IMPROVEMENTS IN THE FORM OF THE AFTER PART OF THE HULLS OF SCREW SHIPS, AND IN THE CONSTRUCTION AND ARRANGEMENT OF SCREW PROPELLERS.
Year: 1878

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LETTERS PATENT to Walter James Griffiths, of Bayswater, in the County of
Middlesex, for the Invention of "IMPROVEMENTS IN THE FORM OF THE AFTER
PART OF THE HULLS OF SCREW SHIPS, AND IN THE CONSTRUCTION AND
ARRANGEMENT OF SCREW PROPELLERS.".
Sealed the 25th February 1879, and dated the 29th August 1878
PROVISIONAL SPECIFICATION left by the said Walter James Griffiths at the
Office of the Commissioners of Patents on the 29th August 1878.
"IM-
WALTER JAMES GRIFFITHS, of Bayswater, in the County of Middlesex.
PROVEMENTS IN THE FORM OF THE AFTER PART OF THE HULLS OF SCREW SHIPS,
AND IN THE CONSTRUCTION AND ARRANGEMENT OF SCREW PROPELLERS."
These improvements consist in forming the after body or run of screw ships so as
to allow the water free access to the screw propellers, which I propose doing in the
following manner :-The run for a suitable distance in front of the propeller, and
as far up as the top of the propeller, is made flat and of about the thickness of the
sternpost, and will then widen out in the usual manner. The length of the flat
part will be such that time will be allowed for the water to close on the tapered
part of the run, and will be about one-fourth of the beam of the ship, more or less,
according to the diameter of the screw and the amount of power employed; or, if
desirable, the flat part may be dispensed with, in which case the screw frame would
be attached at the top to the counter and to the keel at the bottom.
According to the present method of construction the taper of the run is con-
tinued to the screw frame, and is fullest at the upper part of the stern post, and the
propeller by acting on and sucking back the dead water which collects about that
part materially increases the resistance of the ship. This is obviated by the method
described above, and by widening out the stern above the screw extra displacement
can be there obtained, equal, or nearly so, to that which is lost by making part of
the run flat.

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In those cases in which the draught of water will not allow of a single
screw of sufficient size for the power, I propose to apply two screws on the
same shaft, one to be placed in the flat part of the run, and the other in the screw
frame.
According to another part of my improvements two-bladed screws are constructed
with most of the surface of the blades extending aft of the middle of the boss.
The blades are connected in a suitable manner, and are so attached to the part of
the boss fixed to the shaft that they can turn on the line through the middle of the
boss as axis, and vary the pitch to a suitable extent, the pitch of one blade
increasing as the pitch of the other decreases. When therefore the pressure on one
blade is greater than the pressure on the other, the excess of pressure on that blade
causes it to turn, and fine its pitch and increase the pitch of the other until the
pressure on each blade is equal.
In screw propellers as at present constructed the pressure on the blades varries
during the revolution of the screw, the pressure being greatest on the blade when
it is passing over that part of the screw's disc at which the currents of water are
flowing at the least velocity, and least when passing over that part of the disc at
which the currents are flowing at the greatest velocity. This causes an irregular
thrust to be obtained from the screw, and is also a cause of vibration; and the power
being chiefly expended in increasing the velocity of the currents where they are
flowing slowest, more suction is caused on the after part of the ship than if the
power were equally expended over the screw's disc. The inefficiency of screws from
these causes would be reduced by the above arrangement.
Four-bladed propellers could also be constructed in the same manner, the opposite
blades being connected: A similar result could also be obtained without the blades
being connected, for the blades being of the form above described and arranged to
turn could be held in position by springs,, which would counterbalance, the ten-
dency of the pressure on the surface of the blades to fine the pitch, and cause the,
blades to meet with nearly the same resistance throughout the whole of the
revolution.
Cams or other mechanical appliances could also be used to regulate the pitch of
the blades as the screw revolved, in which case the surface of the blades on each
side of axis could be made equal or nearly so.
Screws with three or any number of blades could be constructed with either of
the last two arrangements.

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A
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 1879.
WALTER JAMES GRIFFITHS, of Bayswater, in the County of Middlesex. “Iú-
PROVEMENTS IN THE FORM OF THE AFTER PART OF THE HULLS OF SCREW SHIPS,
AND IN THE CONSTRUCTION AND ARRANGEMENT OF SCREW PROPELLERS."
The first part of my improvements consists in forming the after body of run of
screw ships so as to allow the water free access to the screw propellers, which I
propose doing in the following manner-The run for a suitable distance in front
of the propeller, and as far up as the top of the propeller, is made Ant and of about
the thickness of the stern post, and then widens out in the usual manner. The
length of the flat part will be such that time will be allowed for the water to
close on the tapered part of the run, and will be about one-fourth of the beam of
-the ship, or two-thirds of the diameter of the screw, more or less, according to the
.diameter of the screw and therainount of power employed; or the flat part may be
dispensed with, in which case the screw framo would be widened, so as to admit of
& space before the screw equal to two-thirds of its diameter..
According to the present method, of construction the taper of the run is con-
tinued to the screw frame, and is fullest at the upper part of the stern post, and the
propeller by acting on and sucking back the dead water which collects about that
ipart materially increases the resistance of the ship. This disadvantage is obviated
by the method described above, and by widening out the stern above the screw
fextra displacement can be there obtained, equal, or nearly so, to that which is lost
by making the under part of the counter fuller.
In those cases in which the draught of water will not allow of a single screw of
sufficient size for the power, I propose to apply two screws on the same shaft, one
to be placed in the flat part of the run, and the other in the screw frame.
According to my improvements I construct twin screw vessels with a flat dead
Wood, which will extend forward of the screws to a distance equal to two-thirds
their diameter, and as high up as one-quarter of the screw's diameter above the
shafts, the hull beyond that being formed in the usual manner; or when screws of
large diameter are unnecessary, the dead wood may be made thick, so as to
strengthen the stem, and the screws placed as far apart as will allow of their
working. Through this thickening of the dead wood there will be no taper in the
hull near the screws. By these means the screws will be prevented from increasing
the resistance of the vessel by sucking back the dead water, as has already been
explained in the case of single screws.
When single or twin screws are placed in tunnels I construct the tunnels square,
and place inside rings which shall extend from the after end to the middle of the
screws. The tunnels will be continued straight for some distance in front of the
screws, and will then turn downwards. The straight part will be of such a léngth
as will allow time for the water to flow into the space left by the inclined surface
as the vessel moves forward. The water required by the screws will be considerably
more than would be supplied by a round tunnel of the screw's diameters, but this
extra:quantity will be supplied through the increased area of the square form. The
surplus quantity can pass out through the corners between the ring in which the
screw works and the angles of the tunnels, but these spaces may be partly or
wholly stopped if desirable.
According to another part of my improvements two-bladed screws are constructed
with most of the surface of the blades extending aft of the middle of the boss. The
blades are connected in a suitable manner, and are so attached to the part of the
boss fixed to the shaft that they can turn on the line through the middle of the
boss as axis, and vary the pitch to a suitable extent, the pitch of one blade
increasing ins the pitch of the other decreases. When therefore the pressure on one

page_text: blade is greater than the pressure on the other, the excess of pressure on that blade
causes it to turn and fine its pitch and increase the pitch of the other until the
I pressure on each blade is equal.
In screw propellers as at present constructed the pressure on the blades varies
during the revolution of the screw, the pressure being greatest on a blade when it
is passing over that part of a screw's disc at which the currents of water are
flowing at the least velocity, and the least when passing over that part of the disc at
which the currents are flowing at the greatest velocity. This causes an irregular
thrust to be obtained from the screw, and is also a cause of vibration, and the power
-being chiefly expended. in increasing the velocity of the currents where they are
'flowing slowest, more suction is caused on the after part of the ship than if the
power were expended equally over the screw's disc. The inefficiency of screws from
these causes is reduced by the above arrangement.
:
Four-bladed propellers are also constructed according to my improvements in the
same manner, the opposite blades being connected. A similar result is also obtained
without the blades being connected. The blades being of the form above described
and arranged to turn, are held in position by a cam or by springs, which counter-
balances the tendency of the pressure on the surface of the blades to fine the pitch,
and thus cause the blades to meet with nearly the same resistance throughout the
whole of the revolution.
...Cams or other mechanical arrangements may also be used to regulate the pitch of
the blades as the screw revolves, in which case the surface of the blades on each side
of axis may be made equal or nearly so.
Screws with three or any number of blades may also be constructed with either of
the last two arrangements.
And in order that my improvements may be clearly understood and readily carried
into practice, I will proceed to describe the Drawings hereto annexed.
DESCRIPTION OF THE DRAWINGS.
Figures 1, 2, and 3 show side and end views and plan of the stern of a single
screw ship constructed in accordance with the first part of my improvements. The
screw frame is of a width nearly equal to the diameter of the screw. The screw B is
placed at the after end, and is about two-thirds its diameter from where the tapered
'part of the hull ends at A. When so placed the screw will be out of the dead
water which follows the ship, and when working will not suck back the ship as
it does when the taper of the hull ends only a short distance in front of the
.бcrew.
Large screw frames may be strengthened by having an upright post about the
middle in front of the screw propeller.
Figures 4, 5, and 6 show side view, half end view, and half plan of the stern of
a twin screw vessel. The hull is of the usual form except the dead wood C, which
is considerably thicker than usual. The screws B are placed further apart than
usual on account of the thickening of the dead wood. By this alteration the taper
of the hull, which usually extends as far aft as the rudder, does not come nearer to
the screw than A, and, as in the previous arrangement, the screws are prevented
from working in the dead water.
Figures 7, 8, and 9 show separate views of the stern of a single screw ship, the
screw being enclosed in a tunnel formed in the hull of the vessel. This tunnel
tapers upwards from C to A, and from A to the screw B it is straight. The screw
being at some distance from the inclined surface C, A, it will not suck back the
dead water nearly as much as when the inclined surface is continued until it comes
close to the screw, and consequently the ship will move forward with less resistance,
as described with reference to open or external screws.
11-T
Figures 10, 11, and 12 show separate views of the stern of a twin screw ship,
the screws being enclosed in tunnels. These tunnels, in order to facilitate con-
struction, are made as follows:-A-rectangular-space E is made in the after part of

page_text: the hull, and extends straight forward to A; from there it is inclined downwards,
and dies off at C. In this space a partition G is fixed, which acts, as stern post, and
rings H, H, are fixed for the screws B, B, to work in Plates K; K the width of
the rings H, H, are fixed underneath these rings, and are attached at the ends to
the hull. Tunnels of this form can be easily constructed, and by leaving sufficient
space between A and the screws the screws will be prevented from drawing the
dead water from the inclined surface A, C, as in the previously described arrange-
ments.
Figures 13, 14, and 15 show separate views of the stern of a twin screw vessel.
The dead wood in this case is of the same thickness 'as the stern post, and is flat for
a considerable distance, in front of the screws. When the stern is formed thus the
screws may be kept of the usual diameter and distance apart:
Figure 16 is a side view of the stern of a screw ship similar to the stern' shown
in Figures 1, 2, and 3, but in this case two screws are arranged to work in the
screw opening. The forward screw B has a large boss, the rim being lined to the
same size. By thus filling up the centre of the screw the part of the disc, that is
used for propulsion is at a greater distance from the tapered part of the hull than if
the whole of the disc is employed. The after screw D is placed about two-thirds
its diameter further aft: By this arrangement a large screw area can be obtained
in light draught vessels, very little suction being caused by the propellers.
I
Figures 17, 18, and 19 show respectively side and end views and plan of a screw
propeller constructed in accordance withi iny improvements, the boss in each case
being shown in section. The construction is as follows:-A casting B which fits
on to the shaft A has two sockets C, C, on opposite sides of the shaft. The shell
or skin D of the boss is constructed with an elliptical hole in the forward end. This
shell will just pass over the socket C, C, the end of the casting B going through
the elliptical hole. The blades H, H, are constructed with flanges E, E, and
shanks F, F. These shanks F, F, pass through the shell D of the boss, and slip
into the sockets C, C, the flanges E, E, fitting into spaces. formed in the shell D of
the boss, to which they are secured by bolts in the usual manner. A cap G, in
which is also an elliptical hole, fits on to the shell D of the boss, and completes the
spherical form. A collar K is fixed on the shaft in front of the boss, and prevents
floating surfaces getting in the hole in the shell D.
The blades H, H, which may be constructed of various forms, have most of their
surfaces aft of the middle of the shank, so that the pressure on their face or pro-
pelling sides tends to turn the blades in the direction that fines or reduces the pitch.
The action of the propeller is as follows:-When one blade meets with more
resistance than the other, the excess of pressure on that blade causes it to turn,
thus fining its pitch. The shell D of the boss moves with the blade, for the flange E
of the blade is bolted fast to D, and the shell D moves the opposite blade, increasing
its pitch until the pressures on the blades are equal.
By these means, as before explained, the work will be more equally distributed
over the screw's disc, and less power will be expended in driving back the dead
water at the top of the disc than when the blades are fixed at a constant pitch, and
consequently the ship will move forward more easily.
Having thus described the nature of my improvements, and the manner of
performing or carrying the same into practice, I would remark that I make no
claim to any of the parts separately, which are well known and in common use,
but what I claim is,―
Firstly. The widening of the screw frame of single screw ships to about two-
thirds of the diameter of the screw or more, substantially in the manner and for.
the purpose
herein-before described, with reference to Figures 1, 2, 3, and 16 of the
Drawings hereto annexed.
Secondly. I claim the placing of the screw at the after end of the screw frame, in
contradistinction to the existing plan of placing it in the middle or nearer the
forward end, substantially as herein-before described, with reference to Figures 1,
2, 3, and 17 of the Drawings hereto annexed.

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Thirdly. I claim the forming of the after part of the stern of screw ships above
the level of the shafts, and as high as the top of the screws, of the same thickness,
or nearly so, as the stern post for a distance forward of the screws equal to two-
thirds, more or less, of the diameter of the screw propellers before the taper or wedge
form of the ship commences, substantially as herein-before described, with reference to
Figures 13, 14, and 15 of the Drawings.hereto annexed.
Fourthly. I claim the forming of the stern of twin screw ships with the screws
placed as far apart as will allow the dead wood to be of considerable thickness, the
dead wood being continued parallel until it reaches the tapered part of the hull,
substantially as herein-before described, with reference to Figures 4, 5, and 6 of the
Drawings hereto annexed.
Fifthly. In ships that are propelled by screws in tunnels I claim that the tunnels
forward of the screws for a distance equal to two-thirds of the screw's diameter,
more or less, be made with the upper part parallel with the keel before the tapered
or inclined part commences, substantially as and for the purpose herein-before
described, with reference to Figures 7, 8, 9, 10, 11, and 12 of the Drawings hereto
annexed.
Sixthly. I claim the construction of screw propellers with blades either connected
and allowed to, vary their pitch automatically, or have their pitch regulated by
mechanical arrangement, by which means the power is more equally distributed
over the screw's disc, and the vessel less retarded by the action of the propeller,
substantially as described, with reference to Figures 17, 18, and 19 of the Drawings
hereto annexed.
In witness whereof, I, the said Walter Jaines Griffiths, have hereunto set my
band and seal, this Twenty-sixth day of February, in the year of our Lord
One thousand eight hundred and seventy-nine.
WALTER JAMES GRIFFITHS. (L.S.)