velocity and direction of motion of the water surrounding the propeller, caused by
the vessel's pitching and rolling. These alterations also are causes of shocks and
commotions, and diminish the useful effect of the propeller when it is immovably
fixed to the shaft and provided with blades of an invariable inclination.
My foreign correspondent has found that all the aforementioned defects can be
overcome by so making the propeller that the angle of inclination of the blades
changes automatically in accordance with the alterations in the relative velocity
and direction of the notion of the water wherein the propeller is working.
This end is attained either by making the blades so that they are springy
or elastic blades or yield to pressure or by fixing the screw propeller to the shaft
in a manner permitting an oscillation of the propeller in a plane perpendicular to 4
the plane of its revolution and consequently permitting alterations in the angle of
inclination of its blades.

page_text: And in order that the said Invention may be fully understood I shall now
proceed more particularly to describe the same and for that purpose shall refer to
the several figures on the annexed sheet of Drawings the same letters of reference
indicating corresponding parts in all the figures.
Figure 1 is a longitudinal section and Figure 2 is a transverse section of the boss
"muff" or nave of a screw propeller constructed according to this Invention
shewing the mode of fixing it to the propeller shaft. Figure 3 is an end elevation
of the boss and Figure 4 is a longitudinal section of the said boss representing it
in its most inclined position with regard to the axis upon which it rotates.
Figures 5 and 6 represent respectively a longitudinal section and a transverse
section of the boss in a locked or normal position relatively to the shaft as herein-
after described. The remaining figures represent various modifications as herein-
after described.
+
A is the propeller shaft provided at the place where the propelling screw is fixed
to it with a screw thread a (see Figure 1) whereon is screwed the spherical collar B
provided with two pivots b b on which are fitted (tightly but with slight friction)
square or rectangular "muffs" or bearings 6161 fitting the sides of a cavity or
chamber F in the boss C of the propeller and bearing against projections G in the
said boss so as to compel the propeller to rotate with the shaft A.
The boss C is set on the collar B and is held thereon by a cover C¹ provided
with an aperture preferably of the shape shewn in Figure 1 through which the
shaft A passes..
The outside end of the boss C is formed with a spherical surface concentric with
the surface of the spherical collar B. In the body of the boss C is a cavity or
recess D of a rectangular shape (see Figure 3) and provided with inclined sides
narrowing towards the inner part of the boss (see Figure 1) The end of the
propelling shaft A passes through this recess and is provided with a bearing
piece E having flanges which fit tightly and slide in the recess D. The bearing
piece E is held on the shaft by the nuts e.
It is to be observed that the blades of the propeller are not placed in one plane
with the pivots bb but are situated somewhat backwards thereof as shewn in
Figure 7 so that the resultants of the pressures exercised on the blades by the
water do not pass through the continuation of the axles of the pivots bb since
under this condition only can a momentum of rotation be attained, as the aforesaid
resultants of the pressures compel the propeller to rotate on the pivots and to
alter accordingly the angle of inclination of the blades. It is easily seen that by
disposing the blades not behind but at the side of the axis of .revolution of the
pivots as shewn for example in Figures 11 to 15. a momentum of rotation can be
obtained even when placing the blades in one plane with the pivots which some-
times may be found necessary for instance in cases where the space for the
propeller shaft between the stern and the rudder is not sufficiently large.
With a propeller constructed as herein before described when its blades meet in
their motion an increased resistance from the water they will deviate in the
direction in which the angle of their meeting with the water decreases such
deviation diminishing in proportion as the resistance met by them is greater. It
is by this means that an equalizing of the thrust power of two opposite blades is
obtained. When however the propeller is revolving in the opposite direction the
increased resistance will turn the blade to the opposite side the movability of the
blade contributing not to diminish but on the contrary to further increase the
aforesaid angle of meeting. Therefore, when the propeller is revolving in this
direction (backwards) it must not remain movable (in regard to the shaft) but
must automatically fix itself firmly on the shaft which result is obtained as
follows:-
As soon as the shaft A begins to revolve in the said opposite direction the
pivots bb leave the projections G with which their bearings b¹ were in contact and
moving in the cavity or recess F pass to the opposite sides of the said projections G
as shewn in Figures 5 and 6 and when in this position the boss C can no longer

page_text: -oscillate on the pivots hence the screw remains fast or immovably fixed on the
shaft A.
The collar B instead of being screwed on the shaft A may be forged on the said
shaft or be otherwise formed or fixed thereon. The blades of the propeller are
cast on or otherwise strongly attached to the boss C.
In Figures 7 and 8 are respectively shewn (drawn to a smaller scale) a plan and
an end elevation of a two bladed propeller and in Figures 9 and 10 are shewn
similar views of a four bladed propeller constructed according to this Invention.
In the latter case the recess or cavity D is shewn as being situated at an angle
of 45° to the line of the blades.
.
Figures 9 and 10ª shew similar views of a combination of two two bladed
-propellers fitted on one shaft each of which propellers when the vessel is moving
ahead, can have an oscillating motion as hereinbefore described.
Figures 16 and 17 shew a way in which the object of this Invention can be
obtained by making the blades springy or elastic or so as to be capable of yielding
to pressure.
In this case the boss C of the propeller is fixed immovably on the
shaft A and is provided with solid arms or spokes II on which are fixed the
flexible yielding or springy plates iii which correspond to the outlines of
the screw propeller.
It is easily understood that when during the action of such a propeller the
water opposes an exceedingly strong pressure to the blade, the flexible plates i i
will bend or yield to that pressure and the angle of inclination of the blade will
thereby automatically diminish and on the contrary when the resistance offered to
the blade by the water diminishes, the angle of inclination of the blade increases.
A propeller of this kind is best suited for small vessels.
It will be observed that an essential feature in the action of the oscillating
-propeller herein before described is that owing to the movableness of its boss C on
the pivots, two opposite blades will always automatically take a position in which
the pressures undergone by the blades are exactly alike and consequently the
resultant of these pressures will pass near the axis of the shaft and this is the
_condition necessary for preventing shocks, both blades meeting the water at equal
angles whereby a very efficient action of the propeller is secured.
In the annexed drawings the blades of the propellers are shewn as being cast in
one with their bosses but for large propellers where this is not practicable the
practice in this respect with ordinary propellers may be adopted and adjustable
blades of various systems can also be applied to propellers constructed as herein-
⚫before described. The oscillating propeller may be arranged to be raised and
lowered in the ordinary way as applied to ordinary propellers.
To protect the boss B of the propeller from the entry of dirt or sea-plants or
animals the aperture or recess D may be closed by a metallic cover D' fastened to
the boss C as shewn in Figure 18 and for the same purpose the aperture in the
cover C¹ may be protected by providing the shaft A with a collar a¹ to which is
fastened a flexible or corrugated metallic disc K and cylindrical or conical casing L
closing the aperture in the cover C¹ whatever position the boss C may take. It
will be, evident that the details of construction can be varied without departing
from the nature of the Invention.
Having now particularly described, and ascertained the nature of the said
Invention and in what manner the same is to be performed I declare that what
I claim is
First. A screw propeller so constructed that the angle of inclination of the
blades (the pitch of the screw) can automatically accommodate themselves to the
alterations in the force and direction of the pressure exercised on the propeller by
..the water, substantially as hereinbefore described.
Second. Connecting screw propellers with their shaft by means of a boss
permitting the propeller to oscillate in the direction required substantially as
herein before described and illustrated by the accompanying drawings.

page_text: Third. In screw propellers forming the connection of the propeller with tho
shaft by means of a boss provided with a cavity or recess (F) wherein pivots on or
carried by the propeller shaft can move, the said pivots bearing against projections
in the said cavity or recess, the said boss also having another cavity or recess (D)
in the boss all being arranged so that the boss can oscillate on the end of the
propelling shaft when the vessel is moving ahead whilst when the vessel moves
backwards the boss becoines automatically fixed on the shaft substantially as
herein before described and illustrated in the accompanying drawings.
Fourth. In screw propellers arranging the blades behind or excentrically to
pivots on which the boss can oscillate whereby the propeller is rendered sensitive
and adapted for automatically regulating its position substantially as herein before
described and illustrated in the accompanying drawings.
Fifth. A screw propeller having springy flexible or yielding blades sub-.
stantially as herein before described and illustrated by Figures 16 and 17 of the
accompanying drawings.