EP4230517A1 - Cargo ship with multiple propeller drive with improved efficiency - Google Patents

Abstract

Cargo ship with a multi-propeller drive as the main drive, comprising at least two drive trains (1, 2) each with a propeller (12, 22) and a propeller shaft (11, 21) mechanically driving the propeller. According to the invention, the drive trains (1, 2) are driven jointly by the same heat engine (3). A first drive train (1) is mechanically driven and mechanically coupled to an output shaft (31) of the heat engine (3). A second drive train (2) is driven electrically by means of a direct electrical connection (4), which includes a traction current generator (41) coupled to the output shaft (31) and an electric traction motor (43) driving the second propeller shaft (21) of the second drive train (2). , wherein the traction current generator (41) and the electric traction motor (43) are connected to one another via a direct electrical line (42). The direct connection (4) does not require a frequency converter and is therefore efficient. Thanks to the electrical power transmission to the second drive train (2), a single heat engine is sufficient without requiring complex and efficiency-reducing transmission shafts. This increases efficiency and makes it easier to accommodate the components in a space-saving manner.

Description

The invention relates to a cargo ship with a multi-propeller drive as the main drive, which comprises at least two drive trains, each with a propeller and a propeller shaft that mechanically drives the propeller.

In the case of cargo ships, the efficiency of the ship's drive is a particularly important criterion. An efficient drive is essentially characterized by two important properties. On the one hand, it requires little effort and as few components as possible in order to enable inexpensive production. On the other hand, it enables economical operation, which is reflected in particular in the low fuel consumption. But maintenance costs also play a role, and a simple and less complex design can make a significant contribution to reducing them.

It is generally the case that an efficient heat engine, in particular an efficient internal combustion engine, can be used to achieve low fuel consumption and thus form an efficient drive configuration. When considering the efficiency of the drive configuration, it should be noted that losses of various types can occur. Mechanical, electrical and/or hydrodynamic losses can thus occur. Mechanical losses arise, for example, from heat generation as a result of friction on bearings or in gears. Electrical losses are caused by the construction principle of electric motors or generators, by heat generation in electrical lines or by losses in AC or rectification. The hydrodynamic losses of the ship's propulsion system are essentially determined by the inflow to the propeller, the propeller geometry, the interaction of the propeller with the ship and the power density at the propeller.

It has proven to be favorable for a hydrodynamic drive that is as efficient as possible to provide the largest possible drive area (determined by the propeller diameter) or to provide as many propellers as possible in order to achieve a larger drive area. However, the increase in the propeller diameter is limited in terms of the maximum size on the one hand by practical circumstances, such as the required draft or the hull shape required for this. Therefore, ships with a two-screw propulsion (two-screw) often have a higher hydrodynamic efficiency than ships with only one propulsion (single-screw). However, drives with multiple propellers require a more complex drive concept that may be associated with greater mechanical losses. In particular, in the case of drive concepts with two propellers, either at least two drive motors are required, which then turn out to be correspondingly smaller, or else a complex transmission design, which requires more manufacturing effort and can reduce efficiency. However, several smaller drive engines have the disadvantage that they usually require a higher specific fuel consumption. Furthermore, the typically higher rated speed of smaller internal combustion engines usually requires a reduction gear between the engine and propeller, which in turn entails mechanical losses, or a higher propeller speed, which in turn leads to correspondingly greater hydrodynamic losses. Complexity and manufacturing costs for drives with two or more screws are therefore often not fully satisfactory.

The object of the invention is to provide a cargo ship with an improved main drive which is cheaper to manufacture and more efficient to operate.

The solution according to the invention lies in a cargo ship and a main propulsion system for a cargo ship with the features of the independent claims. Advantageous developments are the subject of the dependent claims.

In a cargo ship comprising a hull through which a center line of the ship extends from the stern to the bow, with a hold and a multi-propeller drive as the main drive, which has at least two drive trains, each with a propeller and a propeller shaft mechanically driving the propeller, and a heat engine with a output shaft for driving the drive trains, the invention provides that the drive trains are jointly driven by the same one heat engine, with a first drive train being driven mechanically and mechanically coupled to the output shaft of the heat engine, and with a second drive train being driven electrically by means of an electric Direct connection comprising a traction current generator coupled to the output shaft and an electric traction motor driving the second propeller shaft of the second drive train, the traction current generator and the electric traction motor being connected to one another via a direct electric line.

The invention is based on the idea of providing a common heat engine for the two drive trains of the main drive. This enables the use of a larger and therefore more efficient internal combustion engine as a heat engine. As a special feature, however, the heat engine drives only one of the two drive trains directly mechanically on, while the other of the two drive trains is not driven mechanically but electrically. A direct electrical connection is provided for power transmission, which includes a traction generator driven by the heat engine for generating electrical power, a direct electrical line to an electric traction motor for transmitting the electrical power generated in this way to the electric traction motor, and finally the electric traction motor, which connects the drive shaft and thus the Propeller of the second drive train drives. A single heat engine can thus be used, and no transmission shafts, which are complicated and expensive to lay and reduce efficiency, are required in order to transfer the mechanical power from the heat engine to the second drive train. This is significantly simplified by means of the direct electrical line according to the invention. This applies in particular to those cargo ships that, due to their nature, have structurally limited conditions for accommodating the heat engine, such as cargo ships with ramps for vehicles (especially ferries), which typically take up a lot of space on at least one side of the ship.

The solution according to the invention achieves a number of advantages. First, it allows one larger heat engine to be used instead of two smaller ones through the use of a single shared heat engine, thereby realizing the inherent efficiency advantages of the larger heat engine. Furthermore, the invention has recognized that when using two smaller thermal engines, because of their small size, typically faster-running motors are required, which in turn require a reduction gear for the propeller shaft. The additional effort required as a result and the associated efficiency losses can be reduced by using a larger and thus slower running heat engine can be avoided or reduced. Thirdly, the use of a common engine with two propellers allows the advantage of having smaller propellers compared to a conventional concept where the single engine acts on only one large propeller and thus achieve the required propulsion area at a reduced draft. Fourth, the direct line between the traction current generator and the electric traction motor avoids conversion losses that would inevitably occur with conventional routing of the electrical power via frequency converters. In this way, maximum efficiency is achieved both hydrodynamically and mechanically and on the engine side.

The first drive train and the second drive train are designed in such a way that they each apply essentially the same power contribution, ie approximately half of the propulsive power of the ship. This results in a favorable distribution of the propulsion power and there is also an advantageous left/right symmetry of the propulsion power, which avoids unwanted yaw and benefits from improved stability, and this also ensures (since there is no constant asymmetric rudder position or lead) a more efficient propulsion.

Some of the terms used are explained below:
A cargo ship is understood to mean a surface ship designed for commercial sea transport. The term includes in particular cargo ships in the narrower sense, in particular general cargo carriers, bulk carriers and container ships, as well as ferries. The term does not include military ships, especially warships, and submarines.

The main drive of the ship is understood to mean a drive that forms the propulsor that acts essentially in the direction of the center line of the ship. For reasons of efficiency, the propulsor or propeller assigned to it is typically not pivotable.

"Left" and "right" are understood to mean directions that are related to a ship's center line, which extends from the stern of the ship towards the bow of the ship. This direction is also the ship's intended direction of travel. The terms "left" and "right" therefore coincide with the nautical terms "port" and "starboard".

The maximum power that can be transmitted by a drive train is understood to mean that power for which the drive shaft and its propeller are designed to transmit the maximum. This is technically known as the "Maximum Continuous Power" of the propeller/shaft.

The term alternating current includes single-phase alternating current and multi-phase alternating current, in particular three-phase alternating current ("three-phase current"). Three-phase current is a technical term for three-phase alternating current.

The direct electrical line is preferably designed purely as a cable and/or line connection and in particular has no converter, ie it does not include a frequency converter. Only one cable connection is therefore required for the direct line. This is extremely cheap to manufacture and not only avoids the expense required for a frequency converter, which would be considerable given the powers in question here of often several megawatts, but also avoids them also the current exchange losses occurring with a frequency converter during operation. In addition, the risk of failure is reduced in this way, which a frequency converter could bring with it due to its highly loaded semiconductor switches. An increase in reliability as well as a further improvement in efficiency with simultaneous cost savings is thus achieved.

It is convenient if the direct electrical connection is an AC connection. This avoids rectification and the losses associated with rectification (on the traction current generator) or commutation (on the electric traction motor) can be avoided. Furthermore, the design as an AC connection makes it possible for the frequency of the alternating current to depend on the speed at which the traction current generator is driven. Thus, the frequency in the AC connection is in a fixed ratio to the mechanical drive speed, which (when using a synchronous generator and a synchronous motor) speed-synchronous operation of the electric traction motor is significantly easier. The required electrical power can thus be transmitted in a particularly efficient and expedient manner.

The traction current generator can be designed as a shaft generator. This means that it is driven directly by the output shaft of the heat engine by means of a mechanical power tap on the output shaft.

The traction current generator is preferably designed as a synchronous machine. On the one hand, this offers a high level of efficiency. On the other hand, this offers the advantage that the alternating current generated has a frequency that strictly correlates with the speed of the mechanical drive. the frequency of the alternating current in the direct electrical connection is therefore a measure of the speed of the mechanical drive. It is particularly expedient here if the electric traction motor is also designed as a synchronous machine. In addition to the high level of efficiency, this offers the advantage that the speed of the drive shaft driven by the electric traction motor and thus of the propeller is also strictly correlated with the frequency of the alternating current in the direct electrical connection. As a result, this means that the speed of the electric drive train with its propeller corresponds to the speed of the mechanical drive train with its propeller. In this way, speed synchronization of the two drive trains can be achieved without additional effort. This results in an intrinsic direction and speed-following operation of the electrically operated second drive train, without the need for separate control and synchronization devices. In terms of stability and operational safety, this offers considerable advantages without any additional effort.

When using a (structurally less complex) asynchronous generator and motor, the characteristics of the electrical machines result in a lower speed for the second drive train. This can be compensated for, for example, by using controllable pitch propellers with different pitches. In particular, the propeller of the second drive train, which is designed as a variable-pitch propeller, is regulated by a corresponding control system to a different pitch than the pitch of the propeller of the mechanical drive train. The efficiency can thus be improved. However, it can also be provided that the design of the propeller of the second drive train is designed for a greater pitch. This has merits in terms of a lower complexity. Depending on the design, the resulting efficiency losses can be classified as low.

According to a further particularly advantageous aspect of the invention, which may deserve independent protection, the heat engine is preferably systematically oversized in relation to the maximum transmittable power of one of the drive trains, in such a way that the heat engine can preferably deliver at least twice as much mechanical power like the maximum transferrable power of one of the drive trains. In this way, the heat engine can also provide the power required to drive the second drive train, without there being a risk of overloading as a result.

It can be provided that, in addition to the second drive train, one (or more) further electrically driven drive train is provided. To this end, it is expedient if the heat engine is (n+1) times oversized, with "n" denoting the number of electrically driven drive trains. If, in addition to the mechanically driven drive train, there are also two electrically driven drive trains (n=2), the heat engine is expediently dimensioned three times as large as is required for driving one mechanically driven drive train.

It is advantageously provided that the heat engine is designed as an internal combustion engine, in particular as a two-stroke ship engine. The design as an internal combustion engine, in particular as a ship's engine such as a ship's diesel engine, offers low production costs combined with high efficiency. Because a common internal combustion engine is provided according to the invention, it has large dimensions. This makes it possible to provide a large, slow-running internal combustion engine which brings significant advantages in terms of high efficiency. A design as a slow-running two-stroke ship engine is particularly useful. Slow running is typically understood to mean a speed between 60 and 140 rpm. This design, which is particularly suitable for combustion engines with very high performance, offers the advantage of particularly high efficiency over a wide speed range. Another advantage of a two-stroke engine is the flexible use of different fuels such as LNG (Liquified Natural Gas), ammonia or methanol, so that very low-emission ship operation is possible.

The cargo ship expediently has a ramp, in particular a vehicle ramp, for loading and the heat engine is arranged below the ramp. This enables a particularly space-saving concept, since the otherwise difficult-to-use space below the ramp can be optimally used. Especially when using a structurally higher two-stroke engine, the space below the ramp can be used optimally. In addition, this space is often located aft, which allows shorter drive shafts to the propellers.

Advantageously, the first, mechanical drive train is gearless. By not providing a gear for the mechanical drive train, on the one hand the expense associated with the gear for procurement and manufacture is saved, and on the other hand the loss of efficiency that is inevitably associated with a gear can be avoided. This increases the overall efficiency of the mechanical drive train.

It is preferably further provided that the first, mechanical drive train is provided with a clutch. With that can be achieved that the propeller of the mechanical drive train can be disengaged. With the clutch, the mechanical connection and thus the power transmission between the heat engine and the propeller of the mechanical drive train can be separated. In this way, this propeller can be rendered non-driven, for example if the propeller is defective or if, for other reasons, no power output is desired from this propeller despite the heat engine being running.

Advantageously, a power split unit is provided between the output shaft of the heat engine and the first, mechanical drive train, which is designed to split the power of the heat engine to the first, mechanical drive train and the traction current generator of the second drive train. With the power branching, the power provided by the heat engine can be divided up in a simple and expedient manner. It is preferably provided for this purpose that the power splitting unit drives the traction current generator at a speed that is in a fixed ratio, in particular at the same speed as the speed of the first, mechanical drive train. There is thus a speed-related relationship between the speed of the mechanical drive train and that of the traction current generator. That may mean it's the same RPM. However, the speed is preferably not in a ratio of 1:1, but in another fixed ratio. This means that the speed of the traction current generator can, for example, be twice as high (or even more) in order to enable the use of a traction current generator with the same performance but smaller dimensions due to the higher speed and to make better use of it.

It is particularly expedient if the power splitting unit drives the traction current generator with an increased torque compared to the first mechanical drive train. In this way, the losses that are small, but still present in the traction current generator and the electric traction motor, can be compensated by correspondingly branching slightly more power to the electrically driven drive train due to the increased torque. This is expediently chosen such that, taking into account the efficiency losses of the direct electrical connection, the mechanical power finally generated by the electric traction motor is as great as the drive power in the mechanical drive train. If the efficiency losses are 7%, for example, of which three percent are due to the traction current generator, one percent to current heat losses in the electrical line and three percent to the electric traction motor, the power split unit is expediently designed in such a way that the traction current generator receives a torque that is 7% higher than the mechanical drive train . It should not be ruled out that more torque can also be branched off if other units may also be supplied with electrical power from the direct electrical line. Preferably, the torque is increased in a range from 3% to 35%.

A tap can expediently be provided on the direct line, to which an auxiliary feed device is connected, which connects the direct line to a main electrical system of the cargo ship, which is preferably provided with its own generator, via a frequency converter. In this way, additional power can be provided from the traction generator for use in the ship's main electrical system, if desired. For example, this can be supplied in an efficient manner if the heat engine is only driven by the ship's operation is little loaded, so as to lead the operation of the heat engine in a more favorable higher load condition.

The auxiliary feed device is preferably dimensioned for a lower power than the electric traction motor, and/or the auxiliary feed device is dimensioned for a power of less than 20% of the power of the heat engine. Since the auxiliary power supply does not have any tasks as part of the regular traction drive, such a low power is completely sufficient for it. This reduces the effort involved in production and provision.

If two drive trains are provided, one is expediently arranged to the left and the other to the right of the center line of the ship. This enables a symmetrical distribution of propulsive power and provides good course stability. Furthermore, three drive trains can be provided, one of which is arranged in the center line of the ship and one further to the left and the other to the right of the center line of the ship. The advantage here is that the mechanical drive is in the center line of the ship, and the two outer ones are the electric drives. In a variant of the invention, however, it can also be provided that the main drive is designed in duplicate, each with at least two drive trains, which are preferably arranged symmetrically to the left and right of the center line of the ship. This enables the invention to also be used in cargo ships with a multi-screw propulsion concept, such as a four-screw.

It should be noted that the propeller shafts are typically aligned substantially parallel to the keel line. Substantially parallel is understood here to mean that there is a deviation of no more than 10° in each spatial direction exhibit. Good price stability with high efficiency can thus be achieved.

Advantageously, the propeller shaft of the first, mechanical drive train is connected to the output shaft without deflection, preferably in an extended line of the output shaft. This avoids the efficiency losses caused by deflections.

The invention also extends to a main propulsion system for a cargo ship according to the independent claim. For the more detailed description, to avoid repetition, reference is made to the above statements.

Fig. 1

eine schematische Aufsicht auf ein Frachtschiff gemäß einer Ausführungsform der Erfindung;

Fig. 2

eine teilweise Schnittansicht entlang einer Schiffmittellinie des Frachtschiffs gemäß der in Fig. 1 dargestellten Ausführungsform;

Fig. 3

eine Hauptspantansicht von Achtern darstellend eine Wärmekraftmaschine unterhalb einer Rampe; und

Fig. 4

eine funktionale Systemansicht eines Hauptantriebs des Frachtschiffs sowie seines elektrischen Schiffsystems.

The invention is described below by way of example with reference to an advantageous embodiment. Show it:

1

a schematic plan view of a cargo ship according to an embodiment of the invention;

2

a partial sectional view along a ship center line of the cargo ship according to in 1 illustrated embodiment;

3

Figure 14 is aft main frame view showing a heat engine below a ramp; and

4

a functional system view of a main propulsion system of the cargo ship and its electrical ship system.

A cargo ship designated in its entirety by reference number 9 has a hull 90 . The longitudinal axis of the hull 90 extends from the aft end 91 (stern) of the hull 90 to the bow end 92 (bow) of the Hull 90 has a ship center line 99. The cargo ship 9 has in its hull a main propulsion system which has a heat engine designed as an internal combustion engine 3 as the main propulsion source. Furthermore, two drive trains 1, 2 are provided, which are arranged symmetrically to the left and right of the center line 99 of the ship. Each of the two drive trains 1 and 2 has a propeller 12, 22 which is driven by means of a propeller shaft 11, 21 in each case. A rudder 95 of a rudder system for steering the cargo ship 9 is arranged behind each of the two propellers.

The ship 9 has in its hull 90 in a manner known per se a cargo-carrying deck 93 which delimits a cargo space 97 below an upper deck 94 of the ship 9 . Also provided is a ramp 96 assigned to the loading space 97 and which enables vehicles to drive onto the upper deck 94 . In the illustrated exemplary embodiment of the cargo ship 9, the ramp 96 is arranged eccentrically, namely on the port side.

The internal combustion engine 3 is also arranged in the hull 90 on the port side below the ramp 96 . In the exemplary embodiment shown, this is designed as a slow-running two-stroke ship engine. This design requires a slim but high design of the internal combustion engine 3. By arranging it below the ramp, the internal combustion engine 3 can optimally use the space that is otherwise difficult to use.

The power delivered by the internal combustion engine 3 is preferably routed aft directly, that is to say without an intermediate reduction gear, via an output shaft 31 which is preferably arranged essentially parallel to the center line 99 of the ship. The output shaft 31 runs to the point at which the power transmitted by the output shaft 31 is divided. A power branching unit 5 is provided for this purpose. A first part of the power is transmitted mechanically to the first drive train 1, and the other part of the power is routed via a direct electrical connection 4 to drive the second drive train 2. This is explained in more detail below.

The first drive train 1 is a mechanical drive train and includes a first propeller shaft 11 which, at its rear end, drives a main drive propeller 12 arranged in the stern area of the cargo ship 9 . A clutch 15 is provided in the area of the front end of the first propeller shaft 11 . This makes it possible to interrupt the flow of power along the first propeller shaft 11 and thus render the propeller 12 powerless. The first drive train 1 is arranged on the same side of the cargo ship 9 as the internal combustion engine (in the exemplary embodiment shown on the left, i.e. on the port side), preferably in such a way that the first propeller shaft 11 is arranged in an extended line of the output shaft 31 . This avoids a deflection in the mechanical power flow path and the associated loss of efficiency.

The second drive train 2 comprises a second propeller shaft which drives a second main drive propeller 22 arranged in the stern area of the cargo ship 9 in the same way as in the first drive train 1 . The second drive train is arranged on the other side of the cargo ship 9 (shown in the exemplary embodiment on the right side, ie on the starboard side). A direct electrical connection 4 is provided for transmitting the power to the second drive train 2 . It includes a traction current generator 41, which generates polyphase alternating current (three-phase current in the exemplary embodiment) and via a direct electric line 42 to an electric traction motor 43 arranged on the bow of the second propeller shaft 21. The traction current generator 41 is arranged at the end of the output shaft 3, namely on the power split unit 5. This is designed to transmit the power generated by the internal combustion engine 3 and via the Output shaft 31 to split the power supplied to the first, mechanical drive train 1 with its propeller shaft 11 and to the traction current generator 41 to generate electrical power to drive the second, electric drive train 2. The power split unit 5 and the traction current generator 41 can be structurally combined, this can be expedient be designed as a shaft generator, which is driven by the output shaft 31.

The traction current generator 41 is preferably designed as a synchronous generator and the direct electrical line 42 is directly connected to it, ie without a frequency converter. The frequency of the alternating current transmitted in the direct electric line 42 is determined by the speed of the electric generator 41, which in turn depends on the speed of the output shaft 31 and thus the speed of the internal combustion engine 3. The electric traction motor 43 is designed as a three-phase motor and this is the electrical direct line 42 directly, ie connected without a frequency converter. Due to its design as a three-phase motor, the speed of the electric traction motor 43 is therefore dependent on the frequency of the three-phase current in the direct electrical line 42. In this way, the speed at which the second drive train 2 is driven is coupled with the speed of the mechanically driven one first drive train 1, without the need for special additional facilities or complex speed control systems. In addition the electric drive motor 43 is expediently designed as an asynchronous motor or, in the case of particularly high demands on speed synchronization of the second drive train 2 with the mechanically driven first drive train 1, as a synchronous motor. In the embodiment as an asynchronous motor, the propeller 22 of the second drive train 2 is preferably designed as a variable-pitch propeller.

The power split unit 5 is designed in such a way that the output speed, i.e. the speed at which the first propeller shaft 11 of the first drive train 1 is driven, is the same as the speed at which the traction current generator 41 for supplying the second drive train 2 is driven, or at least is in a fixed relationship. This ensures speed synchronism, as described above. The torque split is preferably such that the traction current generator 41 is driven with a slightly higher torque than the first propeller shaft 11, for example with a torque increased by 7%. In this way, compensation can be provided for losses occurring along the direct electrical connection 4, which are caused by (e.g. 3%) efficiency losses of the traction current generator 41 on the one hand, (e.g. 1%) current heat losses of the direct electrical line 42 and (e.g. 3rd %) Efficiency losses of the traction motor 43. If the losses total 7%, for example, the power splitting unit 5 is preferably designed in such a way that the torque for driving the traction current generator 41 is 7% higher than the torque with which the first propeller shaft 11 is driven. As a result, the same drive power is obtained at the output of the traction motor 43, ie at the drive of the second propeller shaft 21, as is the case in the first drive train 1, taking into account the efficiency losses of the direct electrical connection 4. With that are the two drive trains 1 and 2 are balanced in terms of power, also taking into account efficiency losses along the direct electrical connection 4, ie both provide the same power.

An example of a corresponding functional system view is in figure 4 shown. Numerical values are also shown there by way of example, in particular for outputs and speeds. In the example, the internal combustion engine 3 has an output of 6800 kW at a speed of 100 revolutions per minute, which is typical for a slow-running two-stroke marine diesel engine, at an operating point of 85% of its maximum continuous output. This power is supplied via the output shaft 31 to the power splitting unit 5 in the form of a shaft generator, in which the functions of the power splitting unit 5 and the traction current generator 41 are combined. The mechanical output of the power splitting unit 5 goes via the first propeller shaft 11 to the first propeller 12, specifically with a mechanical output (shown in the example) of 3026 kW. The traction current generator 41 generates three-phase current with an output of 3641 kW at a frequency of 20 Hz. The frequency depends on the speed of the internal combustion engine 3 and thus changes depending on changes in the speed of the internal combustion engine 3. The traction current generator 41 is in the example as Synchronous generator with 12 pairs of poles, which results in a frequency of f = 20 Hz for the three-phase current generated at a speed of n = 100 rpm.

The three-phase current generated is routed via the direct electrical line 42 to the other side of the ship to the electric traction motor 43. This generates a mechanical output of 3026 kW. If it is designed as a synchronous motor, it drives the propeller shaft 21 and the propeller 22 of the second drive train 2 with a mechanical speed of 100 rpm, i.e. a speed corresponding to that of the first drive train 1. Not only do the propellers 12, 22 on both sides of the ship receive the same power, but they also rotate at the same speed when using synchronous machines. This ensures high stability and better maneuverability. Thanks to the direct electrical line 42, the transfer of power from one side of the ship to the other is completely unproblematic and can be done in a space-saving manner and with little effort even in difficult structural conditions.

In figure 4 Also shown is an optional tap 7 on the direct electrical line 42. Connected to this tap 7 is an auxiliary power supply 70 comprising a frequency converter 71 with a switch 72, which in turn is connected to a distribution bar 80 of a main electrical system 8 of the cargo ship 9. The main electrical system 8 of the ship feeds the electrical consumers required for the crew, their accommodation and for the rest of the operation (apart from the main drive) of the cargo ship. These consumers are symbolized by so-called hotel loads 84, 85, 86 at different voltage levels of 690 V, 450 V or 230 V thereof driven generator 83 for generating the electrical energy.

Also connected to the main electrical system 8 are maneuvering elements which serve to maneuver the ship, in particular in the lateral direction. They are not part of the main drive. These are in particular bow thrusters. In the embodiment, two bow thrusters are provided, a bow thruster 61 of the CPP type with pitch adjustment (start-up concept not shown) and a bow thruster 62 of the FPP type with fixed propeller pitch, which, however, is controlled via a converter 63 for start-up and for varying the transverse thrust.

The tap 7 makes it possible to provide the power required for the main system 8 of the cargo ship 9 at least partially by means of the traction current generator 41 via the auxiliary power supply device 70 (as symbolized by the arrow on the frequency converter 71), so that the independent generator set 81 of the main electrical system 8 does not needs to be operated. This not only increases the operational reliability thanks to this second power supply option for the main electrical system 8, but can also lead to a more efficient supply of the main electrical system 8 due to the high efficiency of the internal combustion engine 3 and the traction current generator 41.

Claims (16)

Cargo ship comprising a hull (90) through which a ship center line (99) extends from the stern (91) to the bow (92), with a hold (97) and a multi-propeller drive as the main drive, which has at least two drive trains (1, 2) each with a propeller (12, 22) and a propeller shaft (11, 21) mechanically driving the propeller (12, 22), and a thermal engine (3) with an output shaft (31) for driving the drive trains (1, 2). , characterized in that the drive trains (1, 2) are jointly driven by the same heat engine (3), wherein a first drive train (1) is driven mechanically and is mechanically coupled to the output shaft (31) of the heat engine (3), and wherein a second drive train (2) is driven electrically by means of a direct electrical connection (4) comprising a traction current generator (41) coupled to the output shaft (31) and an electric traction motor (43) driving the second propeller shaft (21) of the second drive train (2), the traction current generator (41) and the electric traction motor (43) being connected to one another via a direct electrical line (42). Cargo ship according to Claim 1, characterized in that the direct electrical line (42) is designed purely as a cable and/or line connection and in particular does not include a frequency converter. Cargo ship according to Claim 1 or 2, characterized in that the direct electrical connection (4) is an alternating current connection, in particular for multi-phase alternating current, preferably for three-phase current. Cargo ship according to the preceding claim, characterized in that the traction current generator (41) and/or the electric traction motor (43) is designed as a synchronous machine. Cargo ship according to one of the preceding claims, characterized in that the heat engine (3) is systematically oversized in relation to the maximum transferable power of one of the drive trains (1, 2), and can preferably deliver at least twice as much mechanical power as the maximum transmittable power in each case of one of the drive trains. Cargo ship according to the preceding claim, characterized in that the heat engine (3) is (n+1) times oversized, where "n" denotes the number of electrically driven drive trains. Cargo ship according to one of the preceding claims, characterized in that the heat engine (3) is designed as an internal combustion engine, in particular as a two-stroke ship engine, more preferably as a slow-running two-stroke ship engine. Cargo ship according to one of the preceding claims, characterized in that the first mechanical drive train (1) is gearless and/or the first mechanical drive train (1) is provided with a clutch (15) so that its propeller (12) can be disengaged and is therefore not powered, and/or the propeller shaft (11) of the mechanical drive train (1) is connected to the output shaft (31) without deflection, preferably in an extended line. Cargo ship according to one of the preceding claims, characterized in that between the output shaft (31) of the heat engine (3) and the first, mechanical drive train (1), a power splitting unit (5) is provided, which is designed to distribute the power of the heat engine (3 ) divided between the first, mechanical drive train (1) and the traction current generator (41) of the second drive train (2). Cargo ship according to the preceding claim, characterized in that the power splitting unit (5) drives the traction current generator (41) at a speed that is in a fixed ratio, in particular at the same speed as the speed of the first, mechanical drive train (1). Cargo ship according to the preceding claim, characterized in that the power splitting unit (5) drives the traction current generator (41) with an increased torque compared to the first, mechanical drive train (1), the torque preferably being increased in a range from 3 to 35% . Cargo ship according to one of the preceding claims, characterized in that a tap (7) is provided on the direct line (42), to which an auxiliary feed device (70) is connected, which connects the direct line (42) to a main electrical system (8) of the Cargo ship (9), which is preferably provided with its own generator (81), via a frequency converter (71). Cargo ship according to the preceding claim, characterized in that the auxiliary feed device (70) is dimensioned for a lower power than the electric traction motor (43), and/or the auxiliary feed device (70) is dimensioned for a power of less than one fifth of the power of the heat engine ( 3). Cargo ship according to one of the preceding claims, characterized in that the cargo ship (9) has a ramp (96), in particular a vehicle ramp, for loading and the heat engine (3) is arranged below the ramp (96). Main propulsion system for a cargo ship, comprising at least two drive trains (1, 2) each with a propeller (12, 22) and a propeller shaft (11, 21) mechanically driving the propeller (12, 22), and a heat engine (3) with a Output shaft (31) for driving the drive trains (1, 2), characterized in that the drive trains (1, 2) are jointly driven by the same heat engine (3), wherein a first drive train (1) is driven mechanically and is mechanically coupled to the output shaft (31) of the heat engine (3), and wherein a second drive train (2) is driven electrically by means of a direct electrical connection (4) comprising a traction current generator (41) coupled to the output shaft (31) and one driving the second propeller shaft (21) of the second drive train (2). Electric traction motor (43), the traction current generator (41) and the electric traction motor (43) being connected to one another via a direct electrical line (42). Main propulsion system according to Claim 15, characterized in that it is further developed according to one of Claims 2 to 13.

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