Year: 1887

page_text: Date of Application, 13th Sept., 1887
Complete Left, 12th June, 1888
Complete Accepted, 13th July, 1888
I, GEORGE ALEXANDER CALVERT, 5 Adelaide Villas, Cork, in the County of Cork
Ireland, Engineer, do hereby declare the nature of this Invention to be as follows, that
is to say:
My said Invention has for its object to improve the construction and operation of
screw propellers; and it comprises means for avoiding the reduction of efficiency
which I believe to be due, in the cases of most existing screw propellers, to the action
between the propeller and the part of the water to which some forward motion is
imparted by the forward motion of the vessel.
In carrying out my Invention I make each propeller blade to consist of an outer
propelling part and of an inner part which serves as an arm for carrying the outer
propelling part; and in determining the shape of the outer propelling part in any case
I use data of the kind obtainable by experiments with obliquely moving blades as
described in my paper published in the Transactions of the Institution of Naval
Architects, Volume 28, A.D. 1887. I prefer to make the propelling surface truly
helicoidal and to give the necessary strength by forming a convex back; but the pitch
may be uniform or increasing.
The inner part or arm of the blade I make of a double convex section and of such a
pitch, uniform or varying, as will correspond most nearly with the speed of the vessel
diminished by the forward motion imparted by the vessel to the water in which the
blade arm works. I determine the forward speed of such water by experiment or by
estimating it with the guidance of recorded results obtained with existing vessels and
propellers. The blade arm will have no appreciable propelling or other action on the
water beyond that due to mere surface friction or body resistance and where the
propelling part joins it there will be an abrupt change of pitch as though the propelling
part were twisted relatively to the arm. I prefer to have the middle radial line of a
blade continuous through the arm and propelling part, with the change of pitch or
angle, half on each half of the blade; the metal is however radially continuous at all
points across the blade, the arm and propelling part being joined by curved or filleted
parts where not exactly in line. Or the propelling part of each blade may be fixed on

page_text: the arm by means of flanges and bolts; and in that case the propelling parts may be
made of the same or of a different metal from that of the boss and arms the propelling
parts being by preference made of steel or bronze.
In the case in which a ship is fitted with a single screw propeller of my improved
construction the propelling parts of the blades (of which there may be four or other
number) will each work in water having no appreciable forward motion throughout a
large part of their circular course, but when crossing the highest point each will work
in water having considerable forward motion, whilst on crossing the lowest point each
will work in water having much less forward motion, if any, than the water at the
highest point. In consequence of this each blade will receive thrust pressures of
different intensities at different points of the circuit and thus be subjected to varying
strains productive of shocks vibration and inefficiency. By a further part of my
Invention I to a large extent compensate for the varying action referred to by placing
the propeller with its shaft or axis slightly inclined to the ship's longitudinal centre
plane so that each blade makes with that plane a larger anglo when passing the highest
point than when passing the lowest point. The effect of thus placing the shaft is to
virtually reduce the pitch at the highest point and to virtually increase the pitch at
the lowest point thus rendering the strain on each blade of the propeller more uniform
throughout its circuit and thereby diminishing shocks and vibration and increasing the
propulsive efficiency.
When a ship is fitted with twin screws I also obtain a similar compensating or
equalising effect by placing them with their shafts or axes at suitable slight inclinations,
the places where the blades work in water having the most forward motion being not
at the highest points but at the inner sides of those points, and the propeller shafts or
axes being inclined in a corresponding manner.
In some cases the inclination of the propeller shaft or shafts may be made greater
than what would be required to merely equalise the propelling action.
Dated this Twelfth day of September 1887.
EDMUND HUNT,
Applicant's Agent.

page_text: I, GEORGE ALEXANDER CALVERT, of 5 Adelaide Villas, Cork, in the County of Cork,
Ireland, Engineer, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement, that is to say :-
My said Invention has for its object to improve the construction and operation of
screw propellers; and it comprises means for avoiding the reduction of efficiency which
I believe to be due, in the cases of most existing screw propellers, to the action between
the propeller and the part of the water to which some forward motion is imparted by
the forward motion of the vessel.
In carrying out my Invention I make each propeller blade to consist of an outer
propelling part and of an inner part which serves as an arm for carrying the outer
propelling part; and in determining the shape of the outer propelling part in any case
I use data of the kind obtainable by experiments with obliquely moving blades as
described in my paper published in the Transactions of the Institution of Naval
Architects, Volume 28, A.D. 1887. I prefer to make the propelling surface truly
helicoidal and to give the necessary strength by forming a convex back; but the pitch
may be uniform or increasing.
The inner part or arm of the blade I make of a double-convex section and of such a
pitch, uniform or varying, as will correspond most nearly with the speed of the vessel
diminished by the forward motion imparted by the vessel to the water in which the
blade arm works. I determine the forward speed of such water by experiment or by
estimating it with the guidance of recorded results obtained with existing vessels and
propellors. The blade arm will have no appreciable propelling or other action on the
water beyond that due to mere surface friction or body resistance; and where the
propelling part joins it there will be an abrupt change of pitch as though the propelling
part were twisted relatively to the arm. I prefer to have the middle radial line of a
blade continuous through the arm and propelling part, with the change of pitch or
angle half on each half of the blade; the metal is however radially continuous at all
points across the blade, the arm and propelling part being joined by curved or filleted
parts where not exactly in line, the propelling part of each blade may be fixed on the
arm by means of flanges and bolts; and in that case the propelling parts may be made
of the same or of a different metal from that of the boss and arms, the propelling parts
being by preference made of steel or bronze.
Figure, 1, on sheet, 1, of the accompanying explanatory drawings is an end elevation
of a four-bladed screw propeller constructed in accordance with my Invention; and
figure, 2, is a corresponding longitudinal vertical section. Figures, 3, 4, and 5, show
the construction of a blade with the propelling part and arm in separate pieces.
Figure, 6, is a diagram comprising enlarged transverse sections of a blade and arm of
the propeller shown in figure, 1. In this example the pitch of the propelling
part, a, b, c, d, of each blade is uniform, and is represented in figure, 6, by the
distance, a, c. The transverse sections as at gh, and ik, in figure, 1, are marked with
the same reference letters in figure, 6. The inner part or arm, c d e f, of each blade is

page_text: also of a uniform pitch which is represented by the distance, ae, in figure, 6, ad,
representing the distance advanced by the vessel during one revolution of the propeller,
and de, the mean or average forward motion of the water in which the blade works
during the same time. The distances, ab, ab 1, ab 2, ab 3, in figure, 6, represent the
circumferencos corresponding to the radii at which the sections, no, lm, ik, gh, are
respectively made. The sections, no, lm, of the inner part or arm are convex on both
sides. The abrupt change of pitch where the arm joins the propelling part is shown
at cd, figure, 1, the shading in figures, 1, and 2, indicating the curved or filleted parts
of the junction, on each side of the middle radial line.
In the modification shown in figures, 3, 4, and 5, the propelling part, a b c d, of each
blade is in a separate piece fixed to the arm, cdef, by means of flanges and bolts, the
angle of the propelling part immediately outside the flange being shown at ik, in
figure, 5, and the angle of the flanges and of the part of the arm immediately inside
the flanges, at I m. This construction will facilitate the renewal of one or more of the
propelling parts of the blades, without the expense and detention involved by placing
the vessel in a graving dock.
When a ship is fitted with a single screw propeller the propelling parts of the blades
will each work in water having no appreciable forward motion throughout a large part
of their circular course, but when crossing the highest point each will work in water
having considerable forward motion, whilst on crossing the lowest point each will work
in water having much less forward motion, if any, than the water at the highest point.
In consequence of this each blade will receive thrust pressures of different intensities
at different points of the circuit, and thus be subjected to varying strains productive
of shocks, vibration, and inefficiency. By a further part of my Invention I, to a
large extent, compensate for the varying action referred to by placing the propeller
with its shaft or axis slightly inclined to the ship's longitudinal vertical centre
plane, so that each blade makes with that plane a larger angle when passing the
highest point than when passing the lowest point. The effect of thus placing the
shaft is to virtually reduce the pitch at the highest point, and to virtually increase
the pitch at the lowest point, thus rendering the strain on each blade of the propeller
more uniform throughout its circuit, and thereby diminishing shocks and vibration
and increasing the propulsive efficiency.
Figure, 7, on sheet, 2, of the accompanying explanatory drawings is a transverse
vertical section as through the propeller aperture of a screw steamer and shows
in end elevation a two-bladed propeller of 10 feet extreme diameter. The numerals
marked on the figure represent the fore-and-aft components of the forward motion
imparted to the water by the motion of the vessel, when the said vessel is moving
ahead at a speed of 10 knots per hour; each numeral representing the forward
velocity in feet per second at the part where the numeral is placed. The manner
in which the efficiency of the propeller is affected by the unequal forward motion
of the water is shown by the diagram, figure 8, where fg, represents a cross
section of the blade as at fg, in figure, 7, and hi, a cross section as at hi, in figure, 7.
The distances, a b, a 16, are each made equal to the circumference corresponding to
the radius at which the sections, fg, and hi, are made. The distances, a c, a 1 c 1,
are each made equal to 15 feet (on the scale of the diagram) the pitch of the
propeller shown in figure, 7, at the sections, fg, and hi. The revolutions per
minute of this propeller for a speed of 10 knots being 80, the distance, ad,
or a 1 d 1, equals the speed of the vessel per revolution; the forward speed of the
water per revolution equals de, when the blade is crossing the lowest part hi,
figure, 7, and d1e1, when the blade is crossing the highest part, fg. As the
slip angle" e1bc 1, at which the blade meets the water when crossing the highest
part, is so much greater than the "slip angle," ebe, at which it meets the water
when crossing the lowest part (the angle varying between these limits at inter-
mediate positions in the circuit) the result is a considerable inequality of thrust
pressure on the blade at different parts of the circuit and the maximum thrust
pressure being developed when the blade is passing through that portion of the
following water which has the greatest forward velocity, and is nearest the vessel,
"

page_text: the forward pressure of the body of water lying between the propeller and the
vessel is lowered to a greater extent than it would be if the thrust required for
propelling the vessel were developed more equally throughout the circuit of the
blade. The incessant variation in the "slip angle" renders it impossible, with
propellers arranged in the ordinary way, to maintain that "slip angle" which is
the most favorable to efficiency, and results in shocks and vibration. The diagram
figure, 9, shows the manner in which I determine the inclination of the propeller
shaft or axis, bl, with the ship's longitudinal centre plane, bk, so as to compensate
to a large extent, for the varying action referred to. The inclination chosen is such
as to make the "slip angle," cbe, approximately equal to the "slip angle," c 1 be 1,
and to make the virtual pitch at the upper part about 12 feet and that at the
lower part about 18 feet. The inclination shown in figure, 9, is about 5° 14′ and
the forward end of the axis is to the right or starboard side, the propeller being
right-handed. For a left handed propeller the inclination should be to the left or
port side.
When a ship is fitted with twin screws I also obtain a similar compensating or
equalising effect by placing the propellers with their shafts or axes at suitable
slight inclinations, the places where the blades work in water having the most
forward motion being, not at the highest points but, at the inner sides of those
points, and the propeller shafts or axes being inclined in a corresponding manner.
Figure, 10, on sheet, 2, of the accompanying drawings is a diagram showing an
example of the conditions to be considered in determining the inclinations of the
axes of twin screws. In the case of each propeller the line, ab, is drawn
through the centre of the propeller and through that point, b, in the screw's disk
at which the following water has the greatest forward velocity. The line, cd,
being drawn at right angles to a b, represents in end elevation the axis of the
propeller as inclined, the points, d, and c, being respectively the forward and after
ends for propellers revolving in the directions of the arrows, when driving the vessel
ahead. The angle of inclination to be given to the axes can be determined by means
of a diagram like figure, 9, which is hereinbefore explained.
In some cases the inclination of the propeller shaft or shafts may be made greater
than what would be required to merely equalise the propelling action.
The shafting connecting the propeller with the engine may be in a straight line
throughout; or the engine shaft and more or less of the intermediate shafting may be
longitudinal and be connected to the inclined shafting fixed to the propeller by gearing
or by a universal joint or its equivalent; or the connection may be made within the
propeller boss.
Having now particularly described and ascertained the nature of my said Inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1-Constructing screw propellers with blades having outer propelling parts and
inner non-propelling parts, in the improved manner substantially as hereinbefore
described with the aid of figures 1, to 6 of the accompanying drawings.
2-Arranging or placing screw propellers, single or twin, with their axes inclined
substantially in the manner and for the purposes hereinbefore described with the aid
of figures, 7 to 10, of the accompanying drawings.
Dated this Eleventh day of June 1888.
EDMUND HUNT,
Applicant's Agent.