Improvements in Screw Propellers for Ships.
Year: 1899

page_text: Date of Application, 21st July, 1899-Accepted, 24th Feb., 1900
COMPLETE SPECIFICATION.
Improvements in Screw Propellers for Ships.
I, GIOVANNI CARDOSA, of Via Santa Chiara, 1-11, Genova, Italy, 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:
-
The blades of screw propellers as at present in use are formed with a helicoidal
surface generated by a line, moved perpendicular to the axis of the nave on the
cylindrical surface of the nave of the propeller.
The part of the helicoidal surface utilized for the blades is that included
between the bases of the nave and the length of the blades and is proportionate
to the size of the ship, to the power of the engine and to the speed of the ship
desired.
This form of propeller causes vigorous reaction between the water and the
blades, which produces a great resistance to the angular velocity of the screw.
The improvement which I have introduced and which is the object of the
present invention does away with these disadvantages, a fact which has been
established by numerous satisfactory experiments, because the blades of the pro-
peller of the present invention extend beyond the nave and operate on less agitated
water and therefore more adapted for utilising the blow of the propeller for the
advancement of the ship.
And in order that my invention may be more fully understood I have caused
to be appended hereunto one sheet of drawings marked with letters of reference
indicating like parts in the various figures.
Fig. 1 is a side view of the propeller, Fig. 2 a plan and Fig. 3 a plan in
section on line A-B of Fig. 1.
In carrying out my invention I fix around the nave a at equal distances apart
from each other a certain number of blades b, c, d, the drawing showing a nave
with three blades Each is determined by a plane passing through the centre of
the nave and forming with the axis of the latter an angle of 45 degrees.
In Fig. 1 the position of the blades relative to the nave a is shown, the blade d
is perpendicular to the plane of projection and thus extends in a straight line.
The plane of each blade cuts the cylindrical surface of the nave as a segment
of an ellipse.
9,
which
The
From any point of the said ellipse a straight line perpendicular with the axis
of the nave is drawn on the plane of the blade, say the straight line
passes through the axis; tracing then the straight line r, also on the plane of the
blade, and forming with the straight line 7 an angle of about 45 degrees, this
angle projected on the horizontal plane, appears diminished in size and in Fig. 2
is represented by a, whose theoretical value is 35 degrees 16 minutes.
straight liner is considered as the generating line of the blade and moved in a
parallel sense to itself on the plane forming the blade, determines its form and cir-
cumference. The long sides are the two straight parallel lines m, n, the free
end p forms an arched line, preferably circular, with its centre coinciding with
that of the nave a, or an elliptical arch determined by the intersection of the

page_text: blade with the cylinder S (Fig. 2). In Fig. 2 the elliptical arch is shown as
extended into an arch concentric with the axis of the nave. As will be readily
understood the generating liner forms thus an angle of 60 degrees with the axis of
the nave.
The determination of the angles described according to the theoretical trigo-
nometrical relations, must not be taken in an absolute sense, it being understood
that they may be increased or diminished singly or in relation to each other,
according to practical cases.
The tips which have to cut the water are tapered off in order to facilitate the
movement of the blades.
From the aforesaid results that the invention does not precisely consist in the
determination of the said angles, but in the system, that is to say, in the adoption
of flat blades (which are also of easier construction) they are not placed in per-
pendicular sense to the axis, but are inclined towards the prow of the ship.
It must here be observed that part of this invention forms already the subject
of my Patent No. 25713 dated Dec. 6th 1898, and that the present specifi-
cation is intended to claim only that part which has not been claimed already in
the said patent, that is to say, the method of determining the circuit of the
blades with the generating line and with the circumferential lines m, n & p.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:
In a screw propeller for ships having a nave a with three or more blades b, c, d,
bent towards the prow of this ship, the shape of these blades, determined by a
straight line in perpendicular sense to the axis of the nave and then by the
generating line r forming an angle of about 45 degrees with the line and
finally by the circumferential lines m, n, & p, the whole substantially as set forth
and illustrated in the drawings.
Dated th 201 df T..1.. 1000
F. BOSSHARDT & Co.,
4, Corporation Street, Manchester, Agents to Applicant.