IMPROVEMENTS IN SCREW PROPELLERS
Year: 1871

page_text: LETTERS PATENT to Everden Wimshurst, of Weighton Road, South
Penge Park, Anerley, in the County of Surrey, Engineer, for the
99
Sealed the 12th September 1871, and dated the 16th March 1871.
PROVISIONAL SPECIFICATION left by the said Everden Wimshurst at
the Office of the Commissioners of Patents, with his Petition, on
the 16th March 1871.
I, EVERDEN WIMSHURST, of Weighton Road, South Penge Park,
Anerley, in the County of Surrey, Engineer, do hereby declare the
nature of the said Invention for "IMPROVEMENTS IN SCREW PROPELLERS," to
be as follows:-
-
The object of my Invention is to obviate the tremulous motion com-
municated to vessels by the action of screw propellers and to economize
the driving power and render it more effective than heretofore.
I have discovered that the difference in the density or resistance of
the water at different depths from the surface is considerable, and that
consequently the resistance offered by the water to the lowermost blade

page_text: of the propeller is greater than that offered to the uppermost blade,
while the area of resistance remains the same.
I have further discovered that if the area of resistance of the lower
blade which is acting in the denser medium be slightly reduced, and the
area of resistance of the uppermost blade be correspondingly increased,
then an equilibrium of resistance will be obtained, the slip of the pro-
peller will be much reduced, and the power of the engine be more
economically applied. In order to obtain these results the propeller
blades are fixed in a moveable block which forms part of the boss of
the propeller. The inner end of this block is forked so as to embrace
an excentric or cam piece which is fixed on the stern post and through
which the horizontal propeller shaft passes excentrically. The effect of
this arrangement will be to allow the block (in which the propellor
blades are fixed) to swivel to and fro within certain limits so as to cause
the blades to turn round slightly on their vertical or longitudinal axis,
thereby decreasing the area of resistance of one blade and increasing in
a corresponding ratio that of the other. The excentric will only act as
a controller to keep the feathering action of the blades within definite
limits.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Everden Wimshurst in the Great Seal Patent Office
on the 16th September 1871.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, EVERDEN
WIMSHURST, of Weighton Road, South Penge Park, Anerley, in the
County of Surrey, Engineer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Sixteenth day of March, in the year of
our Lord One thousand eight hundred and seventy-one, in the thirty-
fourth year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto me, the said Everden Wimshurst, Her special licence
that I, the said Everden Wimshurst, my executors, administrators, and
assigns, or such others as I, the said Everden Wimshurst, my executors,
administrators, and assigns, should at any time agree with, and no others,
from time to time and at all times thereafter during the term therein
expressed, should and lawfully might make, use, exercise, and vend,
within the United Kingdom of Great Britain and Ireland, the Channel

page_text: Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN SCREW
PROPELLERS," upon the condition (amongst others) that I, the said
Everden Wimshurst, my executors or administrators by an instrument in
writing under my, or their, or one of their hands and seals, should
particularly describe and ascertain the nature of the said Invention,
and in what manner the same was to be performed, and cause the same
to be filed in the Great Seal Patent Office within six calendar months
next and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Everden Wimshurst, do hereby
declare the nature of my said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and
by the following statement, reference being had to the Drawing here-
unto annexed, and to the letters and figures marked thereon (that is to
say) :-
The object of my Invention is to obviate the tremulous motion com-
municated to vessels by the action of screw propellors, and to economize
the driving power and render it more effectual than heretofore.
I have discovered that the difference in the density or resistance of
the water at different depths from the surface is considerable, and that
consequently the resistance offered by the water to the lowermost blade
of the propellor is greater than that offered to the uppermost blade,
while the area of resistance remains the same.
I have further discovered that if the area of resistance of the lower
blade (which is acting in the denser medium) be slightly reduced, and the
area of resistance of the uppermost blade be correspondingly increased,
then an equilibrium of resistance will be obtained, the slip of the pro-
pellor will be much reduced, and the power of the engine be more
economically applied. In order to obtain these results I fix the pro-
pellor blades in a moveable block which forms part of the boss of the
propellor. The propellor blades with their block are thus left free to
turn on their vertical or longitudinal axis, and therefore (supposing the
whole propellor or both blades to be submerged) the increased resistance
offered by the greater density of the water to the lowermost blade will
cause this latter to turn round on its longitudinal axis, thereby
diminishing the area of resistance of the lower blade and correspondingly
increasing the area of resistance of the uppermost blade until the
resistance to both blades_is equalized. The pressure of the water alone
will be sufficient to bring the blades into equilibrium when both are

page_text: submerged, but as in sea-going vessels the pitching and rolling of the
ship will sometimes cause one of the blades to be temporarily exposed
above the surface, it becomes necessary in practice to limit this axial
motion of the blades to what is found to be necessary for the purpose of
my Invention:
In the accompanying Drawing I have shewn a method of effecting
this object. Fig. 1 is a side elevation of a screw propellor constructed
and arranged according to my Invention; Fig. 2 is a similar view, the
only difference being in the form of the propellor or mode of adapting
the blades. In Fig. 1 the blades are so arranged that the line of the
longitudinal axis will be central, so that the area of the resistance will
be the same on both sides of this line. In Fig. 2 the area of resistance
is greater on the after side than on the other. This is found by practice
to be the best form. Fig. 3 is an end or front view of the blades a, a,
fixed on their block b, but detached from the propellor shaft c, Figures 1.
and 2; Fig. 4 is a plan view looking down on the blades from above;
Figures 5, 6, and 7 are horizontal sections taken in the lines 1, 2, 3, 4,
and 5, 6, of Figures 2 and 3. The inner end of the block 6 on which
the blades a, a, are mounted is forked as shewn at Fig. 5, so as to
embrace an exentric or cam piece c which is fixed on the stern post d
as shewn at Figures 4 and 7, and also in Fig. 8, which is a front view
of the stern post through which the horizontal propellor shaft e passes,
as shewn at Fig. 8. The effect of this arrangement will be to allow
the block 6 (in which the propellor blades a, a, are fixed) to swivel to
and fro in a horizontal direction within certain limits, so as to cause
the blades a, a, to turn round slightly on their vertical or longitudinal
axis, thereby decreasing the area of resistance of one blade and increasing
in a corresponding ratio that of the other as and for the purpose already
explained. The forked block of the propellor blades is received between
a double forked block g, g, at the end of the propeller shaft e, and
the two forked parts band 9, 9, are held together (so as to form the
spherical boss) by means of two capping pieces g³, g¹, which are bolted
onto the ends of the forks g, g. The forked ends of the parts g, g, will
embrace the journals 6º, 6º, of the blades a, a, but will allow them to
turn freely so as to feather the blades as already explained.
It will now be understood that as the propellor boss rotates the forked
ends b¹, &, of the block b will bear against the periphery of the fixed
excentric c on the stern post d, and the block b will therefore be made to

page_text: "
swivel or oscillate on its vertical axis between the forks g, g, thereby
turning the blades slightly round on this axis so as to decrease the area
of resistance of the lowermost blade and increase that of the upper blade
as shewn at Figures 1 and 2. The excentric c will only act as a
controller to keep the feathering action of the blades within definite
limits, such as those indicated by the dotted lines in Fig. 4. The effect
produced by causing the block 6 with the blades a, a, to swivel or turn on
their longitudinal axis will be more clearly understood by referring to
Fig. 4, in which a represents the upper blade and a* the lower blade.
The upper blade being in less dense water than the lower one will offer a
greater area of resistance to the water, and this area of resistance is
indicated by the dotted lines 1, 1, in Fig. 4, whereas the area of resistance
of the lower blade will be diminished in exact proportion, as indicated
by the dotted lines 2, 2, Fig. 4. When the blades are in a horizontal
position in the water they will of course be in water of the same density,
and therefore should both offer the same area of resistance.
It will be understood that when the blades are in a horizontal position
the forks ¹, b, of the block b will be in a vertical position one above
the other, and in this position they will both be equidistant from the axis
of the propellor shaft e as the radii of the excentric care of the same
length above and below the propellor shaft.
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Having now described my Invention of Improvements in Screw
Propellors," and having explained the manner of carrying the same into
effect, I would observe that although I have in practice found an excentric
(such as that shewn) to act most satisfactorily as a controller of the
swivelling or feathering motion of the blades, I do not intend to confine
myself thereto, especially as I find that in moderately smooth water
where the blades are not liable to be lifted out of the water, the blades
will act and adjust themselves to their work without the assistance of
any mechanical device as a controlling agent, I therefore claim as the
Invention secured to me by Letters Patent, mounting the blades of a
screw propellor in a moveable block or other equivalent mechanical
device, so that they will be left free to turn on their longitudinal axis,
and thereby vary the area of their resistance and allow them to adjust
themselves to their work, as herein set forth.
I claim this mode of mounting the blades of screw propellors and
adapting them to the propellor shaft, whether used or not used in com.....

page_text: bination with any controlling device for limiting the feathering action of
the blades.
I also claim the mode shewn and described or any equivalent device
for controlling the action of the blades when any limitation of their
action is required.
In witness whereof, I, the said Everden Wimshurst, have hereunto
set my hand and seal, the Sixteenth day of September, in the
year of our Lord One thousand eight hundred and seventy-
one.