U.S. patent application number 13/418938 was filed with the patent office on 2012-10-04 for water jet propulsion device.
This patent application is currently assigned to ROLLS-ROYCE PLC. Invention is credited to Paul FLETCHER, Paul J. NEWTON, John R. WEBSTER.
Application Number | 20120252286 13/418938 |
Document ID | / |
Family ID | 45894153 |
Filed Date | 2012-10-04 |
United States Patent
Application |
20120252286 |
Kind Code |
A1 |
FLETCHER; Paul ; et
al. |
October 4, 2012 |
WATER JET PROPULSION DEVICE
Abstract
A water jet propulsion device 10 for a water vehicle, such as a
boat, is disclosed. The propulsion device 10 comprises a main duct
12 having a main inlet 14 that is arranged to be submerged in use
and a main outlet 16, an impeller 30 disposed within the main duct
12 between the main inlet 14 and the main outlet 16, and at least
one auxiliary duct 24 having an auxiliary inlet 26 that is arranged
to be submerged in use and an auxiliary outlet 28 that opens into
the main duct 12 upstream of the impeller 30.
Inventors: |
FLETCHER; Paul; (Rugby,
GB) ; NEWTON; Paul J.; (Derby, GB) ; WEBSTER;
John R.; (Derby, GB) |
Assignee: |
ROLLS-ROYCE PLC
London
GB
|
Family ID: |
45894153 |
Appl. No.: |
13/418938 |
Filed: |
March 13, 2012 |
Current U.S.
Class: |
440/39 |
Current CPC
Class: |
B63H 11/04 20130101;
B63H 2011/043 20130101 |
Class at
Publication: |
440/39 |
International
Class: |
B63H 11/00 20060101
B63H011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 2011 |
GB |
1105554.8 |
Apr 1, 2011 |
GB |
1105558.9 |
Claims
1. A water jet propulsion device for a water vehicle, comprising: a
main duct having a main inlet that is arranged to be submerged in
use and a main outlet; an impeller disposed within the main duct
between the main inlet and the main outlet; and at least one
auxiliary duct having an auxiliary inlet that is arranged to be
submerged in use and an auxiliary outlet that opens into the main
duct upstream of the impeller, wherein a valve is disposed within
at least one auxiliary duct.
2. A water jet propulsion device according to claim 1, wherein
there are a plurality of auxiliary ducts, each having an inlet that
is arranged to be submerged in use and an outlet that opens into
the main duct upstream of the impeller.
3. A water jet propulsion device according to claim 2, wherein at
least some of the plurality of auxiliary ducts are arranged
side-by-side.
4. A water jet propulsion device according to claim 2, wherein at
least some of the plurality of auxiliary ducts are arranged
downstream from one another.
5. A water jet propulsion device according to claim 1, wherein at
least part of the main duct is inclined.
6. A water jet propulsion device according to claim 5, wherein the
inclined main duct defines a main duct lip.
7. A water jet propulsion device according to claim 5, wherein the
or each auxiliary duct extends through the main duct lip.
8. A water jet propulsion device according to claim 1, wherein the
valve is a door disposed in the auxiliary duct and movable between
at least a closed position in which the passage of fluid through
the auxiliary duct is restricted and an open position.
9. A water jet propulsion device according to claim 8, wherein the
or each valve is a non-return valve.
10. A water jet propulsion device according to claim 9, wherein the
or each non-return valve only allows the flow of water into the
main duct through the or each auxiliary duct.
11. A water jet propulsion device according to claim 8, wherein the
or each valve is arranged to open at a pre-determined pressure
threshold.
12. A water jet propulsion device according to claim 11, wherein
the or each valve is spring loaded.
13. A water jet propulsion device according to claim 8, wherein the
or each valve can be selectively opened and/or closed.
14. A water jet propulsion device according to claim 8, wherein the
or each valve is arranged to be automatically opened and/or closed
on the basis of a detected parameter.
15. A water jet propulsion device according to claim 8 comprising
one or more auxiliary ducts which include a valve arranged to allow
water to flow from the auxiliary duct outlet in the main duct to
the auxiliary duct inlet.
Description
[0001] The invention relates to a water jet propulsion device for a
water vehicle such as a boat.
[0002] Water jet propulsion devices are often used to power water
vehicles such as boats. They are also sometimes known as pump-jets
or hydro-jets. Water jet propulsion devices typically comprise a
pump having an inlet that is submerged in use and an outlet that is
located above the water level. In use, the pump ejects a jet of
water rearwards out of the outlet which provides a propulsive force
to the boat to drive it forwards.
[0003] When the boat is travelling at low-speed the pump sucks
water in through the inlet. For optimum performance it is desirable
to have a relatively large inlet so that the necessary volume of
water can be sucked through the inlet by the pump. However, when
the boat is travelling at high-speed water is forced into the inlet
due to the speed of the boat. This usually results in too much
water being forced into the inlet and therefore it is desirable to
have a smaller inlet. The dimensions chosen for the inlet are
therefore a compromise for both low-speed and high-speed
operation.
[0004] However, the inlet is usually still too small for low-speed
operation and too large for high-speed operation. This can result
in cavitation and the associated erosion occurring at various
positions around the inlet at both low-speed and high-speed
operation. Cavitation can also create imbalances on the pump and
pressure pulses which impact the mechanical components of the pump
and can result in excessive noise, erosion, and potential damage.
Further, avoiding cavitation can help increase thrust at low
speeds.
[0005] It is therefore desirable to provide a water jet propulsion
device having an improved water inlet design.
[0006] According to an aspect of the invention there is provided a
water jet propulsion device for a water vehicle, such as a boat or
ship, for example, comprising: a main duct having a main inlet that
is arranged to be submerged in use and a main outlet; an impeller
disposed within the main duct between the main inlet and the main
outlet; and at least one auxiliary duct having an auxiliary inlet
that is arranged to be submerged in use and an auxiliary outlet
that opens into the main duct upstream of the impeller.
[0007] In use, the impeller accelerates water within the main duct
and ejects a jet of water out of the main outlet to propel the
water vehicle. Typically, at low speeds water is sucked into the
main duct through the main inlet by the impeller and at high speeds
water is forced into the main duct through the main inlet due to
the speed of the water vehicle. At low speeds additional water may
be sucked into the main duct through the or each auxiliary duct,
thus improving the performance of the propulsion device. At high
speeds water may not be sucked into the main duct through the
auxiliary duct. In some arrangements, water forced into the main
duct at high speeds may in fact exit the main duct through the
auxiliary duct, thus improving the performance of the propulsion
device and preventing cavitations along the hull. Further, the
addition of the auxiliary duct helps to reduce the compromise
between low and high speed flow which provides design freedom in
the shape of the main inlet. The water jet propulsion device may be
integrally part of a water vehicle or may be a separate device that
can be attached to a water vehicle. The impeller may be coupled to
a drive shaft which may be coupled to a motor which is arranged to
rotationally drive the drive shaft and hence the impeller. At least
part of the drive shaft may be substantially horizontal such that
the impeller can be rotated about a substantially horizontal
axis.
[0008] There may be a plurality of auxiliary ducts, each having an
inlet that is arranged to be submerged in use and an outlet that
opens into the main duct upstream of the impeller. At least some of
the plurality of auxiliary ducts may be arranged side-by-side. At
least some of the plurality of auxiliary ducts may be arranged
downstream from one another.
[0009] At least part of the main duct may be inclined. The main
duct may be inclined rearwards (downstream) and upwards. The
inclined main duct may define a main duct lip. The main duct lip
may have a forward facing edge. The or each auxiliary duct may
extend through the main duct lip. The or each auxiliary duct may be
at least partially inclined. The auxiliary inlet may be larger than
the cross-section of a main portion of the auxiliary duct.
[0010] A valve may be disposed within the or each auxiliary duct,
or only some of the auxiliary ducts. The or each valve, or only
some of the valves may be non-return valves. The or each non-return
valve may only allow the flow of water into the main duct through
the or each auxiliary duct. The or each valve, or only some of the
valves may be arranged to open at a pre-determined pressure
threshold. The or each valve may be spring loaded.
[0011] The or each valve may arranged to be selectively opened
and/or closed. The or each valve may be arranged to be
automatically opened and/or closed on the basis of a detected
parameter. There may be a sensor for detecting the parameter. The
or each valve, or only some of the valves, may open or close when
the detected parameter reaches a predetermined threshold. The
parameter may relate to pressure, speed, impeller power, impeller
rotational speed, ship speed or differential pressure across the
valve, for example.
[0012] The water jet propulsion device may include one or more
auxiliary ducts which each include a valve arranged to allow water
to flow from the auxiliary outlet in the main duct to the auxiliary
inlet.
[0013] Control of the valves may be achieved as part of an closed
loop system. Alternatively or additionally, the valves may be
controlled by an open loop. Preferably, the valves are operable
upon command by an operator.
[0014] The invention also concerns a water vehicle, such as a boat
or ship, comprising a water jet propulsion device in accordance
with any statement herein.
[0015] According to another aspect of the invention there is
provided a water jet propulsion device for a water vehicle, such as
a boat or ship, for example, comprising: a pump having a main inlet
which is arranged to be submerged in use and a main outlet; and at
least one auxiliary passage that opens upstream of the pump and is
arranged to be submerged in use.
[0016] In yet another aspect, the a water jet propulsion device for
a water vehicle, comprising: a main duct having a main inlet that
is arranged to be submerged in use and a main outlet; an impeller
disposed within the main duct between the main inlet and the main
outlet; an auxiliary duct having an auxiliary inlet arranged to be
submerged in use and an auxiliary outlet that opens into the main
duct upstream of the impeller; and a door disposed in the auxiliary
duct and movable between at least a closed position in which the
passage of fluid through the auxiliary duct is restricted and an
open position.
[0017] The closed position the door may be substantially flush with
a surface within which the auxiliary inlet and/or the auxiliary
outlet is formed. The door may permit flow through the auxiliary
duct when in an open position. When in an open position the door at
least partially projects below a surface within which the auxiliary
inlet is formed. When in an open position the door may at least
partially project into the main duct. The door may be pivotable
between the closed position and an open position. The door may be
biased to either the closed position or an open position.
[0018] The device may further comprise an actuator which can be
controlled to move the door between at least the closed position
and an open position. The door may be actuated based on a
determined parameter. Alternatively, the door may be arranged to be
passively moved between the closed position and an open position by
local pressure changes. There may be a plurality of doors disposed
in the auxiliary duct, each movable between at least a closed
position and an open position, There may be an inlet door and an
outlet door in the region of the auxiliary inlet and the auxiliary
outlet respectively.
[0019] There may be a plurality of auxiliary ducts, and wherein at
least one door, moveable between at least a closed position and an
open position, is disposed in each auxiliary duct.
[0020] At least part of the main duct may be inclined. The incline
may be part of the main duct and may define a main duct lip.
[0021] The or each auxiliary duct may pass through the main duct
lip.
[0022] The invention may comprise any combination of the features
and/or limitations referred to herein, except combinations of such
features as are mutually exclusive.
[0023] Embodiments of the invention will now be described, by way
of example only, with reference to the accompanying drawings, in
which:
[0024] FIG. 1 schematically shows an embodiment of a water jet
propulsion device;
[0025] FIG. 2 schematically shows the underside of the water jet
propulsion device of FIG. 1;
[0026] FIG. 3 schematically shows the water jet propulsion device
of FIG. 1 when operating at low-speed;
[0027] FIG. 4 schematically shows the water jet propulsion device
of FIG. 1 when operating at high-speed;
[0028] FIG. 5 schematically shows a second embodiment of a water
jet propulsion device.
[0029] FIG. 6 schematically shows an embodiment of a water jet
propulsion device in accordance with the invention;
[0030] FIG. 7 schematically shows a second embodiment of a water
jet propulsion device in accordance with the invention;
[0031] FIG. 8 schematically shows a third embodiment of a water jet
propulsion device in accordance with the invention, with inlet and
outlet doors in closed positions;
[0032] FIG. 9 schematically shows the water jet propulsion device
of FIG. 8 with inlet and outlet doors in open positions;
[0033] FIG. 10 schematically shows the water jet propulsion device
of FIG. 8 with the inlet door in an alternative open position;
[0034] FIG. 11 schematically shows the underside of a further
embodiment of a water jet propulsion device in accordance with the
invention.
[0035] FIG. 1 shows an embodiment of a water jet propulsion device
10 which is integrally part of a water vehicle which in this
embodiment is a boat. In should be appreciated that in other
embodiments the water jet propulsion device 10 could be a separate
device arranged to be attached to a water vehicle. The propulsion
device 10 comprises a main duct 12 having a main inlet 14 and a
main outlet 16. The main inlet 14 lies in a substantially
horizontal plane and is formed in the lower surface of the hull 18
of the boat. In use, the main inlet 14 is submerged underwater. The
main outlet 16 lies in a substantially vertical plane and is formed
in a side surface of the hull 18 of the boat. In use, the main
outlet 16 is located above the water line. A nozzle (not shown) may
constitute or form part of the main outlet.
[0036] The main duct 12 comprises an inclined portion 12a and a
substantially horizontal portion 12b. The inclined duct portion 12a
extends from the main inlet 14 rearwards (downstream) and upwards
and transitions into the horizontal portion 12b that extends
rearwards to the main outlet 16. In other embodiments the main duct
12 may be entirely inclined along its length. The main duct 12
defines a main duct lip 20, the lower surface of which forms part
of the hull 18. The duct lip 20 has a forward-facing edge 22 which
is also part of the edge of the main inlet 14.
[0037] A plurality of auxiliary ducts 24 extend through the duct
lip 20 and open into the main duct 12. Each auxiliary duct 24
comprises an auxiliary inlet 26 that is formed in the lower surface
of the hull 18 and an auxiliary outlet 28 that opens into the main
duct 12. The auxiliary inlets 26 are arranged to be submerged
underwater in use. In this particular embodiment there are six
auxiliary ducts.
[0038] As can be seen in FIG. 2, there are two rows of auxiliary
ducts 24 with one row located downstream from the other row. Each
row of auxiliary ducts comprises three individual auxiliary ducts
24 that are located side-by-side. The auxiliary duct inlet 26 of
each duct 24 is larger that the cross-section of the main portion
of the auxiliary duct 24.
[0039] The water jet propulsion device further comprises a pump
having a ducted impeller 30 which is disposed in the horizontal
portion 12b of the main duct 12. The impeller 30 is mounted to a
substantially horizontal rotational drive shaft 32 that passes
through the upper wall of the main duct 12 into the interior of the
boat. The drive shaft 32 is coupled to a motor (not shown) which is
arranged to rotationally drive the drive shaft 32 and hence the
impeller 30 about a horizontal axis.
[0040] In use, the hull 18 of the boat is partially submerged in
water so that the main inlet 14 and the auxiliary inlets 26 are
submerged. The impeller 30 is rotated about a horizontal axis by
the drive shaft 32 and water in the main duct 12 is accelerated by
the impeller 30 and forced out of the main outlet 16 as a jet of
water which causes the boat to be propelled forwards. The speed of
the impeller 30 can be increased or decreased in order to increase
or decrease the propulsive force generated by the water jet
propulsion device 10.
[0041] The operation of the water jet propulsion device 10, and the
flow of water through the main duct 12 and the auxiliary ducts 24,
differs depending on whether the boat to which the water jet
propulsion device 10 is attached (or integrated) is travelling at
low speed or high speed.
[0042] FIG. 3 schematically shows the operation of the water jet
propulsion device 10 when the boat is travelling at low speed. Low
speed may be considered to be less than 20 knots. When the boat is
travelling at low speed the impeller 30 acts to suck water into the
main duct 12 through both the main inlet 14 and through the
auxiliary inlets 26 of the auxiliary ducts 24. The overall inlet
area (the sum of the areas of the main inlet 14 and the auxiliary
inlets 26) is larger than the overall inlet area of a conventional
water jet propulsion device 10 having only a main inlet 14. The
auxiliary ducts 24 therefore allow for the additional flow of water
into the main duct 12 upstream of the impeller 30. Thus, it is
easier for the impeller 30 to suck, or draw, water into the main
duct 12 and expel it out of the main outlet 16 in order to generate
a propulsive force.
[0043] When a conventional water jet propulsion device operates at
low speed, water is drawn from behind the main inlet and is turned
around the duct lip into the main duct. This can lead to flow
separation at A which is a position on the upper surface of the
duct lip 20 rearward of the edge 22. In turn, this flow separation
can lead to cavitation if the pressure of the liquid falls below
its vapour pressure and gas bubbles form. Cavitation can cause
significant damage to the pump impeller due to pressure imbalances
and the creation of pressure pulses.
[0044] The provision of auxiliary ducts 24 that extend through the
main duct lip 20 means that during operation at low-speed less, or
no water is forced to flow around the edge 22 of the duct lip 20.
This reduces the likelihood of flow separation occurring at
position A and hence cavitation is less likely to occur. Avoiding
cavitation may also increase the life of the water jet propulsion
device and provide a beneficial increase in flow rate and
thrust.
[0045] FIG. 4 schematically shows the operation of the water jet
propulsion device 10 when the boat is travelling at high speed.
High speed may be considered to be greater than 20 knots. At high
speed water is in forced, or rammed, into the main duct 12 through
the main inlet 14 due to the forward speed of the boat. In fact, at
certain speeds too much water may be forced into the main duct 12
through the main inlet 14 and the impeller 30 may not be able to
eject all of the water forced into the duct 12. In such
circumstances excess water may be forced out of the main duct 12
through the auxiliary ducts 26. This can improve the performance of
the water jet propulsion device 10.
[0046] When a conventional water jet propulsion device operates at
high speed, if too much water is forced into the main inlet due to
the speed of the boat, water must also exit through the main inlet.
The excess water tends to exit the main inlet and flow rearward
around the lip edge 22 and under the duct lip 20. The flow of the
excess water around the lip 20 can cause flow separation and hence
cavitation at B which is a position on the lower surface of the
duct lip 20 rearward of the edge 22.
[0047] In certain embodiments of the invention excess water can
exit the main duct 12 through the auxiliary ducts 24, as opposed to
through the main inlet 14, and therefore flow separation and hence
cavitation can be prevented or reduced at position B during high
speed operation.
[0048] The solution provided by the water jet propulsion device 10
described above is particularly advantageous as it comprises no
moving parts. This makes it particularly reliable and resistant to
debris that may impact the propulsion device 10 during use.
[0049] FIG. 5 shows a further embodiment of a water jet propulsion
device 10 which is similar to the embodiment described with
reference to FIGS. 1-4. The only difference is that there is a
fluid control valve 34 disposed within each auxiliary duct 24 which
can control the flow of water through the respective duct 24.
[0050] The valves 34 may be passive non-return valves, for example,
arranged such that water can only flow into the main duct 12 or
arranged such that water can only flow out of the main duct 12
through the auxiliary ducts 24. In one embodiment, the fluid
control valves 34 may be arranged to open at a specific pressure.
The valves 34 may be spring-loaded so that they only open and allow
flow through the auxiliary ducts 24 at a particular pressure
threshold. In other embodiments, the valves 34 may be connected to
a pressure pick-up (not shown) disposed at the edge 22 of the duct
lip 20, for example, or elsewhere near the main inlet 14. The
pressure pick-up may be coupled to the valves such that they open
and close at specific pressure thresholds. It will be appreciated
that the pressure pick ups could actuate the valve directly or may
operate the valves via hydraulic or electrical actuators.
[0051] In a further embodiment the valves 34 may be fully
externally controlled. The valves 34 may be connected to control
circuitry (not shown) which in turn is connected to one or more
sensors (not shown) that are arranged to detect or measure various
parameters. The parameters could be boat speed, pressure levels at
a particular point or shaft power, impeller rotational speed, ship
speed or differential pressure across the impeller, for example.
The control circuitry could be arranged to open or close the valves
individually, or as a group, in response to the detected parameter
values. For example, if the boat speed is detected as "low" (e.g.
less than 20 knots) the valves 34 could be opened to allow one-way
flow into the main duct 12 through the auxiliary ducts 24, and if
the boat speed is detected as "high" (e.g. greater than 20 knots)
the valves could be opened to allow one-way flow out of the main
duct 12 through the auxiliary ducts 24.
[0052] In yet another embodiment, the valves may be operable on
command by a person so as to provide open loop control.
[0053] As will be appreciated by one skilled in the art, any
combination of the aforementioned valves may be used.
[0054] It will be appreciated that the auxiliary ducts may be
configured to allow the optimisation of the main duct above and
below the duct lip for different flow conditions. In one
embodiment, there is included at least one duct which includes a
valve configured to allow unidirectional flow during particular
flow conditions. In another embodiment there is one or more
auxiliary ducts arranged to provide an auxiliary flow from below
the duct lip to the main duct and one or more auxiliary ducts to
provide flow from the main duct to below the duct lip.
[0055] In a yet further embodiment, two or more of the auxiliary
ducts are interconnected towards the main duct. The interconnection
may be between all of the auxiliary ducts. In this way, the
effective shape of the main inlet can be altered to accommodate low
and high speed flows.
[0056] FIG. 6 shows an embodiment of a water jet propulsion device
110 which is integrally part of a water vehicle which in this
embodiment is a boat. It should be appreciated that in other
embodiments the water jet propulsion device 110 could be a separate
device arranged to be attached to a water vehicle. The propulsion
device 110 comprises a main duct 112 having a main inlet 114 and a
main outlet 116. The main inlet 114 lies in a substantially
horizontal plane and is formed in the lower surface of the hull 118
of the boat. In use, the main inlet 114 is submerged underwater.
The main outlet 116 lies in a substantially vertical plane and is
formed in at the rear surface of the hull 118 of the boat. In use,
the main outlet 116 is located above the water line. A nozzle (not
shown) may constitute or form part of the main outlet.
[0057] The main duct 112 comprises an inclined portion 112a and a
substantially horizontal portion 112b. The inclined duct portion
112a extends from the main inlet 114 rearwards (downstream) and
upwards and transitions into the horizontal portion 112b that
extends rearwards to the main outlet 116. In other embodiments the
main duct 112 may be entirely inclined along its length. The main
duct 112 defines a main duct lip 120, the lower surface of which
forms part of the hull 118. The duct lip 20 has a forward-facing
edge 122 which is also part of the edge of the main inlet 114.
[0058] An auxiliary duct 124 extends through the duct lip 120 and
opens into the main duct 112. The auxiliary duct 124 comprises an
auxiliary inlet 126 that is formed in the lower surface of the hull
118 and an auxiliary outlet 128 that opens into the main duct 112.
The auxiliary inlet 126 is arranged to be submerged underwater in
use. In this particular embodiment there is one auxiliary duct 124,
however, in other embodiments there may be a plurality of auxiliary
ducts which may be arranged side-by-side, in a longitudinally
extending line behind the main duct lip 20 or arranged in rows
behind the main duct lip 120, for example.
[0059] The water jet propulsion device further comprises a pump
having a ducted impeller 130 which is disposed in the horizontal
portion 112b of the main duct 112. The impeller 130 is mounted to a
substantially horizontal rotational drive shaft 132 that passes
through the upper wall of the main duct 112 into the interior of
the boat. The drive shaft 132 is coupled to a motor (not shown)
which is arranged to rotationally drive the drive shaft 132 and
hence the impeller 130 about a horizontal axis.
[0060] An inlet door 140 is disposed in the auxiliary duct 124 and
is located substantially in the region of the auxiliary inlet 126.
The inlet door 140 is pivotable between a closed position (not
shown) in which the door is substantially flush with the lower
surface of the lip 120 and an open position (shown in FIG. 6). The
door 140 is pivotably mounted to the duct lip 1120 at a pivot 142
that is connected to the upstream edge of the door 140.
[0061] In the open position, water is able to flow through the
auxiliary duct 124 into the main duct 112. In the closed position
the flow of water through the auxiliary duct 124 is restricted.
[0062] In use, the hull 118 of the boat is partially submerged in
water so that the main inlet 114 and the auxiliary inlet 126 is
submerged. The impeller 130 is rotated about a horizontal axis by
the drive shaft 132 and water in the main duct 112 is accelerated
by the impeller 130 and forced out of the main outlet 116 as a jet
of water which causes the boat to be propelled forwards. The speed
of the impeller 30 can be increased or decreased in order to
increase or decrease the propulsion force generated by the water
jet propulsion device 110.
[0063] The operation of the water jet propulsion device 110, and
the flow of water through the main duct 112 and the auxiliary duct
124, differs depending on whether the boat, to which the water jet
propulsion device 110 is attached (or integrated) is travelling at
low speed or high speed.
[0064] When the water vehicle is travelling at low speed, the inlet
door 140 can be moved to an open position (shown in FIG. 6). This
allows additional water to be sucked into the main duct 112 through
the auxiliary duct 124. Therefore, water may not be forced to flow
forward around the edge 122 of the duct lip 120 into the main duct
112. This reduces the likelihood of flow separation and hence
cavitation occurring at position A. Avoiding cavitation may
increase the life of the water jet propulsion device. Further,
avoiding separation may result in a higher effective inlet area,
thereby increasing the flow of water to the impeller resulting in
increased thrust and acceleration capability at low speed.
[0065] The auxiliary duct inlet 126 may be shaped to facilitate the
smooth flow of water into the auxiliary duct 124. For example, for
improved performance at low to intermediate speeds, the duct may be
shaped to accept flow from a forward direction.
[0066] When the water vehicle is travelling at higher speeds,
additional flow through the auxiliary duct 124 may not be required
to maintain efficiency and thrust capability. Therefore the inlet
door 140 can be moved to the closed position in which it is
substantially flush with the lower surface of the duct lip 120. In
the closed position, the inlet door 140 restricts or prevents the
flow of water through the auxiliary duct 124 into the main duct
112. The closure of the inlet door 140 at higher speeds also
protects it from damage by foreign objects in the flow.
[0067] The inlet door 140 is designed to be substantially flush
with the lower surface of the duct lip 120 when in the closed
position such that it does not present an obstruction to the flow
and is not susceptible to damage. In the closed position, the door
substantially blends with the hull profile as if it were part of
the lower surface of the duct lip 120.
[0068] In this particular embodiment the door 140 is biased towards
the closed position and automatically moves to the open position at
low speed. At low speed there is a pressure reduction within the
main duct 112 which pulls the door 140 to the open position in
order to permit flow through the auxiliary duct 124 into the main
duct 112. When the speed of the boat increases, the pressure within
the main duct 112 increases and therefore the door 140 returns to
the closed position.
[0069] It should be appreciated that in other embodiments an
actuator (not shown) may be provided in order to move the door 140
between open and closed positions. This actuator could be manually
controlled or could be connected to a controller (not shown) which
automatically opens or closes the door based on detected data. For
example, the controller could be connected to one or more sensors
(now shown) arranged to measure various parameters such as water
pressure, impeller speed, vehicle speed, for example. The
controller could be configured to open or close the door when the
measured parameter exceeds or falls below a threshold.
[0070] FIG. 7 shows a second embodiment of a water jet propulsion
device 110 which is similar to the embodiment described with
reference to FIG. 6. However, the pivot 142 by which the door 140
is pivotally attached to the boat is positioned at a mid-point
along the length of the door between the upstream and downstream
ends. The inlet door 140 can be rotated about the pivot 142 between
a closed position in which it is substantially flush with the lower
surface of the hull 118 and an open position (FIG. 7). When the
inlet door 140 is in this open position an upstream portion 144 of
the inlet door 140 (which is the upstream portion of the door
beyond the pivot) projects below the general lower surface of the
duct lip 120 in which the auxiliary inlet 26 is formed. The
downstream portion 146 of the inlet door 140 projects into the
auxiliary duct 124. When the water vehicle is travelling at low
speeds in a forward direction, the inlet door 140 is moved to the
open position and the upstream portion 144 of the door 140 directs
the water into the auxiliary duct 124 from where it flows into the
main duct 112. The upstream part 144 of the inlet door 140
therefore acts as a scoop when in the open position shown in FIG.
7.
[0071] FIGS. 8-10 show a third embodiment of a water jet propulsion
device 110 which is similar to the second embodiment. However, the
water jet propulsion device 110 further comprises a second outlet
door 150 that is disposed in the auxiliary duct 124 in the region
of the auxiliary outlet 128. The outlet door 150 is pivotably
mounted by a pivot 152 which is position at a mid-point along the
length of the door. The outlet door 150 is pivotably between at
least a closed position (FIG. 8) in which it is flush with the
upper surface of the lip 120 and restricts fluid flow through the
auxiliary duct 124 and an open position (FIGS. 9 and 6).
[0072] In the open position of the outlet door 150, a downstream
portion 156 of the door 150 projects into the main duct 112 and a
upstream portion 154 projects into the auxiliary duct 124.
[0073] The inlet door 140 is movable between a closed position
(FIG. 8), a first open position (FIG. 9) and a second open position
(FIG. 10). The inlet door 140 is moved from the closed position to
the first open position by clockwise rotation about the pivot 142
and is moved to the second open position by anticlockwise rotation
about the pivot 142. The first open position (FIG. 9) is the same
as the open position of the second embodiment and the upstream
portion 144 of the door 140 projects below the lower surface of the
duct lip 120. In the second open position (FIG. 10) the downstream
portion 146 of the door 40 projects below the lower surface of the
duct lip 120.
[0074] When the inlet and/or outlet doors 140, 150 are in the
closed position flow through the auxiliary duct 124 is restricted
or prevented. When the inlet door 40 is in the first or second open
position and the outlet door 150 is in an open position water can
flow through the auxiliary duct 124.
[0075] FIG. 9 shows the water jet propulsion device 110 of FIG. 8
in use at low speeds with the inlet door 140 in the first open
position and the outlet door 150 in an open position. Water is able
to flow through the auxiliary duct 124 into the main duct 112.
[0076] In the first open low-speed configuration additional water
can be directed into the main duct 112 and therefore less flow
turning is required at A. Further, the sloped position of the
outlet door 150 further reduces the flow turning required at A, and
separation and cavitation is therefore reduced or prevented when
the water vehicle is travelling at low speeds. The outlet door 150
also acts to direct water from the auxiliary duct 124 upwards and
towards the impeller 130. Further, the inlet door 140 may act as a
scoop to force water into the auxiliary duct.
[0077] FIG. 10 shows the water jet propulsion device 110 of FIG. 9
in use at high speeds with the inlet door 140 in the second open
position. This deployment may prevent separation and cavitation at
high speeds by allowing excess water to flow out of the main duct
112 through the auxiliary duct 124. The outlet door 50 deflects the
main duct flow upwards towards position C, therefore reducing the
risk of separation and cavitation and provides a more uniform water
flow to the impeller 130. The inlet door 140 is in the second open
position, allowing excess water to flow out of the main duct 112
through the auxiliary duct at high water vehicle speeds, thereby
providing additional flow at B where the flow may otherwise be
separated and/or cavitated.
[0078] Excess water may also flow out of the main duct 112 through
the auxiliary duct 124 by rotating the outlet door 150 in the
opposite direction such that the upstream portion 154 projects into
the main duct 112 and the downstream end of the 156 projects below
the auxiliary outlet 128.
[0079] Providing at least one auxiliary duct 124 with at least one
inlet and/or outlet door 140, 150 may reduce or prevent separation,
cavitation and pump face distortion at both low and high speed.
This may therefore extend the operating range of the device,
providing improved thrust capability at low and high speeds whilst
avoiding damage and low efficiency performance.
[0080] It should be appreciated that any of the embodiments
described may comprise more than one auxiliary duct, each with an
inlet door 140 and/or an outlet door 150. FIG. 11 shows the
underside of the hull in an embodiment where multiple auxiliary
ducts are arranged in rows downstream of the main duct lip 120.
[0081] In some embodiments, the doors 140, 150 may be arranged to
open and close under the action of local pressure forces. They may
be spring-loaded so that they open and allow flow through the
auxiliary ducts 124 at a particular pressure threshold. In other
embodiments, the doors 140, 150 may be connected to a pressure
pick-up (not shown) disposed at the edge 122 of the duct lip 120,
for example, or elsewhere in the main inlet 114. The pressure
pick-up may be coupled to the doors 140, 150 such that they open
and close at specific pressure thresholds.
[0082] In a further embodiment the doors 140, 150 may be fully
externally controlled. The doors 140, 150 may be connected to
control circuitry (not shown) which in turn is connected to one or
more sensors (not shown) that are arranged to detect or measure
various parameters. The parameters could be boat speed, pressure
levels at a particular point or shaft power, for example. The
control circuitry could be arranged to open or close the doors 140,
150 individually, or as a group, in response to the detected
parameter values. For example, if the boat speed is detected as
"low" (e.g. less than 20 knots) the doors 140, 150 could be opened
to allow flow into the main duct 112 through the or each auxiliary
duct 124, and if the boat speed is detected as "high" (e.g. greater
than 20 knots) the doors 140, 150 could be opened so as to allow
flow out of the main duct 112 through the or each auxiliary duct
124.
[0083] The doors 140, 150 may be arranged to open and close under
the action of local pressure forces and be movable by an
actuator.
[0084] The actuation of the doors 140, 150 may be hydraulic or
electrical, for example.
[0085] Although the main outlet 116 has been described as being
above the water line, it will be appreciated that the main outlet
116 may also be below the water line, which may be useful for
certain applications.
[0086] As will be appreciated by one skilled in the art, any
combination of the aforementioned doors and door positions may be
used.
[0087] In a yet further embodiment, two or more of the auxiliary
ducts are interconnected towards the main duct. The interconnection
may be between all of the auxiliary ducts. In this way, the
effective shape of the main inlet can be altered to accommodate low
and high speed flows.
* * * * *