Improvements in Screw Propellers for Ships.
Year: 1892

page_text: Date of Application, 31st May, 1892-Accepted, 10th Sept., 1892
COMPLETE SPECIFICATION.
Improvements in Screw Propellers for Ships.
I, EDOARDO BERLINGIERI, of 34 Salita San Girolamo, Genoa, in the Kingdom
of Italy, Captain, 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 :-
My invention relates to screw propellers for ships.
The improved propeller is a screw having two or more blades of a uniform or
varying pitch, and differing from ordinary screw propellers only in that the extremity
of its blades terminates in an elliptic are fornied by the extreme obliquity of the
blade upon a cylinder which has for its radius that of the screw itself, and the
blades at this part are bent rearwards, towards the stern of the ship, at a right
angle parallel with the axis of rotation, or on each blade is provided at the rear a
portion of the surface of a straight cylinder having for its radius that of the screw,
as hereinafter described with reference to the accompanying drawing.
A, Figures 1 and 2, is the axis, and B B B B are the four blades of the screw,
cccc are the flanges having a cylindrical surface on each blade, that is to say
fractions of the surface of the cylinder generated by the revolution of a rectangular
plane which has for its sides the radius and the length of the screw, and which has
its axis of rotation upon the axis of the said screw and parallel therewith.
Screw propellers of this kind have heretofore been made of malleable metal; but
in order to possess the necessary rigidity and to obviate vibrations they may advan-
tageously be made of cast metal with a reinforce of homogeneous malleable sheet
metal instead of using cast metal alone. Accordingly I propose to cover the blades
of screws, made of cast iron or bronze or any other cast metal, with plates of homo-
geneous metal riveted together at their outer edge, adhering to their front and rear
surface, and bent rearwards as shown for about one-twentieth of the radius of the
screw.
My improved screw propeller possesses the following advantages:
(1) With the flanges cccc having a cylindrical surface the portion of water
which is displaced by the screw in the centrifugal direction and has heretofore been
useless for the propulsion of the ship becomes a force which aids in the propulsion
when the water is obliged by this means to leave the screw in streams parallel with
the direction of the ship.
(2) As the aforesaid phenomenon takes place by the natural shock of this water
produced by the centrifugal motion interiorly of the flanges c c c c in the direction
of the tangent to the circle of rotation, this water will act upon the screw in the
manner of a fly wheel and impart to the same a more regular and uniform motion.
(3) The blades of the screw reinforced by the metallic casing cannot become
blunt during the navigation and diminish the speed of the ship, as has hitherto been
the case.
(4) As it is possible by the use of the sheet-metal casing to diminish the section
of the blades the latter will part the water with a more acute angle, and thus
decrease the resisting force.
(5) With the metallic casing I can suitably augment the surface of the blades
without augmenting the thickness beyond that of screws made only of cast metal,
thereby augmenting the momentum of the propelling force without increasing the
lever arm.
(6) As the flanges prevent the water being thrown against the periphery of the
circle of rotation this momentum is brought to bear nearer to the centre of the
circle to increase the strength of the screw so that the vacuum will be lessened
which is caused at the centre of ordinary screws.

page_text: (7) By reason of the greater polish of wrought metal in comparison with cast
metal a diminution of friction, will be effected for equal surfaces.
(8) Greater facility for repairing accidental damages the screw being left in its
place.
The work required by a marine engine with a screw propeller is giving by the
following formula.
L = KSV³ +
* R2V
2g
[K¹ (ra tang
A―
V)² + K"p²]
in which L is the total work consumed by the engine. KK'K" are the coefficients
to be determined by experiments. S is the main submerged section of the vessel.
is the ratio of the circumference to the diameter. R is the outside radius of the
propeller g is the force of gravity. r. a tang, a is the speed of the propeller p² is the
rotation speed of the water moved by the centrifugal force of the propeller.
The proposed modification in the screw will thus reduce to zero the third term of
the second member of this equation represented by
TT R2V
2g
-K"p², and will diminish
the value of the coefficient K of the second term.
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 :
A screw propeller with any desired number of blades of any suitable shape and
with either a varying or a uniform pitch, which propeller has the extremities of its
blades bent rearwards, towards the stern of the ship, at a right angle to the surface
of a cylinder generated by the radius of the screw itself, this cylindrical flange being
made either entirely of cast metal or with a casing of sheet metal, the aforesaid
angle being in some cases rounded, substantially as and for the purposes hereinbefore
described with reference to the accompanying drawing.
Dated this 31st day of May 1892.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.