ENERGY TRANSMISSION DEVICE AND METHOD FOR ENERGY TRANSMISSION

Description

[0001] The invention relates to an energy transmission device for a watercraft according to the features of patent claim 1.

[0002] Energy transmission equipment for watercraft is required, for example, to charge electrically powered ferries.

[0003] US 2012 / 031721 A1 discloses a power transmission device for a watercraft. A boom is arranged on a shore-based tower and can pivot about a horizontal and a vertical axis. The boom has a connector at its free end, which can be coupled to a second connector on the watercraft for transmitting electrical power. The arm has several pivotally connected sections that can be pivoted relative to each other to bring the connector into the desired position.

[0004] US 2018 / 326857 A1 also discloses an arrangement for supplying ships with electrical power. Electrical connectors are mechanically coupled to the ship during the docking process. Docking requires the pier itself to be floating, because the mechanical coupling elements are intended to prevent transverse, vertical, or longitudinal movement of the watercraft or ferry relative to the pier. This eliminates the need for outriggers that can compensate for relative movements. The disadvantage here is that the pier itself must be floating.

[0005] US 2013 / 341144 A1 discloses a power transmission device for watercraft with a land-based, horizontally movable support on a rail system. A connector is attached to a boom of the support, which can be moved horizontally and vertically. The boom itself has several joint elements that are connected to each other according to the scissor principle and can therefore be extended and retracted.

[0006] The invention is based on the object of further developing the state of the art with regard to energy transmission devices for watercraft.

[0007] This object is achieved by an energy transmission device according to the features of patent claim 1. A method for energy transmission is the subject of patent claim 10.

[0008] The power transmission device according to the invention provides a tower arranged onshore that supports a boom. The boom is pivotally connected to the tower about a horizontal axis and a vertical axis. The boom is telescopic. At its free end, the boom has a first connector that can be coupled to a second connector on the watercraft for transmitting electrical power.

[0009] The plug on the boom is designed to come into electrical contact with the second, upwardly oriented plug on the watercraft for energy transmission in a vertical plugging movement from above by pivoting the boom relative to the tower about the said axes.

[0010] The energy transmission device according to the invention can be designed for both low-voltage and medium-voltage power transmission.

[0011] The term "plug" represents a plug-in component as a male and / or female part. The plug, within the meaning of the invention, can refer to a complex assembly that may include multiple contacts, positioning aids (electrical, mechanical, electromechanical), actuators, heating means, holding and locking means, etc. Since the plug on the boom is movable and lowered, the plug on the watercraft, as a stationary assembly during insertion, can be referred to as a socket. This term "socket" is used below analogously to the term "plug" for ease of understanding. The plug / socket on the watercraft is also to be understood as an assembly in the sense of a plug head. The term "socket" is not restrictive with regard to the function as a male / female connector.

[0012] After the successful docking and mooring of the vessel, especially a ferry, the first shore-side plug is positioned above the ship's socket or plug by pivoting / rotating / extending or retracting the boom and moving the first plug. Positioning is not trivial, as the position of the socket changes relative to the plug. The position depends on the tide, the vessel's load and loading conditions, the wave swell, and the tolerances in the engagement of a land ramp between the shore and the vessel.

[0013] To ensure that the plugging process can take place in any position within the defined work area and that the plug can be moved along by the socket in the plugged-in position when the vessel moves within the defined loading area, the boom and the plug can be moved relative to one another. The boom can be pivoted around the central axis of the tower and around an axis that is orthogonal to the central axis of the tower. This is particularly a vertical and a horizontal axis. The land-based tower is designed according to the location with regard to the work area to be covered. The land-based unit therefore consists of at least one column or tower with the pivoting boom, at the front end of which the plug is arranged, preferably including heating devices. The land-based unit includes at least one control cabinet and a necessary terminal box for power transmission.When the system is not in operation, the shore-side connector is protected by a cover. The ship-side unit is preferably equipped with a closure, particularly a protective roof. Appropriate control cabinets and, preferably, heaters are also provided on the ship to keep the connector ice-free.

[0014] In short, after the vessel is moored, the shore-side plug is positioned vertically over the vessel-side socket. The roof-side lock of the socket is then opened. The shore-side plug is lowered. The plug is then finely positioned relative to the socket to insert the power contact. After the power transfer, the plug is uncoupled again, the boom is raised, and pivoted into a parking position. The plugs are covered.

[0015] The invention is characterized by the fact that the boom covers a very wide area, which makes it easier to connect the boom to very different types of watercraft. All that's required is a suitable plug / socket on the water side.

[0016] Precise positioning of the connectors is achieved with the assistance of sensors. For this purpose, at least one sensor is arranged on at least one of the connectors to position the first connector relative to the second connector. An evaluation and control unit converts data from the at least one sensor into control signals for controlling boom drives, thereby pivoting the boom and coupling or uncoupling the connectors. The boom is pivoted or telescoped about its respective pivot axes via the boom drives.

[0017] The position of the plug relative to the water-side plug or socket is preferably detected using a so-called 3D sensor. The 3D sensor detects the position of the plug and socket using reflectors arranged on the plugs. The roof-side socket lock is only opened when the plug has been moved close to the socket. This measure serves to protect the system from environmental influences. A control logic ensures that the plug is not lowered further until the socket lock is opened. Communication between the land-side and watercraft-side parts is primarily wireless, preferably via a WLAN connection. If the WLAN connection is interrupted or lost, the plugging process is immediately aborted and the system goes into emergency disconnect mode.In this case, the boom is raised and the plug is pulled out of the socket.

[0018] The fine positioning of the plug relative to the socket is preferably carried out using ultrasonic sensors. In addition, mechanically triggered contacts can be installed to detect the correct position of the power contacts relative to one another so that they are not damaged when an attempt is made to plug them in. The mechanical contacts can be provided in particular because, despite the fine positioning provided by ultrasonic sensors, incorrect positioning of the contacts between the plug and sockets can still occur. The following are examples of causes for incorrect positioning: The plug is connected to the boom so that it can rotate on three axes, giving it a very high degree of freedom. It can be connected to the boom via a ball joint or a ball-joint-like connection. If the plug is lowered too quickly, it may hit one side of the socket without the fine positioning based on ultrasonic sensors being able to react quickly enough.In this case, the plug rotates and is no longer parallel to the socket. As a result, the ultrasonic sensors may report equal distances on all sides, even though the plug is not yet in the correct position relative to the socket.

[0019] A further misalignment can occur if the tolerance in the distance measurement permitted by the fine positioning is so large that the system reports an incorrectly correct position of the plug in relation to the socket.

[0020] Finally, if the vessel tilts due to waves, land vehicles driving onto the ferry, or tolerances in the engagement between the land ramp and the ferry, the plug and socket may not be parallel. In this case, the plug would sometimes touch the socket too early and rotate. Even in this case, the ultrasonic sensors could potentially report equal distances on all sides, even though the plug is not yet in the correct position relative to the socket.

[0021] It is therefore considered advantageous to provide centering elements and centering receptacles on the plugs or sockets in addition to the ultrasonic sensors. The centering receptacles can be funnel-shaped. The centering elements can also have inclined surfaces, such as conical projections. In this case, further fine centering is achieved via the mechanically interlocking centering elements and centering receptacles.

[0022] During positioning and during the plugging process, the torques of the boom drives are set so that neither the drives nor other parts of the system can be damaged if the position of the watercraft changes within a short period of time, e.g. because the ship's socket pushes the shore-side plug in a certain direction. When plugged in, the boom drive applies a certain torque for the lowering movement to ensure safe plugging. The corresponding boom arm must also apply the desired torque when plugged in to maintain the plugged-in position. At the same time, this boom drive is set to a minimum required torque. The torque can be reduced if the plugs are connected to one another via switchable locking elements, e.g. electric holding magnets.The other cantilever drives for translational displacement or lateral displacement do not apply any torque when plugged in, in order not to stress the plug connection.

[0023] The individual electrical plug contacts are preferably designed so that, when plugged in, the PE contacts (if PE is used) are inserted first, followed by the main current contacts, and only then the pilot contacts are inserted into each other or rest on each other. A signal to enable the main current can be sent via the pilot contacts.

[0024] It is considered particularly advantageous if the boom has conductor rails and current collectors in contact with the conductor rails in order to transfer electrical energy to be transmitted from a non-telescoping section of the boom to a telescoping section of the boom.

[0025] It is also considered particularly advantageous if the boom is coupled to a boom jack. A boom jack is not the same as a boom drive that raises or lowers the boom jack. The boom jack should function even if the entire system fails, and it should also be able to disconnect the plug connection in this case. To do this, the boom jack exerts a boom lifting force on the boom. The boom lifting force can be drawn from an energy storage device. This could be, for example, a spring force accumulator, a gas pressure accumulator, a magnetic force, or a weight force (potential energy).

[0026] This force is so great that the plug can be separated from the socket by the boom lifting force alone. The boom jack is based in particular on a weight force. In particular, it is a counterweight that is arranged on the end of the boom facing away from the first plug, comparable to a counterweight on a tower crane. Alternatively, the counterweight can also be arranged elsewhere, e.g. in / on the tower, and can exert the desired boom lifting force on the boom, for example via a cable pull. The boom lifting force always acts upwards for the plug. The boom drive, which is intended to lower the plug, counteracts this boom lifting force. To uncouple, the torque of the corresponding drive only needs to be reduced enough that the boom lifting force exerts a greater moment on the plug than the corresponding drive.Even if the drive fails, the plug is automatically pulled out of the plug-in position by the boom lifting force.

[0027] If the vessel moves outside the defined working range that the shore-based boom can compensate for, or if a communication signal is lost between the shore and vessel sides, the power transmission system is switched to emergency disconnect mode. The drive torque of the drive for vertically lowering the boom is reduced to a minimum, allowing the boom jack to remove the plug from the socket within a short time. The outer limits of the permissible working range of the boom are detected using sensors. If one of these sensors is triggered, the system is switched to emergency disconnect mode.Even after a ferry has been loaded or the vessel has been released, the torque of the boom drive, which is responsible for lowering the boom, is switched to a lower value so that the plug is lifted from the socket by the boom lifting force, which results primarily from weight. The boom is pivoted into a parking position with the help of a boom drive. Only then may the vessel be released and cast off. When docking, the process is reversed.

[0028] It is considered particularly advantageous if the shore-side connector consists of two assemblies that can move relative to each other. A releasable lock can be positioned between these assemblies, holding the two assemblies in a starting position. In the starting position, the assemblies are spaced apart (top / bottom). The releasable lock applies a locking force, e.g., through electromagnets and / or a minimum force to be overcome, e.g., through compression springs. The principle is explained below using compression springs.

[0029] The compression springs act in the plug-in direction, i.e. vertically up / down. A lower assembly of the first plug is connected to the upper assembly and can be moved relative to the upper assembly. If the plug is already close to the socket or if positioning using ultrasonic sensors is not possible with absolute precision, mechanical positioning can be achieved using the centering elements and centering receptacles. Preferably, the releasable lock or the compression springs are designed to be so strong that they do not initially give way during mechanical positioning. This means that the plug is initially only pushed into the socket until the centering elements engage and lie on top of one another. This ensures that the two plugs are positioned exactly.Only when the centering elements and centering receptacles, preferably conical surfaces, rest on one another and the cantilever drive presses the connector further down do the compression springs or the releasable lock give way. At this point, however, it is already ensured that the electrical contacts are positioned exactly one above the other. When the lock gives way, the upper assembly of the connector moves further downwards relative to the lower assembly and the electrical contacts are plugged in. This means that when the connector is pushed in, a first assembly of the connector is already positioned and its position is not changed further, while the upper assembly, which is supported opposite the first assembly, continues to be lowered against the lock, e.g. against a spring force or a magnetic force, and is held in this position by the cantilever drive throughout the entire plugging process.

[0030] Due to the coarse positioning, subsequent fine positioning, and in combination with the mechanical centering elements, the energy transmission device according to the invention can be precisely plugged in even if the watercraft is not exactly parallel to the first plug. The plug can be rotated into the correct position using additional drives; in particular, it can be pivoted around a vertical axis of the plug.

[0031] The invention is explained below using schematically illustrated embodiments. They show: Figure 1A perspective view of an energy transmission device; Figure 2The energy transmission device of the Figure 1 during a positioning process; Figure 3The positioning device of the Figure 1 before lowering onto a socket on a vessel; Figure 4The energy transmission device of the Figure 1in the plugged-in state; Figure 5The energy transmission device of the Figure 1 in a parking position; Figure 6A further embodiment of an energy transmission device in a purely schematic representation; Figure 6aA further embodiment of an energy transmission device in a purely schematic representation; Figure 7The energy transmission device of the Figure 6 with the plug raised; Figure 8The energy transmission device of the Figures 6 and 7 with the plug deflected sideways; Figure 9A perspective view from above of the plug of the Figure 8 ; Figure 9aIn an enlarged view, the plug 5 of the Figure 6a ; Figure 10The plug of the Figure 9 in the coupled state in a side view and Figure 11 the plug of the Figure 10 in view from below.

[0032] The Figure 1 shows an energy transmission device 1 for a watercraft 2, as shown in the Figures 2 to 5is shown. The watercraft 2 is an electrically powered ferry. The energy transmission device 1 comprises a tower 3 and a boom 4 arranged at the top of the tower 1. It has two legs. The tower 3 is arranged in a middle section of the boom 4 and divides it into a longer and a shorter section. The boom 4 can be pivoted relative to the tower 3. The Figure 1 The arrows indicate that the boom 4 can be pivoted both around a horizontal axis, designated Y, and around a vertical axis, designated Z. The Figure 6 shows the kinematic principle in a simplified representation. In addition, the boom 4 is telescopic in its longitudinal direction. The Figures 1 and 6The positions of the boom 4 shown each point in the X direction of one Cartesian coordinate system. The boom 4 is telescopic even if it has previously been pivoted about the horizontal Y axis or the vertical Z axis, i.e., it does not point in the X direction.

[0033] The boom 4 has a connector 5 at its free end. The connector 5 represents a larger assembly (plug head, coupling unit) whose primary function is to establish an electrically conductive contact for energy transmission from the land side to the watercraft 2. For this purpose, the connector 5 must be brought into the correct position relative to the counterpart on the watercraft 2. The Figure 2 shows that the arm 4 is first pivoted so that the plug 5 is above a plug 6 serving as a socket ( Figure 3, concealed) on the watercraft 2. The socket is located in a tower-like structure 7 on the watercraft 2. The tower-like structure 7 has an upper end that supports the socket. The socket itself is located within a housing 8 at the upper end of the structure 7 to protect the socket from the elements when not in use. The housing 8 has a roof-like closure 9 on the top. Figure 2 the shutter 9 is closed. In the Figure 3 the closure 9 is open. It can be a flat roof construction consisting of one or more segments which are displaced horizontally relative to each other for opening, thereby exposing the internal socket (sliding roof).

[0034] To establish a plug connection, the plug 5 must be lowered onto the socket 6. This shows the Figure 4. The plug contact is maintained as long as energy and / or data are to be transferred. The boom 4 is then raised again and pivoted into a parking position, as shown in Figure 5 is shown. The closure 9 on the housing 8 above the socket 6 is closed again. The watercraft 2 can cast off.

[0035] The method according to the invention is described in detail below using the Figures 6 to 11 explained. The previously introduced reference symbols continue to be used for the essentially identical components.

[0036] The Figure 6shows the kinematic principle of the energy transmission device 1 according to the invention. On the tower 3, the boom 4 can be pivoted about the horizontal axis Y shown and about the vertical axis Z. A translational movement in the X direction is possible. The connector 5 is arranged at one end of the boom 4. At the other end of the boom 4, a counterweight is arranged, which serves as a boom lifter 10. The boom lifter 10 exerts an upward boom lifting force F on the boom 4 or the connector 5 via its weight force G. Since the horizontal axis Y is located between the boom lifter 10 and the connector 5, the movements of the ends of the boom 4 are opposite in the vertical direction. If the boom 4 is raised, as shown in Figure 7As shown, a rigid connection between the connector 5 and the boom 4 would result in an angle change at the connector 5. To avoid this, a drive can be provided on the connector 5, which tilts the connector 5. This ensures that the connector 5 is always parallel to the ground. The connector 5 is mounted in a ball joint.

[0037] The Figure 6a shows an embodiment with different drives. The energy transmission system has a drive 24 for the vertical axis of rotation and a drive 25 for a horizontal axis of rotation. Additionally, a drive 26 is located at the rear end of arm 4, which is responsible for telescoping and the counterweight.

[0038] Another drive 27 at the opposite end tilts the plug 5 in the desired direction. Finally, another drive 28 is provided to rotate the plug 5 in the desired direction. The drives are shown purely schematically and enlarged in the Figure 9a shown.

[0039] The Figure 8 shows the interaction of the drives. If, for example, the connector 5 is to be pivoted only parallel to the starting position or also relocated, the pivot angle W1 must be adjusted on both the tower 3 by pivoting the arm horizontally. At the same time, the pivot angle W1 must be pivoted by pivoting the connector 5 in the opposite direction relative to the boom 4. Depending on how far the boom 4 is telescoped, the position of the boom lifter 10 in the form of the counterweight may also need to be adjusted.

[0040] The rough positioning of the shore-side connector 5 relative to the vessel-side socket is achieved using a 3D sensor system. The operating principle of the sensors is based primarily on a time-of-flight method. The sensors can be installed on either the shore-side connector 5 or the waterside socket. The initial positioning is performed using a photoelectric mixer device (FMD). The photoelectric mixer device detects the relative spatial position of the shore-side reflectors to the ship-side reflectors. The shore-side connector 5 is then moved so that the preset target value for the position of the shore-side reflectors relative to the ship-side reflectors is achieved.

[0041] Subsequently, fine positioning is carried out using ultrasonic sensors. The outer plates or positioning surfaces of the plug 5 or the socket 6 are preferably designed in a funnel shape. Figures 9 and 9ashow that the positioning surfaces 11, which are arranged in a rectangle or square, are each angled to form a downwardly tapered truncated pyramid. On each of the four longitudinal positioning surfaces 11, there is a sensor 12 in the form of an ultrasonic sensor. The sensors 12 use ultrasound to determine the distance to the corresponding positioning surfaces on the socket. The plug is aligned until all four ultrasonic sensors 12 report an approximately equal distance to the corresponding positioning surface 11 on the socket. The desired distance is defined in advance.

[0042] The two successive steps of coarse positioning and fine positioning generally result in a sufficiently precise position of the plug 5 relative to the socket 6.

[0043] The Figures 9 and 10further show that the plug 5 consists of two assemblies that can move relative to one another. The plug 5 comprises, on the one hand, a support plate 13. Several power contacts 14 are arranged on the support plate 13. The support plate 13 is suspended from the boom 4 via a strut 15. The strut 15 can be pivoted relative to the boom 4 in three spatial directions. The strut 15 allows the plug 5 to be raised and lowered by means of the boom 4 and also rotated into the correct position.

[0044] The support plate 13 has connecting elements 16 in each corner area. Via the connecting elements 16, the support plate 13 is movably connected to a positioning frame 17 as the lower assembly. The positioning frame 17 comprises the funnel-shaped positioning surfaces 11. The positioning frame 17 is optionally supported on the support plate by compression springs 18 surrounding the connecting elements 16. Electromagnetic holding magnets 19 can be provided alternatively or in addition to the compression springs 18 to initially hold the connecting elements 16 in the extended position.

[0045] In this embodiment, centering elements 20 in the form of several centering cones are also located on the ship's side. These centering cones engage in the correct position in centering receptacles 21. The centering receptacles 21 are located below the connecting elements 16. The connecting elements 16 are firmly connected to the positioning frame and mounted on the support plate 13 for longitudinal displacement. The connecting elements 16 guide the support plate 13 against lateral displacement and prevent rotation of the support plate 13 relative to the positioning frame 17. Therefore, if the connecting elements 16 are precisely centered on the centering receptacles 21, not only the positioning frame 17 is in the correct position, but also the support plate 13 with the electrical contacts. Figure 10 shows that the centering receptacle 20 has a funnel shape, while the centering element 21 has a matching conical shape.

[0046] If the plug 5 is twisted in relation to the socket or if the positioning by the ultrasonic sensors is not quite precise enough, then mechanical positioning takes place via the centering elements 20 and the centering receptacles 21. At this time, the anchoring of the connecting elements, ie either compression springs acting between the support plate 13 and the positioning frame 17 or electromagnets, keeps the support plate 13 at a vertical distance from the positioning frame 17. The plug 5 is now lowered further by overcoming the spring force or the retaining force via the boom 4. This causes the current contacts 14 of the plug 5 to come into contact with the corresponding plug contacts on the socket.

[0047] During plugging, contact first occurs between a grounding contact mounted on the support plate 13 and the opposite side (watercraft). The main current contacts then mesh. Only then do pilot contacts mounted on the support plate 13 and the opposite side (watercraft) make contact. A signal sent via the pilot contacts releases the current to switch on electromagnets 23 mounted on the support plate 13. Instead of electromagnets, other anchoring means can be provided to hold the plug 5 to the socket during power transfer. These anchors, e.g., electromagnets, hold the shore-side plug together with the ship-side socket so that the boom drive of the boom 4 does not have to continuously apply as much torque to ensure secure contact.

[0048] The Figure 11shows, in a bottom view, the external positioning frame 17 with its funnel-shaped positioning surfaces 11, as well as the support plate 13 with five evenly distributed power contacts 14 and several pilot contacts 22 arranged in a square. In addition, alternating with the power contacts 14, electromagnets 23 are located on the underside of the support plate 13.

[0049] The positioning frame 17 also shows the sensors 12 for ultrasonic positioning as well as the conical centering receptacles 21, which are each arranged in the corner area of ​​the positioning frame 17. The Figure 9a shows additional reflector plates 29 arranged in the corner area. Reference symbols:

[0050] 1 - Energy transmission system 2 - Watercraft 3 - Tower 4 - Boom 5 - Plug 6 - Socket 7 - Structure 8 - Housing 9 - Lock 10 - Boom lifter (counterweight) 11 - Positioning surface 12 - Sensor 13 - Support plate 14 - Power contact 15 - Strut 16 - Connecting element 17 - Positioning frame 18 - Compression spring 19 - Electromagnetic holding magnet 20 - Centering elements 21 - Centering holder 22 - Pilot contact 23 - Electromagnetic holding magnet 24 - Drive 25 - Drive 26 - Drive 27 - Drive 28 - Drive 29 - Reflector plates F -Boom lifting force G -Weight force W1 -Swivel angle Y -horizontal axis Z -vertical axis

Claims

1. Energy transmission device (1) for a watercraft (2) with the following features: a) on the land side, a tower (3) is disposed which carries a boom (4), wherein the boom (4) is connected to the tower (3) so as to be pivotable about a horizontal and a vertical axis (Y, Z); b) the boom (4) has at its free end a first plug (5) which can be coupled to a second plug (6) on the watercraft (2) for transmitting electrical energy; c) the plug (5) on the boom (4) is configured to come into electrical contact with the second, upwardly oriented plug (6) on the watercraft (2) in a vertical plugging movement from above for transmitting energy by pivoting the boom (4) relative to the tower (3), characterized in that d) the boom (4) is telescopic.

2. The energy transmission device (1) according to claim 1, characterized in that at least one sensor (12) for positioning the first plug (5) relative to the second plug (6) is disposed on at least one of the plugs (5, 6), wherein, in an evaluation and control unit, data from the sensors (12) can be converted into control signals for controlling boom drives in order to pivot the boom (4) and to couple or uncouple the connectors (5, 6).

3. The energy transmission device (1) according to claim 2, characterized in that reflectors are disposed on the plugs (5, 6) in order to reflect sensor signals of a sensor (12) which is disposed on the respective other plug (5, 6).

4. The energy transmission device (1) according to any one of claims 1 to 3, characterized in that the first plug (5) is connected to the boom (4) in a 3-axis rotatable manner.

5. The energy transmission device (1) according to any one of claims 2 to 4, characterized in that in the coupling position of the plugs (5, 6) centering elements (20) having inclined surfaces engage with centering receptacles (21) on the other plug (5, 6).

6. The energy transmission device (1) according to claim 5, characterized in that compression springs (18) are disposed on at least one of the plugs (5), the spring force of which counteracts a further approach of the electrical contacts after the mechanical centering via the centering elements (20) and centering receptacles (21), such that electrical contact between the plugs (5, 6) only exists when the spring force is smaller than the force generated by actively lowering the boom (4).

7. The energy transmission device (1) according to any one of claims 1 to 6, characterized in that the boom (4) has contact lines and current collectors in contact with the contact lines in order to transfer electrical energy to be transmitted from a non- telescoping section of the boom (4) to a telescoping section of the boom (4).

8. The energy transmission system (1) according to any one of claims 1 to 7, characterized in that the boom (4) is coupled to a boom lifter (10), wherein the boom lifter (10) exerts a boom lifting force (F) on the boom (4) which is so great that the first plug (5) can be separated from the second plug (6) solely by the boom lifting force (F).

9. The energy transmission device (1) according to claim 8, characterized in that the boom lifter (10) has a counterweight which is disposed on the end of the boom (4) facing away from the first plug (5).

10. A method for transmitting electrical energy to a watercraft by means of an energy transmission device (1) according to any one of claims 1 to 9, characterized in that the watercraft (2) with its second plug (6) is brought within range of the first plug (5), then the boom (4) is brought by telescoping and horizontal and vertical pivoting into a position in which the first plug (5) is located above the second plug (6), then a distance measurement of the plugs (5, 6) is carried out by means of sensors in order to lower the boom (4) as far as possible depending on the control data calculated from the measured data, that mechanical centering elements (20) and centering receptacles (21) engage between the plugs (5, 6), wherein the boom (4) is lowered after the mechanical centering against a spring force acting between the plugs (5, 6) until an electrical contact is established between the plugs (5, 6) for transmitting energy.

11. The method according to claim 10, characterized in that, in order to release the plug connection, a force which lowers the first plug (5) is reduced until the first plug (5) is lifted by the boom lifting force (F) of a boom lifter (10).