Improvements relating to Screw Propulsion.
Year: 1890

page_text: Date of Application, 16th Dec., 1890-Accepted, 14th Mar., 1891
COMPLETE SPECIFICATION.
Improvements relating to Screw Propulsion.
A communication from HERMAN DOCK, of Philadelphia, Pennsylvania, United
States of America, Mechanical Engineer.
I, ALFRED JULIUS BOULT, of 323, High Holborn, in the County of Middlesex,
M.I.M.E., 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 marine propulsion and has for its object the more
efficient action of screw-propellers and may be briefly stated to consist in a guide or
casing surrounding the propeller, guiding the water into the propeller and confining
it in such a manner that none of the force intended for propulsion is wasted in
centrifugal effect, or in radially or tangentially agitating the surrounding water, but
on the contrary, all of the fluid currents are so directed as to contribute to the
propulsion of the vessel.
The construction of this apparatus is shown in the accompanying drawings, in
which
Figure 1.shows a front view of a screw-propeller with this invention applied
thereto.
Figure 2 a vertical section thereof.
Figure 3 a central vertical section of a modified form.
Figures 4, 5, 6, 7 and 8 central vertical sections of other modifications thereof.
Figures 9 and 10 forward and end views of the form shown in Figures 5 and 6.
Figures 11 and 12 respectively show in elevation and section the application of a
segment of the bell-mouthed guide to a propeller as usually located in a vessel in
the dead wood forward of the rudder.
Figure 13 shows a vertical longitudinal section of another modified form of the
propeller casing embodying this invention, as applied to a screw propeller at the stern
of a vessel.
Figures 14 and 15 show similar sections of other modified forms of the casing,
and Figures 16, 17 and 18, respectively, transverse sections in the planes indicated by
the dotted lines, y and, in Figures 13, 14 and 15.
1 represents a propeller shaft, 2 the hub of a propeller and 3 the blades thereof.
(The propeller is assumed to travel in the direction of the large arrows from left to
right. 4 is a casing surrounding the propeller, made flaring at the forward
end 5, and, by easy curves, converging to a cylindric form of the diameter of
the propeller blades, which fit and turn in it, but without contact or friction.
The water is directed towards the propeller blades by guides 4, so that it passes
at its highest velocity through the throat 6 of the guide, where the propeller
engages it, and thus is prevented from diverging or spreading away from the
propeller 3, and is delivered, with the fullest effect, in a solid stream from the after
end 7 of the guide 4; and, since the inertia of the fluid is most effectually operative,
when opposed to bodies moving at highest velocities, the support afforded by the
water as a nut for the screw 3 to act upon, being at the place of greatest
velocity, it has the least slip possible, and the propelling effect is proportionably
improved.
The current of water is forced by the propeller blade 3, through the guide 4 in the
direction of the small arrows, to the left of Figures 2, 3 and 4, and induces a con-
verging current in the direction of the arrows above and below the guide 4, instead
of the wide-spread lateral agitation of the water produced astern by ordinary
propellers.

page_text: In order to prevent objects or animals being drawn into and fouling the propeller,
a grill or framework of bars 11, may be placed at the entrance to the guide or
casing.
water.
In the form shown in Figure 3, guiding blades 9 are placed in the forward end of
the guide, directing the water torsionally to the propeller, in such direction as most
effectively to engage the blades 3, so as to better avoid any slip or waste of power,
and the contracted tube or guide 4 has a slightly flaring conical adjutage at the rear
end of the cylindric part which serves to support the column of water delivered
through the guide and direct it to easy and forcible confluence with the surrounding
The guide is held in position by braces 10 securing it to contiguous
parts of the vessel, which braces should be so beveled or shaped as to present the
least resistance to progress through the water. In the form shown in Figure 4, the
external lines of the guide are concave like a bell, and the flow of water around
the guide 4, is in corresponding direction, the guide being lighter and of less bulk.
In the form shown in dotted lines in Figure 7, the external form of the casing is
cylindric and the propeller is located forward of the smallest diameter, and in the
form shown in Figure 8, the external form of the casing, is that of a truncated cone
with the base forward, and the propeller is shown located therein, similarly to
Figure 7. In both Figures 7 and 8, the direction of rotation of the propeller is
indicated by the vertical arrow, and the direction of motion of the vessel in the
water, by a horizontal arrow.
In the form of this invention, illustrated in Figure 9, the bell-mouthed inlet 5 to
the casing or guide 4, is made polygonal in transverse section; and in the form
shown in Figures 6 and 10, it is made with helical flutes in this portion. As shown
in Figures 11 and 12, instead of a complete ring or bell shaped guide 4, leading the
water to and confining it diametrically about the propeller, segments of the bell-
mouthed portion are employed, so that the guidance of the water is secured upon
each side of the keel, and dead wood with the same guiding effect.
Referring-to-Figures-13,-14,-15,-16,-17-and-18,-4-is-the-casing-made-cylindrical
or conical in-external-form-and-internally-tapering-in-curved-lines-from-the.forward.
end toward the centre, where it is of smallest internal diameter, and enlarging in
straight or curved lines aft thereof: Through the casing 4 are oblique openings 14
(preferably tapering in form) inclined so as to diverge toward the rear of the casing,
which openings 14 permit water to enter from the exterior of the casing and
discharge the water-rearwardly. The direction-of-motion-of-the-vessel-is-indicated.
by the horizontal arrows marked on Figures 13, 14 and 15 and the direction of
rotation of the propeller by the vertical arrows, in Figures 13, 14 and 15, and also
by the curved arrows in Figures 16, 17 and 18.
As shown in Figures 13 and 16, the opening 14 is single and annular.
As shown
in Figures 14 and 18 there are several annular openings, and as shown in Figures 15
and 17, the openings 14 are made helical, with an angular inclination in the direction
of the motion of the propeller, similar to the manner in which the guides of reaction
water wheels are inclined oppositely to the inclination of the blades or floats of the
rotating wheel. The effect of such guides, applied to a screw-propeller is, to
increase the progress of the propeller and vessel through the water and to exert a
stronger propelling effect with the same driving power.
Having-now-particularly described-and-ascertained-the-nature-of the-said-inven-
tion, as communicated to me by my foreign correspondent, and in what manner the
same is to be performed, I declare that what I claim is :-
1. In combination with a screw-propeller, a surrounding guide having a flaring
inlet or mouth forward, and contracting in curved lines, and diminishing in cross
sectional area, toward the throat, substantially as shown and described.
2. In combination with a screw-propeller, a guide of cylindric form surrounding
the propeller, and provided with a forward bell shaped inlet, diminishing in cross
sectional area toward the propeller in curved lines, substantially as set forth.
3. In combination with a screw-propeller, the circular casing surrounding the

page_text: propeller without contact therewith, and provided with a forward bell-mouthed exten-
sion diminishing in cross sectional area toward the propeller and an aft slightly
expanded adjutage, substantially as set forth and described.
4. In combination with a screw propeller and a cylindric case surrounding the
same, bell-mouthed segments arranged to form a conduit of diminishing area of cross
section toward the cylindric case, to guide the water with augmented velocity into
said cylindric case, substantially as set forth and described.
5. In a marine propelling apparatus, a screw propeller in combination with a
surrounding externally cylindric or conical case, having the forward internal portion
contracting in curved lines and rearwardly expanding therefrom substantially as set
forth.
6. In a marine propelling apparatus, a screw propeller in combination with a
surrounding externally cylindric or conical case, having an interior converging from
the forward end in curved lines, and rearwardly expanding therefrom and provided
with diverging apertures, substantially as shown and described.
7. In a marine propelling apparatus, a screw propeller in combination with a
cylindric or conical surrounding case, having an exterior contracting in curved lines
from the forward end, expanding aft of said contraction and provided with diverging
helically inclined apertures, substantially as set forth.
Dated this 16th day of December 1890
W. P. THOMPSON & BOULT,
Agents for the Applicant.