The present invention relates to a water jet propulsion system for
vessels according to the preamble portion of claim 1. More particularly, it relates
to a water jet propulsion system for vessels of a displacement type which has streams
of water taken in from a bottom of a vessel and changed at an impeller into water
jets, and ejects the water jets at a stem of the vessel substantially in parallel
with a surface of water, to thereby travel.
Such a water jet propulsion system for vessels typically has an arrangement
in which a single ejection nozzle is fixed to a transversely central part at a
stem of a vessel, and water jets to be ejected from the nozzle have an ejection
quantity changed, as a rotation speed of an impeller is changed, and an ejection
velocity controlled, as a bore diameter of the nozzle is controlled.
The changed ejection quantity of water jets shifts propulsive power
of the vessel, and the controlled ejection quantity provides a controlled travel
Accordingly, the ejection quantity and the ejection velocity of water
jets are adequately varied in accordance with a weight of loads on the vessel,
to thereby enable a saved fuel consumption at a drive for the impeller, allowing
an economical travel.
However, the load weight of a vessel has an inseparable relationship
to a drafting state of the vessel, such that a lighter load weight provides a shallower
draft level, and a heavier load weight provides a deeper draft level.
If the draft is deep, a hull of the vessel has an increased fluid
resistance, and besides, water jets hit waves, having a fraction of propulsive
power killed, whereas a compensation therefor would cause an inflexible controllability
of water jet ejection quantity and ejection velocity.
As a result, the economical travel has conventionally been allowed
within a relatively narrow range of load weight.
To this point, there has been proposed an arrangement, which had a
pair of ejection nozzles arranged side by side.
This arrangement allowed a sufficient ejection quantity to be secured,
with a postponed problem of water jets hitting waves when with a heavy load.
There has been proposed another arrangement, which had a pair of ejection
nozzles vertically arranged for a concurrent use, with a wave-hitting problem still
left on a lower nozzle.
JP-A-09039888 discloses a water jet propulsion system for vessels,
comprising jet stream supply means for changing streams of water taken in from
a bottom of a vessel into jet streams to supply jet streams in a flow rate variable
manner; and water jet ejection means for ejecting supplied jet streams, rearwardly
of a stem of the vessel, as velocity variable water jets along an ejection axis
having a variable vertical position.
Disclosure of Invention
The present invention has been achieved with such points in view.
It therefore is an object of the invention to provide a water jet propulsion system
for vessels, allowing an economical travel, whether the load is much or little.
To achieve the object, according to the invention, there is provided
a water jet propulsion system for vessels as defined in claim 1.
According to the water jet propulsion system for vessels, the ejection
axis of water jets can be vertically shifted in accordance with a varying draft
level of the vessel, and the ejection quantity of water jets as well as the ejection
velocity is controllable at a shifted position, thus allowing an economical travel,
whether the load is much or little.
The water jet ejection means may preferably comprise a plurality of
ejection nozzles arranged in a vertically spacing manner, a plurality of valve
members provided in fluid paths connected to the plurality of ejection nozzles,
and control means adapted to individually control the plurality of valve members,
thereby permitting a selective use of an ejection nozzle having an adequate vertical
position in accordance with a varying draft level of the vessel.
The water jet ejection means may preferably further comprise bore
diameter control means adapted to control an ejection bore diameter individually
of the plurality of ejection nozzles, thereby permitting the water jet ejection
velocity to be controlled in a voluntary manner.
The plurality of ejection nozzles may preferably be arranged in a
plurality of upper and lower rows, thereby allowing the ejection quantity of water
jets to have a relatively large variation at a respective position, and adaptive
to a large-scale vessel to be large in variation of load weight.
The water jet ejection means may preferably comprise an ejection nozzle
having a controllable ejection bore diameter, and drive means for vertically driving
the ejection nozzle, thereby allowing an economical travel of the vessel, whether
the load is much or little, in addition to a reduced weight, a reduced construction
cost and an improved appearance of the vessel to be expected.
Brief Description of Drawings
Best Mode For Carrying Out the Invention
- Fig. 1 is a schematic side view of a water jet propulsion system for vessels
according to an embodiment of the invention.
- Fig. 2 is a side view of an ejection nozzle of the water jet propulsion system
for vessels according to the embodiment of the invention.
- Fig. 3 is a longitudinal section of an essential portion of the ejection nozzle
of Fig. 2.
- Fig. 4 is a front view of the ejection nozzle of Fig. 2.
- Fig. 5 is a graph describing actions of the water jet propulsion system for
vessels according to the embodiment of the invention.
- Fig. 6 is a graph describing a variation in propulsion efficiency of an impeller
of the water jet propulsion system for vessels having actions described in Fig.
- Fig. 7 is a schematic sectional view of an ejection nozzle of a water jet propulsion
system for vessels according to an embodiment of the invention.
- Fig. 8 is a schematic sectional view of an ejection nozzle of a water jet propulsion
system for vessels according to an embodiment of the invention.
Fig. 1 shows a water jet propulsion system for vessels according to
an embodiment of the invention. This water jet propulsion system comprises a jet
stream supply system (5, 9, 10, 11) for changing streams of water taken in at a
bottom of a hull 1 of a vessel into jet streams to supply jet streams in a flow
rate variable manner, and a water jet ejection system (2, 3, 4, 6, 7, 8, 16) for
ejecting supplied jet streams, rearwardly of a stern of the vessel, as water jets
along horizontal ejection axes J1, J2 or J3 different in vertical position.
The jet stream supply system comprises an intake opening 10 for taking
in streams of water from a location near the stem at the bottom of the hull 1,
an impeller 9 for changing taken streams of water into jet streams to deliver jet
streams in a flow rate variable manner, a supply piping 5 for supplying delivered
jet streams to a passage branched vertically in three stages and transversely in
three columns, and an engine 11 for driving the impeller 9 with a gear-ratio variable
The water jet ejection system includes a plurality of ejection nozzles
2, 3, 4 spaced vertically in three stages (upper, middle, lower) and transversely
in three columns (port, central, starboard) to be arranged at the stern, vertically
three stages and transversely three columns of normally close type open close valves
6, 7, 8 installed in jet stream supplying branched paths connected to the ejection
nozzles, and a control system 16 adaptive for individual control of the valves.
Ejection nozzles 2 in the upper stage have a large-diameter ejection
bore, ejection nozzles 3 in the middle stage, a middle-diameter ejection bore,
and ejection nozzles 4 in the lower stage, a small-diameter ejection bore. Each
stage may preferably comprise an ejection nozzle merely of a central column.
The control system 16 has, in a vessel steering cabin, a display for
displaying a detected value of a draft of the hull 1 and shipment data representative
of an amount of loads.
When the load has a large weight and the draft is a deep level L1,
valves 6 are opened to eject water jets from the ejection nozzles 2. After reduction
in load weight, if the draft is a normal level L2, valves 7 are opened to eject
water jets from the ejection nozzles 3. If the draft is a shallow level L3, as
the vessel is in an unloaded state or similar state thereto, valves 8 are opened
to eject water jets from the ejection nozzles 4.
While at the deep draft L1, strong propulsive power (drive power)
is needed, not simply for a heavy weight transfer, but also because of an increased
water fluid resistance of the hull 1. To this point, the ejection nozzles 2 are
large in bore diameter, and eject a large quantity of water jets, achieving a sufficient
At the shallow draft L3, the vessel is in an unloaded state, where
the hull 1 has a relatively small resistance, and the ejection nozzles 4 with a
small bore diameter can cope with.
The ejection nozzles 2 to 4 are selected for use in accordance with
a shipping load, permitting an economical travel.
Figs. 2 to 4 show a slide valve 12 adapted for diameter control of
ejection bores of the ejection nozzles 2 to 4.
As a tip-end cylindrical part for a nozzle body 3a, a lancer 3b has
the slide valve 12 installed therein, which slide valve 12 is vertically driven
for a throttling of ejection bore diameter. Drive control for the slide valve 12
is effected by with a hydraulic cylinder 13, and a hydraulic system for the hydraulic
cylinder 13 is controlled by the control system 16. The bore diameter of ejection
nozzles 2, 3, 4 selected in dependence on a draft is additionally controllable,
allowing for the engine 11 to work with an optimum efficiency by ejection control
in accord with load weight and travel speed. Incidentally, for some vessels, the
ejection nozzles 2-4 may preferably have an identical bore diameter subjected to
bore diameter control by slide valves 12.
Fig. 5 shows relationships between a thrust T (propulsive force) of
water jets and a fluid resistance R of the hull 1 and a travel speed Vs [m/sec]
of the vessel.
As the vessel speed Vs increases, the resistance R of the hull 1 increases
with a steep gradient, and the thrust T of water jets decreases, as the impeller's
suction rate is increased with the increasing vessel speed Vs.
Designated by R1 is a hull resistance R when at a deep draft, and
R2 is a hull resistance R when at a shallow draft. When traveling with a thrust
T1 (impeller revolution number N1), if at the deep draft (resistance R1), the impeller
revolution number is balanced with the resistance at a vessel speed V1 (coordinate
PI), and if at the shallow draft (resistance R2), it is balanced at a vessel speed
V2 (coordinate P2). This means, in the case of a shallow draft, the impeller with
light load has an excessive revolution, tending to cause cavitations. Then, the
lower-staged ejection nozzles 4 are employed (or nozzle diameters are throttled),
to thereby enable an efficient travel (vessel speed V2') with a balanced state
(coordinate P2') between thrust and resistance.
Fig. 6 shows a relationship between the impeller's propulsion efficiency
and a change in ratio of a water jet ejection velocity Vj to the vessel speed Vs.
The water jet propelling vessel has, between water jet ejection velocity Vj and
vessel speed Vs, a ratio range (K = 1.5 to 6, where K = Vj/Vs) for propulsive power
to be efficiently obtained.
Changing the ejection velocity Vj relative to the vessel speed Vs
can be achieved by selection/control of ejection bore diameter, and the present
embodiment allows for propulsive power to be obtained with high efficiency in dependence
on a varying draft, permitting an economical travel.
Figs. 7 and 8 show embodiments having ejection nozzles 50, 60 constituted
as vertical slide types for reduction in number of nozzles.
The ejection nozzle 50 is level-controlled with a motor 51 connected
to a control system (16), for ejecting jet streams, as they are introduced from
a flexible tube 52 and velocity-controlled by an adjustable throttle 55 controllable
from the control system (16), rearwardly of a stem in the form of water jets along
a horizontal axis J5.
For the ejection nozzle 60, a nozzle holding plate 62 is water-tightly
level-controlled with a motor 61 connected to a control system (16). Jet streams
introduced from a vertical duct 53 are velocity-controlled by an adjustable throttle
55 controllable from the control system (16). and are ejected rearwardly of a stem
in the form of water jets along a horizontal axis J6.
The ejection nozzles 50, 60 may preferably be arranged in rows, or
serve in combination with or substitute for an arbitrary array of ejection nozzles
2 to 4.
According to the invention, vessels equipped with water jet propulsion
systems can economically travel, whether their loads are much or little, and have
greatly reduced traveling costs, with fuel consumption inclusive, and significant
contribution may be provided for profits to be enhanced in vessel flight services.