Improvements in the Construction of the Screw-propellers of Steamers.
Year: 1886

page_text: Date of Application, 14th Sept., 1886.
Complete Left, 28th Sept., 1887.
Complete Accepted, 13th Sept., 1887.
Improvements in the Construction of the Screw-propellers of
Steamers.
We, WILLIAM NELSON HUTCHINSON, General in Her Majesty's Army, of Welles-
bourne near Bideford in the County of Devon, and EDWARD NEWALL MOLESWORTH-
HEPWORTH Esquire of Manchester, do hereby declare the nature of the said invention
to be as follows:-
There is at the present time some uncertainty as to the number of blades that
could with the most advantage be attached to the shaft of the screw-propellers of
steamers, and as to the exact curve (pitch) to be given to the blades. Many blades
militate against progress by interfering with the useful action of each other, and from
the many edges that strike the water being inimical to rapid revolution. Further,
the greater the number of blades the greater the risk of fouling. To avoid these
evils, while securing the advantages derived from many blades, is the aim of this
invention, and to provide a more stable fulcrum for them to act against than is usual.
By the said invention many blades, from the novel, hollowed concave form given
to the face that impinges against the water, and from the blades being fixed to the
shaft of the propeller more tangentially than radially, momentarily retain the water
in the hollow, thereby making it an unusually stable fulcrum, and press against it in
the direction most favorable to the steamers progress. To then may be attached
the flat or slightly coned bottom of a gas-tight cone-or a flat or slightly coned disc
or they may have no such additions.

page_text: COMPLETE SPECIFICATION.
Improvements in the Construction of the Screw-propellers of.
Steamers.
We, WILLIAM NELSON HUTCHINSON, General in Her Majesty's Army of Welles-
bourne near Bideford, and EDWARD NEWALL MOLESWORTH HEPWORTH Esquire of
Manchester in the County of Lancaster, do hereby declare the nature of our said
invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
There is at the present time some uncertainty as to the number of blades that
could with most advantage be attached to the shaft of the screw-propellers of steamers,
and as to the exact curves to be given to the blades. The best designed, force much
water centrifugally, and allow much to pass rapidly laterally-further, useing many
blades militates against the steamer's progress by interfering with the useful action
of each other. It is the aim of the present invention to give the blades such a
concaved hollow form that the water will be momentarily retained, thereby affording,
comparatively speaking, a firm fulcrum for the blades in their revolution to momen-
tarily press against the water in the direction most favourable to progress, viz., in a
line parallel to the shaft of the propeller, and whereby no blade can interfere with the
useful action of another.
Figs. 1, 4, and 5 are drawings taken from far astern, looking towards the steamer
in a line coincident with the axis of the shaft of propellers respectively with five,
three, and seven blades, marked from A alphabetically. The shaded parts T Fig. 1,
will be described hereafter. Except in their breadth they are identical in form, all
being hollowed on the same principle. Any breadth could be given to them. When
the whole of the circular space traversed in the revolution of the propeller is filled
with blades, as in Figs. I and 5, the forward-edge of one (the striking, entrance
edge) is just overlapped by the aft-edge of the next. Thus a portion of the forward
edge of B is just overlapped and hidden by a small portion of the aft-edge of A as
shewn by the part of the line that is dotted in Fig. 1, and the whole dotted line in
Fig. 5. Similarly, part of the forward-edge of C is just overlapped and hidden by
a portion of the aft-edge of B and so on with the rest.
The body of the blade is by degrees bent from the forward-edge m and from the
part close to the shaft into such a hollow-deepest near the periphery and aft-edge n
―that all parts of the depressed surface so act against the particles of water it presses
against in its revolution, as to prevent their immediate centrifugal or lateral flow,
and forces them for an almost infinitesimal distance, as a close compact column, in a
direction parallel to the axis of the shaft-the direction that most favours progress.
Truly the particles being driven in that direction for even less than half an inch
would quite suffice.
Fig. 2 must be regarded in connection with Fig. 1. HK is an imaginary plane
in which lie the aft, upper, and forward rims of the hollowed body of the blade-the
curve on the aft-rim, and the flange on the upper rim (the periphery) being above
that plane. The curved lines ab, cd, ef, gh, (similarly lettered in Fig. 1), all taken

page_text: at right angles to that plane, shew the depression at those several parts. The
flange, y tot Fig. 1, is of one depth and gradually lessens into the curves as seen
at c, e, g, ceasing at i. The hollow is deeper and more abrupt towards the periphery
than elsewhere because the water is rebutted from that part, and the flange does not,
like the curve on the aft-edge, militate against revolution. It is for this reason that
the flange is so much deeper above the plane than is the aft-edge curve. As this
curve would not be deeper than is necessary, its resistance to revolution is abundantly
compensated for by the stability it helps to impart to the fulcrum. It is very narrow
close to the shaft, to let the water pass more readily there than near the periphery,
thereby diminishing its tendency to take a centrifugal direction. Its curves, as
drawn below the plane H K, are intended to shew that the part close to the forward-.
edge of the blade, as well as the part close to the shaft is nearly flat. The figures
are drawn on too small a scale to admit of correct proportions. In the wish to clearly
explain the principle of the novel form given to the blade, the curves (a b, cd, &c.)
are exaggerated. Were the hollow great no aft-curve would be required above HK,
and but little flange. The greater the pitch the less would be the hollow, and the
depth given to the curve on the aft-rim. With an extreme pitch none might be
necessary. The blades are usually cast with the shaft, or are screwed to the hub, in
the direction to the axis of the shaft shewn in the slightly curved dotted line p Fig. 3.
This slight curve gradually expands in breadth and increases in depth as it approaches
the periphery. The exact angle at which the blade is set-or rather at which the
chord of the represented short curve is set-in some measure depends upon the
estimated ordinary speed of the steamer during her voyages. The greater the speed
the less forcibly do the surfaces of the blades impinge upon the water, for they
retreat as it were, therefore the greater the speed the more would the angle deviate
from the plane passing, through its centre, longitudinally in the axis of the shaft..
Further the greater the speed, the less does the Hange on the periphery prevent the
centrifugal flow of the water, therefore it would be made proportionately deeper, for
such increased depth would but little increase resistance to revolution. The greater
the speed the greater would be the inclination of the blades outwards from the
steamer. With the view to steadiness in revolution propellers with an odd number of
blades are preferred, as with them the curves on no two aft-edges could be similarly
acted on by the water simultaneously. When there are as many blades as seven,
part of their forward edges would be cut off in a curve as in Fig. 5, for the usual
straight edges would be so overlapped by the several following blades that the driving
pressure on the water, caused by the described usual bend near the said straight lines,
would be wastefully employed. As by this arrangement, howevor numerous the
blades, none can interfere with the usefulness of others, it is argued that with
propellers of large diameter (diameter meaning the width traversed in the revolution)
the number of blades should not be less than seven, whereby no space available for
propulsion would be lost. The tangential direction given in Figs. 1, 4, 5 to the
chord of the segment embraced by the aft-edge n throws the flange at y so forward
in the line of revolution that it (the flange) sweeps in towards the hollow a body of
water that most usefully opposes the flow of the water driven tangentially. A small
lip along the rim of the flange, curved inwards, would aid in retaining the water but
not add to the steamer's speed. An unceasing supply of fresh particles instantly
replace those forced away by the impact of the revolving hollowed surface-thus a
driving power, not attainable by any blade made on the ordinary principle, is given
to the hollowed blade even with decreased rapidity of revolution.
Fig. 3. In equatorial regions where navigation by steamers is often impeded by
the rapid growth of vegetation, by snags, and by floating islands of tangled roots in
sluggishly flowing waters, the fouling of the blades or paddles could be greatly, if
not entirely prevented, for the shape of the newly designed blades would allow of
their forward edges m being attached to the bottom of a cone (by preference made
of metal) of the same diameter as the propeller. This Fig. 3, shews a vertical
longitudinal section in the centre of a portion of the shaft S of the propeller through
the cone CC-the forward edge m of the blade A, seen in contact with the slightly-

page_text: coned (in preference to flat) bottom x, which gives the blades an inclination outwards
-and sectional parts of B & C as seen in Fig. 1; which sections are at some
distance from ¹ on account of the angle (the pitch) at which the blade is set on the
shaft. The curve drawn near x¹ is intended to be almost identical with the section a b
Fig. 2. The end of the propeller within the steamer is at S. The flange runs in
alignment with the circular edge of the cone. Instead of ending abruptly the upper-
most rim of the flange is prolonged in a gradual slope until it meets and coincides
with the edge of the cone. The flange of B Fig. 2 being thus gradually sloped as
far as t avoids an angle that would offer a slight resistance to revolution and might
possibly lead to fouling-and so with every flange. The bottom xx³ of a gas-tight
cone, fixed centrically on the shaft S, is shewn attached to the forward-edge m of
the blade A in Fig. 1. The shaded spots T represent the only parts of the bottom
that would meet the eye of a spectator situated in the position before named. When
blades overlap each other as much as is shewn in Fig. 5, the opposition their back
faces offer to progress would not be greatly exceeded by that of a smooth cone with
its apex towards the steamer. Its adoption has other advantages besides preventing
fouling. There are no jars from radial edges striking the water. The cone running
smoothly through the water supercedes all the resistances that would otherwise be
presented by blades at right angles to the line of progress, and the skin-friction of
its smooth surface would be less adverse than that of the back-faces of numerous
blades, and of the part of the shaft within the cone. Instead of two there is but one
risk of things getting jammed between the blades and their supporting stanchions.
The blades can be made much thinner than is usual from the support derived from
their fixture to the cone, and the cone when submerged decreases the weight of the
propeller. It is enabled to resist great external pressure by being filled with .com-
pressed air or gas. The greater the available space between the stanchions supporting
the shaft the more would the cone be tapered. This Fig. 3 is practically, but not
mathematically correct, for the whole of the forward-edge m should not be drawn as
if in contact with for the whole of the edge is never in contact with a plane
passing longitudinally through the centre of the shaft.
With the view to prevent fouling, when sufficient space cannot be provided for
the cone, it might, under unusual circumstances, be considered advisable to fix merely.
the bottom of the said cone to the blades as a disc, though doubtless the opposition to
progress would thereby be much increased. At any time were a steamer ordered on
special service of expected difficulties in navigation the disc could be attached.
a
Were a rotation given to the shaft of the propeller the reverse of the one
represented, the revolution of the spiral and flatter blades would obviously be the
reverse of what is described.
Having now particularly described and ascertained the nature of our said Invention
and in what manner the same is to be performed we declare that what we claim is :-
1st. The construction of the blades of the screw-propellers of steamers with the
hollowed form, substantially as described.
2ndly. The attaching to the said blades, when required, a cone with a flat or coned
bottom, or a flat or coned disc, substantially as described.
Dated this 27th day of September 1886.