Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a ducted propeller
assembly for marine applications and a method of operating such an
assembly. The advantages of mounting a ship's marine propeller in
a duct to improve its effectiveness are well known.
The duct is normally followed by a conventional rudder but
it has also been proposed to have the duct unted so that it can
swivel about a roughly vertical axis to direct the propeller wake to
one or other side of the ship's centre line, and thereby provide a
sideways force and steering moment on the ship.
According to the present invention, an apparatus, for use
in manoeuvring a ship, comprises a ducted propeller assembly and
spoiler means situated in an intermediate region of the duct between
the propeller and one end of the duct, said spoiler means being
located downstream of the propeller and operable to deflect the
propeller wake horizontally thereby to provide a sideways force and
steering moment on the ship, said duct diverging downstream of said
spoiler means whereby a significant overall sideways movement of the
propeller race is produced during steering.
The method of the invention consists of a method of
operating an apparatus comprising a ducted propeller assembly and
control means situated in the duct between the propeller and one
end of the duct and operable to deflect the propeller wake horizontally
thereby to provide a sideways force and steering moment on the ship
on which the apparatus is mounted, the control means comprising
apertures in the duct walls and means for introducing interfering
secondary flows through the apertures into one or other side of the
propeller wake to detach the boundary layer flow and hence the
propeller wake from one or o~her side of that region of the propeller
duct downstream of the propeller, and the velocity of the secondary
flow when it issues from a control aperature being up to two or
three times the velocity of the main flow leaving the duct.
The terms "front" and "rear" used throughout the specification
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assume the usual "straight ahead" motion of the duct. It follows
that when~ for example, the propeller is operating in reverse,
then the "rear" end of the duct or of any other item referred to
will precede its "front" end.
The duct preferably includes a parallel-sided portion
and the propeller is then situated in this portion. The control
means is also preferably situated in the parallel-sided portion
where present e.g. at the rear or front extremity of the parallel-
sided portion if this is confined to a central portion of the duct.
The control means may operate by introducing the interfering
secondary flow through slots or rows of holes in the duct walls.
In other embodiments, the control means achieves the same
effect by introducing a small mechanical obstruction into the
boundary layer flow at one or other side of the propeller wake.
The control means preferably consists of two separate
controls symmetically arranged one on one side and one on the
other side of an imaginary vertical reference plane containing the
axis of rotation of the propeller. The transverse reference plane,
referred to below, is an imaginary reference plane that contains the
axis of rotation of the propeller but is perpendicular to the
vertical reference plane.
Reference in the specification to the control means being
"inoperative" is intended to cover any situation in which the control
means is not operating to deflect the propeller wake to one or
other side of the vertical reference plane.
When the control means is inoperative, the apparatus will
behave like a conventionalducted propeller in so far as the
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propeller wake is symmetrically disposed in the duct and
attaching to all or part of the downstream region of the duct
above referred to. When the control on just one side of the
duct is operating, however, this will destroy or reduce the
attachment of the boundary layer of the propeller wake on that
side of the duct and as a consequence the propeller wake as a
whole will swing more towards the other side of the duct.
The cross-section of the duct region to the rear of the
propeller, as viewed in the transverse reference plane, may be
increasingly divergent as it approaches the rear end of the duct.
In such a case, when the control means is operated to deflect the
propeller wake to one or other side of the vertical reference
plane, then it is thought that the natural tendencyfor the
propeller wake to attach to the walls of the duct will result
in the propeller wake being increasingly deflected in the
transverse reference plane as it is pulled by this wall attachment
effect on to increasingly divergent portions of the duct. The
result of this is that the final horizontal deflection of the
wake may be significantly greater than it could be using a duct
with a conical cross-section in the transverse reference plane
and having the same inlet and outlet diameters in this plane as
the preferred version just referred to.
However, in the cross-section of the duct in the vertical
reference plane, it is advantageous to have the duct region
downstream of the propeller straight-walled e.g. parallel sided
so as to reduce diffusion of the propeller wake flow in the
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vertical direction. Alternatively the duct walls might be slightly
divergent or slightly convergent in this plane.
The walls of the duct may be hollow. Thus where secondary
flows are used to detach the propeller wake, the thickness of the &ct
wall may be used to house associated ducting. Where, instead, obstructions
are used for this purpose, then the actuating mechanism for moving the
associated members into or out of the propeller wake can be housed in
the thickness of the duct wall.
In one embodiment, where the duct walls are hollow, baffles
are provided in the duct wall to separate the interior of the wall into
two control chambers. Each control chamber is apertured at the front
edge of the duct and at a region further towards the rear of the duct.
A valve is included in each control chamber between the two apertured
regions to permit or prevent flow of ambient liquid through the chamber.
Embodiments of the invention will now be described, by way of
example only, with reference to the accompanying drawings in which Figures
1 and 2 respectively show an end view, looking forward, and a simplified
vertical section of one embodiment.
Figures 3 and 4 show schematically, with simplified horizontal
sections, the operation of the assembly for the 'straight-ahead' situation
and the 'turn to port' situation;
Figure 5, which appears on the same sheet as Figure 3 and Figure
6 show diagrammatically the overall lay-out for the embodiment of Figures
1-4;
Figures 7 and 8 show alternative embodiments to Figures 1-4;
Figure 9 shows a simplified hori~ontal section of a preferred
embodiment;
Figures lOa and lOb show a vertical section and an end view
(looking forwards) of an apparatus according to the present invention fitted
on to a ship's hull;
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Figure 11 shows a diagrammatic horizontal section illustrating
the use of a suction effect to deflect the propeller wake;
Figures 12 and 13 show similar sections illustrating how the
apparatus can be used as a side thruster (Figure 12) and with a
pinched propeller wake (Figure 13);
Figures 13-17 show modifications of earlier embodiments;
Figure 18 shows a further general modification;
Figures 18a and 19 show diagrammatic end viewsof two
apparatus embodiments;
Figure 20 shows a vertical section depicting the common
features of the embodiments shown in Figures 18a and 19; and
Figure 21 shows a submersible with the apparatus fitted in
place.
m us referring first to Figures 1-3, a ducted propeller
assembly 10 comprises a propeller 12 situated in a parallel sided
portion 13 of a hollow-walled duct 14.
Reference numeral 16 indicates the region of the duct down-
stream of the rear face of the propeller 12. In Figures 2 and 3, plane
A-A is the plane containing this face. Upstream of plane A-A, the
duct 14 has an intake and converging section of a suitable form
conventionally used in ducted propeller assemblies. The downstream region
16 of the duct differs from such assemblies, however, in its shape and
in the provision, at the downstream end of portion 13 of two slots lô,
20 through which secondary flows can be introduced into the propeller
wake. m e slots in this embodiment preferably each subtend an angle of
at the axis 21 of the duct (as may be seen from Figure 1) but
obviously, if desired, the design can be
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modified by having the slots longer or shorter than shown in Figure 1. The
general form of the slots can best be seen from Figure 2.
As may be seen from Figures 1-3, region 16 of the duct 14 has
internal walls which define a passage which is increasingly divergent in
cross-section in the transverse reference plane (Figure 3) and parallel sided
in the vertical reference plane (Figure 2). According to a preferred
feature of the invention the divergent walls in the transverse reference
plane lie on the axis of two circles preferably having their centres lying
in the transverse reference plane on a line containing or closely adjacent
to the rear face of the propeller. Figures 1-3 show one such embodiment in
which the circles have a radius of 3.75 times the diameter of the duct along
this line (Figure 3). The duct section (as viewed in Figure 3) should also
have a large trailing edge exit angle (30-35 from the duct axis) in the
transverse reference plane. With the illustrated embodiment the waIl
attachment effect associated with the curvature of the side walls is expected
to make sideways deflections of + 35 or so possible for the propeller wake.
In vertical sections perpendicular to both the two reference
planes above referred to, the duct varies, in preferred embodiments, smoothly
from a substantially circular cross-section at the rear face of the propeller
to a cross-section at the rear end of the duct which includes two side
portions lying on a common circle and top and bottom portions lying on chords
of that circle and parallel to the transverse reference plane. In the
embodiment shown in Figures 1-3 the side portions each subtend about 90 at
the centre of the circle and the top and bottom portions each subtend about
60 there, the remaining "corner" portions of the duct being curved so as to
lead smoothly from the side portions of the duct into the top and bottom
portions (Figure 1). As already explained the flattened shape of the duct
section shown in Figure 1 reduces vertical diffusion and hence improves the
efficiency of the assembly.
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Baffles 22, 24 (Figure 2) divide~the duct wall into two control
chambers 26, 28 (Figure 3) respectively associated with slots 18, 20, and
liquid for the secondary flows is pumped to control chambers 26, 28 through
ducting 30 shown diagrammatically in Figure S which illustrates the ducted
propeller assembly in place in a ship 31. Reference numerals 32 and 33
indicate the pump and its motor, and numerals 34, 35 indicate the supply
intake and by-pass pipes for the secondary flow liquid. In a typical case,
the pump might be a single stage axial low head pump e.g. operating at less
than 30 feet of water.
Figure 6 shows the control system for the pump. This comprises
valves 36, 38 connected in the ducting leading to chambers 26, 28, a master
valve 40 to control flow upstream of valves 36, 38 and a valve 42 in the
by-pass pipe 35. All the valves are hydraulically or pneumatically actuable
from the ship's control room.
When no side force and steering moment is required on the ship
assembly 10 will be working as a normal ductedopropeller and pump 32 will not
be used. In such circumstances valves 40, 42 will be closed. Valves 36, 38
may also be closed but it is thought preferable that they be maintained open
to equalise the pressure in the duct slots 18, 20. Figure 3 illustrates the
symmetrical distribution of the propeller wake (43) in the 'straight ahead'
mode of operation just described.
If, for example, it is desired to turn the ship to port, valve 40
is opened, and valves 36 and 38 are operated so that valve 36 is closed and
valve 38 is open. Pump 32 will now operate to suck sea water in through the
intake pipe 34 and via open valves 40, 38 to the control chamber 28 associat-
ed with slot 20. This liquid, issuing from slot 20 as a secondary flow into
duct 14 will detach the duct flow from that part of region 16 containing the
slot whereupon the propeller wake as a whole will veer towards the other wall
of region 16 as shown, diagrammatically, in Figure 4. The deflected propeller
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wake will of course produce a corresponding turning moment on the ship to
port. To turn the ship to starboard, valve 38 is closed and valve 36 opened.
It will be appreciated that varying the amount of secondary flow
will vary the amount of side force produced so as to result in an analogous
effect to that produced in conventional ducted propeller systems when the
appliedrudder angle is varied or the angle of the duct is changed as the
case may be.
For the ~straight ahead~ situation valves 36, 38 are open, and valve
40 is closed after by-pass valve 42 has been opened to allow liquid from
pump 32 to be returned to the sea via pipe 35.
Figures 7 and 8 are sections of other embodiments and correspond
to the section of the first embodiment shown in Figure 3.
In the Figure 8 embodiment, ambient liquid is drawn through
apertures 100, 101 for the secondary control flows. Remotely controlled
mechanically-hydraulically-(or pneumaticaIly-) operated flap valves 102, 103
determine which of the two control chambers 26, 28 is in operation at any
given moment.
According to a preferred feature, the two control chambers are
interconnected by a valve controlled loop (not shown) operating in exactly
the same way as above described with reference to the Figure 6 embodiment
to prevent the occurrence of unintentional deflection of the propeller wake
when neither control is operating. It will be noted that the parallel sided
duct section of the earlier embodiments is absent.
In the Figure 7 embodiment, the slots of the earlier embodiments
have been replaced by small obstructions in the form of flaps. Four such
flaps (48) are shown in Figure 7 in place of slots 20. The flaps are hinged
at their front edges and mechanical, hydraulic (or pneumatic) rams (not
shown) contained within the wall thickness of the duct are operable to de-
flect the flaps into the propeller wake or to hold them substantially flush
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with the duct walls, as desired. The opening of the flaps is analogous
to the provision of a secondary flow at the slots they replace.
In variations of the two embodiments above described, duct region
16 is modified to be slightly divergent or slightly convergent in the
vertical reference plane. A divergence or convergence of a few degrees,
e.g. one or two degrees, is envisaged at present. When duct region 16 is
convergent in this plane, it is preferably never so convergent that it is
not possible to extract the propeller 12 through theduct exit e.g. for
maintenance or repair work.
Referring now to Figure 9, this shows a longitudinal section of
a preferred embodiment of the invention in which the duct of assembly 10
is symmetrical aboutits longitudinal axis 60 and the control slots of the
earlier embodiments have been re~laced by rows of holes 62 at the rearward
extremity of the par~llel sided duct portion 13. The Figure actually shows
a section of the well known "NSMB nozzle number 37" adapted in accordance
with the present invention. The principle advantage of using holes instead
of slots is that they are ea9ier to form. The holes are fed from rectangular-
section manifold chambers 64, 65 in the duct which are sealed by cover plates
66 which allow access to the manifold chamber and holes.
Figures lOa and lOb show how the embodiments of the earlier Figures
are fitted to the hull 67 of the vessel. The controls may take the form of
pipes (68) leading through the duct waIl into the manifold cha~bers (for the
embodiment shown in Figure 9), to the control chamber (for the embodiment
shown in Figures 3 and 7) or to mechanical pneumatic, or hydraulic means
housed in the thickness of the duct waIls (for the embodiment shown in Figure
8~. As Figure 10 clearly shows, in each case the controls, whatever their
form~ may be housed wholly within the hull of the vessel. This greatly
facilitates maintenance work on the apparatus.
Variations in the apparatus illustrated and described may be
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considered under two separate headings, namely the design of the duct, on
the one hand and the design of the control equipment on the other. Consider-
ing the duct first, although, if desired, ducted propeller assemblies may be
specially designed for a particular case, the principles involved in the
present invention are applicable to any of the conventional fixed-duct
assemblies at present available. Thus the normal design p~ocedure will be
to select the ducted propeller assembly according to the usual criteria and
then to modify the assembly in accordance with the present invention.
Modification will of course invo~ve the provision of some sort of appropriate
control means but this presents little or no practical difficulties especially
where control apertures are to be used. The Figures show various designs
of duct and in view of what has been written above, it will be clear that
the duct of one embodiment may e~ually well be substituted for that of
another embodiment with~ut significantly affecting the performance of the
control means involved.
The rudder conventionally required with fixed duct assemblies
may be dispensed with as steering can be satisfactorily accomplished according
to the present invention in the manner already described above.
Unlike the two alternatives offered at present, (fixed duct follow-
ed by a rudder, or pivotted duct3, the apparatus of the present invention
involves no movement of any buIky part of the assembly relative to the vessel
on which it is mounted. The advantages of this will be obvious to those
versed in marine constructional design.
Considering now the apparatus of the present invention under the
second heading, the design of the control means, it will again be o~vious to
those skilled in the art that many minor variations in the described embodi-
ments are possiblè within the scope of the present invention. For example
the control apertures shown in Figure 9 could equally well be used with the
ducts of Figures 1 to 4, and 8 instead of the control slots shown, or vice
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versa. Similarly, as above indicated, different designs of duct can be used.
Useful guidelines can be given however when considering what
design of control means to aim at. The most satisfactory method must never-
theless be to check conclusions experimentally. Where control apertures are
used, for example, then (i) the area of each control slot or, if more than
one control aperture is present, the aggregate area of these apertures,
on one side of the duct (and of the propeller), should preferably lie
between 2% and~5~ of the area of the duct passage at its narrowest bore (i.e.
the parallel sided portion in the embodiments illustrated). (ii) The ends
of each slot, or if more than one aperture is present, of the group of
apertures, should subtend an angle at the longitudinal axis of the duct lying
in the range 60 ~o 90 . Values in the middle part of this range are normal-
ly to be preferred. In the embodiment of Figure 9, for example, the ang~e
subtended is 75 . (iii) Where the control means takes the form of apertures
and these are supplied from manifold chambers or other control chambers in
the walls of the duct, then the cross sectional area (or the average cross-
sectional area) of each chamber in planes intersecting the axis of the duct,
should preferably be at least twice the area (or the aggregate area) of the
aperture~s) fed by that chamber (Figure 9 again illustrates this feature).
The procedure for operating the various "control flow" embodiments
is exactly the same in each case and has been already described above.
Typically the velocity of the secondary flow when ~ issued~from a control
aperture will be up to two to three times the velocity of the main flow
through the duct. Deflections of 25 - 35 of the propeller race can be
achieved, for example with the embodiment of Figure 9.
Other modes of operation are also possible. For example it may be
desirable where secondary flows are used to detach the propeller wake, to
provide a control flow (70) on one side of the duct and to apply suction (71)
at the control aperture(s)(by connecting these to the pump inlet 301) on the
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other side of the wake (illustrated diagrammatically in the horizontal section
shown in Figure 11). It may also be advantageous with such embodiments to
provide secondary flows (73, 74 in Figure 12) through the control aperture(s)
on both sides at once soas to pinch the propeller wake with the purpose of
improving he performance of the propeller duct in the ahead condition.
Another possibility is to use the apparatus, with the propeller
stationary, as a side thruster (as shown diagrammatically in the horizontal
section of Figure 13). Figure 13 shows the case where this is done by
providing a secondary flow 75 on one side of the duct and suction 76 to a
control aperture on the other side. However the apparatus may be made to
work satisfactorily as a side thruster by having the "suction" duct closed
and relying entirely on the action of the "control flow" duct.
It has been found that when the control means are situated between
the propeller and the rear end of the duct, they are effective when the
propeller is driven in reverse to deflect the propeller wake leaving the
forward end of the duct. This means that it is not usually neces~ary to
provide a 9econd set of control means between the propeller and the forward
end of the duct. Indeed model tests have indicated that the control means
may be even more efficent in turning the propeller wa~e when the propeller
is operating in reverse than they are when it is operating normally. This
has indicated an alternative design of apparatus in which the control means
are situated on the upstream side of the propellers. Figures 14, 15, 16 are
diagrammatic horizontal sections illustrating, by way of example, how the
embodiments of Figures 3, 7, 9 may be modified by repositioning the control
means in this way.
As already stated, it will not normally be necessary to include two
sets of control means but if it is desired, this may be done very simply.
Figure 17 shows, by way of example, one such apparatus in which the control
slots shown in Figures 3 and 14 have been included in the one embodiment.
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Obviously other embodiments may be similarly combined.
Figure 18 shows a modification which can be applied to any of the
above described embodiments or variations of these embodiments, namely the
addition to duct 14 of a terminal portion 150 including two sets of fixed
turning vanes 152, one on~ either side of the duct centre line. When the
propeller wake leaves duct 14 substantially undeflected, then vanes 152
have little or no effect~ butwhen the wake has already been deflected by
operation of the detachment means (not shown) in duct 14, then the vanes will
be effective to turn the flow even further, thereby increasing the sideways
force produced.
Apart from its other ad~antages, the apparatus of the present
invention is expected to give the vessel a smaller tD~ning circle than is at
present possible with presently available marine steering systems.
Although so far the invention has been described in respect of
surface vessels, there is of course no reason why the same principles should
not be made use of to provide an apparatus for manoeuvring submersibles.
Thus in an apparatus according to another aspect of the invention,
the control means is additionally operable to deflect the propeller wake
vertically and/or in directions lying between the vertical and the horizontal
thereby to provide a corresponding steering force on the submersible.
Figures 18a and 19 show somewhat diagrammatic end views of two
such apparatuses and Figure 20 shows a vertical section depicting the common
features of the two embodiments. Figure 21 shows a submersible with the
apparatus fitted in place.
The apparatus shown in Figures 18a and 20 differs in two important
respects from that shown in earlier Figures. First the control apertures 62
go completely around the duct and secondly there are four manifold chambers
each occupying a respective 90 sector 165, 166, 167, 168 (Figure 18a) of
the duct. If it is desired to steer the submersible upwards, then the control
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apertures in sector 167 and/or sector 165 are used in an exactly analogous
way to the way in which the apertures associated with manifold chambers 65,
66 are used in the Figure 9 embodiment. Of course for left and right
steerage the apertures in sectors 168 and/or 166 are used instead. Steering
in intermediate directions can be achieved by using first one set of control
apertures (e.g- in sector 165 and/or 167) and then the other (in sector 168
and/or 166), or byusing the two sets differenti~lly.
In the embodiment of Figures 19 and 20, each of the control
apertures 62 is fed by an appropriate feed pipe e.g. as indicated by reference
numeral 170. With this embodiment, if it is desired to steer the submersi-~le
in a direction lying between the vertical and horizontal this can be done
directly by using only the appropriate control apertures. The arrows 172
in Figure 19 indicate by way of example the control flows present~*o produce
a steering force F.
It will be obvious that the various modifications, substitutions
and design guidelines already discussed with reference to the earlier
embodiments will be equally applicable to the embodiments of Figures 18a
to 20.
As Figure 21 makes clear, these latter embodiments will also have
the advantage of allowing the controls to be housed in the hull of the
vessel (submersible 174).
