IMPROVEMENTS IN AND RELATING TO SCREW-PROPELLERS FOR STEAM
Year: 1881

page_text: LETTERS PATENT to William Robert Lake, of the Firm of Haseltine, Lake,
& Co., Patent Agents, Southampton Buildings, London, for an Invention of
" IMPROVEMENTS IN AND RELATING TO SCREW-PROPELLERS FOR STEAM-
A communication from abroad by John B. Root, of Port Chester,
New York, United States of America.
SHIPS.
PROVISIONAL SPECIFICATION left by the said William Robert Lake at the
Office of the Commissioners of Patents on the 14th May 1881.
WILLIAM ROBERT LAKE, of the Firm of Haseltine, Lake, & Co., Patent
Agents, Southampton Buildings, London. "IMPROVEMENTS IN AND RELATING
TO SCREW-PROPELLERS FOR STEAM-SHIPS." [A communication from abroad by
John B. Root, of Port Chester, New York, United States of America.]
"
The present Invention relates to that class of vessels which are driven through
the water by the action of screw-propellers, and its principal object is to obtain
greater speed with the expenditure of the saine amount of power, or the same
speed with a less amount of power as compared with such vessels as at present
constructed and operated.
According to the said Invention I place the shaft or axis of the propeller or
screw in an inclined position, that is, inclined downward and backward, or at an
angle to the line of movement of the vessel, and at the same time I increase the
diametric or propelling area of the screw, and decrease its pitch relatively to the
inclination or angle of the shaft.
Although shafts of screw-propellers have generally been attached to vessels so as
to lie in a horizontal plane, yet in some instances they have been placed in an
inclined position, for the purpose of adapting the shaft to driving machinery of the
hull, and perhaps for giving more perfect submergence of the screw in the water.
In all such cases however, so far as I am aware, the construction of the screw has
been such that the speed of the vessel has been less than the pitch of the screw
multiplied by the number of its revolutions, owing to the "slip " due to the

page_text: .
yielding nature of the water; and I am not aware of any case in which the area of
the screw has been increased, and at the same time its pitch diminished by reason
of such inclination given to the shaft.
By giving the shaft of a screw-propeller a sufficient inclination downward and
backward, or at an angle to the line of movement of the vessel, and by increasing
the diametric or propelling area of the screw relatively to the inclination or the
angle of the shaft, the vessel can be propelled very much farther by a given number
of revolutions of the screw than the pitch of the screw multiplied by the number
of its revolutions would call for, provided the shaft were arranged horizontally in
the vertical plane of the keel as usually applied.
Whenever the shaft of a propeller is placed in an inclined position without
increasing the diametric or propelling area of the screw, there will be a greater slip
resulting from the upward action of the screw against the weight of the vessel,
whereby an increased thrust is required to give the same forward push upon the
vessel than would be the case were the shaft in a horizontal position; and if the
diametric or propelling area of a screw upon an inclined shaft is increased so as to
give the requisite resistance upon the water to counteract the increased slip, then a
greater power will be required to give a given number of revolutions to the screw
in the given time, owing to its increased thrust, than would be required to give the
same number of revolutions in the same time if the screw-shaft were horizontal ;
but if the pitch of a screw of increased area acting on an inclined shaft is reduced
or diminished relatively to the inclination of the shaft, a point is reached at which
the same power will give to such screw the same number of revolutions in the
same time, as would be given to a screw of the pitch and area adapted to a shaft
working horizontally and in the vertical plane of the keel. With a screw thus
constructed and arranged a greater speed can be attained with the same expenditure
of power than with the known constructions of horizontal or inclined screws.
One method by which to determine the pitch and area of a screw embodying my
Invention is shewn in the diagram below.
The line a, b, c, d, represents the line of movement of the vessel, and the
part c, d, (or a, b, which is laid off equal to c, d,) represents the pitch of a screw
adapted to a shaft working horizontally in the fore-and-aft line of the vessel. The
curve c, o, d, is a half circle constructed on c, d, and a; c, m, is the quadrant of a circle
constructed on the radius a, c. The angles which the radial lines a, c, e, c, f, c, &c.,
make with the perpendicular c, m, represent different degrees of inclination that
may be given to the axes of screw-propellers, and each of which, were there no slip,
would with the proper pitch and area of screw move the vessel from c to d with a
single turn of the shaft, and the dotted portion of any one of these lines, as
compared with the line a, b, represents approximately the relative pitch which the
screw should have when its axis coincides with such line, as compared with its
pitch if its shaft were horizontal and in the fore-and-aft line of the vessel. The
diameter of the screw should be increased in approximately the same proportion
as the pitch is diminished. A rule then for proportioning the pitch and the

page_text: propelling area of the screw to the inclination of the shaft will be as follows:-
Ascertain by the established methods the area and pitch of a screw on a horizontal
shaft lying in the plane of the keel, which will propel the vessel at a given speed
with a given number of revolutions of the screw. If now it is desired to incline
the shaft at, say, thirty degrees from the perpendicular, ascertain from the above
diagram the relative length of the dotted radial line on this angle of inclination, as
compared with the line a, b, representing the ascertained pitch of the screw on a
horizontal shaft. It will be found to be approximately one half, and consequently
to secure the best results the pitch of a screw placed on an inclination of thirty
degrees from the perpendicular should be about one half that of a screw having its
axis horizontal and in the plane of the keel. At the same time the diameter of the
screw should be increased in substantially the same ratio, that is, in this case
should be about doubled, which approximately would quadruple its propelling area.
The reason for thus increasing the propelling area of the screw as its pitch is
reduced is, that the water acted upon by a screw of a given pitch will be propelled
backward with double the velocity imparted by a screw of one half such pitch;
and as the resistance is as the square of the velocity, it follows that in order to
avoid an increase of slip, the diameter of the propelling surface of the screw should
be increased as the pitch is diminished.
The same rule will apply, mutatis mutandis, to any other angle of inclination
at which it may be desired to place the shaft.
While it is considered that the above furnishes a convenient and approximately
accurate rule for determining the relation of the area and pitch of the screw to
the inclination or angle of the shaft, in order to produce the best results it is
doubtless true that many other methods or rules may be employed to obtain the
same result, and it is not intended to limit this Invention by any special rule or
method of determination in this respect, nor is the Invention limited to the exact
proportions of inclination of shaft, propelling area, and pitch of screw suggested
above as producing the best results. The endeavour has been to state the general
principle of the Invention, and it is probable that varied conditions and require-
inents of construction and use will often call for variations from the proportions
given which under ordinary circumstances would give the best results.
The advantages resulting from the above described construction and arrangement
of screw-propellers are that the resistance of the vessel is diminished by the lifting
action of the screw, also that the loss from slip is diminished by reducing the pitch
of the screw.
By "diametric or propelling area," as herein used, is understood the area of a
circle described by the blades in their revolution, and not simply the area of the
blades themselves, and by the term "pitch," as herein used, is meant the distance
along the line of the shaft that a blade of the screw would travel at one revolution
if moving without slip.
The same effect which is produced by reducing or diminishing the pitch of a
screw, as above explained, may be obtained within certain limits by increasing its
diametric or propelling area, for in such case the blades will act upon the water
If a
more directly, that is, more nearly in a line with or parallel with the shaft.
screw were placed with its axis at an angle sidewise to the line of movement of
the vessel, its action would be the same, excepting that its lifting action upon the
vessel would be diminished, and in such case there should be two screws, one upon
each side, so that one may counteract the side action of the other.
The above described method of constructing and arranging screw propellers,
which consists in inclining the shaft and at the same time increasing the propelling
area of the screw and diminishing its pitch, is particularly applicable to vessels of
two or more hulls, as in all such cases the shaft or shafts, if more than one propeller
is applied, can pass through the deck, so that the power above the deck can easily
be connected with the screw acting below the deck and between the hulls; and by
giving the proper inclination to the shaft a screw of larger diameter can be
submerged in a small draft of water.

page_text: When the shaft is placed at a large angle of inclination from the horizon it is
very desirable to diminish the pitch of the screw as much as practicable in order
to lessen the unequal action of the blades which takes place at different parts of
their revolution. This inequality of the action of the blades in different parts of
their revolution is largely increased by the inclination of the shaft, which causes
one of the blades when their radial length is in a horizontal position to exert its
force more in the direction of the line of movement of the vessel, and the other
When the
blade to exert its force at a greater angle to such line of movement.
radial length of two opposite blades is in a vertical plane passing through the
shaft the action of each blade upon the water is substantially equal and the force
is exerted in the same direction. If the shaft were very much inclined with a
screw of high pitch this unequal action of the blades would be quite objectionable,
but by diminishing the pitch of the screw as the inclination of the shaft is
increased the advantage gained by the lifting thrust far more than compensates the
loss arising from the unequal action of the blades.
In order to largely obviate this unequal action of the blades and prevent the
tendency to jar the vessel, I prefer to attach the blades to inclined shafts by casting
or forming the two opposite blades with a round connecting shank or journal,
which is secured in a proper bearing formed in the hub and the cap-piece, by which
means the screw is attached to the end of the shaft by a hinge connection at right
angles to the line of the shaft. This cross shank or journal is attached to the
blades at their forward edges, so that as they pass through the water the blades
will trail behind the hinge, and any excess of pressure upon one of the blades will
cause its angle of action to be diminished and will at the same time increase the
angle of action of the opposite blade, and thus automatically equalize their work.
I provide a cap piece having screws by which it is firmly secured to the hub and
which serves to hold the shank or journal of the blades in its bearing.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said William Robert Lake in the Great Seal Patent Office on the
11th November 1881.
WILLIAM ROBERT LAKE, of the Firm of Haseltine, Lake, & Co., Patent
Agents, Southampton Buildings, London. "IMPROVEMENTS IN AND RELATING
TO SCREW-PROPELLERS FOR STEAM-SHIPS." A communication from abroad by
John B. Root, of Port Chester, New York, United States of America.
The present Invention relates to improvements in screw-propellers for steam-
ships, and its principal object is to obtain greater speed with the expenditure of
the same amount of power, or the same speed with a less amount of power, as
compared with such vessels as at present constructed and operated.
The said Invention consists in placing the shaft or axis of the propeller or screw
in an inclined position, that is, inclined downward and backward, or at an angle to
the line of movement of the vessel, and at the same time increasing the diametric
or propelling area of the screw, and decreasing its pitch relatively to the inclination
or angle of the shaft.
Although shafts of screw-propellers have generally been attached to vessels so as
to lie in a horizontal plane, yet in some instances they have been placed in an
inclined position for the purpose of adapting the shaft to the driving machinery of
the hull, and perhaps for giving more perfect submergence of the screw in the
water. In all such cases however, so far as I am aware, the construction of the
screw has been such that the speed of the vessel has been less than the pitch of
the screw multiplied by the number of its revolutions, owing to the "slip" due to
the yielding nature of the water, and I am not aware of any case in which the
area of the screw has been increased, and at the same time its pitch diminished by
reason of such inclination given to the shaft.
It has been discovered that by giving the shaft of a screw-propeller a sufficient
inclination downward and backward or at an angle to the line of movement of the
vessel, and by increasing the diametric or propelling area of the screw relatively to
the inclination or the angle of the shaft, the vessel can be propelled very much
farther by a given number of revolutions of the screw than the pitch of the screw
multiplied by the number of its revolutions would call for, provided the shaft were
arranged horizontally in the vertical plane of the keel as usually applied.
Whenever the shaft of a propeller is placed in an inclined position, without
increasing the diametric or propelling area of the screw, there will be a greater slip
resulting from the upward action of the screw against the weight of the vessel,
whereby an increased thrust is required to give the same forward push upon the
vessel than would be the case were the shaft in a horizontal position; and if the
diametric or propelling area of a screw upon an inclined shaft is increased, so as to
give the requisite resistance upon the water to counteract the increased slip, then a
greater power will be required to impart a given number of revolutions to the
screw in the given time, owing to its increased thrust, than would be required to
give the same number of revolutions in the same time if the screw-shaft were
horizontal;
but if the pitch of a screw of increased area, acting on an inclined shaft,
is reduced or diminished relatively to the inclination of the shaft, a point is reached
at which the same power will give to such screw the same number of revolutions
in the same time as would be given to a screw of the pitch and area adapted to a
shaft working horizontally, and in the vertical plane of the keel.
With a screw
thus constructed and arranged, a greater speed can be attained with the same
expenditure of power than with the known constructions of horizontal or inclined
screws.

page_text: In the Drawing, Figure 10 illustrates one method by which to determine the
pitch and area of a screw embodying my Invention. In this Figure, the line a, b, c, d,
represents the line of movement of the vessel, and the part c, d, (or a, b, which is
laid off equal to c, d,) represents the pitch of a screw adapted to a shaft working
horizontally in the fore-and-aft line of the vessel. The curve c, o, d, is a half-circle
constructed on c, d, and a, c, m, is the quadrant of a circle constructed on the
radius ac.
The angles which the radial lines ac, ec, fc, gc, hc, ic, jc, kc, l c,
make with the perpendicular c, m, represent different degrees of inclination that
may be given to the axes of the screw-propellers, and each of which, were there no
slip, would with the proper pitch and area of screw move the vessel from c to d
with a single turn of the shaft, and the dotted portion of any one of these lines, as
compared with the line a, b, represents approximately the relative pitch which the
screw should have when its axis coincides with such line, as compared with its
pitch if its shaft were horizontal and in the fore-and-aft line of the vessel. The
propelling area of the screw should be increased as the pitch is diminished. A rule
then for proportioning the pitch and the propelling area of the screw to the incli-
nation of the shaft will be as follows:-Ascertain by the established methods the
area and pitch of a screw on a horizontal shaft lying in the plane of the keel, which
will propel the vessel at a given speed with a given number of revolutions of the
screw. If now it is desired to incline the shaft at, say, thirty degrees from the
perpendicular, ascertain from a diagram, constructed as in Figure 10, the relative
length of the dotted radial line on this angle of inclination as compared with the
line a, b, representing the ascertained pitch of the screw on a horizontal shaft. It
will be found to be approximately one half, and consequently to secure the best
results the pitch of a screw placed at an inclination of thirty degrees from the
perpendicular should be about one half that of a screw, having its axis horizontal
and in the plane of the keel. At the same time the propelling area of the screw
should be increased, that is, in the case given above, best results should be doubled.
The reason for increasing the propelling area of the screw as its pitch is reduced is
that the water acted upon by a screw of a given pitch will be propelled backward
with greater velocity than would be imparted to it by a screw of diminished
pitch; and as the resistance increases with the velocity, it follows that in order to
avoid an increase of slip the area of the propelling surface of the screw should be
increased as the pitch is diminished.
The same rule will apply, mutatis mutandis, to any other angle of inclination
at which it may be desired to place the shaft.
While it is considered that the above furnishes a convenient and approximately
accurate rule for determining the relation of the area and pitch of the screw to the
inclination or angle of the shaft in order to produce the best results, it is doubtless
true that many other methods or rules may be employed to obtain the same result,
and it is not intended to limit this Invention by any special rule or method of
determination in this respect; nor is the Invention limited to the exact proportions
of inclination of shaft propelling area and pitch of screw suggested above as
producing the best results. The endeavour has been to state the general principle of
this Invention, and it is probable that varied conditions and requirements of
construction and use will often call for variations from the proportions given,
which under ordinary circumstances would give the best results.
The advantages resulting from the above described construction and arrangement
of screw-propellers are, that the resistance of the vessel is diminished by the lifting
action of the screw; also, that the loss from slip is diminished by reducing the
pitch of the screw.
By "diametric or propelling area," as herein used, is understood the area of the
circle described by the blades in their revolution, and not simply the area of the
blades themselves; and by the term "pitch," as herein used, is meant the distance
along the line of the shaft that a blade of the screw would travel at one revolution
if moving without slip.
The same effect which is produced by reducing or diminishing the pitch of a

page_text: screw as above explained may be obtained within certain limits by increasing its
diametric or propelling area, for in such case the blades will act upon the water
more directly, that is, more nearly in a line with or parallel with the shaft. If a
screw were placed with its axis at an angle sidewise to the line of movement of the
vessel, its action would be the same, excepting that its lifting action upon the
vessel would be diminished, and in such case there should be two screws, one upon
each side, so that one may counteract the side action of the other.
The above described method of constructing and arranging screw-propellers,
which consist in inclining the shaft, and at the same time increasing the propelling
area of the screw and diminishing its pitch, is particularly applicable to vessels
having two or more hulls, as in all such cases the shaft or shafts, if more than one
propeller is applied, can pass through the deck, so that the power above the deck
can easily be connected with the screw acting below the deck and between the
hulls; and by giving the proper inclination to the shaft, a screw of larger diameter
can be submerged in a small draught of water.
Referring to the accompanying Drawing,
Figure 1 is a plan or top view of a double-hulled vessel, and
Figure 2 a section of the same with the screw-propellers and their shafts in
elevation.
The bulls are represented by A, and the inclined shafts by B and B¹. These
shafts are fixed in suitable bearings C, C, on the deck, and are provided with
cranks D, D, for the direct application of power. The shaft B' is applied near the
longitudinal centre of the hulls, and has a greater inclination than the shaft B, and
other things being equal will tend to lift the entire vessel upward with greater
force.
Figures 3 and 4 represent in side view and plan a vessel with a screw-propeller,
whose shaft is applied at its stern and at a large angle of inclination from the
horizon. The engines E, E, and their connections with the crank-arm of the shaft
and the boiler F are shown.
Figures 5 and 6 represent in side view and plan a vessel showing the application
of screw-propellers to the sides of the same.
When the shaft is placed at a large angle of inclination from the horizon, it is
very desirable to diminish the pitch of the screw as much as practicable, in order
to lessen the unequal action of the blades, which takes place at different parts of
their revolution. This inequality of the action of the blades in different parts of
their revolution is largely increased by the inclination of the shaft which causes one
of the blades, when their radial length is in a horizontal position, to exert its force
more in the direction of the line of movement of the vessel, and the other blade to
exert its force at a greater angle to such line of movement. When the radial
length of two opposite blades is in a vertical plane passing through the shaft, the
action of each blade upon the water is substantially equal, and the force is exerted
in the same direction. If the shaft were very much inclined with a screw of high
pitch, this unequal action of the blades would be quite objectionable; but by
diminishing the pitch of the screw as the inclination of the shaft is increased, the
advantage gained by the lifting thrust far more than compensates for the loss
arising from the unequal action of the blades.
In order to largely obviate this unequal action of the blades and prevent the
tendency to jar the vessel, I prefer to attach the blades to inclined shafts, as shewn
in Figures 7, 8, and 9, by casting or forming the two opposite blades with a round
connecting shank or journal which is secured in a suitable bearing formed in the
hub and the cap-piece, by which means the screw is attached to the end of the shaft
by a hinge-connection at right angles to the line of the shaft. This cross shank or
journal is attached to the blades at their forward edges, so that as they pass
through the water the blades will trail behind the hinge, and any excess of pressure
upon one of the blades will cause its angle of action to be diminished, and will at
the same time increase the angle of the action of the opposite blade, and thus
automatically equalize their work.

page_text: By reference to the Drawing, H represents a shaft; I, I, screw-blades; J, a hub
attached to the end of the said shaft; and K, the shank or journal attached to the
forward edges of the blades, as seen in Figure 7. M is a cap-piece provided with
screws by which it is firmly secured to the hub, and which serves to hold the
sbank or journal of the blades in its bearing.
Having thus fully described the said Invention as communicated to me by my
foreign correspondent, and the manner of performing the same, I wish it understood
that I claim,
The herein described improvements, consisting in placing the screw-shaft
at an inclination or angle to the line of movement of the vessel, and diminishing
the pitch of the screw, and increasing its diametric or propelling area according to
the inclination or angle of the shaft, and relatively to the pitch and area which the
screw would have were its shaft horizontal, and in the fore and aft line of the
vessel, substantially as and for the purpose set forth.
In witness whereof, I, the said William Robert Lake, have hereunto set my
hand and seal, this Eleventh day of November, in the year of our Lord
One thousand eight hundred and eighty one.