IMPROVEMENTS IN SCREW PROPELLERS
Year: 1871

page_text: LETTERS PATENT to Robert Griffiths, of Rhual Issa, near Mold, in
the County of Flint, Engineer, and Walter James Griffiths, of the
same Place, Gentleman, for the Invention of "IMPROVEMENTS IN
SCREW PROPELLERS."
Sealed the 2nd June 1871, and dated the 28th February 1871.
PROVISIONAL SPECIFICATION left by the said Robert Griffiths and
Walter James Griffiths at the Office of the Commissioners of Patents,
with their Petition, on the 28th February 1871.
We, ROBERT GRIFFITHS, of Rhual Issa, near Mold, in the County of
Flint, Engineer, and WALTER JAMES GRIFFITHS, of the same Place,
Gentleman, do hereby declare the nature of the said Invention for
“IMPROVEMENTS IN SCREW PROPELLERS," to be as follows :—
The first part of our improvements has for its object the arranging
and forming the blades of screw propellers so that they may have greater
hold on the water for propelling the vessel, and this we accomplish when
two or more blades are used by having one blade straight or at right

page_text: angles, or bent backwards with the line of the screw shaft, and the other
blade bent or inclined forward towards the ship at an angle of 10 to 20
degrees, more or less, for about one-half its length from the boss to
point of blade, as shewn and described in the Specification of a Palent.
granted to one of us, dated February 19th 1858, No. 319. When four
blades are used we then have two blados bent forward and the other two
straight or inclined backwards.
Another method of carrying out our improvements is to curve the
blades at about half way from point to the boss, one part to be made
straight or inclined backwards, and the other part to bend or incline
forwards, as before named.
Another part of our improvements relates to the construction of the
boss of the propellers and the mode of securing the blades thereto. The
boss is cast with sockets (to receive the shanks of the blades), and has a
recess on one or both sides of each socket, in which place a piece of
metal or wood is fitted having one or more pins through them and
through the blade shanks, so as to tighten the metal or wood pieces on
to the blade shanks and secure them from coming out or twisting
round in the sockets, or a recess is cast in the boss on one or both sides
of the sockets having a gland fitted to it, which is screwed tight against
the shank of the blade to secure it from either coming out or twisting
round.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Robert Griffiths and Walter James Griffiths in the
Great Seal Patent Office on the 28th August 1871.
TO ALL TO WHOM THESE PRESENTS SHALL COME, wc, ROBERT
Griffiths, of Rhual Issa, near Mold, in the County of Flint, Engineer,
and WALTER JAMES GRIFFITHS, of the same Place, Gentleman, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-eighth day of February, in the
year of our Lord One thousand eight hundred and seventy-one, in the
thirty-fourth year of Her reign, did, for Herself, Her heirs and suc-
cessors, give and grant unto us, the said Robert Griffiths and Walter
James Griffiths, Her special licence, that we, the said Robert Griffith's

page_text: and Walter James Griffiths, our executors, administrators, and assigns,
or such others as we, the said Robert Griffiths and Walter James
Griffiths, our executors, administrators, and assigns, should at any time
agree with, and no others, from time to time and at all times there-
after during the term therein expressed, should and lawfully might
make, use, exercise, and vend, within the United Kingdom of Great
Britain and Ireland, the Channel Islands, and Isle of Man, an Invention
for "IMPROVEMENTS IN SCREW PROPELLERS," upon the condition (amongst
others) that we, the said Robert Griffiths and Walter James Griffiths,
our executors or administrators, by an instrument in writing under our,
or their, or one of their hands and seals, or under the hand and seal
of one of us or them, should particularly describe and ascertain the
nature of the said Invention, and in what manner the same was to
be performed, and cause the same to be filed in the Great Seal Patent
Office within six calendar months next and immediately after the date
of the said Letters Patent.
NOW KNOW YE, that we, the said Robert Griffiths and Walter
James Griffiths, do hereby declare the nature of the said Invention,
and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement thereof,
that is to say:-
The first part of our improvements has for its object the arranging
and forming the blades of screw propellers so that each alternate blade
(or when the blades are divided each part) strikes the water at different
angles to the screw shaft, so that they may have greater hold on the
water for propelling the vessel; and this we accomplish when two or
more blades are used by having one blade straight and at right angles,
or bent backwards with the line of the screw shaft and the other blade
bent or inclined forward towards the ship at an angle of 10 to 20 degrees,
more or less, for about one-half its length from the boss to point of
blade, as shewn and described in the Specification of a Patent granted
to one of us, dated February 19th 1858, No. 319, for bending the blades
of screw propellers forwards towards the ship. Or the blades may be
inclined from the boss to the points, and also fixed to the boss on each
side of the centre line of the spherical boss, so that each alternate blade
will not follow in the same thread of screw through the water as here-
toforc. When four blades are used we then have two blades bent
forward and the other two straight or inclined backwards.

page_text: Another method of carrying out our improvements is to curve the
blades at about half way or from point to the boss, one part of each
blade to be made straight or inclined backwards, and the other part to
bend or incline forwards, as before named.
Another part of our improvements relates to the construction of the
boss of the propellers and the mode of securing the blades thereto. The
boss is cast with sockets (to secure the shanks of the blades), and has a
recess on one or both sides of each socket, in which place a piece of
metal or wood is fitted, having one or more pins through them and
through the blade shanks, so as to tighten the metal or wood pieces on
to the blade shanks, and secure them from coming out or twisting round
in the sockets. Or a recess is cast in the boss on one or both sides of
the sockets, having a gland fitted to it which is screwed tight against
the shank of the blade to secure it from either coming out or twisting
round.
And in order that our improvements may be most fully understood.
Figure 1, Sheet 1, represents a front view and section of a screw
propeller having blades A and B arranged and constructed in accordance
with our Invention, the blade A being straight or at right angles with
the line of the screw shaft a (or it may be bent backwards), whilst the
other blade B is bent or inclined forward towards the ship at an angle of
from 10 to 20 degrees, more or less, for about one-half its length from
the boss to point of blade, as shewn. When four blades A, B, C, D, are
mounted upon the same boss, as shown by parts of the blades C, D, in
Figure 1, then in accordance with this part of our improvements the
two opposite blades A, B, will be straight, and the two opposite
blades C, D, bent or inclined forward towards the vessel, so as to rotate
alternately in succession through the water, and thus pass through or
produce different currents whereby the screw propeller will have a
greater hold upon the water towards its outer circumference for pro-
pelling the vessel. Or in place of the opposite blades A, B, being
straight, as previously described, they may be bent or inclined aft, the
opposite blades C, D, being bent or inclined forward towards tho vessel.
In place of bending the blades, as proviously described, cach blade may be

page_text: straight, and where two are employed one is set so as to incline forwards
towards the vessel, as shown at Figure 1°, and the other at right angles
with the screw shaft or inclined aft. Or both blades may be placed at
an angle, as shewn at Figure 1b. When four straight blades are
employed according to this part of our improvements then cach alternate
blade is set or inclined towards the vessel, and the opposite blades are
set at right angles to the shaft (or inclined aft).
Figure 2, Sheet 1, represents an end view and section of a two-bladed
screw propeller, the blades being split or divided into separate leaves,
according to this part of our improvements, at about the middle towards
the point. One part of the blade in this arrangement is straight, as
shown in section at b, whilst the other part 6* of the same blade is bent
forward towards the ship or vessel, the two parts of the same blade being
thus caused to rotate in different currents, whereby a greater hold is
obtained upon the water for propelling the vessel.
Figures 3 and 4, Sheet 1, show end views of a right-hand screw
propeller constructed according to our Invention, the blades being
divided transversely of their thickness, the forward part or half A of the
blade, as shown at Figure 3, being bent forward towards the vessel, the
other half or part B being bent slightly backwards. The end view,
Figure 4, shows the blades full width, with the part A bent forward
commencing at C, the part B slightly inclining backwards. Or the
blades may be made with the part A straight or at right angles with
the screw shaft, and the part B bent forwards.
By thus constructing and arranging the blades of screw propellers a
better hold will be obtained upon the water than when the blades arc
arranged to travel or rotate through the same current of water as
heretofore. The circumference, weight, and consequent cost of screw
propellers constructed in accordance with our improvements is also
considerably reduced.
Figure 5, Sheet 2, represents an end view and section of another form
of screw propeller constructed in accordance with our improvements, the
blades of which are split or divided in the direction of their thickness
down to about the centre of the blades between the boss and the outer
circumference of the blades. The part or leaf b* of each blade in this
arrangement is placed forward and bent towards the vessel, the other
part 6 being placed aft or backwards, and set at right angles or nearly so
with the screw shaft a.

page_text: Figure 6, Sheet 2, shows a similar blade to that previously described,
cach blade being split or divided into threo parts or leaves, as shewn, the
two outer parts being set off at some distance from the central part, by
which arrangement each separate part towards the outer circumference
of the blade will act upon different currents of water, and thus increase
the propelling power of the screw.
In place of fixing or arranging the blades of screw propellers in the
same circumferential line upon the bo as heretofore, we find it advan-
tageous to set the alternate blades a short distance apart so as to rotate
in separate circumferential lines, thus causing the blades to act upon
separato or distinct currents of water.
In carrying out our improvements it is not necessary that the blades
should be movable, as shown in the Drawings, as they may be cast in
one piece, as is well understood.
We will now describe our improvements in the construction of the
bosses of screw propellers and improved methods of securing the blades
thereto.
8
Figures 7, 8, and 9, Sheet 3, of the Drawings shew sectional views of
one of our improved methods of constructing the boss of a screw
propeller, and the mode of securing the shanks of the blados thereto.
In this arrangement the boss is cast with sockets & for the shanks of tho
blades to fit into, and a recess r is formed in one or both sides of the
sockets, into which blocks of wood wo are driven tightly on to the blade
shanks 8', which we prefer to form with a recess or with screw threads,
as shown. The blocks w are held securely in position by metal plates
m, m, and pins p, p, which pass through the plates m, blocks w, and
shanks s³, being secured by screw nuts and cotters, as shewn. Allowance
is made by forming tapered holes through the shanks 8', through which
the pins p are passed in order that the blades may be moved when it is
desired to alter the pitch of the screw, as will be readily understood on
examining the Drawing.
Figure 10 shows a horizontal section of the boss of a screw propeller
in which the shanks of the blades are secured by a gland g on cach side
fitting into a recess formed around the shank of the blade, the glands g
being screwed tightly into such recess by means of the pins p fitted with
nuts and cotters, as shown, so as to secure the shank of the blade from
cither coming out or twisting round.

page_text: Other methods of carrying out this part of our improvements are also
shewn in Figures 1, 2, 2", and 6, differing slightly from the arrange-
ments previously described, as will be readily understood on examining
the Drawings.
Having thus described the nature of our improvements in screw
propellers, and the manner of carrying the same into practice, we would
have it understood that we do not confine ourselves to the exact details
herein described; but what we claim is,―
First. The improved methods of arranging and forming the blades of
screw propellers, substantially in the manner and for the purpose
herein-before described and shewn in reference to Figures 1, 1ª, 1, 2, 3,
4, 5, and 6, of the Drawings hereunto annexed.
Secondly. We claim the improved methods of constructing the bosses
of screw propellers, and also the improved arrangements for securing the
shanks of the blades thereto, substantially in the manner herein-before
described and shewn in the Drawings hereunto annexed.
In witness whereof, the said Robert Griffiths and Walter James
Griffiths, have hereunto set our hands and scals, this Twenty-
third day of August, in the year of our Lord One thousand eight
hundred and seventy-one.
25
Witness,
FRANCIS SCHMADHORST,
Hosier,
48, Bull St.,
ROBERT GRIFFITHS.
(L.S.)
WALTER JAMES GRIFFITHS. (L.S.)
Birmingham.