An Appliance to Increase the Efficiency of and Prevent Injury to Screw Propellors.
Year: 1885

page_text: An Appliance to Increase the Efficiency of and Prevent Injury
to Screw Propellors.
I GEORGE MOLYNEUX Manager to the Gt Grimsby Fish and Steam Trawling
Company Ltd No 134 King Edward Street Grimsby do hereby declare the nature
of iny invention for AN APPLIANCE TO INCREASE THE EFFICIENCY OF & PREVENT
INJURY TO SCREW PROPELLORS, and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement :—
The object of my invention is to reduce the slip of screw propellers by con-
centrating their power upon a point directly astern of the vessels thereby greatly
increasing speed and steering powers, the rudder on being brought over being acted
upon by the stream of water produced by the propeller revolving within the said
casing. To stop vessels at very short distances when the engines are reversed by
immediately creating a large disc or discs of water under the stern or quarters.
My invention also reduces the swell of water made by screw propellers in river or
cauals and guards propellers from injury under some conditions such as raising
gear or loose ropes, etc.
The following is a description of my invention; it consists of a broad casing of
steel, copper, or other metal, fixed horizontally between the stern post and false
stern post of a steamer, or in the case of twin or more screws under the quarters,
or in such positions as are most convenient to encircle the screw propeller without
touching same, or in any way obstructing the motion of the screw propeller which
will revolve within the circle. formed by the said casing so as to act in a manner
similar to a centrifugal pump; the width of the said casing to be one third (rd) or
more of the diameter of the propeller which can be adapted to the requirements of
any existing screw steamer. The said casing to be set in a horizontal position just
clear of the points of the screw fans, and to be set slightly more open forward than
aft so as to nip the water at exit. The casing to be made of thinnest steel, copper,
or other metal consistent with strength.
Referring to the Drawings:-
Figure 1. is a transverse section of the casing in position around the propeller of
a steam vessel taken through line C. D. in figure 2.
Figure 2. is a sectional elevation of the same taken through A. B. in figure 1.
Figure 3. is an elevation of same in position.
Referring to Figure 1. which shows the space allowed for clearance between the
ends of the blades of the propeller and the inside of the casing, I prefer to allow
about inch clearance in the forward part of the casing reducing this clearance to
about th of an inch at the after part of the casing, these dimensions varying
with the diameters of the propeller blades, my object being to nip the water at the
point of exit by lessening the clearance between the ends of the blades, and the
inside of the casing as described above, and thus allowing the propeller blades to
obtain a better hold upon the water, by checking the flow of water from the pro-
peller blades at its exit from the casing in the manner described, thereby lessening

page_text: the tendency towards slip of propeller blades when running under the usual
conditions.
With the same object, I make the inside diameter of the casing less at the point
of exit aft than at the point of inlet forward, the casing being made to taper
between the inlet and exit ends thereof, as shown in the sectional elevation through
casing at Figure 2.
I prefer to make the inside diameters of the casing, as described above,
dependent upon the pitch of the propeller blades, the difference between the
diameters forward and aft being made less in the case of propeller blades of coarser
or larger pitch, and greater in the case of propeller blades of finer or lesser pitch,
or where the blades of propellers have by their construction a greater tendency
towards slip, my object being to prevent the tendency towards slip in the case of
propeller blades running under the usual conditions, and resulting from the discs of
water put in motion by the propeller blades in the same direction in which the
propeller blades are revolving, and thereby tending to escape the grip of the pro-
peller blades, my invention preventing this tendency towards slip by checking the
water at its exit from the casing aft.
My invention also greatly increases the steering powers of vessels, the water
being driven from the ends of the propeller blades in a concentrated stream
through the casing aft, this concentrated stream, acting with great force upon the
rudder when the helin is brought over, the rudder thereby coming, within the
concentrated stream flowing through the casing aft, the force of this stream then
coming directly upon the rudder, the force with which the said stream of water
acts upon the rudder being still further increased as the helm is brought fully over
see figure 2 and the rudder thereby placed at right angles to the stream of water
produced by the propeller blades revolving within the casing and flowing aft in a
concentrated form as described above.
My invention also increases the rapidity with which a vessel may be stopped
when going ahead or at full speed, as upon reversing the engines a very greatly
increased grip upon the water is obtained by the propeller blades meeting in an
opposite direction, the concentrated stream of water created by the propeller blades
before the reversing of the engines, this concentrated stream of water flowing in an
opposite direction upon reversing of the engines offers greatly increased resistance
to the propeller blades thereby causing the vessel to stop with much greater
rapidity than when running under the usual conditions.
My invention by reducing the slip of propellers, also allows of the use of
propeller blades of much coarser or larger pitch.
My invention also protects propeller blades from injury from ropes, gear, or
tackle, from striking against objects and from injury to the blades of propellers
occasioned by passing through Canals, or rivers of small depth, resulting from the
propeller blades coming into contact with the mud or deposit at the bottom, and in
the case of Steam Trawlers or towing boats preventing the net gear, or tow ropes
from coming into contact with the blades.
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:
1. The fixing of a cylindrical casing of steel, copper, or other metal, having the
ends open, around the propeller of a vessel horizontally between the stern post and
the false stern post of a vessel, or in the case of twin or more propellers horizontally
and in such positions as are most convenient to encircle the blades of the propellers
without touching the same, sufficient clearance being left between the ends of the
propeller blades and the casing, whereby the power of the propeller is concentrated
directly astern of the vessel, and also producing a concentrated stream of water
aft which acts immediately upon the rudder when brought over, and so greatly
increases the rapidity with which the vessel answers to her helm.

page_text: 2. The length of the said casing to be made equal to one third or thereabouts of
the diameter of the propeller.
3. The diameter of the said steel casing to be slightly larger forward than aft
when placed in a horizontal plane or position around the propeller so as to nip the
water at exit, thereby increasing the hold of the propeller blades upon the water
and greatly reducing the slip by which a large percentage of power of propellers is
at present lost.
Dated this mantinth day of Tanu 1996