IMPROVEMENTS IN SCREW PROPELLERS AND IN THE CONSTRUCTION OF PARTS OF VESSELS ADJACENT THERETO
Year: 1883

page_text: LETTERS PATENT to Robert Moore Steele, of Park Road, in the County of
Middlesex, Accountant for an Invention of IMPROVEMENTS IN SCREW
PROPELLERS AND IN THE CONSTRUCTION OF PARTS OF VESSELS ADJACENT
THERETO
PROVISIONAL SPECIFICATION left by the said Robert Moore Steele at
the Office of the Commissioners of Patents on the 10th February 1883.
ROBERT MOORE STEELE, of Park Road, in the County of Middlesex, Accountant,
IMPROVEMENTS IN SCREW PROPELLERS AND IN THE CONSTRUCTION OF PARTS OF
VESSELS ADJACENT THERETO.
My invention relates to the arrangement and driving of propellers, known as
twin screws, and to the strengthening of parts of the vessel adjacent thereto. It
is designed to effect better protection for the propellers, by a reduction of their
ath wart-ship area, to reduce the length of the stern-tubes, to facilitate the simul-
taneous driving of the two propeller shafts by one engine, and to strengthen and
support the keel and rudder post.
My improvements consist firstly in placing one of the twin propellers behind
the other, so as to enable me to bring the two shafts considerably closer together,
without the revolving blades fouling each other. The athwartship measurement
over the pair of propellers can thus be reduced considerably, and as a maximum,
by an amount about equal to half the diameter of a propeller, as compared with
known methods.
A much increased and valuable cover or protection by the athwartship overhang
of the stern and counter is thus given, thereby avoiding injury to the propellers
when the vessel is entering narrow dock gates, and also at other times.
The propellers, so arranged relatively to one another, may be placed either
forward of, or abaft the rudder, the rudder if necessary in the latter case having a
recess formed in it to avoid contact with the stern tubes or the shafts. The
propeller shafts may be driven isochronously by cranks through a pair of con-
necting rods from the cross-head of the same engine; through cranks linked by &
connecting rod from independent engines; by gearing one with the other or to a

page_text: centre engine shaft; or by separate and independent engines for each propeller;
or by any other known method.
When right and left handed propellers are driven as above described, so as
to revolve isochronously, one propeller may be set on its shaft so that its blades,
looking endwise to the ship, occupy the spaces between blades of the other
propeller.
Owing to the additional closeness with which the shafts are brought together in
my improved arrangement, the driving of the two shafts from a single cross-head
or by gearing is much facilitated.
"
For the same reason the points of issue of the stern tubes from the hull or "ran
of the vessel are brought further astern, and the stern-tubes are thus shorter, and
consequently stronger.
As the two stern-tubes are not of the same length, one of the propellers is fitted
with a specially elongated boss; or, alternatively, I add a boss-tail to the back of
that propeller which is most forward in its position, so as to bring the termination
of the two shafts and their surrounding bosses uniform with each other as to
position and displacement. Or, where the propellers are double hung, the aft-
bearing of the forward propeller may if preferred be so constructed as to take the
place of revolving boss-tail.
Fixed known tapering tail pieces behind large propeller hosses may be used if
desired with my improved twin-screws, and in that case the revolving elongation
on the boss of one propeller may, if preferred, give place to an elongation of the
--fixed tail-piece
Owing to the length of the keel-piece-supporting the rudder post, when my over-
lapping twin propellers are used before the rudder, the keel-picce may be made
extra deep without detriment to the propellers or draught of the vessel.
I also strengthen the keel-piece, when considered necessary, by side flanges or
supports, which may conveniently be formed from strong angle irons, secured to
each side of the keel-picce.
This flanging may be arranged parallel to the loud water line, or, alternatively,
parallel to the keel.
The checks of the angle irons may be packed up with timber if desired or other
material, either above, or below, or on both faces, so as to offer smooth and curved
faces to the run of the water and a tapering exit sternward specially on the under
and upper surfaces. The side flanges or supports with the timber or other filling
are continued forward and merged in the ship's afterbody, so as to offer no direct
resistance.
In some cases the keel-flanges may be built up hollow of angle iron, ribs and
plates, of any required outline, and sweep, to form an easy run and to offer
practically no resistance as before described.

page_text: '
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Robert Moore Steele in the Great Seal Patent Office on
the 16th August 1883.
ROBERT MOORE STEELE, of Park Road, in the County of Middlesex, Accountant,
"IMPROVEMENTS IN SCREW PROPELLERS AND IN THE CONSTRUCTION OF PARTS OF
VESSELS ADJACENT THERETO."
My invention relates to the arrangement and driving of propellers, known as
twin screws, and to the strengthening of parts of the vessel adjacent thereto. It
is designed to effect better protection for the propellers by a reduction of their
athwart ship area, to reduce in some cases the length of the stern tubes, to facilitate
the simultaneous driving of the two propeller shafts by one engine, and to
strengthen and support the keel and rudder post; my arrangement further allowing
of screws of increased diameter where desirable.
In order that my invention may be the better understood, I now proceed to
describe the same in relation to the drawings annexed hereto, reference being had
to the letters and figures marked thereon.
Like letters refer to like parts in each of the figures.
Figure 1. is a side elevation of a vessel's stern, showing my twin propellers in a
screw port with keel stiffener.
Figure 2. is a transverse section of hull showing independent vertical engines
suitable for driving my twin propellers.
Figure 3. is a side elevation of a vessel's stern, showing my twin propellers abaft
the rudder.
Figure 4. is a transverse section of hull, showing a duplex engine suitable for
driving my twin propellers isochronously.
Figures 5. and 6. are an end elevation and a plan respectively of the stern of a
vessel, showing propellers in screw port.
Figures 7. and 8. are an end elevation and plan respectively of the stern of a
vessel, showing the propellers abaft the rudder.
My improvements consist mainly in placing one of the twin propellers hebind
the other, so as to enable me to bring the two shafts considerably closer together
without the revolving blades fouling each other, whilst at the same time they
retain all the advantages of the usual well known system of twin propellers; viz,
when driven by independent engines, the power, in a modified degree, of largely
aiding the rapid steering of the vessel, and offering greater safety from disaster on
account of the independent and duplicate sets of engines and propellers in case of
one set being disabled.
By my improved arrangement the athwartship measurement over the pair of
propellers can thus be considerably reduced for any given diameter of propeller, as
compared with any known system of twin propellers, the reduction as a maximum
being about equal to half the diameter of a propeller.
A much increased and valuable cover or protection by the athwartship overhang
of the stern and counter is thus given, thereby avoiding injury to the propellers
when the vessel is entering narrow dock gates and also at other times.
The propellers A A¹, so arranged relatively to one another, may be placed either
forward of the rudder B, in a screw port, as shown in Figures 1, 5, and 6, or placed
abaft the rudder B, as shown in Figures 3, 7, and 8, in which latter case a recess C
may be formed in the rudder, to avoid contact with the projecting stern tubes D
or shafts.
The propeller shafts may be conveniently driven by separate and independent
engines for each screw, as shown in Figure 2, like twin screws of existing systems,
giving all the advantages for safety against accident of complete duplication of
engines and propellers.
Or, in order to reduce the number of cylinders to effect economy of space

page_text: occupied by the engines, the propeller shafts, by reason of their reduced distance
apart, may be conveniently driven by a duplex engine, as shown in Figure 4, that
is, by a pair of connecting rods E E from a cross-head F of the same engine.
Or, the propeller shafts may be connected by gearing, or driven by any other
known method. The pair of propellers, driven as above described, so as to revolve
isochronously, may be one right handed and the other left handed, or both right
handed, or both left handed.
Where stepped and overlapped twin propellers are driven as above described, so
as to revolve isochronously, the blades of one propeller may be placed in any
convenient relative angular position to those of the other, there being a variety of
reasons for such variety of disposition :-as for instance; when the blades of one
propeller occupy the spaces between those of the other, as in Figure 5, the blades
operate upon the most uniformly compact body of water; On the other hand,
when the blades are placed to cover each other, as shown for the sake of example
in Figure 7, the resisting area of the blades, when rotation is stopped, is thereby
lessened and risk of breakage reduced.
When the propellers are placed in a screw port (Figure 6), the additional
closeness with which the shafts are brought together in my improved arrangement
causes the stern tubes DD to issue from the hull or "aun" of the vessel further
astern, and thus to be shortened in longth and rendered proportionately stronger.
As the stern-tubes, D D, are not of the same length, the more forward one of the
propellers, A', is fitted with a specially elongated boss, or, alternatively, I add a
boss-tail H, Figures 6 and 8, to the back of that propeller A¹ which is most
forward in its position, so as to bring the terminations of the two shafts and their
surrounding bosses and stern-tubes uniform with each other as to position and
displacement.
The revolving boss-tail H, Figures 6 and 8, whether formed as part of the boss,
or as a separate casting or structure, may be keyed on a prolongation of the shaft
in any of the known methods of keying a screw propeller boss on its shaft.
Where after-bearings are employed with over-lapped twin screws, the revolving
boss-tail before mentioned may, if so preferred, be dispensed with, giving place to
a fixed boss-tail of similar bulk or displacement, but of any required form; and
such fixed boss-tail may be cast or formed with the after-bearing as part of its
structure.
In some cases, with the view of causing the aft propeller to work against the
spiral current of water caused by the forward propeller, and so obtain a greater
thrust, I make my overlapped propellers both right-handed or both left-handed,
and I may in some such cases dispense with a boss tail in whole or in part behind
the boss of the forward propeller, with the view of counteracting any tendency of
such propellers to turn the ship. This arrangement applies, whether the propellers.
are driven by independent engines for each, or by a duplex engine, or coupled
engine for both propellers.
Owing to the length of the keel-piece K, Figure 1, supporting the rudder post,
when my overlapping twin propellers are used before the rudder, the keel K
may be made extra deep with advantage and without detriment to the propellers
or increasing the draught of the vessel.
Again, I may in some cases make the stern-tubes equal in length, and clongate
both the bosses; that is to say, the boss of the forward propeller may have a boss-
tail added on its aft end as before described, and the boss of the aft propeller may
have an approximately similar elongation on its forward end. In such cases,
likewise, the respective elongations may be modified as to their relative size, where
the propellers are both right handed or both left-handed.
I may also further strengthen the keel piece, when considered necessary, by side
flanges or supports M, Figures 1 and 5, which may conveniently be formed from
strong angle irons, secured to each side of the keel piece and to the vessel's after-
body. This flanging may be arranged parallel or approximately parallel to the
load water line.

page_text: The cheeks of the angle irons may be packed up with timber or other material N,
Figure 5, if desired, either above or below, or on both faces, so as to offer a
tapering exit sternward, especially on the under and upper surfaces, as thereby
the tapering "exit" is adapted to varying conditions of the vessel's trim by the
stern.
The side flanges or supports, with their timber or other filling, are continued
forward and merged in the ship's afterbody, so as to offer no direct resistance to
the water.
In some cases the horizontal width of the angle irons may be increased by metal
plating, rivetted or secured thereto.
Further, in some cases, the keel supports may be built up hollow of angle iron
ribs and plates, of any required outline and sweep, to form an easy run and to
offer little resistance to the water as before described.
Having now fully described the nature and objects of my invention and the
manner of carrying the same into effect, be it known that what I consider novel
and desire to protect by Letters Patent is :-
First. The combination of two parallel shafts and propellers, one of which
propellers is partly behind and overlapping the other, both being placed forward of
the rudder in a screw port, substantially as set forth.
Second. The combination of two parallel shafts and propellers, one of which
propellers is partly behind and overlapping the other, both being placed abaft or
behind the rudder, a portion of the rudder blade, if and where necessary, being
recessed, to prevent contact with the stern tubes or the shafts when the rudder is
put over to large angles, substantially as set forth.
Third. The combination with the more forward one of a pair of overlapping
stepped screw propellers of an elongation or "boss-tail," whether attached to a
prolongation of the shaft or formed with the boss or attached thereto or formed
with or attached to an after bearing when this is used, substantially as and for the
purposes set forth.
Fourth. The combination with a pair of stepped screw propellers of elongations
on or adjacent to each of the two bosses, that of the forward propeller being in the
aft direction as above described, and that of the aft propeller in the forward
direction, or any mere modification of such device, substantially as and for the
purposes hereinbefore set forth.
Fifth. In a vessel fitted with overlapped twin propellers, the construction of a
deep keel piece for the stern frame, fitted with lateral supports in the form of
flanges set approximately parallel to the load water line, and with or without
timber fillings either above or below, substantially as and for the purposes set
forth.
Sixth. The combination of a pair of overlapping stepped propellers with any
known "duplex" engine by which the propellers may be driven isochronously,
substantially as set forth.
In witness whereof I, the said Robert Moore Steele, have hereunto set my hand
and seal this fifteenth day of August in the year of our Lord One thousand eight
hundred and eighty-three.
Witness
S. P. WILDING
23 Rood Lane, London EC.
Patent. Agent
R. M. STEELE (L.S.)