Note: Descriptions are shown in the official language in which they were submitted.
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ARRANGEMENT FOR STEERING A SHIP AND FOR SUPPLYING POWER TO ITS PROPULSION
SYSTEM
Field of the invention
The present invention relates to an arrangement for steering and supplying
propulsion
power to a contra rotating propellers (CRP) propulsion system in a marine
vessel
Background of the invention
The propulsion power of the large ships or marine vessels is generated by
rotating power
unit, whose energy source is oil, gas, nuclear power. The rotating power unit
may be a
diesel engine, gas turbine or nuclear power reactor rotating turbine. The
mechanical output
shaft is either directly or via a gear coupled to the shaft of the propeller
or the rotating
power unit drives a generator, which supplies electric power to the propeller
motors of the
ship. Furthermore, several different combinations of these two main manners to
drive the
propeller have been utilized.
The power and energy efficiency of the marine vessel necessitate that the
propulsion power
is generated as economically as possible in different operation modes. The
overall energy
consumption should therefore be optimized. That means that the electric energy
must be
generated using the most economical power production system that is available
on board
and that the electric energy is utilized as efficiently as possible when
supplying the electric
energy to the devices and motors using the electric energy.
As is well-known in the art the propulsion devices consume the majority of the
energy
expended in the marine vessels. Further, the propulsive force or thrust is
generated using
simultaneously different kind of engines or motors. Therefore it is important
that these
cooperate so that when producing the required propulsive power and steering
their
combined energy consumption is as low as possible. At the same time the total
energy
consumption and the generation of electricity must be as efficient as
possible. While it is
important that the total energy of the vessel is generated effectively and the
electric power
is supplied and used to all the electric power consuming devices effectively
in different
operating situations, the efficiency of the propulsion unit is of supreme
importance as most
of the energy is used when moving straight ahead under constant conditions.
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Publication WO 02/072418 suggests a CRP-propeller arrangement where one
propeller is
driven by a main engine and another propeller is driven by an electric motor.
The shafts
of the first and second propellers are coaxial and the shaft of the first
propeller is arranged
in the hollow shaft of the second propeller. The main engine drives the first
propeller
coupled to the shaft of the main engine and the generator arranged to the
shaft of the main
engine supplies electric power to a motor that drives the second propeller. In
addition,
there are other engines that rotate generators that supply power to the motor.
Summary of the invention
An object of the invention is to create a new and cost-effective arrangement
to supply
electric power in a ship or marine vessel.
In one aspect, the present invention provides an arrangement for steering and
supplying
propulsion power to a contra rotating propellers (CRP) propulsion system in a
marine
vessel, which arrangement comprises a first propeller driven by a rotating
power unit and a
second propeller driven by an AC motor whereby the second propeller is rotated
in the
opposite direction as the first propeller, and an AC generator coupled to
mechanical output
shaft of the power unit and driven by a rotating power unit, whereby the AC
generator is
electrically connected to the AC motor, characterized in that the arrangement
comprises
that
- (i) the AC motor and the AC generator have the same electrical frequency,
- (ii) another electrical power source is electrically connectable to the AC
motor
parallel to the AC generator,
- (iii) the shaft of the second propeller is mounted rotatable in a support
structure
which is attached to a hull of the marine vessel, and
- (iv) a rudder, which is supported in a manner allowing pivotal movement of
the
rudder relative to the support structure.
In another aspect, the present invention provides an arrangement for steering
and
supplying propulsion power to a contra rotating propeller (CRP) propulsion
system in a
marine vessel, which arrangement comprises:
a first propeller driven by a rotatable power unit;
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a second propeller driven by an AC motor, whereby the second propeller will
rotate in an opposite direction relative to the first propeller; and
an AC generator coupled to a mechanical output shaft of the rotatable power
unit
to be driven by the rotatable power unit, the AC generator being electrically
connected to
the AC motor, wherein:
(i) the AC motor and the AC generator have a same electrical frequency;
(ii) another electrical power source is provided which is configured to be
electrically connectable to the AC motor in parallel to the AC generator;
(iii) a shaft of the second propeller is rotatably mounted in a support
structure which is attached to a hull of the marine vessel; and
(iv) a rudder is supported in a manner allowing pivotal movement of the
rudder relative to the support structure.
The rudder can be supported to the hull of the marine vessel. Hubs of the
first propeller
and the second propeller can form a continuous streamlined shape.
The arrangement for steering and supplying propulsion power to a contra
rotating propellers
(CRP) propulsion system in a marine vessel comprises a first propeller driven
by a rotating
power unit and a second propeller driven by an AC motor whereby the second
propeller is
rotated in the opposite direction as the first propeller, and an AC generator
coupled to
mechanical output shaft of the power unit and driven by a rotating power unit,
whereby
the AC generator is electrically connected to the AC motor. The arrangement
comprises
that (i) the AC motor and the AC generator have the same electrical frequency,
(ii)
another electrical power source is electrically connectable to the AC motor
parallel to the
AC generator, (iii) the shaft of the second propeller is mounted rotatable in
a support
structure which is attached to a hull of the marine vessel, and (iv) a rudder,
which is
supported in a manner allowing pivotal movement of the rudder relative to the
support
structure.
According to one embodiment of the invention the rudder is supported to the
hull of the
marine vessel.
According to one embodiment of the invention that hubs of the first propeller
and the
second propeller form a continuous streamlined shape.
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When using the arrangement of the invention there is more freedom in ship's
general
arrangement and hull design. The electric power generators can be positioned
in a more
advantageous way and the hydrodynamic efficiency of the vessel is thereby
improved.
The energy is generated by the most efficient way in different operation
situations and
when fulfilling varying power demand of the vessel. Thereby the electrical
losses of the
marine vessel also are minimized compared to conventional electrical
propulsion systems.
Brief description of the drawings
The invention will be described in more detail in the following by referring
to the
appended figures, in which
- Figure 1 shows an embodiment of the invention,
Detailed description of the invention
Figure 1 shows a schematic diagram of an embodiment of the invention. A CRP
(contra
rotating propellers) propulsion arrangement 4 is installed in the aft portion
of the marine
vessel 2. The CRP-propulsion arrangement comprises a forward propeller 44 and
the aft
propeller 48 that are arranged to rotate in the opposite directions that is
well-known to the
men skilled in the art. A main rotating power unit 40 that is e.g. a two-
stroke diesel engine
drives a propulsion power ac generator 42, whose rotor is fastened to the one
output shaft
of the rotating power unit 40. A main propeller 44 of the vessel is fastened
onto another
output shaft 46 of the rotating power unit 40. Though the generator 42 and the
propeller 44
are on the opposite sides of the rotating power unit 40 in the embodiment
shown in the
figure 1, the generator may as well be on the same side of the rotating power
unit 40 as the
propeller 44. Opposite to the main propeller 44 is arranged a second propeller
48 which is
fixed to the output shaft 47 of an ac motor 50 and driven by the ac motor 50.
The main or
the forward propeller 44 is fitted with bearings (not shown) to the hull of
the vessel. The
second or the aft propeller 48 is supported with the ac motor 50 is installed
to a pod-like
housing 24 that is supported to the hull of the vessel by a support arm or
strut 16. The
propulsion ac generator 42 is connected to the ac motor 50 by an electrical
power
connection 52. Thereby the ac current generated by the ac generator 42 is
directly supplied
to the ac motor 50. A circuit breaker 54 is arranged on the electrical power
connection 52
by which the connection between the ac motor 50 and the propulsion ac
generator 42 can
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be switched on and switched off. When the circuit breaker 54 is switched on,
the ac motor
50 and the propulsion ac generator 42 have the same frequency.
A rudder 10 is arranged in the stern of the vessel 2. The rudder 10 is
supported via a first
rudder shaft 18 to the hull of the vessel 2 and via a second rudder shaft 14
to the housing
24. The first rudder shaft 18 is supported via bearings 20 that allow the
pivotal movement
of the rudder 10 to the hull. The second rudder shaft 14 is on the same
vertical axial line 22
as the first rudder shaft 18 and the rudder 10 is allowed to have pivotal
movement to the
housing 24 and to the support strut 16. The second rudder shaft 14 is fixed to
the housing
24 and the rudder 10 is supported thereto via a bearing 12. The rudder 10 is
turned around
the vertical axial line by a control unit well-known in the art.
The propellers 44 and 48 are designed to have a high efficiency in a CRP mode.
The hub
45 of the propeller 44 and the hub 49 of the propeller 48 are formed to have a
streamlined
shape. The propellers are arranged to the axial line and their common outer
surface form a
streamlined entirety. The pod-like housing 24, the supporting strut 16 and the
rudder 10
also form a streamlined shape.
Three auxiliary rotating power units 56, 57 and 58 are coupled to three
generators 60, 61
and 62, which are via electrical power connections connected to a main
switchboard or a
main bus 64 of the ship. The switchboard 64 is connected to the electric
distribution mains
of the vessel and the generators 60, 61 and 62 supply the electric power to
the consumers.
The auxiliary rotating power units 56, 57 and 58 are preferably four-stroke
diesel engines
having lower power than the rotating power unit 40. They may also be gas
turbines or
waste heat recovery systems, for example. The auxiliary rotating power units
56, 57 and
58 can be located in a suitable space in the hull of the vessel and they need
not be
positioned near the propellers 44 or 48 of the vessel or near the other
consumers of the
electric power. A frequency converter 66 is coupled between the main
switchboard 64 and
the junction 68 of the electrical power connection 52 via an electrical power
connection 70
and via an electrical power connection 72 connecting, respectively. There is a
second
circuit breaker 74 between the main switchboard 64 and the frequency converter
66 and a
third circuit breaker 76 between the frequency converter 66 and the junction
68.
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The propulsion system shown in the figure 1 can be operated and controlled in
several
ways depending on the operation mode.
In one mode the propulsion power is generated by the main rotating power unit
40. The
main rotating power unit 40 is functioning at full power and the ac generator
42 is directly
5 connected to the ac motor 50. The circuit breaker 54 is switched on and
also the circuit
breakers 74 and 76 are switched on and the frequency converter 66 is connected
between
the main switchboard 64 and the junction 68 of the line 52. The ac motor 50 is
totally
supplied from the ac generator 42 via the electrical power connection 52. As
the ac
generator 42 is directly connected to the ac motor 50 via the electrical power
connection
52, the ac generator 42 and the ac motor has the same frequency. When the ac
generator 42
and the ac motor 50 has the same number of poles they are thereby rotating
essentially on
the same rotational speed, in the case of synchronous machines the speed is
the same and
in the case of asynchronous machines the speed differs on the amount of the
slip. When the
ac generator 42 and the ac motor 50 have different pole numbers, their
rotational speeds
differ from each other on the basis of the pole numbers of the machines.
Correspondingly
the rotational speeds of the aft and forward propellers differ on the same way
as they are
fastened to the shafts of the machines.
In a second mode the propulsion power is generated by the auxiliary rotating
power units
56, 57 and 58 and the main rotating power unit 40. The ac motor is supplied
both from the
ac generators 50 and ac generators 60, 61 and 62 via the frequency converter
66 and from
the ac generator 42 via the electrical power connection 52. The circuit
breakers 74 and 76
are switched on and the electric power is supplied to ac motor 50 via the
frequency
converter 66 and via the main switchboard from the generators 60, 61 and 62.
The power
and frequency supplying the electric energy from the generators 60, 61 and 62
to the ac
motor 50 is controlled by the frequency converter 66. Depending on the power
demand of
the propulsion system and the power demand of the other electric power users
in the
vessel, the frequency converter may also supply electric power to the main
switch board 64
via the frequency converter 66.
The propulsion power of the marine vessels according to the invention is
generated by
rotating power unit, whose energy source is oil, gas, nuclear power. The
rotating power
unit may be a diesel engine, gas turbine or nuclear power reactor rotating
turbine. Further,
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waste heat recovery system may be used that utilizes the exhaust gases of main
engines by
turbochargers.
The ac generator may also be connected to the shaft of the main engine via a
gear.
Between the second propeller and the ac motor rotating it there may be
different kind of
gear arrangements. These modifications allow many varieties that are in scope
of the
invention.
