IMPROVEMENTS IN THE MANNER OF PLACING AND ARRANGING THE SCREW PROPELLER IN SCREW SHIPS, AND IN THE FORM OR CONSTRUCTION OF SCREW PROPELLERS."
Year: 1880

page_text: LETTERS PATENT to Walter James Griffiths, .of Bayswater, in the County of
Middlesex, Engineer, for an Invention of "IMPROVEMENTS IN THE MANNER
OF PLACING AND ARRANGING THE SCREW PROPELLER IN SCREW SHIPS, AND
IN THE FORM OR CONSTRUCTION OF SCREW PROPELLERS."
PROVISIONAL SPECIFICATION left by the said Walter James Griffiths at
the Office of the Commissioners of Patents on the 28th August 1880.
WALTER JAMES GRIFFITHS, of Bayswater, in the County of Middlesex, Engineer.
"IMPROVEMENTS IN THE MANNER OF PLACING AND ARRANGING THE SCREW
PROPELLER IN SCREW SHIPS, AND IN THE FORM OR CONSTRUCTION OF SCREW
PROPELLERS."
These improvements relate, first, to the altering of the stern of existing screw
ships, so that the screw propeller may be placed about two-thirds of its diameter,
more or less, behind the end of the run or tapered part of the hull, in which
position the screw works most efficiently, as stated and for the reasons assigned
in the Specification of Letters Patent granted to me, dated the 29th August 1878,
No. 3416.
In carrying out this part of my improvements I propose to remove the rudder
and lengthen the screw shaft so that it passes right through the screw frame and
through a bearing fixed in the rudder-post, which will be cut to allow of the
passage of the shaft, this bearing being so constructed that the two parts of the
rudder-post are connected by it. A new screw frame of suitable form is placed
behind and firmly attached to the existing screw-frame, and in this the screw is
placed, and the rudder is then attached to the after post of this new screw frame
in the ordinary manner, or when a ship is fitted with an after bearing that may
be bored out to allow of the shaft passing through it, in which case it would not
be necessary to cut the rudder-post.
Instead of fixing a new screw frame behind the present one two pieces may be
attached to the present screw frame for securing the rudder, one attached to the
keel, and of sufficient strength to support the weight of the rudder, and the other
above the screw to steady and afford lateral support to the rudder.
Another method of carrying out my improvements is to lengthen out the screw
shaft as before and make a new rudder, suspended at the same place and in the same

page_text: manner as the rudder with which the ship is fitted; this rudder will be constructed
with an aperture in it of sufficient size for the screw to work in; by these means
no alteration will be required in the ship except such as is necessary for lengthening
the screw shaft. When a rudder is constructed with an aperture in it for the
screw propeller to work in, the rudder may be so arranged as to be wholly or
partly a balanced rudder.
According to another part of my improvements I construct screw propellers so
that the leading and after edges of the blades are lines on the surfaces of spheres of
suitable radii, which spheres have their centres in the centre line of the screw
shaft, or the lines given to the edges of the blades may be curves differing
somewhat from the above.
Radial arms or blades curved to correspond with the screw blades may be
placed behind the propeller for taking out the twist given to the water by the
propeller. When the screw is placed in the rudder as proposed above, a sinaller
aperture would be required in the rudder if the scrow blades are curved in the
above manner.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Walter James Griffiths in the Great Seal Patent Office on the
28th February 1881.
WALTER JAMES GRIFFITHS, of Bayswater, in the County of Middlesex, Engineer.
"IMPROVEMENTS IN THE MANNER OF PLACING AND ARRANGING THE SCREW
PROPELLER IN SCREW SHIPS, AND IN THE FORM OR CONSTRUCTION OF SCREW
PROPELLERS."
These improvements relate, first, to the altering of existing screw ships, so that
the screw propeller may be placed about two thirds of its diameter, or thereabouts,
behind the end of the run or tapered part of the hull, in which position the
screw works most efficiently.
According to the present method of construction the screw propeller is placed
only a short distance from the end of the taper of the run (the middle of the
propeller being usually about one sixth of its diameter from the end of the wedge),
and the propeller by acting on and sucking back the dead water which collects
about the stern, especially near the top of the screw's disc, where the run is fullest,
reduces the pressure of the water on the stern and materially increases the resistance
of the ship.
This detrimental action of the screw is I find practicably obviated by placing the
screw about two thirds of its diameter from the end of the wedge or taper of the
run, which
find to be the most advantageous position for the screw, as it is then
in about the place where the streams which How along the stern meet, and by
operating on which it obtains its maximum thrust.
In order to carry out this part of my improvements I propose in altering a ship
to fix a bearing in the rudder-post and to lengthen the screw shaft so as to come
through this bearing; the screw propeller will then be placed on the end of the
shaft aft of the rudder post, and a new rudder of suitable shape to allow the screw
to work will be used, the rudder being suspended on the rudder post in the same,
or nearly the same, manner in which the original rudder was suspended.
The screw frame may also be wholly or partially plated over, which would
afford additional strength to the stern.
New ships may also be built in a manner similar to the above, the screw being
kept about two thirds of its diameter from the end of the run or tapered part of
the hull, and the rudder being constructed so as to leave space for the screw to
work in, the rudder being suspended on the post which is forward of the screw.
In altering a ship instead of using a rudder of the above description, the screw
being placed aft of the ordinary screw frame as before, a new screw frame of
suitable form can be placed behind and firmly attached to the existing screw frame,
and in this the screw would work, the rudder being suspended on the after post
of this frame in the ordinary manner.
According to another part of my improvements flat radial arms are attached to
the rudder behind the screw; these radial arms prevent the screw propellor from
twisting the water and improve the steering, the screw also giving more thrust.
When in altering a ship 1 merely place in the ordinary screw frame a new screw,
which will be fixed as far aft as practicable (close to the rudder post) in accordance
with Letters Patent granted to me, dated the 29th August 1878, No. 3416, I find
it advantageous to form the blades with the leading edges convex for the whole
length of the blade, and the after edges concave near the point and convex near the
root, the point of inflexion being about half way between the point and the root,
the screw surface from about two thirds the radius to the extremity being either
curved or bent at an angle forward; screws of the above description I consider
suited for giving high speed with little vibration.

page_text: DESCRIPTION OF THE DRAWINGS.
Figure 1, Sheet 1, shows a side view of the stern of an ordinary screw ship
altered in accordance with my improvements, and Figure 2 is an end view of the
rudder post of the same ship. The rudder post A is cut and the bearing B inserted;
the screw shaft C is lengthened to come through this bearing, and the screw
propeller D is placed behind the rudder post; the rudder E is constructed of the
form shown, which shape leaves space for the screw to work in. Plates F, F, are
used to cover the bottom part of the screw frame and assist in strengthening the
rudder post.
Figures 3 and 4 are similar views of a ship altered in the same manner, but in
this case the rudder E is constructed with pieces G, G, which extend up and down
the rudder post to the pivots at their ends, which form additional means of
securing it.
New ships may be built with rudders, as described above, the screw being placed
about two thirds of its diameter from the end of the taper or wedge of the run,
either by having a frame in front of the screw, as in Figure 3, or by having a
parallel piece of suitable length of the thickness of the rudder post before the
screw; a rudder of the form above described has the advantage of being able to
steer the ship when the screw is not working, whereas an ordinary rudder under
those conditions will only steer badly if at all.
To the rudder, Figure 3, are shown attached radial arms H, H, which according to
another part of my improvements I propose using; these radial arms are further
illustrated in Figure 5, which is an end view of the rudder, the radial arins being
shown on one side of it, and in Figure 6, which is a horizontal section of the
rudder at the level of the screw shaft. The radial arms are constructed of the
form shown to prevent their fouling the screw when the rudder is moved over in
steering, and the ring K is used for strengthening them.
Figure 7, Sheet 2, is a side view of a ship altered in accordance with another
part of my improvements, and Figure 8 is an end view of the rudder post of the
same ship. A bearing B is fixed in the rudder post A, and the screw shaft C
lengthened, as before; a frame L is firmly attached to the counter and to the top
and bottom of the screw frame and forms a new space for the screw to work in,
and on this frame L the rudder E is suspended.
By the alteration described in the three above cases it will be seen that the
screw propeller is moved to a distance of two thirds of its diameter, or thereabouts,
from the end of the wedge part of the hull, which prevents the screw from drawing
away the water from the tapered part of the hull, by doing which, screws as at
present placed materially increase the resistance of the ship.
Figures 10 and 11 are end and side elevations of a screw propeller, and Figure 9,
a side view with boss in section. The boss PI find it advantageous to construct
with a recess R; this enables the boss to overhang the nut on the end of the shaft,
and through this, when a screw of this description is placed in an ordinary screw
space, the screw can be brought to the after end of the frame close to the rudder
post without altering the shaft.
The blades I, I, are of the form shown Iª; Figure 10 showing the developed
form of the blade, the leading edge being convex and the after edge being half
concave, and half convex, as previously described in this Specification.
The surface of the blade I find it advantageous to curve forward at the point, as
shewn by the section S, Figure 9, about one third or thereabouts of the length of
the blade being curved. This bending forward of the point of the blade prevents
the point of the blade from fouling the corner of the frame, which would otherwise
Occur in many screw spaces when the screw was placed close to the rudder post.
Instead of curving the points, as shown in the Drawings, the blade surface might
be bent forward at an angle for about one third of the length of the blade.
Screws of the above description when applied to ordinary ships being close to

page_text: the rudder post, do not draw away the water from the wedge part of the hull as
much as screws in the ordinary position and give increased speed, the form of
blade also being suitable for giving a high speed with little vibration.
Having thus described the nature of my improvements and the manner of
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,—
First. I claim the altering of screw ships by placing the screw propeller behind
the screw frame, using a rudder which when suspended on the rudder post leaves
space for the screw to work in, substantially as represented in Figures 1 and 3 of
the Drawings annexed.
Second. I claim building screw ships in which the screw is kept two thirds of
its diameter, or thereabouts, from the end of the taper or wedge form of the stern,
the rudder being suspended on the post in front of the screw, and having a space
formed in it to allow the screw to work in, substantially as represented in
Figures 1 and 3 of the Drawings annexed.
Third. I claim the altering of screw ships by placing the screw propeller behind
the screw frame, and attaching a second frame to the ordinary screw frame for the
screw to work in, the rudder being suspended on the after post of this new or
additional frame, substantially as hereinbefore described and represented in
Figure 7 of the Drawings annexed.
In witness whereof, I, the said Walter James Griffiths, have hereunto set my
hand and seal, this Twenty sixth day of February, in the year of our Lord
One thousand eight hundred and eighty one.
Witness,
J. G. TONGUE,
Patent Agent,
34, Southampton Buildings,
Chancery Lane,
London, W.C.
W. J. GRIFFITHS. (L.S.)