IMPROVEMENTS IN SCREW PROPELLERS FOR STEAM SHIPS AND OTHER VESSELS
Year: 1879

page_text: LETTERS PATENT to John Fisher, of South Norwood, in the County of Surrey,
Engineer, for the Invention of "IMPROVEMENTS IN SCREW PROPELLERS FOR
STEAM SHIPS AND OTHER VESSELS."
ealed the 11th July 1879, and dated the 17th January 1879.
PROVISIONAL SPECIFICATION left by the said John Fisher at the Office
of the Commissioners of Patents on the 17th January 1879.
JOHN FISHER, of South Norwood, in the County of Surrey, Engineer.
PROVEMENTS IN SCREW PROPELLERS FOR STEAM SHIPS AND OTHER VESSELS."
"IM-
This Invention relates to improvements in the arrangement and construction of
screw propellers so as to render them light, strong, and effective. For this purpose
in place of mounting the blades of the screw in a large central boss I form the
central part of the screw with an inner series of blades surrounded by a ring or hoop
so as to allow the water to flow direct through the centre with very little resistance,
thus utilizing this part of the screw to aid in propelling the vessel, and affording a
great advantage over screws made with a large heavy boss and with blades exposed
to accidents by coming in contact with wharves, floating lumber, and other impedi-
ments. A large central boss also offers great resistance by being drawn through
the water at a great velocity, leaving a vacant space as the vessel proceeds to be filled
in behind it, thereby producing broken water just at the point where the blades of
the screw require solid resistance to propel the vessel and avoid slip.
In carrying out this part of my improvements I form the scrow propeller with an
intermediate ring or hoop, the diameter of which may be varied to suit the power
of the ship or vessel to which it is applied. In the centre of the ring there is a nave
or boss with screw blades (which may be varied in number, shape, and size)
attached to the boss in the usual manner. The outer periphery of these screw blades
may either be cast solid with the intermediate ring, or they may be made separate
and be screwed or rivetted to the ring.
On the outer periphery of the ring or hoop a second series of screw blades are
mounted, being either cast solid with the ring, or attached thereto by screws or
other means.
These blades may be of much coarser pitch than the screw blades within the interior
of the ring, and they may also be varied in number, shape, and size. The outer
set of screw blades may or may not be formed with flanges on their outer edge

page_text: and perforated with holes or slots, as described in the Specification of Letters Patent
granted to me, and dated the 9th May 1853, No. 1135.
In cases where it is found desirable to use blades with a flange on the outer
periphery it may either be made straight or it may be varied in form from a straight
line to a true circle of the screw's diameter. It may not be a true curve given by
the radius of the screw, but the curve may commence at the extremity of the leading
edge of the blade and contract more or less towards the centre of the screw for the
purpose of taking in the water and compressing it towards the centre of the blade,
and thus present another means in conjunction with the perforations in the blades
and the water flowing through the interior of the ring of filling up the partially
vacant space or vacuum left in the wake of the screw, which increases with the
speed of the vessel.
Thus the object of the above contrivances is to obtain more solid water, greater
resistance, and less slip with blades of coarser pitch for vessels running at high
speed and applying their motive power direct to the screw.
It frequently happens that vessels meet with accidents which carry away one or
more of the blades of their screw propellers, thus rendering their steam power
useless; but with my improved screw propeller if all the outer blades were broken
off, the inner set of screw blades being protected by the ring or hoop, would serve
to propel the vessel into port at a reduced speed, where spare blades could be
applied in a few hours.
By making my improved screw propellers of steel they would be very suitable for
men of war.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Fisher in the Great Seal Patent Office on the 17th
July 1879.
JOHN FISHER, of South Norwood, in the County of Surrey, Engineer.
PROVEMENTS IN SCREW PROPELLERS FOR STEAM SHIPS AND OTHER VESSELS."
"IM-
My Invention relates to screw propellors used for the purpose of driving steam
ships and other vessels, and it has for its objects improved methods of constructing
and arranging such screw propellors so that they are more effective in their action,
producing a greater speed with the same expenditure of power, and applying the
power more thoroughly to the propulsion of the vessel instead of to the agitation of
the water than in screw propellors as ordinarily heretofore constructed and used.
My present Invention relates more especially to, and in great part consists of
improvements upon the methods of making screw propellors, described and shown
in the Specification and Drawings of Letters Patent obtained by me for "Improve-
ments in Machinery for Propelling Vessels, and in the Mode of Manufacturing the
same," dated May 9th, A.D. 1853, and Numbered 1135.
In screw propellors used for the propulsion of vessels, and especially where such
propellors are of large size, it is of importance that they should be of great strength
with as little weight as is consistent with such strength, and that when at work
every part of their blades should revolve in water as solid as possible, that is to say,
as little as possible broken up or disintegrated by the action of that part of the
blades which first acts upon the water, by the contrifugal force of the water caused
by their revolution, or by other causes; and other things being equal the most
effective screw in its operation for the purpose of propelling vessels will be that
which works in water the most solid or the least broken in the way described.
For this end it is of great importance that the shape or contour of those parts of
the stern or run of the vessel along which the water is conducted to the blades of
the screw as the vessel moves forward should be carefully shaped and proportioned
so as to offer the least possible resistance and to bring the water into contact with
the blades in as solid a condition and as free from lateral or other motion as
possible.
In order further to facilitate this result I construct my improved screw propellor
(according to one part of my present Invention) in two parts or divisions as
follows: I make the centre or boss of the screw, which is fixed upon the driving
shaft and from which the blades spring, in the form preferably of a sphere or
approaching that of a sphere (which it is desirable should be of as small diameter
as possible in order to facilitate its passage through the water and to lessen
the partial void or vacuum caused in its wake) and upon this boss or centro I
make or attach two or more (but preferably three) helical blades of any of the
forms well known and used in the construction of screw propellors.
At a certain distance from the centre of the propellor thus formed, which distance
may be altered and varied to suit varying circumstances, I make and arrango a
cylindrical ring having its axis concentric with that of the driving shaft, and of a
length preferably about as long as, or somewhat longer, than that of the scrow
blades viewed from the side.
This ring either forms a part of the screw blades or is rivetted or otherwise suffi-
ciently firmly and strongly attached to their extremities; and upon its outer
circumference I form or attach firmly a second set of screw blades of greater
diameter, and either as many as, or more or less in number, than those already
described within the cylindrical ring. The effect of the cylindrical ring described
which offers very little resistance to the water through which it passes is to prevent
the water from escaping radially or tangentially when acted upon by the inner
set of screw blades, and so to keep it in a condition more solid and more
capable of evolving the most beneficial result from these blades.

page_text: The propellor, constructed and arranged as described without the outer blades (
may be used in combination with the openings in the blades, as for the purpose
bereinafter described, especially for the propulsion of small vessels, but I prefer to
use it (either with or without such openings) in combination with the external
Beries of screw blades, which may themselves be made either with or without
openings through them, as hereinafter described.
The pitches of the screws formed by the inner and outer sets of blades described
may be the same or they may be different.
The cylindrical ring described may be made slightly bell-mouthed.
By my improved method of constructing screw propellers, as above described,
with an inner and an outer set of blades of the same or different pitch, separated
by a cylindrical ring, I gain the advantage of great strength with a centre or boss
of moderate size, as compared with an ordinary screw propellor of similar diameter
but having only one set of blades. Further, if from any cause one or more of the
outer blades of my improved propellor be broken, the vessel may still be propelled
safely into port by means of the inner set of blades surrounded by the cylindrical
ring, to which in a very short time a fresh set of external blades can be attached
and fixed.
In the accompanying Drawings Figures 1 and 2 are in illustration of this part of
my Invention. Figure 1 is an end view, and Figure 2 a side view, partly in section,
of a three bladed screw propellor. a is the boss; b, b, b, are the blades attached to
the boss; c is the cylindrical ring attached to the blades b, b, b; and d, d, d, are the
second series of blades outside the ring c.
Another part of my Invention consists of an improved method of arranging a
flange at the extremity of the blades of screw propellors of the kind just described
or of other kinds. I arrange such flange in the following manner:-At the outer
extremity of each blade I make or fix a flange at right angles, or nearly so, to the
surface of the blade which it joins, and projecting from such surface for a short
distance, which may be varied in different circumstances, according to the character
and intended speed and power of the vessel to which the apparatus is to be applied.
This flange may be made to project from the back of the screw blade or from its
front, or a flange may be made projecting both from the back and front.
I do not make this flange concentric with the centre of the screw shaft, but I
make it of a curve having the same, or nearly the same, radius as that of the
extremity of the screw blade, but struck from an eccentric centre in such manner
that the leading ends of the flange, or that end which is in advance when the vessel
is being propelled forward, is at a greater distance than the other end from the
centre of the shaft. The effect of this arrangement is that when the screw is
revolving the flange upon each blade as it advances takes in and collects a certain
extra quantity of water, and forces it gradually (on account of the eccentricity of
the curve of the flange) towards the centre of the screw, compressing or consolidating
it against the face of the back or resisting and propelling side of the blades, and
thus preventing, as in the arrangement of apparatus already described, partial void
or light and broken water, which would otherwise be left in the wake of the vessel,
whilst at the same time each flange leaves as it revolves a space momentarily empty
round and outside the diameter of the screw, followed by a reactionary rush of
water toward the centre of the screw in time to aid in supplying with solid water
the next following blade.
The flanges described need not be curved in a circular form, but their curve may
be cycloidal or of other convenient form, to draw the water gradually towards the
centre of the screw in the way described.
Or they may be made straight instead of curved, the leading end of each being
further from the centre of the screw than the other end.
Instead of one I sometimes arrange upon each blado of the screw two or more
flanges of the shape and for the purpose described, such flanges being arranged at
different distances from the centre of the screw. Sometimes I arrange a similar

page_text: flange at or near the inner end of the screw blade, but so shaped as to direct the
water gradually outwards instead of inwards.
In the accompanying Drawings Figures 4 and 5 are in illustration of this part of
my Invention, Figure 3 being an end view, and Figure 4 a section of a three bladed
screw; Figure 5 is an end view of a different screw. a is the central boss; b, b, b,
the screw blades; and c, c, c, the flanges at the extremities of the blades.
In combination with the improved arrangements of the screw propellor, as above
described, I prefer to make holes or openings through the blades of the screw for
the purpose hereinafter described.
I make these openings preferably in the form of diagonal slots completely through
each blade, the number and form of such slots being modified to suit varying
circumstances, but their form and arrangement being preferably as follows:-Looking
at the face of one of the blades in its horizontal position from the stern, the screw
being right band pitch and the advancing edge of the blade being uppermost (ns
shewn in Figure 5), I make a series of horizontal or radial narrow longitudinal
slots completely through the blade. These slots are of such number, and are sepa-
rated from each other by bars or divisions sufficiently strong as to prevent the too
great weakening of the screw blade, and I do not make the slots pass transversely
through the blade, but diagonally upward, so that their edges or mouth on the front
face of the blade are considerably higher, or in advance of their edges or mouth on
the back face of the blade.
The front and back faces of the slots, which approach more nearly to parallelism
with the faces of the blade in proportion as they are made more diagonal or inclined
as they traverse the latter, may be straight, but I prefer to make them of a helical
curve proportioned in pitch to the angle of their inclination with the face of the
blade, and consequently (though always of greater pitch than that of the screw
blades) decreasing in pitch as they approach to parallelism with the face of the
blades, and as the length in traversing the substance of the blade increases.
The action of these inclined or helically shaped openings is as follows:- -When
the screw arranged as described is in motion, its action in passing through the water
approaches nearly to that of a scrow working in a nut of solid material, the propel-
ling faces of the blades working helically, or screwing themselves with more or less
slip through the resisting water. As they do so, the advancing edges of the slots
through their substance catch the water in advance and propel it through them to
the rear of the blades at a greater speed than that at which the scrow is naturally
advancing, and they themselves, together with the blades of which they form a part,
are at the same time driven forward by reaction.
The result of this process is that whilst the pitch of the blades of the screw itself
is truly helical, that of the slots is also practically helical but of greater pitch, and
the combined effect of the two results in producing the advantages of a screw made
with an increasing pitch, but without the disadvantages of the latter, in which the
effect of a gradually increasing pitch is in result the same as if the thickness of the
blade is increased, the resistance to its passage through the water being also increased
in proportion.
Figures 5 and 6 show a screw propellor according to my improved arrangement,
having three blades with flanges of the kind already described at their extremities,
in combination with helically shaped openings through the blades, as last described.
Figure 5 is an end view of the screw, and Figure 6 a transverse section through
one of the blades, showing the helical openings. b, b, b, are the blades, having the
openings d, d, d, d, &c. through them in the shape and for the purpose described;
c, c, c, are the flanges.
Figure 7 shows one blade of a screw of a somewhat different shape, the exterior
flange 6 being straight, and the helical openings c, c, c, c, through the blade being
b
somewhat differently arranged.
I am aware that it is not possible to construct one special form of screw propellor,
which shall be available with advantage for every kind of vessel. For instance, a
screw propellor constructed, as described, with two sets of screw blades, separated

page_text: by a cylindrical ring, would not be advantageously applicable to small vessels o.
very high speed, but in such cases I should adapt my Invention to the circumstances
by combining the screw blades having eccentrically formed flanges upon their outer
edges, and fixed upon a boss or centre preferably spherical, or nearly so, and about
one fourth of the diameter of the screw, with the helical perforations through the
blades, as described. For much larger and more powerful screws I should adopt the
arrangement described and shewn of two sets of blades separated by a cylindrical
ring, the outer set of blades being provided with eccentrically arranged flanges, in
combination with the helical perforations through one or both sets of blades.
In order to reduce the weight of the spherical, or nearly spherical, or elongated
boss or centre, upon which the screw blades are fixed, that part of it which is not
essential to give the necessary strength may be made in such form that the inter-
stices between its parts can be filled up or packed with cork or other light material,
covered with a thin casing of iron or other metal.
Screw propellors constructed according to my Invention may be made of any
sufficiently strong material, but preferably of steel or gun metal.
Having now described my Invention, and the manner in which it is to be per-
formed, I claim, the arrangement of two sets of screw blades, the internal set being
separated from the external set by a ring, and the two sets being of the same or
different pitch, substantially as described and shewn in the Drawing. Also, the
arrangement of curved or straight flanges upon the blades of screw propellors, such
flanges having their leading ends at a greater distance from the centre of the screw
than their other ends, substantially as described and shewn in the Drawing. Also,
the combination with screw blades, having such flanges so arranged upon them, of
diagonal straight or helically shaped openings through the screw blades, substan-
tially as described, and shewn in the Drawing.
In witness whercof, I, the said John Fisher, have hereunto set my hand
and seal, this Fifteenth day of July, in the year of our Lord One thousand
eight hundred and seventy nine.