A RIGID ARM SINGLE POINT MOORING SYSTEM FOR VESSELS

Abstract: A mooring device is disclosed, consisting of a single point mooring (SPM) - buoy or tower - and a rigid arm (15). The stationary part (4) of the SPM is anchored to the sea bottom. The rotatory part (8) of the SPM and the rigid arm (15) are free to rotate about the verticl axis (A-A) of the SPM. The rigid arm (15) is connected to the single point mooring by a hinge arrangement (9) pivotable about a horizontal axis (B-B). A further hinge may be provided in the rigid arm (15) dividing the rigid arm into two independently movable frames to allow for independent pitch and roll motions of the buoy and vessel in relation to the rigid arm. The vessel is connected to the rigid arm (15) by two tension members (6, 7) which could be chains, cables or bars. The rigid arm (15) is ballasted at the vessel end. The weight of the rigid arm (15) and its ballast (13, 14) and the loading on the tension members, combine to produce a restoring force and moment which prevent the vessel (1) from riding up to the SPM or jack-knifing of the assembly when the rigid arm (15) moves out of line with the centre line of the vessel (1).

Description: The invention relates to a mooring system for mooring a vessel on the surface of a body of water. The aim of the invention is to provide such a mooring system of which the parts are subjected to relatively small forces and loadings and which has a simple and sturdy structure. A first embodiment of such a mooring system has the features as mentioned in claim 1 and a second embodiment has the features as mentioned in claim 2. Further embodiments are subject of the subclaims. EP-A-0 096 445 (figures 4, 5) and EP-A-0 096 446 (figures 9, 10) both describe a mooring system of which the arms, which are each connected to a tension member at the side of the moored vessel hull can move independently with regard to each other in a vertical direction. It is observed that a mooring system with a rigid Y-shaped arm, connected to a floating buoy and of which the vessel ends are connected via pivotable tension members to the hull of the moored vessel is subject of EP―A―0.079.404 filed in the name of applicant and published on 25.03.83. In the mooring system described in this application rolling movements of the vessel do not result into a heavy loading of the mooring point due to the fact that the mooring system allows rotational movement along the longitudinal axis of the rigid arm. Further advantageous embodiments of the invention are described in the subclaims. Further and additional objects and advantages of the present invention will become apparent to those skilled in the art when considering the following detailed description and accompanying drawings, wherein like element have been given like numbers, in which is shown in Fig. 1 a perspective view of an embodiment of the rigid arm of the invention, made in the form of a Y, in Fig. 1A a detail thereof; Fig. 2 a schematic view of another embodiment of the rigid arm formed as a polygon and in which the SPM is formed as a tower; Fig. 3 another embodiment of a tower used as SPM. As may be seen from Fig. 1, the vessel 1 is moored to the floor of a body of water 2 by means of two tension members 6, 7, a rigid arm 15, a standard type of single point mooring constituted by a buoy 3, and one or more anchor chains 5. The single point mooring buoy 3 is of a type known to those skilled in the art, and consists of a buoy body 4 on which the turntable 8 is free to rotate about the vertical axis A―A of the buoy body 4. The buoy body 4 is attached to the floor of the body of water 2 by means of one or more anchor chains 5. The rigid arm 15 is attached to the single point mooring buoy 3 by means of the hinges g. These hinges 9 allow relative movement between the buoy 3 and the rigid arm 15 about the horizontal axis B―B. In Fig. 1 a first embodiment of the rigid arm 15 according to the invention is shown, which serves as buffer or distance holder between a single point mooring buoy 3 and a tanker 1, for example a storage tanker. The rigid arm has here the shape of a Y and has at two locations a hinge, viz. a first hinge 10 in the middle leg 19 of the Y near the buoy 3, and a second hinge 21 at the other end of the middle leg 19 where the fork begins, consisting of two side-legs 11, 12. By the positioning of these two hinges 10, 21 when seen in the drawing, the right hand side leg 11 and middle leg 19 are pivotable with respect to the left hand side leg 12. Both side-legs carry ballasts 13 and 14 at their extremities coupled to tension chains 6, 7 running upwards to the vessel 1. The second hinge 21 consists of a disc 22 and a centring pin 23, which is located in a bore 24 in the middle leg 19 of the Y. The left hand side arm 12 on the Y is connected to the hinge 21 via an extension 26 connected to the disc 22; vide Fig. 1A. As may be seen from Fig. 2 the vessel 34 is moored to the floor of a body of water by means of two anchor chains 37, a rigid arm 36, a rotational table 38 and a structure ("tower") 31 rigidly attached to the seabed 33. The rotating table 38 permits the vessel to swing freely around the tower 31 to take up the position of the least resistance to wind and weather. The rigid arm pivots in relation to this rotating table around an axis x―x, through hinges 41, thereby allowing independent pitch motions of the vessel relative to the tower. Hinges at the rigid arm end 42 and at the vessel connection point 43 allow for excursions of the vessel due to surge and sway. Roll motions of the vessel relative to the tower are allowed by two basically triangular frames 44 and 45, which are coupled together at their base and hence form the rigid arm 36. The hinges and 48 allow the rigid arm to be "folded" in itself, around axis and thus allow independent roll between the towe-side end of the rigid arm and the vessel side. The restoring forces required to balance environmental forces acting on the tanker is generated by a weight 49 which forms a part of the rigid arm. This weight can be permanent or mobile, depending on the application of the mooring system. The product is carried up the tower through rigid piping 50 to the top of the tower, where a fluid swivel mounted on a second rotating table 40 allows for orientation of the piping towards the vessel. The piping continues to the vessel in a manner described in published patent application No. EP―A―0079404. It is observed that a hinged connection between the rigid arm structure and the mooring point need only be used when the latter is immovable with respect to the sea-bed, such as is the case with a mooring tower (31, fig. 2).

Claims: Claims for the following Contracting States : FR, GB, IT, LN 1. Mooring system for mooring a vessel (1) on the surface of a body of water (2), comprising a mooring point (3) and a Y-shaped rigid arm (15) of which the middle part (19) is connected at one end to the mooring point (3), the combination of the rigid arm structure and the mooring point allowing for a pivotal movement with respect to a horizontal axis, and carries at the other, vessel, end two outer legs (11,12), one of them (12) via an axial rotational connection (21) between said leg (12) and said middle part (19), such that the legs can move independently of each other in a vertical direction, the end of each leg being connected to a ballasted tension member (6,7) on the side of the vessel hull which is independently pivotable with respect to both the hull and the rigid arm structure (15). 2. Mooring system for mooring a vessel (1) on the surface of a body of water (2), comprising a mooring point (31) and a rigid arm structure (36), said structure consisting of two triangular frames the combination of the rigid arm structure and the mooring point allowing for a pivotal movement with respect to a horizontal axis, (44,45), interconnected by hinges (47,48) allowing an independent movement of the two frames (44, 45) with respect to each other, one of said frames (44) being connected to the mooring point, the apex of each triangular frame (44, 45) remote from the mooring point being connected to a ballasted tension member (37) on the side of the vessel hull which is independently pivotable with respect to both the hull and the rigid arm structure (36). 3. Mooring system according to claim 2, characterized in that the first frame (44) is hingedly connected to the mooring point (31) and the second frame (45) is hingedly connected to the first frame (44). 4. Mooring system according to claim 1-3, characterized in that the tension members consist of chains or cables (37) suspending from the vessel. Claims for the following Contracting States : DE, SE 1. Mooring System for mooring a vessel (1) on the surface of a body of water (2), comprising a mooring point (3, 31, 60) and a rigid arm structure (15, 36, 66) connected at one end 10 said mooring point and at the other end to the respective, ballasted, ends of two tension members (6, 7 ; 37, 67) one on each side of the vessel hull, characterized in thal said tension members (6, 7 ; 37; 67) are independently pivolable with respect to the hull and that the rigid arm structure (15, 36, 66) comprises two parts (11, 19; 12―14, 15) to which the respective tension members (6, 7; 37; 67) are attached and that the two parts can move independently of each other in a vertical direction. the combination of the rigid arm structure and the mooring point allowing for a pivotal movement with respect to a horizontal axis". 2. A mooring system according to claim 1, characterized in that the rigid arm structure (15) is Y-shaped of which the middle part (19) is provided at the vessel end with an axial rotational connection (21) between said part (19) and one of the outer legs (12). 3. A mooring system according to claim 1 or 2, characterized in that the rigid arm structure (36) comprises two triangular frames (44, 45) connected by hinges (47, 48) allowing an independent movement of the two frames (44, 45) with respect to each other. 4. Mooring system according to claim 3, characterized in that the first frame (44) is hingedly connected to the mooring point (31) and the second frame (45) is hingedly connected to the first frame (44). 5. Mooring system according to claim 1―4 characterized in that the tension members consist of chains or cables (37) suspending from the vessel.

Inventors: DE BAAN, J., MR.
Applicants: BLUEWATER TERMINAL SYSTEMS N.V.
Application year: 1982
Main classification: B63B27
IPC codes: B63B22