IMPROVEMENTS IN'APPARATUS FOR INCREASING THE EFFICIENCY OF SCREW-PROPELLERS IN STEAM-SHIPS, AND IN PROTECTING SCREW-PROPELLERS."
Year: 1882

page_text: LETTERS PATENT to Robert Griffiths, of Bayswater, in the County of
Middlesex, Engineer, for an Invention of "IMPROVEMENTS IN'APPARATUS FOR
INCREASING THE EFFICIENCY OF SCREW-PROPELLERS IN STEAM-SHIPS, AND
IN PROTECTING SCREW-PROPELLERS."
PROVISIONAL SPECIFICATION left by the said Robert Griffiths at the Office
of the Commissioners of Patents on the 17th January 1882.
ROBERT GRIFFITHS of Bayswater in the County of Middlesex Engineer.
"IMPROVEMENTS IN APPARATUS FOR INCREASING THE EFFICIENCY OF SCREW
PROPELLERS IN STEAM SHIPS AND IN PROTECTING SCREW PROPELLERS."
According to part of my improvements the screw propeller is surrounded by a
covering formed by two cylindrical rings the diameter of one being such as will
just allow the screw to revolve in it and of the other one-sixth to one-fourth
larger, each ring is one-sixth of the screw's diameter in width, or thereabouts, and
they are attached to each other concentrically by suitable fastenings so that the
after edge of the larger ring overlaps the forward edge of the smaller one.
This covering is attached to the screw-frame so that the forward edge of the
smaller ring is opposite the middle of the points of the propeller blades and radial
arms may be inserted both in front and behind the propeller to prevent floating
substances fouling the screw.
When a screw is working the water all round the periphery of the disc has two
distinct motions, for the first half of the screw draws the water in causing it to
move towards the boss and the after half drives it out. Now in the covering I
propose to use, the ring over the after part of the screw prevents this latter action
and causes the water to offer more resistance in being driven back through which
more thrust is obtained: again the larger ring over the forward part of the screw
does not interfere with the drawing in action of that part of the propeller, for I
find that if that is checked a serious loss of speed results, and by using two rings

page_text: if the forward one takes in more water than the screw requires the excess passes
out of the space between the rings without increasing the resistance of the
vessel.
Coverings of this form will increase the speed, reduce the vibration, improve the
steering and diminish the racing of the screw when the ship is pitching in addition
to protecting the propeller.
With regard to the other part of my improvements, when a screw propeller is
working in the ordinary position at the stern of a ship the water flows into the
sides and bottom part of the screw's disc at nearly the speed at which the ship is
going but at the top part of the disc and especially just above it the water is
greatly dragged forward with the vessel owing to the fulness of the run there.
Now the blades of the propeller meet with little resistance in passing through
the currents which flow through the lower part of the disc but very great resistance
at the top where the water is comparatively standing still, hence most of the
power is expended in driving back the water at the top of the disc, now the
removal of this water reduces the pressure on that part of the stern and a great
increase is caused in the resistance to the ship's progress. In order to reduce this
loss I propose to use two plates one of which will form an arc of a circle of radius
about seven-twelfths of the screw's diameter, the are being described from the
centre of the screw shaft, this plate will extend from the run over the top of the
screw and one-third, or thereabouts, of the screw's diameter on each side of the
screw-frame.
Underneath this and attached to it will be another plate which will come close
to the points of the blades of the screw, the forward edge of this plate will be
opposite the middle of the points of the propeller blades, and it will extend the
same distance on each side of the screw-frame as the upper plate and both will be
rigidly attached to the screw-frame and the space between the upper plate and the
ship's counter may be enclosed by vertical plates or filled in with wood or other
material which will much increase the rigidity of the upper plate.
These plates I find increase the current of water through the top of the screw's
disc and prevent the propeller influencing water beyond them for both of which
reasons the loss previously explained is much reduced.
This arrangement may be used in combination with the covering previously
described in which case as the lower plate coincides with the inner ring of the
covering it is only necessary to attach the upper plate to the outer ring; or if it is
considered sufficient to protect the screw partially the smaller ring only may be
used in conjunction with the upper plate.
Similar arrangements may be used in twin screw ships in which case the plates
instead of being over the top of the screws would be placed more on the side
nearest the hull, which is the place where twin screws act on water which being
dragged with the ship and the plates could be continued down the side lower than
the level of the screw shafts if found desirable.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Robert Griffiths in the Great Seal Patent Office on the 17th July
1882.
ROBERT GRIFFITHS of Bayswater in the County of Middlesex Engineer
"IMPROVEMENTS IN APPARATUS FOR INCREASING THE EFFICIENCY OF SCREW
PROPELLERS IN STEAM SHIPS AND IN PROTECTING SCREW PROPELLERS"
;
According to part of my improvements the screw propeller is surrounded by a
covering formed by two cylindrical rings the diameter of one being such as will
just allow the screw to revolve in it and of the other one sixth to one-fourth larger
each ring is one sixth of the screw's diameter in width or thereabouts and they are
attached to each other concentrically by suitable fastenings so that the after edge
of the larger ring overlaps somewhat the forward edge of the smaller one.
covering is attached to the screw frame so that the forward edge of the smaller
ring is opposite the middle of the points of the propeller blades and radial arms
may be inserted both in front and behind the propeller to prevent floating
substances fouling the screw.
This
When a screw is working the water all round the periphery of the disc has two
distinct motions, for the first half of the screw draws the water in causing it to move
towards the boss and the after half drives it out. Now in the covering I propose
.to use, the ring over the after part of the screw prevents this latter action and
causes the water to offer more resistance in being driven back through which more
thrust is obtained: again the larger ring over the forward part of the screw does
not interfere with the drawing in action of that part of the propeller, for I find
that if that is checked a serious loss of speed results and by using two rings if the
forward one takes in more water than the screw requires the excess passes out of
the space between the rings without increasing the resistance of the vessel.
Coverings of this form will increase the speed, reduce the vibration, improve the
steering and diminish the racing of the screw when the ship is pitching in
addition to protecting the propeller.
With regard to the other part of my improvements when a screw propeller is
working in the ordinary position at the stern of a ship the water flows into the
sides and bottom part of the screw's disc as nearly the speed at which the ship
is going but at the top part of the disc and especially just above it the water
is greatly drawn forward with the vessel owing to the fulness of the run there.
Now the blades of the propeller meet with little resistance in passing through
the currents which flow through the lower part of the disc but very great
resistance at the top where the water is being drawn along with the ship hence
most of the power is expended in driving back the water at the top of the disc,
now the removal of this water reduces the pressure on that part of the stern and
a great increase is caused in the resistance to the ship's progress.
In order to reduce this loss I propose to use two plates one of which will form
an arc of a circle of radius about seven-twelfths of the screw's diameter, the arc
being described from the centre of the screw shaft, this plate will extend from the
run over the top of the screw and one third or thereabouts of the screw's diameter
on each side of the screw frame.
Underneath this and attached to it another plate is placed or arranged which
will come close to the points of the blades of the screw, the forward edge of this
plate will be opposite the middle of the points of the propeller blades and it will
extend the same distance on each side of the screw frame as the upper plate and
both will be rigidly attached to the screw frame and the space between the upper

page_text: .
plate and the ship's counter may be enclosed by vertical plates or filled in with
wood or other material which will much increase the rigidity of the upper plate.
These plates I find increase the current of water through the top of the screw's
disc and the upper one prevents the propeller influencing water above it and the
lower plate I find reduces the friction that the screw would otherwise cause on the 5
top plate, for the screw only accelerates the speed of the water which passes under
the lower plate and the water which is close to the upper surface is not affected by
the screw but passes out between the plates for which reasons the loss previously
explained is much reduced.
This arrangement may be used in combination with the covering previously
described in which case as the lower plate coincides with the inner ring of the
covering it is only necessary to attach the upper plate to the outer ring; or if it is
considered sufficient to protect the screw partially the smaller ring only may be
used in conjunction with the upper plate.
Similar arrangements may be used in twin screw ships in which case the plates
instead of being over the top of the screw's would be placed more on the side
nearest the hull which is the place where twin screw's act on water which is being
dragged with the ship and the plates could be continued down the side lower than
the level of the screw shafts if found desirable.
And in order that my Invention may be clearly understood and readily carried
into practice I will proceed to describe the Drawings hereto annexed.
DESCRIPTION OF THE DRAWINGS.
Figures 1 and 2 (Sheet 1) show the side and end views of the stern of a ship
fitted with apparatus which I use in accordance with my Invention for reducing
the loss caused by the screw propeller increasing the ship's resistance.
This apparatus consists of two plates A and B attached to the screw frame bent
to form arcs of cylindrical surfaces of which the screw shaft is the axis. The upper
plate A extends across the screw frame and the lower one B from opposite the
middle of the screw propeller to the rudder post the radial arms C C in front and
DD aft of the propeller act as stays and prevent the plates from being bent when
the ship is pitching, the after arms D D also check the tendency of the water to be
deflected laterally by the screw and for this purpose may be made of sufficient
width to come close to the after edges of the screw blades as shown. The way in
which the plates increase the vessels speed has already been explained and need
not be further described here.
Figures 3 and 4 are similar views of a modification of the same apparatus the
difference being that instead of using the radial arms to stay the plates, covering
plates E E extending from the hull of the ship to the outer edge of the upper
plate A are used and these plates give the necessary rigidity to the semi cylindrical
plates A B.
Figures 5, 6 and 7 are side end views and plan of the stern of a ship fitted with
a similar arrangement to that previously described but in this arrangement the
upper semi cylindrical plate A is made rather longer extending aft of the rudder
for which a suitable hole is cut and vertical plates F F extending from the outer
edge of this plate to the counter of the vessel are used.
Figures 13 and 14 (Sheet 2.) show an equivalent arrangement of apparatus
which may be used in place of that previously described the upper semi-cylindrical
surface being connected with the lower one by a tapered piece in which holes are
cut to allow the surplus water to pass through. In the Drawing Figures 13 and 14
the plates are shown stayed as in the arrangement Figures 1 and 2.
The application of my improvements to twin screws is shown in Figures 11 and
12 where it will be seen the plates instead of being over the top of the screws
are placed more on the side nearest the hull in which position they are required for
twin screws, but if desired the plates may extend further round the screws.
The covering used for protecting the screw is shown in Figures 8, 9 and 10

page_text: which represent side and end views, and plan of the covering one side of which is
in section. The covering is formed of an outer ring A and an inner ring B attached
by the pieces C C and fastened at top and bottom to the screw frame the after
edge of the outer ring A overlapping the forward edge of the inner one B which
is opposite the middle of the propeller. The radial arms D D in front of the
screw may be put at any angle suitable for pushing off floating substances which
would otherwise enter the covering and foul the propeller, while those arms E E at
the after end are made sufficiently strong to act as struts and stiffen the covering.
Similar coverings can be applied to twin screws.
Having thus described the nature of my improvements and the manner of
performing or carrying the same into practice I would remark that I do not claim
any of the parts separately which are well known and in common use, but what I
claim is as follows:-
First, I claim the placing and arranging over the propellers of single screw ships
of arcs of cylindrical surfaces for reducing the loss caused by the screw acting on
the dead-water substantially as and for the purpose described with reference to
Figures 1 and 2; 3 and 4; 5; 6, and 7; and 13 and 14 of the Drawings hereto
annexed.
་
Second, I claim the placing and arranging of arcs of cylindrical surfaces by the
propellers of twin screw ships on the side adjacent to the hull for the above purpose
substantially as and for the purpose described with reference to Figures 11 and 12
of the Drawing hereto annexed.
Third, I claim the protecting of screw propellers by means of a covering con-
sisting of two rings arranged substantially in the manner and for the purpose
described with reference to Figures 8, 9 and 10 of the Drawings hereto annexed.
In witness whereof I the said Robert Griffiths have hereunto set my hand
and seal this Fifteenth day of July in the year of our Lord. One thousand
eight hundred and eighty two.
Witness
J. G. TONGUE
Patent Agent,
34, Southampton Buildings,
Chancery Lane W.C.
ROB. GRIFFITHS. (L.S.)