Improvements in Screw Propellers.
Year: 1898

page_text: Improvements in Screw Propellers.
I, JACQUES BERNARD SENCHET, of Alfortville, Department of Seine, France, Officer,
do hereby declare the nature of this invention to be as follows:-
The present invention concerns an improved screw propeller, the working parts of
which are prolonged as near as possible to the outside circumference, and the
arrangement of the blades of which prevents the different parts of the propeller from
opposing the water towards which it advances.
With the screw propeller which forms the object of the present invention, the
blades, instead of commencing at the hub, whose radius is generally small with the
screws actually in use, are fitted, by means of a tail, which each blade possesses, in a
crown around an enlarged hub forming a disk whose radius exceeds of the total
radius of the screw, a limit which has already been practically obtained, and which
can be increased to with large screw propellers.
This disk, which forms the solid part of the screw is fixed by its axis to the driving
shaft; its fore-part is covered by the keel of the boat, and its hind-part by a hollow
water-tight cone. With twin-screw boats, this solid part may have its fore-part
covered by a lengthened cone or by the keel terininating in the form of an opera-
glass. The cone fixed behind the screw propeller can turn with it, be fixed or belong
partly to the screw and partly to the rudder, or be movable around the propelling
shaft lengthened with a smaller diameter and moving freely.
The number of blades varies from 3 for small screws to 16 and upwards for large
ones. To prevent any part of the blades from opposing the water towards which it
advances, the entrance edge of these blades is very thin and, from this thin edge, the
fore-surface of the blade instead of being convex, forms a helicoidal surface of a pitch
corresponding with the course of the vessel; the blade which is therefore very thin
at its entrance edge, thickens towards the back face by a slightly rounded side in the
vicinity of the entrance edge, and assuming any pitch desired after this
rounding.
Dated this 17th day of January 1898.
L. DUVINAGE,
Patent Agent, 8, Rue des Princes, Brussels, Belgium,
I, JACQUES BERNARD SENCHET, of Alfortville, Department of Seine, France, Officer,
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:-
This invention relates to a new form of screw propeller for ships which differs from
the propellers at present in use in so far that the whole working surface of the blades

page_text: effects its action upon the water at a considerable distance from the axis of rotation ;
further, no part of the blades beats against the water into which it advances.
The principal advantage gained by this new propeller is that the motive power
transmitted to it is utilized much more effectively than at present in urging the
vessel forward. It has been proved by experience that the most effective work
given by the propellers at present in use is performed by the ends of the blades
whilst the roots of the blades, near the boss, give little or no effective work; in order
to give the best results, it is therefore necessary to make the propellers of the
greatest possible diameter.
By means of the improved screw propeller, which constitutes the subject matter
of this invention, a greater amount of work can be obtained with a smaller diameter
of propeller than is the case with the ordinary propellers. This result is effected
by placing more numerous but shorter blades than usual, with the ordinary
propellers, upon the periphery or rim of a disc which latter is of a much larger
diaineter than the bosses of ordinary screw propellers. The special shape of the
blades contributes to this result as they are so formed that no part of them strikes
against the water into which they advance. Besides the improved result effected this
new propeller possesses the advantage of having interchangeable blades, so that,
should one be broken it can be readily replaced by a reserve blade. In cases where
blades are broken and cannot be replaced the motion of the ship is not stopped but
the speed is merely reduced.
And in order that my said invention may be properly understood I have
hereunto appended an explanatory sheet of drawings which show, by way of
example, one mode of constructing the propeller.
Fig. 1 is a back elevation of the propeller.
Fig. 2 is a vertical section taken through the longitudinal axis of the ship.
Fig. 3 is a detail view showing a blade of the screw and some transverse sections
(A, B, C, D, etc.,) of it taken on the axial lines a, b, c, d, e, f, etc.
On the drawings the same reference numerals wherever repeated indicate similar
parts.
Referring to the drawings:-
1 is the propeller shaft, 2 indicates the conical part or propeller-shaft tube at the
stern of the ship arranged in advance of the solid part of the propeller, 3 indicates the
thin parts of the shell of the ship, 4 is the keel, 5 is an empty space between
the parts 3 of the ship and the rudder 14 for the passage of water and the propeller
blades 9, 6 is the solid part or boss of the propeller, 7 is a screw nut at the end of
the shaft 1 by means of which the propeller is held in place, 8 indicates the tail
parts or securing pins of the propeller blades inserted in the boss 6, 9 indicates the
blades, 10 are screws by means of which each blade is held in place in the boss 6, 11
is a part of a hollow air-tight cone which revolves with the screw propeller and is
terminated by a swivel, 12 is another part of the cone secured to the rudder and
provided with a circular nut which enters the swivel of the cone 11, 13 is a dotted
line indicating the minimum limit of the cone, inclination, 14 is the rudder of
the ship.
The difference between the new propeller and those at present in use is, that,
whilst the latter have bosses of comparatively small radii with blades which spring
from the boss, the new propeller has a boss which is very large and practically con-
stitutes a disc (6) around which the blades 9 are arranged (see Figs. 1 and 2).
The disc or boss 6 of the propeller is covered in front by the propeller shaft-tube 2
of the boat and at the back by the cone 11, 12 which can turn with the screw
propeller, or belong, partly to the screw propeller and partly to the rudder, or finally
can move round the motor-shaft which is elongated and reduced in size; in all cases
the object of using the cone is to reduce the friction of the boss 6 of the screw
propeller.
The radius of the boss 6 extends beyond the third of the total radius of the
propeller (limit already reached) and may extend to of the radius in large

page_text: In vessels which have screw propellers at each side the boss 6 of each propeller
can be covered in front by a very long cone or by the propeller shaft-tube which
may be shaped at the end in the form of a double opera-glass.
The blades 9 of the screw propeller are fixed to the periphery of the boss 6 by
means of the pins 8 with which they are provided and which are fitted in
cylindrical or conical cavities or sockets made in the boss. The pins are locked in
place by means of the screw 10, or cotters.
Owing to the disposition of the blades at the periphery of the disc-like boss
their working surfaces are brought as near as possible to the circumference where
the work can be done under the best conditions. A very special arrangement is
given to the blades in order that none of their parts should strike against the water
into which they advance which is a thing that does not appertain to any of the
propellers at present in use. To effect this it is absolutely necessary that the
entering edge b, B, d, D, f, F, h, H, j, J, l, L, (Fig. 3) should be very fine, and that
from this edge the front face of the blade, instead of being bulged, should form a
helicoidal surface corresponding with the forward movement of the vessel so as to
make the slip as slight as possible. The blade 9 being very thin at the entering
edge and less and less unyielding as it goes towards the centre of rotation it has to
be strengthened, as needful, at the back (a) by making a slight rounding L, M,
(section K, L, Fig. 3) at that side of the blade whilst giving the desired face to the
part, K, M, which is a continuation of the rounding.
The number of blades 9 may vary from three for the small size of propellers up to
sixteen (as in Fig. 1) and even more for the large size of propellers upon the
condition, however, that each blade uncovers, to the normal extent, the following
blade and that it sufficiently projects beyond the boss 6.
The cone 11, 12, arranged at the back of the boss 6 of the propeller is for the
purpose of reducing friction and can be supported entirely by the propeller, or may
have, as in Fig. 2, its part 11 connected with the propeller and its apex 12 secured
to the rudder; or it may be completely independent of the propeller and the rudder
being movably secured upon the end of the motor-shaft 1 which is prolonged for the
purpose. In all these cases the cone 11, 12, is hollow and perfectly air-tight.
The new screw propeller which urges the vessel forward in the same manner
as the ordinary screw-propellers may be made of any size and of any suitable
metal.
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
consider novel and desire to claim is :-
1. A new propeller for ships comprising, in combination, a solid disc-like boss
fixed upon the screw-propeller shaft, screw blades fixed on the periphery of the boss,
and a hollow and air-tight cone arranged at the back of the bess; the said boss, on
its periphery, being provided with cavities or sockets into which pins on the propeller
blades are fixed by means of screws or cotters, and the said cone being made in
either a single piece, or in two pieces, the base and the apex, secured together by a
swivel joint, substantially as herein before described with reference to the drawings
annexed and for the purpose set forth.
2. In a screw propeller, such as claimed in Claim 1, the use of short blades having
a very fine entering edge, a helicoidal working surface, and a strengthened back-face,
the special shape of the blades being for the purpose of preventing any part of the
blades striking against the water into which they advance, substantially as set
forth.
Dated this 19th day of October 1808