Raft management system, raft management device, and raft management method

Abstract

This raft management system includes two positional information transmission devices provided to each of a plurality of rafts, and a raft management device. Each of the positional information transmission devices comprises: a position acquisition unit that acquires the position of the positional information transmission device; and a communication unit that transmits, to the raft management device, positional information including said position and a device identifier of the positional information transmission device. The raft management device comprises: a communication unit that receives the positional information; a storage unit that stores raft information in which raft identifiers of the plurality of rafts are associated with device identifiers of the two positional information transmission devices provided to each of the plurality of rafts; and a raft position identification unit that identifies the position of the raft on the basis of the raft information and the positional information transmitted from each of the two positional information transmission devices provided to the raft.

Description

Raft management system, raft management device, and raft management method

[0001] The present invention relates to a raft management system, a raft management device, and a raft management method.

[0002] Rafts used for marine aquaculture have been known (see, for example, Patent Documents 1 and 2).

[0003] Rafts used for offshore aquaculture have, for example, a rectangular or similar shape when viewed from above, and have a fish cage net attached to their outer periphery in which the farmed fish are placed, as well as multiple floats that allow the raft to float on the sea.

[0004] A single offshore farm has many such rafts, and each raft is fitted with a GPS (Global Positioning System) tracker to manage its location.

[0005] JP 2020-18312 A JP 2019-118330 A

[0006] However, there is a limit to the accuracy of the position acquired by a GPS tracker, and the position may include an error within a certain error range (for example, within 3 to 5 meters). Furthermore, the position and orientation of each raft may fluctuate due to factors such as tidal currents and wind. Furthermore, because it is difficult to install a GPS tracker near the center of a raft due to factors such as the raft's structure and the ease of operation for workers, the tracker is installed near the periphery of the raft (for example, on a floating body). For these reasons, the error ranges of the positions acquired by the GPS trackers of adjacent rafts may overlap, making it impossible to accurately identify the positions of the adjacent rafts.

[0007] Figure 9 is a top view that schematically illustrates multiple rafts present in one marine aquaculture farm. In Figure 9, only two adjacent rafts 201 are labeled as representative rafts. The error ranges 203 of the positions acquired by the GPS trackers 202 attached to the two rafts 201 overlap, which may prevent accurate identification of their respective positions. In this case, for example, when the positions of the two rafts 201 are displayed on a display device, the positions may overlap, making it impossible to distinguish between the two rafts.

[0008] In view of the above circumstances, the present invention aims to provide a raft management system, a raft management device, and a raft management method that can correctly identify the position of each of a plurality of rafts.

[0009] One aspect of the system is a raft management system including two position information transmitting devices provided on each of a plurality of rafts and a raft management device, wherein the position information transmitting device includes a position acquisition unit that acquires the position of the position information transmitting device and a communication unit that transmits position information including the position and the device identifier of the position information transmitting device to the raft management device, and the raft management device includes a communication unit that receives the position information, a memory unit that stores raft information in which the raft identifier of each of the plurality of rafts is associated with the device identifiers of each of the two position information transmitting devices provided on each of the plurality of rafts, and a raft position identification unit that identifies the position of the raft based on the position information and the raft information transmitted from each of the two position information transmitting devices provided on the raft.

[0010] One aspect of the device is a raft management device that manages a plurality of rafts, each equipped with two position information transmitting devices, and includes a communication unit that receives position information transmitted from the position information transmitting device, the position information including the position of the position information transmitting device and a device identifier, a memory unit that stores raft information in which the raft identifier of each of the plurality of rafts is associated with the device identifiers of each of the two position information transmitting devices provided on each of the plurality of rafts, and a raft position identification unit that identifies the position of the raft based on the position information and the raft information transmitted from each of the two position information transmitting devices provided on the raft.

[0011] One aspect of the method is a raft management method for managing multiple rafts, each equipped with two location information transmission devices, in which the raft management device receives location information transmitted from the location information transmission device, the location information including the location and device identifier of the location information transmission device, and determines the location of the raft based on raft information in which the raft identifier of each of the multiple rafts is associated with the device identifiers of each of the two location information transmission devices provided on each of the multiple rafts, and the location information transmitted from each of the two location information transmission devices provided on the raft.

[0012] According to the present invention, the position of each of a plurality of rafts can be accurately identified.

[0013] FIG. 1 is a diagram illustrating an example of the configuration of a raft management system according to one embodiment. FIG. 2 is a diagram illustrating functional blocks of a position information transmission device, a raft management device, and an information terminal. FIG. 3 is a diagram illustrating raft information. FIG. 4 is a diagram (part 1) explaining an example of a method by which a raft position identification unit identifies a raft's position. FIG. 5 is a diagram (part 3) explaining an example of a method by which a raft position identification unit identifies a raft's position. FIG. 6 is a flowchart illustrating a raft management process performed by a raft management device. FIG. 7 is a diagram illustrating the hardware configuration of a computer. FIG. 8 is a top view schematically illustrating multiple rafts present in one offshore aquaculture farm.

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0015] FIG. 1 is a diagram illustrating the configuration of a raft management system according to an embodiment.

[0016] The raft management system 1 illustrated in Figure 1 includes two location information transmission devices 4, a raft management device 5, and an information terminal 6, each of which is provided on a plurality of rafts 3 present in one offshore farm 2, and the location information transmission devices 4 and the raft management devices 5, and the information terminals 6 and the raft management devices 5, can communicate via a network 7. The raft management system 1 may also include a plurality of information terminals 6.

[0017] The raft 3 has a rectangular or similar shape when viewed from above, and is fitted with a fish cage net around its periphery to hold farmed fish, as well as a number of floats to allow the raft 3 to float on the sea. The raft 3 illustrated in Figure 1 is also a schematic illustration of the raft 3 as viewed from above.

[0018] The two position information transmitting devices 4 provided on the raft 3 are attached to diagonal positions (for example, to floating bodies at diagonal positions) of the raft 3. The position information transmitting devices 4 are, for example, GPS trackers.

[0019] The raft management device 5 manages a plurality of rafts 3 present in the marine farm 2. The raft management device 5 is, for example, a computer such as a server.

[0020] The information terminal 6 is a terminal used by a person involved in the marine farm 2 (for example, a worker of the marine farm operator). The information terminal 6 is, for example, a portable information terminal such as a smartphone or a tablet terminal.

[0021] The network 7 includes a wireless network and a wired network, for example, a mobile communication network, and the Internet.

[0022] Fig. 2 is a diagram illustrating functional blocks of the location information transmitting device, the raft management device, and the information terminal, and Fig. 3 is a diagram illustrating raft information.

[0023] As illustrated in FIG. 2 , the location information transmitting device 4 includes a location acquisition unit 41 and a communication unit 42 .

[0024] The position acquisition unit 41 receives radio waves from GPS satellites, performs positioning using the radio waves, and acquires the position (e.g., latitude and longitude) based on the positioning result. That is, the position acquisition unit 41 acquires the position of the position information transmission device 4. The position acquisition unit 41 is, for example, a GPS receiver.

[0025] The communication unit 42 transmits location information including the location acquired by the location acquisition unit 41 and the device ID (device identifier) ​​of the location information transmission device 4 to the raft management device 5. The communication unit 42 is wirelessly connected to the network 7 and can communicate with the raft management device 5 via the network 7.

[0026] The position information transmitting device 4 may further include a vibration detecting unit 43 that detects vibrations. The vibration detecting unit 43 is, for example, a vibration sensor. In this case, the position information transmitted by the communication unit 42 to the raft management device 5 may further include vibration information indicating the vibrations detected by the vibration detecting unit 43.

[0027] The position acquisition unit 41 acquires the position, the vibration detection unit 43 detects vibration, and the communication unit 42 transmits the position information at predetermined time intervals (for example, every few seconds). As a result, the position information including the latest position and vibration information is transmitted to the raft management device 5.

[0028] The raft management device 5 includes a communication unit 51, a memory unit 52, and a raft position identification unit 53.

[0029] The communication unit 51 receives the location information transmitted from the location information transmission device 4. The communication unit 51 is connected to the network 7 by wire or wirelessly, and can communicate with the location information transmission device 4 and the information terminal 6 via the network 7.

[0030] The storage unit 52 stores raft information. As illustrated in FIG. 3 , the raft information is information in which the raft IDs (raft identifiers) of the multiple rafts 3 present in the offshore farm 2 are associated with the device IDs (indicated as location information transmission device ID1 and ID2 in FIG. 3 ) of the two location information transmission devices 4 provided on each of the multiple rafts 3. According to the raft information illustrated in FIG. 3 , for example, the raft ID "IKD001" is associated with the device IDs "TRC0001" and "TRC0002." This association indicates that the raft 3 with the raft ID "IKD001" is equipped with a location information transmission device 4 with the device ID "TRC0001" and a location information transmission device 4 with the device ID "TRC0002."

[0031] The raft position identifying unit 53 identifies the position of the raft 3 based on the position information transmitted from each of the two position information transmitting devices 4 provided on the raft 3 and the raft information stored in the memory unit 52. Note that identifying the position of the raft 3 not only literally means identifying the position, but also identifying which raft 3 (the raft with which raft ID) the raft 3 belongs to. In this way, the raft position identifying unit 53 can identify the position of each of the multiple rafts 3 present in the offshore farm 2 based on the position information transmitted from each of the two position information transmitting devices 4 provided on each of the multiple rafts 3 present in the offshore farm 2 and the raft information stored in the memory unit 52. The identification of the position of the raft 3 performed by the raft position identifying unit 53 will be described in detail below.

[0032] When the position information transmitted from the position information transmitting device 4 includes vibration information, the raft position identifying unit 53 may determine whether the vibration indicated by the vibration information is equal to or greater than a threshold. If the raft position identifying unit 53 determines that the vibration is equal to or greater than the threshold, the communication unit 51 may transmit an alert notification to the information terminal 6, including the location of the raft 3 equipped with the position information transmitting device 4 on which the vibration was detected. This allows an alert notification including the location of the raft 3 on which the vibration equal to or greater than the threshold was detected to be sent to those involved in the marine farm 2. In this case, the location of the raft 3 on which the vibration equal to or greater than the threshold was detected may be displayed on the display unit 63 of the information terminal 6. This display may be performed by displaying the location of the raft 3 on which the vibration equal to or greater than the threshold was detected with a predetermined icon on a map. Possible causes for detecting vibration equal to or greater than the threshold include, for example, a collision with an adjacent raft 3 due to a natural disaster such as a typhoon or tsunami, or a collision with a raging farmed fish.

[0033] The information terminal 6 includes an input unit 61 , a communication unit 62 , and a display unit 63 .

[0034] The input unit 61 receives input from the user. For example, the input unit 61 receives an instruction input from the user requesting raft position information indicating the positions of each of the multiple rafts 3 present in the marine farm 2.

[0035] In response to an instruction input requesting raft position information received by the input unit 61, the communication unit 62 transmits a request signal requesting the raft position information to the raft management device 5, and receives the raft position information from the raft management device 5. In the raft management device 5, when the communication unit 51 receives the request signal, the communication unit 51 transmits raft position information indicating the positions of each of the multiple rafts 3 present in the offshore farm 2 identified by the raft position identification unit 53 to the information terminal 6 in response to the request signal. The communication unit 62 of the information terminal 6 is wirelessly connected to the network 7, and is capable of communicating with the raft management device 5 via the network 7.

[0036] The display unit 63 displays the position of each of the multiple rafts 3 present in the marine farm 2 based on the raft position information received by the communication unit 62. This display may be performed, for example, by representing the position of each of the multiple rafts 3 present in the marine farm 2 with a predetermined icon on a map. This allows the user to confirm the position of each of the multiple rafts 3 present in the marine farm 2.

[0037] 4 to 6 are diagrams illustrating an example of a method by which the raft position identifying unit identifies the position of the raft.

[0038] As illustrated again in Figure 4, the raft 3 has a rectangular or similar shape when viewed from above, and two position information transmission devices 4 (4a, 4b) are provided at diagonal corners. In this example, the raft 3 has a square or similar shape with sides measuring 10 m when viewed from above, and the error range 8 of the positions acquired by the position acquisition units 41 of each of the two position information transmission devices 4 provided on the raft 3 is within 5 m (the range within a circle with a radius of 5 m centered on the position information transmission device 4). In this way, the two position information transmission devices 4 provided on the raft 3 are provided at positions where the error ranges 8 of the positions acquired by both position acquisition units 41 do not overlap, and where the midpoint or approximate midpoint of the positions acquired by both position acquisition units 41 is always located inside the raft.

[0039] The raft position identification unit 53 identifies the position of the raft 3 as the midpoint or approximate midpoint of the positions included in the position information transmitted from each of the two position information transmission devices 4 provided on such a raft 3.

[0040] 5, if the position information transmitted from the position information transmitter 4a indicates a position P1 and the position information transmitted from the position information transmitter 4b indicates a position P2, the raft position identification unit 53 identifies P3, which is the midpoint or approximate midpoint between P1 and P2, as the position of the raft 3. Note that P1 and P2 are positions on a line connecting the position information transmitter 4a and the position information transmitter 4b (a line including the diagonal of the raft 3), and P1 is the outer position of the raft 3 where the error is greatest, and P2 is the inner position of the raft 3 where the error is greatest.

[0041] 6, if the position information transmitted from the position information transmitter 4a includes a position P4 and the position information transmitted from the position information transmitter 4b includes a position P5, the raft position identification unit 53 identifies P6, which is the midpoint or approximate midpoint between P4 and P5, as the position of the raft 3. Note that P4 and P5 are positions on a line connecting the position information transmitter 4a and the position information transmitter 4b (which is also a line including the diagonal of the raft 3), and P4 is the position inside the raft 3 where the error is greatest, and P5 is the position outside the raft 3 where the error is greatest.

[0042] The raft position identification unit 53 identifies which raft (which raft ID) the raft 3 whose position has been identified as illustrated in Figures 5 and 6 is based on the device ID contained in the position information transmitted from the position information transmission device 4a and the device ID contained in the position information transmitted from the position information transmission device 4b, and the raft information stored in the memory unit 52.

[0043] In this way, the raft position identification unit 53 identifies the position of each of the multiple rafts 3 present in the offshore farm 2, thereby making it possible to correctly identify the position of each of the multiple rafts 3. Furthermore, when raft position information indicating the position of each of the multiple rafts 3 present in the offshore farm 2 identified in this way by the raft position identification unit 53 is transmitted to the information terminal 6, and the position of each of the multiple rafts 3 present in the offshore farm 2 is displayed on the display unit 63 based on the raft position information, the positions of adjacent rafts 3 are not displayed overlapping each other, so there is no risk of the positions of adjacent rafts 3 becoming indistinguishable.

[0044] 7 is a flowchart illustrating a raft management process performed by the raft management device 5. The raft management process is also an example of a raft management method performed by the raft management device 5.

[0045] In the raft management process illustrated in FIG. 7, the communication unit 51 of the raft management device 5 receives the position information transmitted from each of the two position information transmitting devices 4 provided on the raft 3 (step S101).

[0046] Next, the raft position identification unit 53 identifies the position of the raft 3 based on the position information transmitted from each of the two position information transmission devices 4 provided on the raft 3 received in step S101 and the raft information stored in the memory unit 52 (step S102).

[0047] The raft management device 5 performs such raft management processing on the location information transmitted from each of the two location information transmitting devices 4 provided on each of the multiple rafts 3 present in the offshore aquaculture farm 2, thereby being able to identify the location of each of the multiple rafts 3 present in the offshore aquaculture farm 2.

[0048] As described above, according to this embodiment, the position of each of the multiple rafts 3 present in the marine farm 2 can be accurately identified.

[0049] In this embodiment, the raft position information transmitted by the raft management device 5 to the information terminal 6 may further include information indicating the position contained in the position information transmitted from each of the two position information transmitting devices 4 provided on each of the multiple rafts 3 present in the offshore farm 2. As a result, the information terminal 6 can display the position of each raft 3 on the display unit 63 based on the raft position information, for example, with an icon of a rectangle or a similar shape whose diagonal corners correspond to the positions contained in the position information transmitted from each of the two position information transmitting devices provided on the raft 3. In this case, personnel involved in the offshore farm 2 can also determine the orientation of each raft 3.

[0050] Furthermore, in this embodiment, the two position information transmission devices 4 provided on the raft 3 are not limited to being located at diagonal positions on the raft 3, but may also be located at other opposing positions near the outer periphery of the raft 3, such as at the midpoints of opposing sides of the shape of the raft 3 when viewed from above. However, in this case too, the two position information transmission devices 4 provided on the raft 3 must satisfy the conditions that, as in the example shown in Figure 4, the error ranges of the positions acquired by both position acquisition units 41 do not overlap, and the midpoint or approximate midpoint of the positions acquired by both position acquisition units 41 is always located inside the raft 3.

[0051] In addition, in this embodiment, the shape of the raft 3 as viewed from above is not limited to a rectangle or a similar shape, but may be other shapes, such as a circle or a similar shape, etc. However, the two position information transmitters 4 provided on the raft 3 having such a shape also satisfy the above conditions.

[0052] Furthermore, in this embodiment, other information may be linked to the raft ID of each of the multiple rafts 3 present in the offshore farm 2 for management. For example, the raft ID of each of the multiple rafts 3 present in the offshore farm 2 may be linked to information regarding the number of years in use of the raft 3, the number of years in use of the netting for the fish cage attached to the raft 3, and the type and growth status of the fish being cultured on the raft 3. This makes it possible to easily identify, for example, the location of a raft 3 approaching the end of its useful life, the location of a raft 3 to which a netting for the fish cage attached to the raft 3 is approaching the end of its useful life, the location of a raft 3 on which a specific fish is being cultured, or the location of a raft 3 on which fish in a specific growth status are being cultured.

[0053] In this embodiment, each of the position information transmitting device 4, the raft management device 5, and the information terminal 6 may be realized by a computer 100 illustrated in Fig. 8. Fig. 8 is a diagram illustrating the hardware configuration of the computer.

[0054] 8 includes a processor 101, a memory 102, a storage device 103, a portable storage medium drive device 104, a communication interface 105, and an input / output interface 106, each of which is connected to a bus 107 and can transmit and receive data to and from each other. Note that when the location information transmission device 4 is realized by the computer 100, the storage device 103 and the portable storage medium drive device 104 may be omitted.

[0055] The processor 101 may be, for example, a single processor, a multi-processor, or a multi-core processor. The processor 101 performs various processes by executing programs such as an operating system (OS) and applications. For example, when the raft management device 5 is realized by the computer 100, the processor 101 performs the raft management process illustrated in FIG. 7 .

[0056] The memory 102 includes a RAM (Random Access Memory) and a ROM (Read Only Memory). The RAM temporarily stores parts of the programs executed by the processor 101. The RAM is also used as a working storage area for the processor 101. The ROM stores the programs executed by the processor 101 and various data required for executing the programs.

[0057] The storage device 103 is a device for storing data, and is a hard disk drive (HDD) or a solid state drive (SSD), for example.

[0058] The portable storage medium drive device 104 drives a portable storage medium 104a, accesses its stored contents, and reads and writes data. The portable storage medium 104a is a memory device, a flexible disk, an optical disk, a magneto-optical disk, etc. The portable storage medium 104a also includes a CD-ROM (Compact Disc Read Only Memory), a DVD (Digital Versatile Disc), a Blu-ray Disc, a USB (Universal Serial Bus) memory, an SD card memory, etc.

[0059] The communication interface 105 is connected to a network (for example, the network 7) by wire or wirelessly, and communicates with external devices connected to the network.

[0060] The input / output interface 106 is connected to an external device and performs input / output of data between the external device and the computer 100. For example, if the computer 100 implements the location information transmission device 4, a GPS receiver and a vibration sensor are connected as external devices to the input / output interface 106. Furthermore, if the computer 100 implements the information terminal 6, an input device such as a touch panel and a display device such as a liquid crystal display are connected as external devices to the input / output interface 106.

[0061] In such a computer 100, the programs executed by the processor 101 and various data required for executing the programs may be stored in the storage device 103 or the portable storage medium 104a, not limited to the memory 102. Furthermore, the programs executed by the processor 101 and various data required for executing the programs may be stored in the storage device 103 or the portable storage medium 104a via the communication interface 105 from an external device connected to the network.

[0062] Furthermore, the computer 100 is not limited to the one illustrated in FIG. 8, and may be configured to include multiple components that are part of the components illustrated in FIG. 8, may be configured without including some of the components illustrated in FIG. 8, or may be configured to further include other components.

[0063] The computer 100 may also be configured to include hardware such as a microprocessor, a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), an FPGA (Field-Programmable Gate Array), etc. For example, the processor 101 may be implemented using at least one of these pieces of hardware.

[0064] When the location information transmission device 4 is realized by the computer 100, for example, the function of the location acquisition unit 41 is realized by a GPS receiver connected to the input / output interface 106, the function of the communication unit 42 is realized by the communication interface 105, and the function of the vibration detection unit 43 is realized by a vibration sensor connected to the input / output interface 106.

[0065] Furthermore, when the raft management device 5 is realized by the computer 100, for example, the function of the communication unit 51 is realized by the communication interface 105, the function of the memory unit 52 is realized by one or more of the memory 102, the storage device 103, and the portable storage medium, and the function of the raft position identification unit 53 is realized by the processor 101.

[0066] Furthermore, when the information terminal 6 is realized by the computer 100, for example, the function of the input unit 61 is realized by an input device connected to the input / output interface 106, the function of the communication unit 62 is realized by the communication interface 105, and the function of the display unit 63 is realized by a display device connected to the input / output interface 106.

[0067] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various improvements and modifications can be made without departing from the spirit and scope of the present invention.

[0068] REFERENCE SIGNS LIST 1 Raft management system 2 Offshore aquaculture farm 3 Raft 4, 4a, 4b Position information transmission device 5 Raft management device 6 Information terminal 7 Network 8 Error range 41 Position acquisition unit 42 Communication unit 43 Vibration detection unit 51 Communication unit 52 Storage unit 53 Raft position identification unit 61 Input unit 62 Communication unit 63 Display unit 100 Computer 101 Processor 102 Memory 103 Storage device 104 Portable storage medium drive device 104a Portable storage medium 105 Communication interface 106 Input / output interface 107 Bus 201 Raft 202 GPS tracker 203 Error range

Claims

1. A raft management system including two position information transmission devices provided in each of a plurality of rafts and a raft management device, wherein the position information transmission device includes a position acquisition unit that acquires the position of the position information transmission device, and a communication unit that transmits position information including the position and the device identifier of the position information transmission device to the raft management device, and the raft management device includes a communication unit that receives the position information, a storage unit that stores raft information in which each raft identifier of the plurality of rafts is associated with each device identifier of the two position information transmission devices provided in each of the plurality of rafts, and a raft position specification unit that specifies the position of the raft based on the position information transmitted from each of the two position information transmission devices provided in the raft and the raft information. A raft management system characterized by the above.

2. The two position information transmission devices provided in the raft are provided at positions where the error ranges of the positions acquired by both of the position acquisition units do not overlap, and the midpoint or substantially midpoint position of the positions acquired by both of the position acquisition units is always inside the raft. The raft management system according to claim 1, characterized by the above.

3. The two position information transmission devices provided in the raft are provided at opposing positions near the outer periphery of the raft. The raft management system according to claim 2, characterized by the above.

4. The raft position specification unit specifies the midpoint or substantially midpoint position of the positions included in the position information transmitted from each of the two position information transmission devices provided in the raft as the position of the raft. The raft management system according to any one of claims 1 to 3, characterized by the above.

5. Further including an information terminal, the information terminal includes a communication unit that transmits a request signal for requesting raft position information indicating the position of each of the plurality of rafts to the raft management device and receives the raft position information from the raft management device, and a display unit that displays the position of each of the plurality of rafts based on the raft position information. The communication unit of the raft management device transmits the raft position information indicating the position of each of the plurality of rafts specified by the raft position specification unit to the information terminal in response to the received request signal. The raft management system according to claim 1, characterized by the above.

6. The position information transmitting device further includes a vibration detection unit that detects vibration, and the position information transmitted by the communication unit of the position information transmitting device further includes vibration information indicating the vibration. The raft position specifying unit determines whether the vibration indicated by the vibration information included in the position information is equal to or greater than a threshold value. When the raft position specifying unit determines that the vibration is equal to or greater than the threshold value, the communication unit of the raft management device transmits an alert notification including the position of the raft provided with the position information transmitting device where the vibration is detected to the information terminal. The raft management system according to claim 5, characterized in that.

7. A raft management device that manages a plurality of rafts, each of which is provided with two position information transmitting devices, the communication unit receiving position information transmitted from the position information transmitting device and including the position and device identifier of the position information transmitting device, and the storage unit storing raft information in which each raft identifier of the plurality of rafts is associated with each device identifier of the two position information transmitting devices provided in each of the plurality of rafts. A raft position specifying unit that specifies the position of the raft based on the position information transmitted from each of the two position information transmitting devices provided in the raft and the raft information. A raft management device characterized by comprising.

8. A raft management method for managing a plurality of rafts, each of which is provided with two position information transmitting devices, the method including receiving position information transmitted from the position information transmitting device and including the position and device identifier of the position information transmitting device, and based on the raft information in which each raft identifier of the plurality of rafts is associated with each device identifier of the two position information transmitting devices provided in each of the plurality of rafts, and the position information transmitted from each of the two position information transmitting devices provided in the raft. A raft management method characterized in that a raft management device specifies the position of the raft.

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