IMPROVEMENTS IN THE CONSTRUCTION, ARRANGEMENT, AND APPLICATION OF SCREW PROPELLERS AT THE STERN, BOW, OR BOTH ENDS OF STEAM SHIPS OR VESSELS
Year: 1877

page_text: LETTERS PATENT to Robert Griffiths, of Bayswater, in the County of Mid-
dlesex, Engineer, for the Invention of "IMPROVEMENTS IN THE CONSTRUCTION,
ARRANGEMENT, AND APPLICATION OF SCREW PROPELLERS AT THE STERN, BOW,
OR BOTH ENDS OF STEAM SHIPS OR VESSELS."
Sealed the 10th May 1878, and dated the 15th November 1877.
PROVISIONAL SPECIFICATION left by the said Robert Griffiths at the Office
of the Commissioners of Patents on the 15th November 1877.
ROBERT GRIFFITHS, of Bayswater, in the County of Middlesex, Engineer. "IM-
PROVEMENTS IN THE CONSTRUCTION, ARRANGEMENT, AND APPLICATION OF SCREW
PROPELLERS AT THE STERN, BOW, OR BOTH ENDS OF STEAM SHIPS OR VESSELS."
These improvements have for their object the forming of the screw propeller with
an enlarged centre boss, the diameter of which will be about half that of the screw,
more or less, according to the power which is intended to be applied for propelling
the vessel, and in fixing projecting pieces to the stern of the vessel the size of the
boss, so that the boss may meet with little or no resistance in moving forward with
the vessel. By this plan the water, which is forced backwards by the action of the
screw, will pass into the space left by the centre boss, thereby avoiding the loss of
power which is caused by the screw drawing the water from the stern of the ship,
and forcing it backwards to meet and obstruct the water which flows into the space
the ship is leaving.
The screw formed with an enlarged centre boss may be worked in a tunnel formed
within the ship or at the stern in the ordinary place with a casing over it, which
causes it to draw its supply of water from below the ship, or with a casing which
only extends a short distance in front of the screw, and in which radial arms or
other flat bars are fixed before and behind the screw to protect the screw, strengthen
the casing, and assist in causing the water to flow into the space behind the centre
Price 6d7

page_text: boss of the screw by taking out the twist that is given to the water by the action
of the screw propeller. These radial arms or flat bars may also be used or applied
in the tunnel or other form of casing.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Robert Griffiths in the Great Seal Patent Office on the 15th May
1878.
ROBERT GRIFFITHS, of Bayswater, in the County of Middlesex, Engineer. "IM-
PROVEMENTS IN THE CONSTRUCTION, ARRANGEMENT, AND APPLICATION OF SCREW.
PROPELLERS AT THE STERN, BOW, OR BOTH ENDS OF STEAM SHIPS OR VESSELS."
These improvements have for their object the forming of the screw propeller with
an enlarged centre boss, the diameter of which will be about half that of the screw,
more or less, according to the power which is intended to be applied for propelling
the vessel, and in fixing projecting pieces to the stern of the vessel the size of the
boss, so that the boss may meet with little or no resistance in moving forward with
the vessel. By this plan the water, which is forced backwards by the action of the
screw, will pass into the space left by the centre boss, thereby avoiding the loss of
power which is caused by the screw drawing the water from the stern of the ship,
and forcing it backwards to meet and obstruct the water which flows into the space
the ship is leaving.
The screw formed with an enlarged centre boss may be worked in a tunnel formed
within the ship or at the stern in the ordinary place, with a casing over it, which
causes it to draw its supply of water from below the ship, or with a casing which
only extends a short distance in front of the screw, and in which radial arms or other
flat bars are fixed before and behind the screw to protect the screw, strengthen the
casing, and assist in causing the water to flow into the space behind the centre boss
of the screw by taking out the twist that is given to the water by the action of the
screw propeller. These radial arms or flat bars may also be used or applied in the
tunnel or other form of casing.
According to the first part of my improvements in the construction, arrangement,
and application of screw propellers to steamships, I enlarge the centre boss of the
screw, and fix projecting pieces to the stern of the vessel, so that the enlarged boss
of the screw may meet with very little resistance when the vessel is under weigh.
By enlarging the centre boss of the screw, the length of the blades is reduced, and
they are thereby increased in strength, the non-effective part of the blades of the
propeller around the centre part thereof being dispensed with.
My improvements also consist in the arrangement and construction of the casing
which serves to cover and protect the screw propeller when applied over the screw
with the enlarged boss, or of screw propellers of the ordinary kind.
It has before been proposed and attempted to place the screw in a casing, but it
was found that it caused a loss in the speed of the ship.

page_text: I have discovered that the loss in speed was caused by the screw being confined,
which deprived it of a sufficient quantity of water. I then applied a lip or projection
on the lower part of the mouth of the casing, so as to draw more water to the screw
as the ship moved forward, which partly made up for the deficiency, as was described
in the Specification of a Patent granted to me, dated 22 November 1873, No. 3817.
I have since discovered that the funnel, mouth, or lip on the mouth of the casing
is required all around or partly around the casing, and its commencement for
enlarging the mouth for taking in more water should be made at the centre of the
blades of the screw, or nearly so, or the casing may be made without any funnel
mouth, but not to extend forward beyond the centre of the screw blades, more or
less, so as to allow the propeller at the forward side, and all around its periphery, to
draw its full supply of water, and force it backwards from its front or face of the
propelling side against the reactionary bars or blades at the after end of the casing
which takes out the twist which the action of the screw gives to the water, which
will then be delivered straight, or nearly so, on each side of the helm, and thus cause
the ship to steer better and reduce the tendency which screw ships have of being
turned from a straight course by the action of the screw propeller.
In place of surrounding the screw with a casing, I find that the upper half only
may be covered by a casing; this part of my improvements being particularly
advantageous in its application to twin screw propellers.
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 (Sheet No. 1) represent one of my improved arrangements
and construction of screw propeller and casing.
Figure 1 is an elevation of the screw frame of the ship.
Figure 2, an end view of the screw and casing; and Figure 3, a horizontol section
at the centre of the screw shaft.
The screw propeller B is constructed with a boss C of about half the diameter of
the propeller, more or less, according to the power and speed of the ship, and pro-
jections D, D, of about the same diameter as the forward end of the boss, are fixed
on the run of the ship, marked S in the Drawings, so that the boss meets with little
or no resistance in its forward motion with the ship. A casing E is fixed over the
screw; this casing is cylindrical from the after end to about midway of the
length of the screw, and is then increased in size as it is continued forward, so
as to form a funnel mouth F. Bars G, G, are attached to this funnel mouth at
their outer ends, and to the projections D, D, at their inner ends, so as to strengthen
the casing and prevent floating substances entering the casing and fouling the screw,
or the casing may be terminated at about midway of the length of the screw, and
the funnel mouth done away with.
Plates may be substituted for the horizontal bars G*, G*, and be set at an angle
so as to direct the water into the upper part of the casing.
Radial arms H, H, attached at their inner ends to the ring K, are fixed in the
after ends of the casing; these arms take out the twist that has been given to the
water by the action of the screw, and assist in causing the water to flow into the
space left by the enlarged boss C, the arms may be either curved or flat, and either
in a line or at an angle with the screw shaft.
Figures 4, 5, and 6 represent a similar arrangement of the screw and casing,
which differs in the following respects from the previous one:-The boss C is made
with the after part C detached from it. This part is fixed and does not revolve
with the screw. The radial arms H, H, (which are closer to the screw than in the
previously described arrangement) are attached at their outer ends to the casing,
and at their inner ends to this part C₁ of the boss, and the ring K is dispensed
with.

page_text: In either of the above-described arrangements the radial arms need not be fixed
at their inner ends.
The casing E is cylindrical from the after end to about midway of the length of
the screw, and from there to the forward edge of the screw increases in diameter,
and forms the funnel mouth E from the edge of which pieces E', E¹, extend to the
run of the ship S, and cause the water which supplies the screw to come from below
the ship. Bars may be fixed, if desired, for strengthening the casing and preventing
floating substances entering it.
Either of the above-described arrangements of the screw may be used without
the casing with or without the radial arms.
In the first arrangement, if the radial arms are used, they will be held by the
ring which is attached to the stern post; and, in the second arrangement, by the
after part of the boss C, which is also attached to the stern post.
Figures 10 and 11 (Sheet No. 2) show a modification of the first arrangement
previously described for use without a casing, the difference being that the screw
is smaller in diameter at the forward end A, A, than at the after end B, B.
Figures 7, 8, and 9 (Sheet No. 2) show a modification of the arrangement illus-
trated in Figures 1, 2, and 3 (Sheet No. 1). The screw B is constructed
with a spherical boss C of about one-third its diameter, and the projections are not
applied. The blades are constructed with their after edges straight, and their for-
ward edges curved. The casing is similar to that described in the first arrangement,
shown by Figures 1, 2, and 3.
Figures 12 and 13 (Sheet No. 2) represent a screw of an ordinary twin screw
ship with a casing of the improved form; the casing would be attached to the
counter of the vessel by the bracket M, and to the stern post by the bracket N.
Figure 14 (Sheet No. 2) shows an arrangement of the casing specially suitable
for canal boats, where the screw is liable to become fouled with weeds and other
substances. The casing E is hinged at H, H, and to the top of each side ropes or
chains I, I, are attached; bolts K, K, are arranged to fasten the casing when it is
pulled up, as shown on the right side of the Figure; and when these are withdrawn
the casing can be lowered by the ropes or chains I, I, as shown on the left side of
the Figure, and access can then be had for clearing away weeds or other substances
that may have collected there. The bolts and chains are carried up in pipes on
each side of the screw frame to a height some distance above the water level,
where they can be secured.
Figure 15 shows an end view of one of the screws of a twin screw ship fitted
with a casing which partially surrounds it. This will be seen to be a modification
of the casing shown in Figures 12 and 13, the lower half of the casing being dis-
pensed with.
The casing used for single screw ships may be modified in the same manner, thus
the casing shown by Figures 1 and 2, and by Figures 4 and 5, may be made without
their lower halves, the casing being terminated at the lines **. These casings may
be terminated at the funnel mouth; or, for the purpose of obtaining greater pro-
tection for the screws, may be continued beyond and attached to the run of the
vessel in like manner to the casing described with reference to Figures 4, 5,
and 6.
Another part of my improvements, which relate to the application of screw pro-
pellers to the bows of steamships, is the forming of the tunnels (for which Letters
Patent were granted to me, 7 November 1871, No. 2991), with enlarged entrances
which are continued as far back as midway of the length of the screws, where the
diameter of the tunnels will be reduced to such a size as will just allow of the screws
revolving, the forward part of the tunnels being similar to the inside of the casing,
shown in Figures 1, 2, and 3 of the Drawings.
Having thus described the nature of my improvements, and the manner of per-
forming or carrying the same into practice, what I claim is,
First. The improved construction and arrangement of screw propellers with bosses
C, of at least one-third to two-thirds of the diameter of the screw, the size of the

page_text: boss depending upon the power and speed of the ship, the fronts of such bosses
being flat, and the form on the after side being conical, paraboloidal, or cylindrical,
where the blades B are attached and conical behind, substantially as herein-before
described, and shown in Figures 1, 2, 2, 4, 5, 6, 10, and 11 of the Drawings
annexed.
Secondly. I claim the fixing of a projection D on the stern of the vessel in com-
bination with my improved form of screw propeller for preventing the water from
coming against the forward side of the boss as the ship goes forward, substantially
in the manner and for the purpose herein-before described, and shown in Figures
1, 2, 3, 4, 5, 6, 10, and 11 of the Drawings annexed.
Thirdly. I claim the arrangement and application to various forms of scrow
propellers of a casing E surrounding or partly surrounding the screw, which casing
extends to midway of the length of the screw, more or less, and with or without
fixed protecting bars G, G*, and radial arms or blades H, H, to take out the twist
that is given to the water by the action of the screw; and I also claim the appli-
cation of a funnel mouth F to the above form of casing, all substantially as herein-
before described, and shown in the Drawings annexed. I also claim the application
of a casing E partly surrounding the screws of twin screw ships, substantially. in
the manner herein-before described, and represented by Figure 15 of the Drawings
annexed.
Fourthly. I claim the improved arrangement and application of radial arms H
behind my improved form of screw propeller when worked in open water, or in
casings or tunnels, the radial arms H being either flat or curved, substantially
as and for the purpose herein-before described, and shown in the Drawings
annexed.
In witness whereof, I, the said Robert Griffiths, have hereunto set my hand
and seal, this Fifteenth day of May, in the year of our Lord One thousand
eight hundred and seventy-eight.
Witness,
J. G. TONGUE,
Patent Agent,
34, Southampton Buildings,
Chancery Lane,
W.C.
ROBERT GRIFFITHS. (L.S.)