CERTAIN IM- PROVEMENTS IN SCREW PROPELLERS AND IN THEIR APPLICATION TO SHIPS, BOATS, AND OTHER VESSELS, AND ALSO IN MACHINERY OR APPARATUS FOR ACTUATING THE SAME."AL SP
Year: 1876

page_text: LETTERS PATENT to Robert Wilson, of the Bridgwater Foundry, Patricroft,
in the County of Lancaster, Engineer, for the Invention of "CERTAIN IM-
PROVEMENTS IN SCREW PROPELLERS AND IN THEIR APPLICATION TO SHIPS,
BOATS, AND OTHER VESSELS, AND ALSO IN MACHINERY OR APPARATUS FOR
ACTUATING THE SAME."
PROVISIONAL SPECIFICATION left by the said Robert Wilson at the Office
of the Commissioners of Patents on the 23rd June 1876.
ROBERT WILSON, of the Bridgwater Foundry, Patricroft, in the County of
Lancaster, Engineer. "CERTAIN IMPROVEMENTS IN SCREW PROPELLERS AND IN
THEIR APPLICATION TO SHIPS, BOATS, AND OTHER VESSELS, AND ALSO IN MA-
CHINERY OR APPARATUS FOR ACTUATING THE SAME."
In propelling vessels by means of screw propellers onc great difficulty to be
overcome is the loss of speed occasioned by what is called the slip of the screw,
which loss frequently amounts to one half of the progress that is due to the pitch
and number of revolutions of the screw in a given time.
Now iny Invention consists in so arranging, constructing, and applying screw
propellers in certain positions and in relation to each other, and in so actuating
them that the slip is reduced to the smallest possible amount, and in some cases
even a negative slip has been obtained, and the vibration so much complained
of so reduced as not to bo felt or even produced from the liko cause as that of the
propelling action to screw vessels.
To obtain these results I find it is necessary to adopt such an arrangement that
the action will produce a similar effect to that of the action of the tail of a fish upon
the water, that is to say, that when the water is moved in one direction by the oblique
action of the angled blades of the screw propeller, like that by the oblique action of
a fish's tail, that motion of the water will in like manner be counteracted by an
opposite action, which I obtain by a second propeller placed directly behind the
first and revolving in the opposite direction, so that a more perfect resistance shall
be obtained for the propeller's blades to act against than if the first motion of the
water was allowed to continue and to go on unobstructed in the one direction
like the revolving motion given to the water when only one propeller is used.
These two propellers which I use may each have two, three, or four blades as
the case may require; and although they may be of the ordinary forms generally
in use with expanding pitch or otherwise, I prefer them to be as near as possible.

page_text: to that of a portion of a thread of a true screw, whether of two, three, or four
threads, according to the number of blades employed, so that the forward tendency
of each portion of each of the blades when in motion may be exactly the same;
and in order to prevent vibration the section of the blades must be such as will
give a direct line of screw action and also the least possible resistance in passing
through the water consistent with the strength required, as described in the
Specification of Letters Patent granted to me in 1861, No. 114.
This principle and arrangement of propellers may be applied as twin screws on
each side of the dead wood or rudder, or behind the rudder, or in an opening in
the dead wood, like most of the ordinary screw propellers now in use, but instead
of that opening in the dead wood being so small as merely to allow space for the
propeller I prefer it to be as wide as circumstances will admit, so that the water
may have free access to the fore propeller and equally free exit from the after one,
and both the main and false stern post bevelled inwards to the opening that the
water may enter and leave freely.
This Invention is also particularly applicable for propelling the fish torpedo, as
by it the highest possible speed can be obtained.
It is also well adapted for canal navigation, as the water is but slightly agitated
in consequence of the motion caused by the first propeller being counteracted by
the action of the second.
My improved machinery for reversing the direction of the motion of the propellers
consists of four bevel wheels, one fixed on the solid driving shaft which gears into
two wheels revolving on fixed studs, and these two impart motion to the fourth
wheel fixed on a hollow shaft, one propeller is fixed to the solid shaft, which passes
through the hollow shaft to which the second propeller is fixed.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Robert Wilson in the Great Seal Patent Office on the 13th December
1876.
ROBERT WILSON, of the Bridgewater Foundry, Patricroft, in the County of
Lancaster, Engineer. "CERTAIN IMPROVEMENTS IN SCREW PROPELLERS AND IN
THEIR APPLICATION TO SHIPS, BOATS, AND OTHER VESSELS, AND ALSO IN MA-
CHINERY OR APPARATUS FOR ACTUATING THE SAME."
In propelling vessels by means of screw propellers one great difficulty to be
overcome is the loss of speed occasioned by what is called the slip of the screw,
which loss frequently amounts to one-half of the progress that is due to the pitch
and number of revolutions of the screw in a given time.
Now my Invention consists in so arranging, constructing, and applying screw
propellers in certain positions, and in relation to each other, and in so actuating
them that the slip is reduced to the smallest possible amount.
And in order that my Invention may be fully understood and readily carried
into operation I will proceed to describe the accompanying Sheet of Drawings.
Fig. 1 is a side view of the stern end of a vessel to which my improvements are
applied; Fig. 2 is an end view, and Fig. 3 a plan of the same; Fig. 4 is a section
on an enlarged scale of the driving gearing.
a and bare two screw propellers revolving in contrary directions within the
frame the outer part of which forms the false stern post to which the rudder d is
hinged; the propeller a is fixed on the solid shaft e, and the propeller b is fixed
on the hollow shaft f, which shafts are driven in contrary directions, as will be
described hereafter.
In order to reduce the slip to the smallest amount I find it is necessary to adopt
such an arrangement that the action of the propellers will produce a similar effect
to that of the tail of a fish, or that of a sculling oar upon the water, that is to
say, that when the water is moved in one direction by the oblique action of the
"

page_text: angled blades of one of the screw propellers like that by the oblique action of a fishi's
tail or a sculling oar, that motion of the water will in like manner be counter-
acted by an opposite action obtained by a second propeller placed directly
behind the first, and revolving in the opposite direction, and with an opposite
angle, so that a more perfect resistance shall be obtained for the propeller's blades
to act against than if the first motion of the water was allowed to continue and to
go on unobstructed in the one direction, like the revolving. motion given to the
water when only one propeller is used. The two propellers may each have two,
three, four, or more blades, as the case may require; and although they may be of
the ordinary forms generally in use with expanding pitch or otherwise, I prefer
them to be as near as possible to that of a portion of a thread of a true screw,
whether of two, three, four, or more threads, according to the number of blades
employed, so that the forward tendency of each portion of each of the blades of
each propeller when in motion may be exactly the same; the pitch or speed of one
propeller may be more or less than the other, according to circumstances, as may be
required; and in order to prevent vibration the section of the blades must be such
as will give a direct line of screw action and also the least possible resistance in
passing through the water consistent with the strength required, as described in the
Specification of Letters Patent granted to me in 1861, Number 114.
This principle and arrangement of propellers may be applied as twin screws on
each side of the dead wood or rudder, or behind the rudder, or in an opening in the
dead wood, like most of the ordinary screw propellers now in use, but instead of
that opening in the dead wood being so narrow fore and aft as merely to allow
a clear space for the propeller I prefer it to be as wide as circumstances will admit,
so that the water may have free access to the fore propeller and equally free exit
from the after one, and both the main and false stern posts are bevelled inwards to
the opening that the water may enter and leave freely with the least possible
resistance.
This Invention is also particularly applicable for propelling the fish torpedo,
shewn in Figs. 5, 6, 7 and 8, in which the double propeller is placed like the fish's
tail at the very extremity, and by which the highest possible speed can be obtained.
In some cases it may be more convenient to place the double propeller not at the
extremity of the torpedo, but it should be as near to it as may be found suitable for
the purpose required.
Fig. 5 is a transverse section of the driving gearing; Fig. 6, a longitudinal view
partly in section; Fig. 7, an end view; and Fig. 8, a plan in section. The propellers
a and
are fixed on shafts e and f, as before described.
These propellers are also well adapted for canal navigation, as the water is but
slightly agitated in consequence of the motion caused by the first propeller being
counteracted by the action of the second.
My improved machinery for driving the screw propellers a and b in contrary
directions is shewn best in Fig. 4. To the solid shaft e of the propeller a is fixed
the nitre wheel g, and to the hollow shaft f of the propeller b is fixed the mitre
wheel h. The shaft e is driven by a steam engine, as usual, and the motion from
the shaft e is transmitted to the shaft f by the wheel g, which gears into the two
intermediate wheels i, i, revolving on fixed studs or axles; these wheels i, i, drive
the wheel h in the contrary direction to the wheel g.
This arrangement of gearing with four wheels instead of three to produce the
reverse action not only reduces the side strain and friction on the bearings of the
solid and hollow shafts, but it diminishes to one-half the strain on the studs or
axles and on the teeth of the wheels, thereby allowing wheels of comparatively fine
bitch and small diameters to be used.
Having thus stated the nature of my Invention, and described the manner of
performing the same, I declare that I claim-
First. The double-acting screw propellers applied in either of the positions
pecified or as shewn in the Drawings, and acting on the water in the manner and
or the purpose described for propelling ships, boats, and other vessels.

page_text: Secondly. The application of double-acting screw propellers for propelling fish
torpedos.
And, Thirdly. The improved arrangement of gearing for actuating double screw
propellers in which four wheels are employed in the manner and for the purpose
described.
In witness whereof, I, the said Robert Wilson, have hereunto set my hand and
seal, this Eighth day of December, One thousand eight hundred and seventy-
ROBERT WILSON. (L.S.)