Patent Publication Number: US-9896164-B2

Title: Float mooring method, mooring member, and method of recovering same

Description:
TECHNICAL FIELD 
     The present invention relates to a float mooring method, a mooring member, and a method of recovering the same. 
     Priority is claimed on Japanese Patent Application No. 2014-142212, filed Jul. 10, 2014, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     In the related art, as a mooring method for tying articles floating (hereinafter, referred to as “floats”) in water areas such as sea areas to the bottom using a cable or a chain, for example, there is a method disclosed by Patent document 1. This is a method for tying the upper parts of marine structures to anchors installed on the seabed via cables. 
     CITATION LIST 
     Patent Document 
     Patent document 1: Japanese Unexamined Patent Application, First Publication No. S63-197712 
     DISCLOSURE OF THE INVENTION 
     Technical Problem 
     However, in Patent document 1, there is room for improvement in facilitating a float mooring operation. 
     The present invention has been made in consideration of the above-described circumstance, and an object of the present invention is to facilitate float mooring operation. 
     Solution to Problem 
     According to a first aspect of the present invention, a float mooring method includes: a transportation step of transporting a mooring member having a mooring cable which can be connected to a float at one end thereof and an accommodation member which is installed at the other end of the mooring cable or between the one end and the other end of the mooring cable and has an accommodation space therein to a mooring position of the float in a working water area; a first accommodation step of accommodating a first heavy weight in at least a part of the accommodation space of the accommodation member at the mooring position; a connection step of connecting the one end of the mooring cable to the float at the mooring position after the first accommodation step; and a second accommodation step of accommodating a second heavy weight in the accommodation space of the accommodation member by adding the second heavy weight to the first heavy weight or exchanging at least part of the first heavy weight with the second heavy weight at the mooring position after the connection step. 
     In this case, in the second accommodation step after the connection step, the second heavy weight is accommodated in the accommodation space of the accommodation member by being added to the first heavy weight or being exchanged with at least part of the first heavy weight at the mooring position. Therefore, it is possible to easily connect the mooring cable to the float before the second accommodation step and increase the specific weight of the accommodation member in the same manner as that of a weight member during the second accommodation step. 
     In the transportation step, the mooring member may be transported in a state in which the accommodation space is filled with air. 
     According to the above-described mooring method, compared with a case in which the heavy weight is included in the accommodation space of the accommodation member, the weight of the accommodation member is decreased, and thus it is possible to easily transport the mooring member. In addition, when the accommodation space of the accommodation member is filled with air, a buoyant force is generated in the accommodation member, and thus it is possible to easily float and tow the mooring member. 
     In a case in which a float is moored in a water area, it can be also considered that a heavy weight is accommodated in advance in an accommodation space of a mooring member which has been manufactured onshore and the mooring member is transported to a mooring position. However, in this case, the heavy weight is accommodated in the accommodation space of the mooring member, and thus the floating and towing of the accommodation member becomes difficult. In contrast, according to this mooring method, since the accommodation space of the accommodation member is filled with air, the floating and towing of the accommodation member become easy. 
     At least one of the first heavy weight and the second heavy weight may have flowability. 
     According to the above-described mooring method, it is possible to easily accommodate heavy weights in the accommodation space of a tube member in at least one of the first accommodation step and the second accommodation step. 
     As the first heavy weight and the second heavy weight, use of solid substances such as broken stones can be considered. However, in this case, for the transportation of broken stones, an equipment such as a grab bucket excavator is required, and there is a possibility of a long time being taken to transport the broken stones. In contrast, according to the mooring method of the present invention, at least one of the first heavy weight and the second heavy weight has flowability, and thus the equipment such as the grab bucket excavator is not required, and it does not take a long time to transport the heavy weights. 
     In the second accommodation step, the same substance as the first heavy weight in the first accommodation step may be used as the second heavy weight. 
     According to the above-described mooring method, compared with a case in which different heavy weights are used in the respective steps, it is possible to easily accommodate the second heavy weight in the second accommodation step. 
     As the first heavy weight and the second heavy weight, water in the water area may be used. 
     According to the above-described mooring method, compared with a case in which water which is different from water in the water area is prepared, it is possible to easily accommodate the heavy weights in the first accommodation step and the second accommodation step. 
     As the mooring member, a weight member which is attached to the other end of the mooring cable or in the accommodation member, is placed at the bottom of the water area, and has a filling space therein may also be used. 
     According to the above-described mooring method, it is possible to easily fill the weight member with the heavy weight. 
     Before the connection step, a buoy-joining step of joining a buoy with the one end of the mooring cable and floating the buoy on a water surface in the water area may be provided. 
     According to the above-described mooring method, it is possible to suppress the one end of the mooring cable sinking into the water and easily connect the mooring cable to the float. 
     As the accommodation member, a tube member which is attached to the other end of the mooring cable may be used. 
     According to the above-described mooring method, it is possible to easily moor the float using a simple constitution. Also, it is possible to easily adjust the weight of the accommodation member and the tensile force of the mooring cable by adjusting the kind, specific weight, and weight of the heavy weight that is accommodated in the tube member, the volume ratio between the heavy weight and air, and the like. 
     As the accommodation member, a variant member which is attached between the one end and the other end of the mooring cable may be used. 
     According to the above-described mooring method, it is possible to easily moor the float using a simple constitution. 
     Multiple variant members may be placed at predetermined intervals between the one end and the other end of the mooring cable. 
     According to the above-described mooring method, it is possible to accommodate the first heavy weight and the second heavy weight in each of the multiple variant members and easily adjust the weight of the accommodation member and the tensile force of the mooring cable. 
     As the mooring member, a first mooring member which is connected to a first connection portion of the float and a second mooring member which is connected to a second connection portion that is placed at a position different from that of the first connection portion in the float may be used. 
     According to the above-described mooring method, since it is possible to cause tensile forces suitable for the respective mooring members to be exerted, compared with a case in which the tensile force is adjusted by varying the length of the mooring cable, it is possible to easily adjust the tensile force of the mooring cable. Also, when only the kinds (specific weights) and amounts of the heavy weights are changed in the respective mooring members, it is possible to individually impart a variety of characteristics to the respective mooring members even when the mooring cables and the accommodation members are the same as each other in the respective mooring members. Also, in a case in which multiple (for example, three) mooring members are placed, when one of the three mooring members is replaced in the recovering step or the like, it is possible to make the remaining two mooring members appropriately heavy, and the recovering work becomes easy. 
     According to another aspect of the present invention, a float mooring member is provided, including: a mooring cable which can be connected to a float at one end thereof; and an accommodation member which is installed at the other end of the mooring cable or between the one end and the other end of the mooring cable and has an accommodation space therein, in which a heavy weight having flowability is accommodated in the accommodation space of the accommodation member. 
     According to the above-described mooring member, since the heavy weight has flowability, an equipment such as a grab bucket excavator is not required, and it does not take a long time to transport the heavy weights, and thus it is possible to easily accommodate and recover the heavy weights. Also, since the weight of the accommodation member is decreased by removing the heavy weight from the accommodation member, that is, filling the accommodation space of the accommodation member with air, it is possible to easily transport the mooring member. In addition, when the accommodation space of the accommodation member is filled with air, a buoyant force is generated in the accommodation member, and thus it is possible to easily float and tow the mooring member. 
     As the heavy weight, use of solid substances such as broken stones or solidified materials such as concrete can be considered. However, in a case in which broken stones are used, the equipment such as the grab bucket excavator is required to transport broken stones, and there is a possibility of a long time being taken to transport the broken stones. In a case in which concrete is used, since concrete is solidified after being accommodated, although maintaining flowability while being accommodated, there is a possibility of a long time being taken to recover the solidified concrete. In contrast, according to this constitution, the heavy weights have flowability, and thus the equipment such as the grab bucket excavator is not required, and it does not take a long time to transport the heavy weights. 
     Also, when the heavy weight is removed from the accommodation member, that is, the accommodation space of the accommodation member is filled with air, the weight of the accommodation member is decreased. 
     Also, when the accommodation space of the accommodation member is filled with air, the floating and towing of the accommodation member becomes easy. 
     Furthermore, the accommodation space can be filled with air by (1) feeding compressed air into the accommodation space so as to discharge the heavy weight, (2) suctioning the heavy weight so as to let air naturally enter the accommodation space, or (3) performing both (1) and (2). 
     According to still another aspect of the present invention, a method of recovering the mooring member is provided, including: a first step of removing the heavy weight from the accommodation space of the accommodation member; and a second step of recovering the accommodation member from a working water area after the first step. 
     According to the above-described recovering method, after the heavy weight is removed from the accommodation member in the first step, the accommodation member is recovered from a working water area in the second step, and thus the accommodation member can be easily recovered, and it becomes possible to reuse the accommodation member. 
     Advantageous Effects of Invention 
     According to the present invention, before the second accommodation step, the mooring cable can be easily connected to the float, and the specific weight of the accommodation member can be increased in the same manner as that of the weight member during the second accommodation step, and thus it is possible to easily moor the float. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an explanatory view of a transportation step of a mooring member according to a first embodiment of the present invention. 
         FIG. 2  is, subsequent to  FIG. 1 , an explanatory view of a water-introduction step to the sinker. 
         FIG. 3  is, subsequent to  FIG. 2 , an explanatory view of a step in which water is introduced to a tube member (that is a first accommodation step). 
         FIG. 4  is, subsequent to  FIG. 3 , an explanatory view of a lowering step of the mooring member. 
         FIG. 5  is, subsequent to  FIG. 4 , an explanatory view of a state in which the weight member arrives on the seabed, that is, a sinker-on-the-seabed state. 
         FIG. 6  is, subsequent to  FIG. 5 , an explanatory view of a buoy-joining step of joining a buoy with one end of the mooring cable in the mooring member. 
         FIG. 7  is, subsequent to  FIG. 6 , an explanatory view of a high-specific gravity liquid introduction step into the weight member. 
         FIG. 8  is, subsequent to  FIG. 7 , an explanatory view of a temporary placement state of the mooring member. 
         FIG. 9  is, subsequent to  FIG. 8 , an explanatory view of an arrival state of the float. 
         FIG. 10  is, subsequent to  FIG. 9 , an explanatory view of a mooring cable connection step. 
         FIG. 11  is, subsequent to  FIG. 10 , an explanatory view of a mooring cable deployment step. 
         FIG. 12  is, subsequent to  FIG. 11 , an explanatory view of a mooring cable-lifting step. 
         FIG. 13  is, subsequent to  FIG. 12 , an explanatory view of a water-introduction step and a high-specific gravity liquid introduction step (second accommodation step) of introducing the high-specific gravity liquid to the tube member. 
         FIG. 14  is, subsequent to  FIG. 13 , an explanatory view of a hose-winding step and an ROV-recovering step. 
         FIG. 15  is, subsequent to  FIG. 14 , an explanatory view of a mooring state of the float. 
         FIG. 16  is a view of a variant member in a mooring member according to the second embodiment of the present invention. 
         FIG. 17  is an explanatory view of the transportation step of the mooring member according to the second embodiment of the present invention. 
         FIG. 18  is, subsequent to  FIG. 17 , an explanatory view of a connector terminal connection step, a wire connection step of connecting the weight member of the mooring member to the lid portion, and a hose-coupling step of coupling a hose to the weight member. 
         FIG. 19  is, subsequent to  FIG. 18 , an explanatory view of a water-introduction step to the sinker and a lowering step of the weight member. 
         FIG. 20  is, subsequent to  FIG. 19 , an explanatory view of a dropping step of the variant member. 
         FIG. 21  is, subsequent to  FIG. 20 , an explanatory view of a water-introduction step to the variant member (first accommodation step). 
         FIG. 22  is, subsequent to  FIG. 21 , an explanatory view of a sinker-on-the-seabed state, a buoy-joining step of joining a buoy with the one end of the mooring cable in the mooring member, and a high-specific gravity liquid introduction step of introducing high-specific gravity liquid to the weight member. 
         FIG. 23  is, subsequent to  FIG. 22 , an explanatory view of a temporary placement state of the mooring member. 
         FIG. 24  is, subsequent to  FIG. 23 , an explanatory view of an arrival state of the float. 
         FIG. 25  is, subsequent to  FIG. 24 , an explanatory view of a mooring cable connection step. 
         FIG. 26  is, subsequent to  FIG. 25 , an explanatory view of a mooring cable deployment step. 
         FIG. 27  is, subsequent to  FIG. 26 , an explanatory view of a mooring cable-lifting step. 
         FIG. 28  is, subsequent to  FIG. 27 , an explanatory view of a high-specific gravity liquid introduction step (second accommodation step) of introducing the high-specific gravity liquid to the variant member. 
         FIG. 29  is, subsequent to  FIG. 28 , an explanatory view of a hose-winding step. 
         FIG. 30  is, subsequent to  FIG. 29 , an explanatory view of an ROV-recovering step. 
         FIG. 31  is, subsequent to  FIG. 30 , an explanatory view of a mooring state of the float. 
         FIG. 32  is an explanatory view of a transportation step of a mooring member according to the third embodiment of the present invention. 
         FIG. 33  is, subsequent to  FIG. 32 , an explanatory view of a water-introduction step to the sinker. 
         FIG. 34  is, subsequent to  FIG. 33 , an explanatory view of a water-introduction step to the variant member (first accommodation step) and a lowering step of the weight member. 
         FIG. 35  is, subsequent to  FIG. 34 , an explanatory view of a sinker-on-the-seabed state and a high-specific gravity liquid introduction step of introducing high-specific gravity liquid to the weight member. 
         FIG. 36  is, subsequent to  FIG. 35 , an explanatory view of a buoy-joining step of joining a buoy with the one end of the mooring cable in the mooring member and a temporary placement state of the mooring member. 
         FIG. 37  is, subsequent to  FIG. 36 , an explanatory view of an arrival state of the float. 
         FIG. 38  is, subsequent to  FIG. 37 , an explanatory view of a mooring cable connection step. 
         FIG. 39  is, subsequent to  FIG. 38 , an explanatory view of a mooring cable deployment step. 
         FIG. 40  is, subsequent to  FIG. 39 , an explanatory view of a mooring cable-lifting step. 
         FIG. 41  is, subsequent to  FIG. 40 , an explanatory view of a high-specific gravity liquid introduction step (second accommodation step) of introducing the high-specific gravity liquid to the respective variant members. 
         FIG. 42  is, subsequent to  FIG. 41 , an explanatory view of an ROV-recovering step. 
         FIG. 43  is, subsequent to  FIG. 42 , an explanatory view of a mooring state of the float. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     Hereinafter, a first embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  is an explanatory view of a transportation step of a mooring member  1  according to the first embodiment of the present invention. 
     As illustrated in  FIG. 1 , the mooring member  1  includes a mooring cable  10 , a tube member  20  (accommodation member), and a weight member  30 . The mooring member  1  moors a float  80  (refer to  FIG. 9 ) such as a floating wind power generation device at a previously-specified mooring position P (refer to  FIG. 2 ) offshore. 
     Furthermore, in the present embodiment, the float  80  is installed in a sea area, but may be installed in other water areas such as lakes or rivers. That is, the mooring position P may be set to other water areas such as lakes or rivers depending on the installation place of the float  80 . 
     The mooring cable  10  is formed of a linear member such as a rope or a chain which can be smoothly bent. One end  10   a  of the mooring cable  10  can be connected to the float  80  (refer to  FIG. 9 ). The other end  10   b  of the mooring cable  10  is joined with the tube member  20 . 
     The tube member  20  is a cylindrical member having an accommodation space  20   s  therein. For example, the tube member  20  is formed of a rigid member such as a steel member. At one end  20   a  of the tube member  20 , a first joining portion  21  with which the other end  10   b  of the mooring cable  10  is joined is provided. At the other end  20   b  of the tube member  20 , a second joining portion  22  with which the weight member  30  is joined is provided. Although not illustrated in the drawings, in the tube member  20 , a hole allowing water or the like to be introduced to or discharged from the accommodation space  20   s  is formed, and closing means such as a valve for closing this hole is provided. 
     The weight member  30  is a rectangular member having a filling space  30   s  therein. For example, the weight member  30  is formed of a rigid member such as a steel member. On a first side surface  30   a  of the weight member  30 , a hinge portion  31  with which the second joining portion  22  of the tube member  20  is joined is provided. Although not illustrated in the drawings, in the weight member  30 , a hole allowing water or the like to be introduced to or discharged from the filling space  30   s  is formed, and closing means such as a valve for closing this hole is provided. 
     Furthermore, the shape of the weight member  30  is not limited to a rectangular shape, and a variety of shapes can be employed. 
     Furthermore, the second joining portion  22  can be fixed to the hinge portion  31  in a state of being joined with the hinge portion  31  and can be turned around the hinge portion  31  when released from the fixing. Therefore, it is possible to adjust the position of the tube member  20  (the slope of the tube member  20  with respect to the weight member  30 ) in a state in which the second joining portion  22  is joined with the hinge portion  31 . 
     The weight member  30  is placed on a seabed  2   c  (refer to  FIG. 5 ) so as to confine the float  80  to a mooring position P (refer to  FIG. 9 ). The weight member  30  functions as a “sinker” which generates a resistance force using its own weight. Furthermore, instead of the weight member  30 , an “anchor” which generates a resistance force (holding force) by digging claws or the like into the seabed  2   c  may be used. For example, there are pile anchors, suction anchors, and the like. 
     Hereinafter, a mooring method according to the present embodiment will be described with reference to  FIGS. 1 to 15 . 
     The mooring method according to the present embodiment includes a transportation step of transporting the mooring member  1  to the mooring position P (refer to  FIG. 2 ) of the float  80 , a first accommodation step of accommodating low-specific weight liquid (seawater  5 , refer to  FIG. 3 ) as a first heavy weight in a part of the accommodation space  20   s  of the tube member  20  at the mooring position P, a connection step of connecting the one end  10   a  of the mooring cable  10  to the float  80 , and a second accommodation step of accommodating high-specific gravity liquid  6  (refer to  FIG. 14 ) as a second heavy weight together with the seawater  5  in the accommodation space  20   s  of the tube member  20  filled with the seawater  5 . 
     Furthermore, the high-specific gravity liquid  6  is liquid ballast having a higher specific weight than the seawater  5  as the low-specific weight liquid. For example, as the high-specific gravity liquid  6 , drilling mud (specific weight of approximately two) may be used or a mixture of powder having a high specific weight and water or the like may be used. The value of the specific weight of the high-specific gravity liquid  6  can be appropriately set, for example, in a range higher than the specific weight of the seawater  5 . 
     As illustrated in  FIG. 1 , in the transportation step of the mooring member  1 , the mooring member  1  is transported in a state in which the accommodation space  20   s  of the tube member  20  and the filling space  30   s  of the weight member  30  are filled with air  3 . That is, in the accommodation space  20   s  of the tube member  20  and the filling space  30   s  of the weight member  30 , any heavy weights such as seawater are not accommodated. 
     In the transportation step, the mooring member  1  is transported by, for example, two tugboats (a main tugboat  50  and a subsidiary tugboat  60 ). 
     A boat body  51  of the main tugboat  50  is provided with a winch  59 , a guide roller  53 , a pump  54 , and a steering portion  52 . 
     The winch  59 , the pump  54  and the steering portion  52  are sequentially placed on the boat body  51  from stern to bow thereof. The winch  59  is a facility capable of winding or paying out a rope  55 . The guide roller  53  is placed at the stern of the boat body  51 . The guide roller  53  guides the rope  55  being wound up or paid out using the winch  59 . 
     One end of the rope  55  is joined with the winch  59  of the main tugboat  50 , and the other end of the rope  55  is joined with the weight member  30 . A predetermined amount of the rope  55  is wound around a drum of the winch  59 . The main tugboat  50  tugs the rope  55  and tows the mooring member  1  with the weight member  30  in the front. In the mooring member  1 , since the accommodation space  20   s  of the tube member  20  and the filling space  30   s  of the weight member  30  are filled with the air  3 , the towing of the mooring member  1  is the floating and towing of the mooring member using a buoyancy force. 
     A boat body  61  of the subsidiary tugboat  60  is provided with a steering portion  62 , an unillustrated winch, and a guide roller  63 . 
     The guide roller  63  is placed at the stern of the boat body  61 . The guide roller  63  guides the mooring cable  10  being wound up or paid out using the unillustrated winch or guides a rope  65 . 
     The one end  10   a  of the mooring cable  10  and one end of the rope  65  are joined with the unillustrated winch of the subsidiary tugboat  60 , and the other end  10   b  of the mooring cable  10  and the other end of the rope  65  are joined with the first joining portion  21  of the tube member  20 . Around the drum of the winch of the subsidiary tugboat  60 , a predetermined amount of the mooring cable  10  is wound, and also a predetermined amount of the rope  65  is wound. The subsidiary tugboat  60  tows the mooring member  1  behind the main tugboat  50  and helps the main tugboat  50  tow the mooring member. 
     The mooring member  1  is placed at the mooring position P (refer to  FIG. 2 ) by means of towing by the main tugboat  50  and the subsidiary tugboat  60 . 
       FIG. 2  is, subsequent to  FIG. 1 , an explanatory view of a water-introduction step to the sinker. In the following drawings including  FIG. 2 , the winch  59  will not be illustrated for convenience. 
     As illustrated in  FIG. 2 , in the water-introduction step to the sinker, the seawater  5  is introduced to the filling space  30   s  of the weight member  30  at the mooring position P. Specifically, in the water-introduction step to the sinker, at the mooring position P, a diver  4  opens an unillustrated valve of the weight member  30  and introduces the seawater  5  into the filling space  30   s  through an unillustrated hole. When the filling space  30   s  is filled with the seawater  5 , and the rope  55  is paid out from the unillustrated winch, the weight member  30  gradually sinks into the sea  2   b.    
     Furthermore, the unillustrated valve of the weight member  30  may be opened and closed by means of remote control using an ROV  56  (refer to  FIG. 4 ) described below. 
     In  FIG. 2 , the tube member  20  is positioned to be inclined with respect to a sea surface  2   a  so that the first joining portion  21  is placed higher than the second joining portion  22 . 
       FIG. 3  is, subsequent to  FIG. 2 , an explanatory view of a water-introduction step to the tube member (first accommodation step). 
     As illustrated in  FIG. 3 , in the water-introduction step to the tube member, the seawater  5  is partially introduced as the first heavy weight to the accommodation space  20   s  of the tube member  20  at the mooring position P. Specifically, in the water-introduction step to the tube member, at the mooring position P, the diver  4  opens an unillustrated valve of the tube member  20  and introduces the seawater  5  into a part of the accommodation space  20   s  through the unillustrated hole. When the seawater  5  is accommodated in the part of the accommodation space  20   s , and the rope  55  is paid out from the unillustrated winch, the weight member  30  sinks deeper than in the water-introduction step to the sinker. 
     Furthermore, in the water-introduction step to the tube member, instead of the seawater  5 , a heavy weight which maintains flowability even after the water-introduction step may be used. 
     In  FIG. 3 , the tube member  20  is positioned to be substantially perpendicular to the first side surface  30   a  of the weight member  30  and be substantially perpendicular to the sea surface  2   a.    
     Furthermore, in the water-introduction step to the tube member, the bow of the subsidiary tugboat  60  faces opposite to the main tugboat  50 , and the stern of the subsidiary tugboat  60  faces the main tugboat  50 . Also, the rope  65  is removed from the first joining portion  21  and is wound around the drum of the unillustrated winch. That is, only the mooring cable  10  is joined with the first joining portion  21 . 
       FIG. 4  is, subsequent to  FIG. 3 , an explanatory view of a lowering step of the mooring member  1 . 
     As illustrated in  FIG. 4 , in the lowering step, the mooring member  1  is lowered using the mooring cable  10  at the mooring position P. Specifically, in the lowering step, at the mooring position P, the mooring cable  10  is guided and paid out from the unillustrated winch of the subsidiary tugboat  60  using the guide roller  63 , and the rope  65  is also paid out from the unillustrated winch at the same time as the paying out of the mooring cable  10  from the unillustrated winch. In the lowering step, the seawater  5  is continuously introduced to the part of the accommodation space  20   s . Therefore, the weight member  30  keeps sinking deeper than in the water-introduction step to the tube member. 
     In  FIG. 4 , the tube member  20  sinks into the sea  2   b  and is positioned to be substantially perpendicular to the first side surface  30   a  of the weight member  30  and be substantially perpendicular to the sea surface  2   a.    
     In the lowering step, the remotely operated vehicle (ROV)  56  is sent into the sea  2   b  from the main tugboat  50  via a cable  57 . The ROV  56  is an underwater explorer operated by means of remote control. The ROV  56  includes a manipulator  56   a  and the like. 
     The manipulator  56   a  performs predetermined works using an operation device such as a robot arm. The ROV  56  sends image data regarding the appearance of the sinking mooring member  1  to the main tugboat  50 . Furthermore, in the lowering step, after a predetermined amount of the seawater  5  is introduced to the accommodation space  20   s , the unillustrated valve of the tube member  20  is closed using the manipulator  56   a.    
       FIG. 5  is, subsequent to  FIG. 4 , an explanatory view of a state in which the weight member  30  arrives on the seabed  2   c , that is, a sinker-on-the-seabed state. 
     When the weight member  30  keeps sinking at the mooring position P due to the lowering step, as illustrated in  FIG. 5 , the weight member  30  arrives at the seabed  2   c , and the sinker-on-the-seabed state is formed. In the sinker-on-the-seabed state, a second side surface  30   b  of the weight member  30  is in contact with the seabed  2   c.    
     In the sinker-on-the-seabed state, the ROV  56  is placed in the vicinity of the weight member  30 . The rope  55  is removed from the weight member  30  using the manipulator  56   a  and is wound up using the unillustrated winch of the main tugboat  50 . Furthermore, in  FIG. 5 , the tube member  20  is positioned to be substantially perpendicular to the first side surface  30   a  of the weight member  30  and be substantially perpendicular to the seabed  2   c.    
       FIG. 6  is, subsequent to  FIG. 5 , an explanatory view of a buoy-joining step of joining a buoy with the one end  10   a  of the mooring cable  10  in the mooring member  1 . As illustrated in  FIG. 6 , in the buoy-joining step, a buoy  11  is detachably joined with in the one end  10   a  of the mooring cable  10 , and the buoy  11  is floated on the sea surface  2   a . When the buoy-joining step is completed, the subsidiary tugboat  60  leaves the mooring position P. 
       FIG. 7  is, subsequent to  FIG. 6 , an explanatory view of a high-specific gravity liquid introduction step of introducing high-specific gravity liquid to the weight member  30 . In  FIG. 7 , the reference sign V indicates the introduction direction of high-specific gravity liquid  6 . 
     As illustrated in  FIG. 7 , in the high-specific gravity liquid introduction step, the high-specific gravity liquid  6  is introduced to the filling space  30   s  of the weight member  30  at the mooring position P. Specifically, in the high-specific gravity liquid introduction step, a hose  58  is coupled to the unillustrated hole of the weight member  30 , and the high-specific gravity liquid  6  is introduced to the filling space  30   s  of the weight member  30  via the hose  58  using the pump  54 . When the high-specific gravity liquid  6  is introduced to the filling space  30   s , the seawater  5  in the filling space  30   s  is appropriately discharged through the hole. 
     Furthermore, in the high-specific gravity liquid introduction step, as the high-specific gravity liquid  6 , a heavy weight which maintains flowability even after the high-specific gravity liquid introduction step is preferably used. 
     In the high-specific gravity liquid introduction step, when the high-specific gravity liquid  6  is introduced to the filling space  30   s  of the weight member  30 , the total weight of the weight member  30  and the substance accommodated in the weight member becomes heavier than that before the high-specific gravity liquid introduction step. 
     Furthermore, in  FIG. 7 , the tube member  20  is caused to substantially stand due to the seawater  5  accommodated in the part of the accommodation space  20   s  and the air  3  accommodated in the remaining part of the accommodation space  20   s.    
     After the high-specific gravity liquid introduction step, the ROV  56  is placed in the vicinity of the weight member  30 , and the hose  58  is removed from the weight member  30  using the manipulator  56   a  and is wound up using the unillustrated winch (hose-winding step). After that, the cable  57  is wound, and the ROV  56  is recovered (ROV-recovering step). When the ROV-recovering step is completed, the main tugboat  50  leaves the mooring position P. 
       FIG. 8  is, subsequent to  FIG. 7 , an explanatory view of a temporary placement state of the mooring member  1 . 
     When the ROV  56  is recovered into the main tugboat  50  by means of the ROV-recovering step, as illustrated in  FIG. 8 , a temporary placement state in which the mooring member  1  which is to moor the float  80  (refer to  FIG. 9 ) is temporarily placed is formed. 
       FIG. 9  is, subsequent to  FIG. 8 , an explanatory view of an arrival state of the float  80 . In  FIG. 9 , the float  80  has a rectangular outline for convenience, but a variety of shapes can be employed as the outline of the float  80 . 
     In the temporary placement state, for example, when the float  80  is transported to the mooring position P by two tugboats (the main tugboat  50  and the subsidiary tugboat  60 ), the arrival state in which the float  80  which is a mooring subject of the mooring member  1  has arrived at the mooring position P as illustrated in  FIG. 9  is formed. 
     Furthermore, in a float transportation step of towing the float  80 , one end of the rope  55  is joined with the unillustrated winch of the main tugboat  50 , and the other end of the rope  55  is joined with a first side surface  80   a  of the float  80 . A predetermined amount of the rope  55  from one end side of the rope  55  is wound around the drum of the unillustrated winch. The main tugboat  50  tugs the rope  55  and tows the float  80 . 
     One end of the rope  65  is joined with the unillustrated winch of the subsidiary tugboat  60 , and the other end of the rope  65  is joined with a second side surface  80   b  of the float  80 . A predetermined amount of the rope  65  is wound around the drum of the winch of the subsidiary tugboat  60 . The subsidiary tugboat  60  tows the float  80  behind the main tugboat  50  and helps the main tugboat  50  tow the float. 
     The float  80  is placed at the mooring position P by means of towing by the main tugboat  50  and the subsidiary tugboat  60 . 
     In the arrival state, the float  80  is positioned so that the first side surface  80   a  and the second side surface  80   b  become perpendicular with respect to the sea surface  2   a . In the arrival state, the main tugboat  50  and the subsidiary tugboat  60  stay at the mooring position P. 
     Tug ropes  81  and  82  of the mooring member  10  are placed in the float  80 . In the float  80 , an unillustrated winch capable of winding or paying out the ropes  81  and  82  is placed. One end of each of the ropes  81  and  82  is joined with the winch. One end  81   a  (first connection portion) of the rope  81  is detachably joined with the first side surface  80   a  of the float  80  in the upper portion. The other end  82   a  (second connection portion) of the rope  82  is detachably joined with the second side surface  80   b  of the float  80  in the upper portion. A predetermined amount of each of the ropes  81  and  82  is wound around the drum of the winch. 
     Furthermore, the intended use of the ropes  81  and  82  is not limited to the drawing of the mooring member  10 . For example, the ropes  81  and  82  may be used to adjust the length of the mooring member  10  by constituting a part of the mooring member  10  with the ropes. 
       FIG. 10  is, subsequent to  FIG. 9 , an explanatory view of a mooring cable connection step. In  FIG. 10 , the main tugboat  50  and the subsidiary tugboat  60  are not illustrated for convenience (also in  FIGS. 11 to 14 ). 
     As illustrated in  FIG. 10 , in the mooring cable connection step, the one end  10   a  of the mooring cable  10  is connected to the other end  81   a  of the rope  81  which is placed in the float  80 . Specifically, in the mooring cable connection step, a workboat  70  is placed at the mooring position P, and the mooring cable is connected to the rope using the workboat  70 . A boat body  71  of the workboat  70  is provided with a steering portion  72 , an unillustrated winch, and a guide roller  73 . 
     In this mooring cable connection step, first, the buoy  11  is pulled up on the boat body  71  of the workboat  70 . Next, the buoy  11  is removed from the one end  10   a  of the mooring cable  10 . Also, the other end  81   a  of the rope  81  is detached from the float  80 . In addition, the detached other end  81   a  of the rope  81  is connected to the one end  10   a  of the mooring cable  10 . 
       FIG. 11  is, subsequent to  FIG. 10 , an explanatory view of a mooring cable deployment step. In  FIG. 11 , the reference sign G indicates the throwing direction of the mooring cable  10 , and the reference sign K indicates the winding direction of the rope  81 . 
     As illustrated in  FIG. 11 , in the mooring cable deployment step, the mooring cable  10  connected to the other end  81   a  of the rope  81  is lowered into the sea  2   b  from the workboat  70  while winding the rope  81  using the unillustrated winch of the float  80 . Therefore, the mooring cable  10  sinks into the sea  2   b  together with the rope  81  and is bent so as to be curved downwards between the first joining portion  21  and the lower portion of the float  80 . 
       FIG. 12  is, subsequent to  FIG. 11 , an explanatory view of a mooring cable-lifting step. In  FIG. 12 , the reference sign U indicates the lifting direction of the mooring cable  10 . 
     As illustrated in  FIG. 12 , in the mooring cable-lifting step, the rope  81  connected to the one end  10   a  of the mooring cable  10  is wound. Specifically, in the mooring cable-lifting step, the rope  81  is wound up using the unillustrated winch provided in the float  80  in a state in which the other end  81   a  of the rope  81  is connected to the one end  10   a  of the mooring cable  10 , and the mooring cable  10  is lifted. Therefore, the mooring cable  10  is bent so as to be slightly curved upwards toward the float  80  from the first joining portion  21  as the starting point. 
       FIG. 13  is, subsequent to  FIG. 12 , an explanatory view of a water-introduction step and a high-specific gravity liquid introduction step (second accommodation step) of introducing the high-specific gravity liquid to the tube member  20 . 
     As illustrated in  FIG. 13 , in the water-introduction step to the tube member, the remaining part of the accommodation space  20   s  of the tube member  20  is filled with the seawater  5 . Specifically, in the water-introduction step to the tube member, an ROV  76  is sent into the sea  2   b  from the workboat  70  via a cable  77 , and the ROV  76  is placed in the vicinity of an unillustrated valve of the tube member  20 . Next, the unillustrated valve of the tube member  20  is opened using a manipulator  76   a , the seawater  5  is introduced to the remaining part of the accommodation space  20   s  through the unillustrated hole, and the accommodation space  20   s  is filled with the seawater  5 . 
     In the high-specific gravity liquid introduction step, the high-specific gravity liquid  6  (refer to  FIG. 14 ) is introduced as the second heavy weight to the accommodation space  20   s  of the tube member  20  which is filled with the seawater  5  together with the seawater  5 . Specifically, in the high-specific gravity liquid introduction step, a hose  78  is coupled to the unillustrated hole of the tube member  20 , and the high-specific gravity liquid  6  (refer to  FIG. 14 ) is introduced to the accommodation space  20   s  of the tube member  20  via the hose  78  using a pump  74 . When the high-specific gravity liquid  6  is introduced to the accommodation space  20   s , the seawater  5  in the accommodation space  20   s  is appropriately discharged through the hole. That is, in the high-specific gravity liquid introduction step, the high-specific gravity liquid  6  (the second heavy weight) is accommodated in the accommodation space  20   s  of the tube member  20  by being added to the seawater  5  or being exchanged with at least part of the seawater  5 . 
     Furthermore, an unillustrated introduction hole for the high-specific gravity liquid  6  and the like is placed on the lower side of the tube member  20 , and a discharge hole (not illustrated) for the seawater  5  and the like is placed on the upper side of the tube member  20 . 
     Also, in the high-specific gravity liquid introduction step, as the high-specific gravity liquid  6 , a heavy weight which maintains flowability even after the high-specific gravity liquid introduction step is preferably used. 
     In the high-specific gravity liquid introduction step, when the high-specific gravity liquid  6  is introduced to the accommodation space  20   s  of the tube member  20 , the total weight of the tube member  20  and the substance accommodated in the tube member becomes heavier than that before the high-specific gravity liquid introduction step. 
     Furthermore, in  FIG. 13 , the tube member  20  is positioned to be inclined so that the tube member collapses toward the first side surface  30   a  of the weight member  30  more than before the high-specific gravity liquid introduction step and thus the first joining portion  21  is closer to the float  80  than the second joining portion  22  (rightwards in  FIG. 13 ). Therefore, the mooring cable  10  is imparted with a predetermined tensile force. 
     A mooring member  1 A (second mooring member) is connected to the second side surface  80   b  of the float  80 . The mooring member  1 A is connected to the second side surface in the same manner as in the mooring cable connection step of the mooring member  1  (first mooring member). A mooring cable  10  in the mooring member  1 A is bent so as to be slightly curved upwards toward the float  80  from the first joining portion  21  as the starting point. 
     Furthermore, the mooring cable deployment step, the mooring cable-lifting step, the water-introduction step, and the high-specific gravity liquid introduction step are performed on the mooring member  1 A in the same manner as on the mooring member  1 . A tube member  20  in the mooring member  1 A is positioned to be inclined with respect to a first side surface  30   a  of a weight member  30  so that the first joining portion  21  is closer to the float  80  than the second joining portion  22  (leftwards in  FIG. 14 ). 
     Furthermore, in  FIG. 13 , two mooring members  1  and  1 A are illustrated, but the number of mooring members installed is not limited to two and may be three or more (multiple). 
       FIG. 14  is, subsequent to  FIG. 13 , an explanatory view of a hose-winding step and an ROV-recovering step. 
     As illustrated in  FIG. 14 , in the hose-winding step, the ROV  76  is placed in the vicinity of the tube member  20 , the hose  78  is removed from the tube member  20  using the manipulator  76   a  and is wound up using the unillustrated winch of the workboat  70 . In the ROV-recovering step, after the hose-winding step, the cable  77  is wound up using the winch of the workboat  70 , and the ROV  76  is recovered. When the ROV-recovering step is completed, the workboat  70  leaves the mooring position P. Also, although not illustrated, the main tugboat  50  and the subsidiary tugboat  60  also leave the mooring position P. 
       FIG. 15  is, subsequent to  FIG. 14 , an explanatory view of a mooring state of the float  80 . 
     When the above-described steps are performed, a mooring state in which the float  80  is moored using the mooring members  1  and  1 A as illustrated in  FIG. 15  is formed. In the mooring state, since a certain tensile force acts on the mooring cables  10  in the respective mooring members  1  and  1 A, the float  80  is stably placed at the mooring position P. 
     As described above, the embodiment shows a mooring method for mooring the float  80  offshore through the mooring member  1 , the method includes a transportation step of transporting the mooring member  1  having the mooring cable  10  which can be connected to the float  80  at the one end  10   a  and the tube member  20  which is joined with the other end  10   b  of the mooring cable  10  and has the accommodation space  20   s  therein to the mooring position P of the float  80 , a water-introduction step to the tube member (first accommodation step) of introducing the seawater  5  (first heavy weight) to a part of the accommodation space  20   s  of the tube member  20  at the mooring position P, a connection step of connecting the one end  10   a  of the mooring cable  10  to the float  80  at the mooring position P after the water-introduction step to the tube member, and a high-specific gravity liquid introduction step (second accommodation step) of accommodating the high-specific gravity liquid  6  (second heavy weight) in the accommodation space  20   s  of the tube member  20  by adding the high-specific gravity liquid to the seawater  5  or exchanging at least part of the seawater  5  with the high-specific gravity liquid at the mooring position P after the connection step. 
     According to this method, since the high-specific gravity liquid  6  is accommodated in the accommodation space  20   s  of the tube member  20  by adding the high-specific gravity liquid to the seawater  5  or exchanging at least part of the seawater  5  with the high-specific gravity liquid at the mooring position P in the high-specific gravity liquid introduction step after the connection step, before the high-specific gravity liquid introduction step, the mooring cable  10  can be easily connected to the float  80 , and, after the high-specific gravity liquid introduction step, the specific weight of the tube member  20  can also be increased in the same manner as that of the weight member  30 . Therefore, it is possible to easily moor the float  80 . 
     Also, in the embodiment, since the mooring member  1  is transported in a state in which the accommodation space  20   s  of the tube member  20  is filled with the air  3  in the transportation step, compared with a case in which a heavy weight is included in the accommodation space  20   s  of the tube member  20 , the weight of the tube member  20  is decreased. Therefore, it is possible to easily transport the mooring member  1 . 
     In a case in which a float is moored in a water area, it can be also considered that a heavy weight is accommodated in advance in an accommodation space of a mooring member which has been manufactured onshore and the mooring member is transported to a mooring position. However, in this case, the heavy weight is accommodated in the accommodation space of the mooring member, and thus the floating and towing of the accommodation member becomes difficult. In contrast, according to this method, since the accommodation space  20   s  of the tube member  20  is filled with the air  3 , the floating and towing of the tube member  20  becomes easy. Therefore, it is possible to easily perform the floating and towing of the mooring member  1 . 
     As the first heavy weight and the second heavy weight, use of solid substances such as broken stones can be considered. However, in this case, for the transportation of broken stones, an equipment such as a grab bucket excavator is required, and there is a possibility of a long time being taken to transport the broken stones. In contrast, in the embodiment, the first heavy weight and the second heavy weight are the seawater  5  having flowability, and thus the equipment such as the grab bucket excavator is not required, and it does not take a long time to transport the heavy weights. Therefore, it is possible to easily accommodate heavy weights in the accommodation space  20   s  of the tube member  20  in the water-introduction step and the high-specific gravity liquid introduction step. 
     Also, in the embodiment, when the weight member  30  which is joined with the other end  10   b  of the mooring cable  10 , is placed on the seabed  2   c , and has the filling space  30   s  therein is used as the mooring member  1 , it is possible to easily fill the weight member  30  with the heavy weight. 
     Also, since the mooring member  1  is transported in a state in which the filling space  30   s  of the weight member  30  is filled with the air  3  in the transportation step, compared with a case in which a heavy weight is included in the filling space  30   s  of the weight member  30 , the weight of the weight member  30  is decreased. Therefore, it is possible to easily transport the mooring member  1 . Also, since the filling space  30   s  of the weight member  30  is filled with the air  3 , the floating and towing of the weight member  30  becomes easy. Therefore, it is possible to easily perform the floating and towing of the mooring member  1 . 
     Also, in the embodiment, since the buoy-joining step of joining the buoy  11  with the one end  10   a  of the mooring cable  10  and floating the buoy on the sea surface  2   a  is provided before the connection step, it is possible to suppress the one end  10   a  of the mooring cable  10  sinking into the sea  2   b  and easily connect the one end  10   a  of the mooring cable  10  to the float  80 . 
     Furthermore, in the present embodiment, since the seawater  5  is accommodated in a part of the accommodation space  20   s  of the tube member  20 , it is possible to reduce the size of the buoy  11  while suppressing the one end  10   a  of the mooring cable  10  sinking into the sea  2   b.    
     If a sufficient buoyant force is imparted by increasing the size of the buoy  11 , it is possible to suppress the one end  10   a  of the mooring cable  10  sinking into the sea  2   b  even when the accommodation space  20   s  of the tube member  20  is fully filled with the seawater  5 . 
     Also, in the embodiment, since the tube member  20  which is joined with the other end  10   b  of the mooring cable  10  is used as the accommodation member, it is possible to easily moor the float  80  using a simple constitution. 
     Also, it is possible to easily adjust the weight of the accommodation member and the tensile force of the mooring cable by adjusting the kind, specific weight, and weight of the heavy weight that is accommodated in the tube member  20 , the volume ratio between the heavy weight and air, and the like. 
     Also, in the embodiment, since the mooring member  1  which is connected to the rope  81  of the float  80  and the mooring member  1 A which is connected to the rope  82  that is placed at a different location from the rope  81  in the float  80  are used as the mooring members, it is possible to individually adjust the weights of the heavy weights for the respective mooring members  1  and  1 A and cause tensile forces suitable for the respective mooring members  1  and  1 A to be exerted without varying the mooring cables  10  and the tube members  20 . Therefore, compared with a case in which the tensile force is adjusted by varying the length of the mooring cable  10 , it is possible to easily adjust the tensile force of the mooring cable  10 . 
     Also, when only the kinds (specific weights) and amounts of the heavy weights are changed in the respective mooring members  1  and  1 A, it is possible to individually impart a variety of characteristics to the respective mooring members  1  and  1 A even when the mooring cables  10  and the tube members  20  are the same as each other in the respective mooring members  1  and  1 A. 
     Also, in a case in which multiple (for example, three) mooring members  1  are placed, when one of the three mooring members is replaced in the recovering step or the like, it is possible to make the remaining two mooring members appropriately heavy, and the recovering work becomes easy. 
     Also, the embodiment is the mooring member  1  that moors the float  80  offshore, including the mooring cable  10  which can be connected to the float  80  at the one end  10   a  and the tube member  20  which is joined with the other end  10   b  of the mooring cable  10  and has the accommodation space  20   s  therein, in which a heavy weight having flowability (at least one of the seawater  5  and the high-specific gravity liquid  6 ) is accommodated in the accommodation space  20   s  of the tube member  20 . 
     As the heavy weight, use of solid substances such as broken stones or solidified materials such as concrete can be also considered. However, in a case in which broken stones are used, the equipment such as the grab bucket excavator are required to remove broken stones from the accommodation space  20   s , and there is a possibility of a long time being taken to remove the broken stones. In a case in which concrete is used, since concrete is solidified after being accommodated, although maintaining flowability while being accommodated, there is a possibility of a long time being taken to remove the solidified concrete from the accommodation space  20   s . In contrast, according to this constitution, the heavy weights (at least one of the seawater  5  and the high-specific gravity liquid  6 ) have flowability, and thus the equipment such as the grab bucket excavator is not required, and it does not take a long time to remove the heavy weights. Therefore, it is possible to easily accommodate and recover the heavy weights. 
     Also, when the heavy weight is removed from the tube member  20 , that is, the accommodation space  20   s  of the tube member  20  is filled with air, the weight of the tube member  20  is decreased. Therefore, it is possible to easily transport the mooring member  1 . 
     Also, when the accommodation space  20   s  of the tube member  20  is filled with the air  3 , the floating and towing of the tube member  20  becomes easy. Therefore, it is possible to easily perform the floating and towing of the mooring member  1 . 
     Furthermore, the accommodation space  20   s  can be filled with the air  3  by (1) feeding compressed air into the accommodation space  20   s  so as to discharge the heavy weight, (2) suctioning the heavy weight so as to let the air naturally enter the accommodation space, or (3) performing both (1) and (2). 
     Furthermore, in the embodiment, the recovering step of recovering the tube member  20  from a working water area by discharging the seawater  5  from the accommodation space  20   s  of the tube member  20  at the mooring position P may be further provided after the water-introduction step to the tube member. In this recovering step, opposite to the water-introduction step, the seawater  5  is discharged from the accommodation space  20   s  of the tube member  20 , the tube member  20  is floated due to the decreased weight of the tube member, and the tube member  20  is recovered from the working water area by the workboat  70  or the like. 
     According to this method, since it is possible to easily decrease the weight of the tube member  20 , it is possible to easily recover the mooring member  1 . 
     Also, in the embodiment, in the high-specific gravity liquid introduction step as the second accommodation step, an example of the high-specific gravity liquid  6  being used as the second heavy weight has been described, but the second heavy weight is not limited thereto. 
     For example, in the water-introduction step as the second accommodation step, as the second heavy weight, the seawater  5  which is the same as the first heavy weight in the water-introduction step to the tube member may also be used. 
     Therefore, compared with a case in which different heavy weights are used in the respective steps, it is possible to easily recover the second heavy weight in the water-introduction step as the second accommodation step. 
     Furthermore, in this case, when the seawater  5  offshore is used as the first heavy weight and the second heavy weight, compared with a case in which water which is different from the seawater  5  offshore is prepared as a heavy weight, it is possible to easily recover the heavy weights in the water-introduction step and the water-introduction step. Also, since it is not necessary to separately prepare water as the heavy weight, no costs are required for the transportation of the heavy weight. 
     Also, in the embodiment, an example in which the seawater is used as the first heavy weight in the first accommodation step and the high-specific gravity liquid is used as the second heavy weight in the second accommodation step has been described, but the heavy weights are not limited thereto. For example, it is possible to use high-specific gravity liquid as the first heavy weight in the first accommodation step and use the same high-specific gravity liquid as the first heavy weight as the second heavy weight in the second accommodation step. In this case, it is possible to perform no work or management for substituting the first heavy weight and the second heavy weight by simply adding the same heavy weight as in the first accommodation step in the second accommodation step, and, compared with a case in which different heavy weights are used in the respective steps, it is possible to easily accommodate the second heavy weight in the second accommodation step. 
     Also, in the embodiment, the installation order of the mooring member has been described, however it becomes possible to recover the mooring member by discharging the heavy weights in an order approximately opposite to the installation order of the mooring member. That is, in the embodiment, the mooring method for the mooring member  1  has been described, but the recovering method according to the present invention may be applied after the installation of the mooring member  1 . 
     A method of recovering the mooring member  1  according to the first embodiment of the present invention includes a first step of removing the heavy weight from the accommodation space  20   s  of the tube member  20  and a second step of recovering the tube member  20  from a working water area after the first step. 
     According to this method, since the tube member  20  is recovered from the working water area in the second step after the heavy weight is removed from the tube member  20  in the first step, it is possible to easily recover the tube member  20 , and it becomes possible to reuse the tube member  20 . 
     Specifically, the recovering method can be performed in the following order. 
     First, the mooring cable  10  is detached from the float  80  (detachment step). Next, an unillustrated hole at the lower end of the tube member  20  and the pump  74  on the workboat  70  are connected to each other using the hose  78 , and the other unillustrated hole at the upper end of the tube member  20  and an unillustrated compressor on the workboat  70  are connected to each other using another unillustrated hose (accommodation member and hose connection step). Next, the heavy weight (not illustrated, at least one of the seawater  5  and the high-specific gravity liquid  6 ) is discharged from the accommodation space  20   s  using the pump  74  while sending compressed air to the accommodation space  20   s  of the tube member  20  from the compressor and is recovered into an unillustrated tank on the workboat  70 . Therefore, the heavy weight in the accommodation space  20   s  of the tube member  20  is substituted with air, and the weight of the tube member  20  in the water is decreased. 
     Similarly, an unillustrated hole at the lower end of the weight member  30  and the pump  74  on the workboat  70  are connected to each other using the hose  78 , and the other unillustrated hole at the upper end of the weight member  30  and the unillustrated compressor on the workboat  70  are connected to each other using another unillustrated hose (weight member and hose connection step). Next, the heavy weight (at least one of the seawater  5  and the high-specific gravity liquid  6 ) is recovered into the unillustrated tank on the workboat  70  using the pump  74  while sending compressed air to the filling space  30   s  of the weight member  30  from the compressor. Therefore, the heavy weight in the filling space  30   s  of the weight member  30  is substituted with air, and the weight of the weight member  30  in the water is decreased. 
     Therefore, the tube member  20  and the weight member  30  can be raised using the unillustrated winch or the like. When a sufficient amount of air is sent to the accommodation space  20   s  of the tube member  20  and the filling space  30   s  of the weight member  30 , it is possible to sufficiently decrease the amounts of the tube member  20  and the weight member  30  in the water and float the tube member  20  and the weight member  30  onto the sea surface. After the tube member  20  and the weight member  30  are floated near the sea surface or on the sea surface, the mooring member  1  is towed by tugboats and is transported to harbors. 
     Furthermore, when the heavy weight is removed from the accommodation space  20   s  of the tube member  20  and the filling space  30   s  of the weight member  30 , it is also possible to remove the heavy weight while letting nearby seawater instead of compressed air naturally enter the spaces. In this case, it is not possible to float the tube member  20  and the weight member  30  as in a case in which air is supplied; however, compared with a case in which the tube member and the weight member are filled with heavy weights, it is possible to decrease the weights of the tube member  20  and the weight member  30  in the water and easily raise the tube member  20  and the weight member  30 . 
     Also, even accommodation members having a different shape from that of the tube member such as variant members and the like in the following embodiments can be recovered in the same order as that in the above-described recovering method. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described with reference to  FIGS. 16 to 31 . Furthermore, in the second embodiment, the same portions as the constitutional elements in the first embodiment will be given the same reference sign and will not be described. 
       FIG. 16  is a view of a variant member  220  in a mooring member according to the second embodiment of the present invention. 
     As illustrated in  FIG. 16 , the mooring member according to the present embodiment includes the variant member  220  instead of the tube member  20 . The variant member  220  is installed between the one end  10   a  (refer to  FIG. 22 ) and the other end  10   b  (refer to  FIG. 18 ) of the mooring cable  10 . The second embodiment is different from the first embodiment in terms of what has been described above. 
     The variant member  220  is a tubular member having an accommodation space  220   s  therein. For example, the variant member  220  is formed of a rigid member such as a steel member. At one end  220   a  of the variant member  220 , a first joining portion  221  with which the mooring cable  10  is joined is provided. On the other end  220   b  of the variant member  220 , a second joining portion  222  with which the mooring cable  10  is joined is provided. Although not illustrated, in the variant member  220 , a hole allowing water or the like to be introduced to or discharged from the accommodation space  220   s  is formed, and closing means such as a valve for closing this hole is provided. 
     For example, regarding the dimensions of the variant member  220 , in  FIG. 16 , the length L 1  is approximately 3 m, the length L 2  is approximately 2 m, the length L 3  is approximately 1 m, and the length L 4  is approximately 1 m. 
     Hereinafter, a mooring method according to the present embodiment will be described with reference to  FIGS. 17 and 31 . 
     The mooring method according to the present embodiment includes a transportation step of transporting a mooring member  201  to a mooring position P (refer to  FIG. 18 ) of the float  80 , a first accommodation step of accommodating the seawater  5  (refer to  FIG. 21 ) as a first heavy weight in the accommodation space  220   s  of the variant member  220  at the mooring position P, a connection step of connecting the one end  10   a  of the mooring cable  10  to the float  80 , and a second accommodation step of accommodating the high-specific gravity liquid  6  (refer to  FIG. 29 ) as a second heavy weight together with the seawater  5  in the accommodation space  220   s  of the variant member  220  filled with the seawater  5 . 
       FIG. 17  is an explanatory view of the transportation step of the mooring member  201  according to the second embodiment of the present invention. 
     As illustrated in  FIG. 17 , in the transportation step of the mooring member  201 , the mooring member  201  is transported in a state in which the accommodation space  220   s  of the variant member  220  and the filling space  30   s  of the weight member  30  are filled with the air  3 . In the transportation step, the mooring member  201  is transported by, for example, one tugboat (only the main tugboat  50 ). 
     The main tugboat  50  has the mooring cable  10  and the variant member  220  on the boat body  51  and transports the mooring member  201  by tugging the rope  55  and towing the weight member  30 . Since the filling space  30   s  of the weight member  30  in the mooring member  201  is filled with air, the weight member  30  is towed by means of floating and towing in which a buoyant force is used. 
     The mooring member  201  is transported by the main tugboat  50  and is placed at the mooring position P (refer to  FIG. 18 ). 
     Furthermore, a lid portion  231  having a joining portion  231   a  which protrudes upwards is joined with the first side surface  30   a  of the weight member  30 . A connection cable  232  which can be flexibly bent is joined with the joining portion  231   a . A connector terminal  232   a  which can be connected to the other end  10   b  (refer to  FIG. 18 ) of the mooring cable  10  is provided on one end portion (an end portion opposite to the joining portion  231   a ) of the connection cable  232 . Therefore, it is possible to rapidly and reliably connect the connection cable  232  and the mooring cable  10  or detach the mooring cable from the connection cable. 
     Also, to the variant member  220 , multiple (for example, two in the present embodiment) buoyant bodies  225  which generate a buoyant force in the variant member  220  are detachably attached. Furthermore, the buoyant force of the variant member  220  may be adjusted by adjusting the water amount and the like of the accommodation space  220   s  of the variant member  220 . Also, the buoyant force may be adjusted by removing the buoyant bodies  225 . 
       FIG. 18  is, subsequent to  FIG. 17 , an explanatory view of a connector terminal connection step, a wire connection step of connecting the weight member  30  of the mooring member  201  to the lid portion  231 , and a hose-coupling step of coupling a hose to the weight member  30 . 
     As illustrated in  FIG. 18 , in the connector terminal connection step, an operator (not illustrated) connects the other end  10   b  of the mooring cable  10  to the connector terminal  232   a  at the mooring position P. 
     In the wire connection step, the operator connects bifurcated ends of a wire  251  to one end and the other end of the lid portion  231  at the mooring position P. 
     In the hose-coupling step, the operator releases an introduction hose  252  from the main tugboat  50  and couples the introduction hose  252  to an introduction opening (not illustrated) of the weight member  30  at the mooring position P. 
     Also, similarly, the operator releases a discharge hose  253  from the main tugboat  50  and couples the discharge hose  253  to a discharge opening (not illustrated) of the weight member  30 . 
     Furthermore, the wire  251  and the mooring cable  10  are wound around the drum of the unillustrated winch of the main tugboat  50  so as to be capable of being wound up and paid out. 
       FIG. 19  is, subsequent to  FIG. 18 , an explanatory view of a water-introduction step to the sinker and a lowering step of the weight member  30 . In  FIG. 19 , the reference sign W indicates the introduction direction of seawater. 
     As illustrated in  FIG. 19 , in the water-introduction step to the sinker, the seawater  5  is introduced to the filling space  30   s  of the weight member  30  at the mooring position P. Specifically, in the water-introduction step to the sinker, the filling space  30   s  is filled with the seawater  5  via the introduction hose  252  and an introduction hole (not illustrated) of the weight member  30  using the pump  54  at the mooring position P. Furthermore, the seawater may be naturally introduced with the force of gravity. 
     In the lowering step, the weight member  30  is lowered using the wire  251  while extending the mooring cable  10  at the mooring position P. Specifically, in the lowering step, the mooring cable  10  and the wire  251  are guided using the guide roller  53  and are paid out from the unillustrated winch of the main tugboat  50  at the mooring position P. When the filling space  30   s  is filled with the seawater  5 , and the mooring cable  10  and the wire  251  are paid out from the unillustrated winch, the weight member  30  gradually sinks into the sea  2   b.    
     In the lowering step, an ROV  66  is sent into the sea  2   b  from the subsidiary tugboat  60  via a cable  67 . The ROV  66  includes a manipulator  66   a  and the like. In the lowering step, the ROV  66  is placed in the vicinity of the weight member  30 . 
       FIG. 20  is, subsequent to  FIG. 19 , an explanatory view of a dropping step of the variant member  220 . 
     As illustrated in  FIG. 20 , in the dropping step, the variant member  220  is dropped toward the sea surface  2   a  at the mooring position P. Since the accommodation space  220   s  of the variant member  220  in the mooring member  201  is filled with the air  3 , the variant member  220  floats on the sea surface  2   a.    
     In the dropping step, the mooring cable  10  and the wire  251  are continuously paid out from the unillustrated winch. Therefore, the weight member  30  keeps sinking deeper than in the lowering step. 
       FIG. 21  is, subsequent to  FIG. 20 , an explanatory view of a water-introduction step to the variant member (first accommodation step). 
     As illustrated in  FIG. 21 , in the water-introduction step to the variant member, the seawater  5  is introduced as a first heavy weight to the accommodation space  220   s  of the variant member  220  at the mooring position P. Specifically, in the water-introduction step to the variant member, at the mooring position P, an unillustrated valve of the variant member  220  is left open in advance, and the seawater  5  is introduced to the accommodation space  220   s  through the unillustrated hole. When the seawater  5  is accommodated in the accommodation space  220   s , and the mooring cable  10  and the wire  251  are paid out from the unillustrated winch, the variant member  220  keeps sinking together with the weight member  30 . 
       FIG. 22  is, subsequent to  FIG. 21 , an explanatory view of a sinker-on-the-seabed state, a buoy-joining step of joining a buoy with the one end  10   a  of the mooring cable  10  in the mooring member  201 , and a high-specific gravity liquid introduction step of introducing high-specific gravity liquid to the weight member  30 . In  FIG. 22 , the reference sign V 1  indicates the introduction direction of the high-specific gravity liquid  6 , and the reference sign V 2  indicates the discharge direction of the seawater  5 . 
     When the weight member  30  continues to sink at the mooring position P due to the lowering step, as illustrated in  FIG. 22 , the weight member  30  arrives at the seabed  2   c , and the sinker-on-the-seabed state is formed. 
     In the buoy-joining step, the buoy  11  is detachably joined with the one end  10   a  of the mooring cable  10 , and the buoy  11  is floated on the sea surface  2   a.    
     In the high-specific gravity liquid introduction step, the high-specific gravity liquid  6  is introduced to the filling space  30   s  of the weight member  30  at the mooring position P. Specifically, in the high-specific gravity liquid introduction step, the high-specific gravity liquid  6  is introduced to the filling space  30   s  via the introduction hose  252  and the introduction hole of the weight member  30  using the pump  54 . Furthermore, when the high-specific gravity liquid  6  is introduced to the filling space  30   s , the seawater  5  in the filling space  30   s  is discharged through the discharge hole and the discharge hose  253 . 
       FIG. 23  is, subsequent to  FIG. 22 , an explanatory view of a temporary placement state of the mooring member  201 . 
     When the ROV  66  is recovered into the subsidiary tugboat  60  by means of the ROV-recovering step after the high-specific gravity liquid introduction step and the hose-winding step, as illustrated in  FIG. 23 , a state in which the mooring member  201  is temporarily placed before the float  80  is moored using the mooring member  201  is formed. 
       FIG. 24  is, subsequent to  FIG. 23 , an explanatory view of an arrival state of the float  80 . 
     In the temporary placement state of the mooring member  201 , when the float  80  is transported to the mooring position P by, for example, two tugboats (the main tugboat  50  and the subsidiary tugboat  60 ), the arrival state in which the float  80  which is a mooring subject of the mooring member  201  has arrived at the mooring position P as illustrated in  FIG. 24  is formed. In the arrival state, the main tugboat  50  and the subsidiary tugboat  60  stay at the mooring position P. 
       FIG. 25  is, subsequent to  FIG. 24 , an explanatory view of a mooring cable connection step. In  FIG. 25 , the main tugboat  50  and the subsidiary tugboat  60  are not illustrated for convenience (also in  FIGS. 26 to 30 ). 
     As illustrated in  FIG. 25 , in the mooring cable connection step, the one end  10   a  of the mooring cable  10  is connected to the other end  81   a  of the rope  81  which is placed in the float  80 . 
       FIG. 26  is, subsequent to  FIG. 25 , an explanatory view of a mooring cable deployment step. 
     As illustrated in  FIG. 26 , in the mooring cable deployment step, the mooring cable  10  connected to the other end  81   a  of the rope  81  is lowered into the sea  2   b  from the workboat  70  while winding the rope  81 . Therefore, the mooring cable  10  sinks into the sea  2   b  together with the rope  81  and is positioned to be inclined between the joining portion  231   a  and the lower portion of the float  80 . 
       FIG. 27  is, subsequent to  FIG. 26 , an explanatory view of a mooring cable-lifting step. 
     As illustrated in  FIG. 27 , in the mooring cable-lifting step, the rope  81  connected to the one end  10   a  of the mooring cable  10  is wound up using the unillustrated winch provided in the float  80 . 
       FIG. 28  is, subsequent to  FIG. 27 , an explanatory view of a high-specific gravity liquid introduction step (second accommodation step) of introducing the high-specific gravity liquid to the variant member  220 . 
     As illustrated in  FIG. 28 , in the high-specific gravity liquid introduction step, the high-specific gravity liquid  6  (refer to  FIG. 29 ) is introduced as the second heavy weight to the accommodation space  220   s  of the variant member  220  which is filled with the seawater  5  together with the seawater  5 . Specifically, in the high-specific gravity liquid introduction step, the hose  78  is coupled to the unillustrated hole of the variant member  220 , and the high-specific gravity liquid  6  (refer to  FIG. 29 ) is introduced to the accommodation space  220   s  of the variant member  220  via the hose  78  using the pump  74 . When the high-specific gravity liquid  6  is introduced to the accommodation space  220   s , the seawater  5  in the accommodation space  220   s  is discharged through the hole. That is, in the high-specific gravity liquid introduction step, the high-specific gravity liquid  6  (the second heavy weight) is accommodated in the accommodation space  220   s  of the variant member  220  by being added to the seawater  5  or being exchanged with at least part of the seawater  5 . 
     In the high-specific gravity liquid introduction step, when the high-specific gravity liquid  6  is introduced to the accommodation space  220   s  of the variant member  220 , the total weight of the variant member  220  and the substance accommodated in the variant member becomes heavier than that before the high-specific gravity liquid introduction step. Therefore, the mooring cable  10  is imparted with a predetermined tensile force as illustrated in  FIG. 29 . 
     A mooring member  201 A (second mooring member) is connected to the second side surface  80   b  of the float  80 . 
     The mooring member  201 A is connected to the second side surface in the same manner as in the mooring cable connection step of the mooring member  201  (first mooring member). Furthermore, the mooring cable deployment step, the mooring cable-lifting step, and the high-specific gravity liquid introduction step are performed on the mooring member  201 A in the same manner as on the mooring member  201 . 
       FIG. 29  is, subsequent to  FIG. 28 , an explanatory view of a hose-winding step. 
     As illustrated in  FIG. 29 , in the hose-winding step, the ROV  76  is placed in the vicinity of the variant member  220 , and the hose  78  is removed from the variant member  220  using the manipulator  76   a  and is wound up using the unillustrated winch. 
       FIG. 30  is, subsequent to  FIG. 29 , an explanatory view of an ROV-recovering step. 
     As illustrated in  FIG. 30 , in the ROV-recovering step, the cable  77  is wound up using the unillustrated winch, and the ROV  76  is recovered. When the ROV-recovering step is completed, the workboat  70  leaves the mooring position P. Also, although not illustrated, the main tugboat  50  and the subsidiary tugboat  60  also leave the mooring position P. 
       FIG. 31  is, subsequent to  FIG. 30 , an explanatory view of a mooring state of the float  80 . 
     When the above-described steps are performed, a mooring state in which the float  80  is moored using the mooring members  201  and  201 A as illustrated in  FIG. 31  is formed. In the mooring state, since a certain tensile force acts on the mooring cables  10  in the respective mooring members  201  and  201 A, the float  80  is stably placed at the mooring position P. 
     As described above, the embodiment is a mooring method for mooring the float  80  offshore through the mooring member  201 , including a transportation step of transporting the mooring member  201  having the mooring cable  10  which can be connected to the float  80  at the one end  10   a  and the variant member  220  which is attached between the one end  10   a  and the other end  10   b  of the mooring cable  10  and has the accommodation space  220   s  therein to the mooring position P of the float  80 , a water-introduction step to the variant member (first accommodation step) of introducing the seawater  5  (first heavy weight) to the accommodation space  220   s  of the variant member  220  at the mooring position P, a connection step of connecting the one end  10   a  of the mooring cable  10  to the float  80  at the mooring position P after the water-introduction step to the variant member, and a high-specific gravity liquid introduction step (second accommodation step) of accommodating the high-specific gravity liquid  6  (second heavy weight) in the accommodation space  220   s  of the variant member  220  by adding the high-specific gravity liquid to the seawater  5  or exchanging at least part of the seawater  5  with the high-specific gravity liquid at the mooring position P after the connection step. 
     According to this method, since the high-specific gravity liquid  6  is accommodated in the accommodation space  220   s  of the variant member  220  by adding the high-specific gravity liquid to the seawater  5  or exchanging at least part of the seawater  5  with the high-specific gravity liquid at the mooring position P in the high-specific gravity liquid introduction step after the connection step, before the high-specific gravity liquid introduction step, the mooring cable  10  can be easily connected to the float  80 , and, during the high-specific gravity liquid introduction step, the specific weight of the variant member  220  can be increased in the same manner as that of the weight member  30 . Therefore, it is possible to easily moor the float  80 . 
     Also, in the embodiment, since the variant member  220  which is attached between the one end  10   a  and the other end  10   b  of the mooring cable  10  is used as the accommodation member, it is possible to easily moor the float  80  using a simple constitution. 
     Third Embodiment 
     Next, a mooring method according to a third embodiment of the present invention will be described with reference to  FIGS. 32 to 43 . Furthermore, in the third embodiment, the same portions as the constitutional elements in the second embodiment will be given the same reference sign and will not be described. 
       FIG. 32  is an explanatory view of a transportation step of a mooring member  301  according to the third embodiment of the present invention. 
     As illustrated in  FIG. 32 , in the mooring member  301  according to the present embodiment, multiple (for example, four in the present embodiment) variant members  220  are placed at predetermined intervals between the one end  10   a  and the other end  10   b  of the mooring cable  10 . The third embodiment is different from the second embodiment in terms of what has been described above. 
     The mooring method according to the present embodiment includes a transportation step of transporting the mooring member  301  to a mooring position P (refer to  FIG. 33 ) of the float  80 , a first accommodation step of accommodating the seawater  5  (refer to  FIG. 34 ) as a first heavy weight in the accommodation spaces  220   s  of the respective variant members  220  at the mooring position P, a connection step of connecting the one end  10   a  of the mooring cable  10  to the float  80 , and a second accommodation step of accommodating the high-specific gravity liquid  6  (refer to  FIG. 41 ) as a second heavy weight together with the seawater  5  in the accommodation spaces  220   s  of the respective variant members  220  filled with the seawater  5 . 
     As illustrated in  FIG. 32 , in the transportation step of the mooring member  301 , the mooring member  301  is transported in a state in which the accommodation spaces  220   s  of the respective variant members  220  and the filling space  30   s  of the weight member  30  are filled with the air  3 . In the transportation step, the mooring member  301  is transported by, for example, one tugboat (only the main tugboat  50 ). 
     The main tugboat  50  tugs the mooring cable  10  in which the four variant members  220  are placed at predetermined intervals and tows the mooring member  301  with the weight member  30  on the tail. Since the accommodation spaces  220   s  of the respective variant members  220  and the filling space  30   s  of the weight member  30  in the mooring member  301  are filled with air, the mooring member  301  is towed by means of floating and towing in which a buoyant force is used. The mooring member  301  is transported by the main tugboat  50  and is placed at the mooring position P (refer to  FIG. 33 ). 
     Furthermore, a hook  231   b  with which the mooring cable  10  is joined is provided at one end of the lid portion  231 . A portion of the mooring cable  10  which is close to the other end  10   b  thereof is joined with the hook  231   b . The joining portion  231   a  is joined with the other end  10   b  of the mooring cable  10 . 
     Also, to each of the variant members  220 , multiple (for example, two in the present embodiment) buoyant bodies  225  are detachably attached. Furthermore, the buoyant forces of the respective variant members  220  may be adjusted by adjusting the water amount and the like of at least one accommodation space  220   s  out of the multiple variant members  220 . Also, the buoyant forces may be adjusted by removing the buoyant bodies  225 . 
     Furthermore, the mooring cable  10  is wound around the drum of the unillustrated winch of the main tugboat  50  so as to be capable of being wound up and paid out. 
       FIG. 33  is, subsequent to  FIG. 32 , an explanatory view of a water-introduction step to the sinker. 
     As illustrated in  FIG. 33 , in the water-introduction step to the sinker, the seawater  5  is introduced to the filling space  30   s  of the weight member  30  at the mooring position P. Specifically, in the water-introduction step to the sinker, at the mooring position P, an operator (not illustrated) releases the portion of the mooring cable  10  which is close to the other end  10   b  thereof from the hook  231   b  and opens an unillustrated valve of the weight member  30 , thereby introducing the seawater  5  to the filling space  30   s  through the unillustrated hole. When the filling space  30   s  is filled with the seawater  5 , and the mooring cable  10  is paid out from the unillustrated winch, the weight member  30  gradually sinks into the sea  2   b.    
       FIG. 34  is, subsequent to  FIG. 33 , an explanatory view of a water-introduction step to the variant member (first accommodation step) and a lowering step of the weight member  30 . 
     As illustrated in  FIG. 34 , in the water-introduction step to the variant member, the seawater  5  is introduced as the first heavy weight to the accommodation spaces  220   s  of the respective variant members  220  at the mooring position P. Specifically, in the water-introduction step to the variant member, at the mooring position P, the unillustrated valves of the respective variant members  220  are left open in advance, and the seawater  5  is introduced to the accommodation space  220   s  through the unillustrated hole. 
     In the lowering step, the mooring cable  10  is extended (paid out) in accordance with the sinking of the weight member  30  and the variant members  220  at the mooring position P. Specifically, in the lowering step, the mooring cable  10  is guided using the guide roller  53  and is paid out from the unillustrated winch of the main tugboat  50  at the mooring position P. 
     When the filling space  30   s  and the accommodation space  220   s  are filled with the seawater  5 , and the mooring cable  10  is paid out from the unillustrated winch, the respective variant members  220  gradually sink into the sea  2   b  together with the weight member  30 . Furthermore, the respective variant members  220  are arranged at predetermined vertical intervals in the sea  2   b . For example, in  FIG. 34 , a series of the variant members  220  are arranged substantially vertically by adjusting the water amount and the like of the uppermost variant member  220  (by introducing air to the variant member so as to decrease the weight of the variant member). 
       FIG. 35  is, subsequent to  FIG. 34 , an explanatory view of a sinker-on-the-seabed state and a high-specific gravity liquid introduction step of introducing high-specific gravity liquid to the weight member. In  FIG. 35 , the reference sign V indicates the introduction direction of the high-specific gravity liquid  6 . 
     When the weight member  30  continues to sink at the mooring position P due to the lowering step, as illustrated in  FIG. 35 , the weight member  30  arrives at the seabed  2   c , and the sinker-on-the-seabed state is formed. 
     In the high-specific gravity liquid introduction step, the high-specific gravity liquid  6  is introduced to the filling space  30   s  of the weight member  30  at the mooring position P. Specifically, in the high-specific gravity liquid introduction step, the hose  78  is coupled to the unillustrated hole of the weight member  30 , and the high-specific gravity liquid  6  is introduced to the filling space  30   s  of the weight member  30  via the hose  78  using the pump  74 . When the high-specific gravity liquid  6  is introduced to the filling space  30   s , the seawater  5  in the filling space  30   s  is discharged through the hole. 
       FIG. 36  is, subsequent to  FIG. 35 , an explanatory view of a buoy-joining step of joining a buoy with the one end  10   a  of the mooring cable  10  in the mooring member  301  and a temporary placement state of the mooring member  301 . 
     As illustrated in  FIG. 36 , in the buoy-joining step, the buoy  11  is detachably joined with the one end  10   a  of the mooring cable  10 , and the buoy  11  is floated on the sea surface  2   a.    
     When the ROV  76  is recovered into the workboat  70  by means of the ROV-recovering step after the high-specific gravity liquid introduction step and the hose-winding step, as illustrated in  FIG. 36 , a state in which the mooring member  301  is temporarily placed before the float  80  is moored using the mooring member  301  is formed. 
       FIG. 37  is, subsequent to  FIG. 36 , an explanatory view of an arrival state of the float  80 . 
     In the temporary placement state of the mooring member  301 , when the float  80  is transported to the mooring position P by, for example, two tugboats (the main tugboat  50  and the subsidiary tugboat  60 ), the arrival state in which the float  80  which is a mooring subject of the mooring member  301  has arrived at the mooring position P as illustrated in  FIG. 37  is formed. In the arrival state, the main tugboat  50  and the subsidiary tugboat  60  stay at the mooring position P. 
       FIG. 38  is, subsequent to  FIG. 37 , an explanatory view of a mooring cable connection step. 
     As illustrated in  FIG. 38 , in the mooring cable connection step, the one end  10   a  of the mooring cable  10  is connected to the other end  81   a  of the rope  81  which is placed in the float  80  by the main tugboat  50 . 
       FIG. 39  is, subsequent to  FIG. 38 , an explanatory view of a mooring cable deployment step. 
     As illustrated in  FIG. 39 , in the mooring cable deployment step, the mooring cable  10  connected to the other end  81   a  of the rope  81  is lowered into the sea  2   b  from the main tugboat  50  while winding the rope  81 . Therefore, the mooring cable  10  sinks into the sea  2   b  together with the rope  81  and is positioned to be curved in a spline shape between the joining portion  231   a  and the lower portion of the float  80 . 
       FIG. 40  is, subsequent to  FIG. 39 , an explanatory view of a mooring cable-lifting step. 
     As illustrated in  FIG. 40 , in the mooring cable-lifting step, the rope  81  connected to the one end  10   a  of the mooring cable  10  is wound up using the unillustrated winch provided in the float  80 . 
       FIG. 41  is, subsequent to  FIG. 40 , an explanatory view of a high-specific gravity liquid introduction step (second accommodation step) of introducing the high-specific gravity liquid to the respective variant members  220 . 
     As illustrated in  FIG. 41 , in the high-specific gravity liquid introduction step, the high-specific gravity liquid  6  is introduced as the second heavy weight to the accommodation spaces  220   s  of the respective variant members  220  which is filled with the seawater  5  together with the seawater  5 . 
     Specifically, in the high-specific gravity liquid introduction step, the hose  78  is coupled to the unillustrated holes of the variant members  220 , and the high-specific gravity liquid  6  is introduced to the accommodation spaces  220   s  of the respective variant members  220  via the hose  78  using the pump  74 . When the high-specific gravity liquid  6  is introduced to the accommodation space  220   s , the seawater  5  in the accommodation spaces  220   s  is discharged through the holes. That is, in the high-specific gravity liquid introduction step, the high-specific gravity liquid  6  (the second heavy weight) is accommodated in the accommodation spaces  220   s  of the respective variant members  220  by being added to the seawater  5  or being exchanged with at least part of the seawater  5 . 
     In the high-specific gravity liquid introduction step, when the high-specific gravity liquid  6  is introduced to the accommodation spaces  220   s  of the respective variant members  220 , the total weight of the respective variant members  220  and the substance accommodated in the variant member becomes heavier than that before the high-specific gravity liquid introduction step. Therefore, the mooring cable  10  is imparted with a predetermined tensile force as illustrated in  FIG. 42 . 
     A mooring member  301 A (second mooring member) is connected to the second side surface  80   b  of the float  80 . 
     The mooring member  301 A is connected to the second side surface in the same manner as in the mooring cable connection step of the mooring member  301  (first mooring member). Furthermore, the mooring cable deployment step, the mooring cable-lifting step, and the high-specific gravity liquid introduction step are performed on the mooring member  301 A in the same manner as on the mooring member  301 . 
       FIG. 42  is, subsequent to  FIG. 41 , an explanatory view of an ROV-recovering step. 
     As illustrated in  FIG. 42 , in the ROV-recovering step, the cable  77  is wound up using the unillustrated winch, and the ROV  76  is recovered. When the ROV-recovering step is completed, the workboat  70  leaves the mooring position P. 
       FIG. 43  is, subsequent to  FIG. 42 , an explanatory view of a mooring state of the float  80 . 
     When the above-described steps are performed, a mooring state in which the float  80  is moored using the mooring members  301  and  301 A as illustrated in  FIG. 43  is formed. In the mooring state, since a certain tensile force acts on the mooring cables  10  in the respective mooring members  301  and  301 A, the float  80  is stably placed at the mooring position P. 
     As described above, in the embodiment, the multiple variant members  220  are placed at predetermined intervals between the one end  10   a  and the other end  10   b  of the mooring cable  10 . 
     According to this method, the seawater  5  and the high-specific gravity liquid  6  can be accommodated in each of the multiple variant members, and it is possible to easily adjust the weights of the variant members  220  and the tensile force of the mooring cable  10 . 
     Furthermore, the technical scope of the present invention is not limited to the embodiments, and the embodiments can be modified in various manners within the scope of the gist of the present invention. 
     For example, in a case in which structures are installed in water areas, the present invention can be applied even when the drafts or positions of the structures are changed. 
     Additionally, it is possible to appropriately replace the constitutional elements in the embodiments with well-known constitutional elements within the scope of the gist of the present invention, or the embodiments may be appropriately combined together. 
     INDUSTRIAL APPLICABILITY 
     The present invention relates to a float mooring method, a mooring member, and a recovering method. According to the present invention, mooring cables can be easily connected to floats before the second accommodation step, and the specific weights of accommodation members can be increased in the same manner as those of weight members during the second accommodation step, and thus it is possible to easily moor floats. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 ,  201 ,  301  MOORING MEMBER 
               2   a  SEA SURFACE (WATER SURFACE) 
               2   c  SEABED (BOTTOM OF WATER AREA) 
               3  AIR 
               5  SEAWATER (FIRST HEAVY WEIGHT) 
               6  HIGH-SPECIFIC GRAVITY LIQUID (SECOND HEAVY WEIGHT) 
               10  MOORING CABLE 
               10   a  ONE END OF MOORING CABLE 
               10   b  THE OTHER END OF MOORING CABLE 
               20  TUBE MEMBER (ACCOMMODATION MEMBER) 
               20   s  ACCOMMODATION SPACE 
               30  WEIGHT MEMBER 
               30   s  FILLING SPACE 
               80  FLOAT 
               81   a  THE OTHER END OF ROPE (FIRST CONNECTION PORTION) 
               82   a  THE OTHER END OF ROPE (SECOND CONNECTION PORTION) 
               220  VARIANT MEMBER 
             P MOORING POSITION