GB2274093A

GB2274093A - Vessel mooring system

Info

Publication number: GB2274093A
Application number: GB9225913A
Authority: GB
Inventors: Baan Jacob De; W J Van-Heijst
Original assignee: Bluewater Terminal Systems NV
Current assignee: Bluewater Terminal Systems NV
Priority date: 1992-12-11
Filing date: 1992-12-11
Publication date: 1994-07-13
Also published as: GB9225913D0

Abstract

A vessel (10) has a stand-off mooring system which comprises an outrigger (14) pivotally mounted on the vessel (10) with one end extending beyond the edge of the vessel (10), and a stiff link (16) connecting the far end of the outrigger (14) to a turntable (13) on a mooring point (12). Means (17) is provided to resist downward tilting of the outrigger (14) so that if the stiff link (16) deviates from a vertical position, a force acts tending to restore the link (16) to the vertical, hence maintaining the position of the vessel (10) with respect to the mooring point (12). The stiff link (16) may comprise a strut or a ram, and the means (17) may comprise a strut, a ram or a counterweight. <IMAGE>

Description

A STAND-OFF MOORING SYSTEM The invention relates to a mooring system for a vessel, such as a tanker and consists of a structure, anchored to the seabed, such as a floating buoy or piled jacket with a turntable on top to which the vessel is moored by a rope. Such a simple mooring system may be employed if it is allowed or required that the vessel may weathervane around the structure. Indeed many of such so-called single point mooring systems are currently employed world-wide.

A disadvantage of such system is that, when wind, current or wave directions change, the vessel may drift toward the buoy and cause damage to either the anchored structure or the vessel itself. Usually there are also floating hoses fitted between the anchored structure and the vessel and these too may be damaged. The invention aims to provide a solution to this problem.

Dutch Patent Application No. 9000363 shows a mooring system which comprises an outrigger rigidly mounted on a vessel which carries pulleys and a steel cable. The cable is attached to the mooring point and kept taut by a counterweight to prevent the vessel moving towards the mooring point. Movement away from the mooring point is prevented by a second cable attached directly between the vessel and the mooring point.

According to the present invention ther is provided a vessel having a mooring structure at one end thereof comprising an elongate outrigger pivotally mounted about a horizontal axis on the vessel to project from the end of the vessel, a relatively stiff link for connecting the projecting end of the outrigger to a mooring, means to tension the link to provide a force which restrains the vessel against movement towards or away from the mooring when the link is non-vertical and means to resist downward tilting of the outrigger.

The invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows an embodiment of the invention in which the stiff link is the form of a ram which provides the tension in the link, while a strut prevents tilting of the outrigger.

Figure 2 is a perspective view of the outrigger and strut of Figure 1.

Figure 3 shows an embodiment of the invention in which the stiff link is in the form of a strut and a ram provides the tension and resists tilting of the outrigger.

Figure 4 is a perspective view of the ram and outrigger of Figure 3.

Figure 5 shows possible relative positions between the vessel and the mooring point using the system of Figure 3.

Figure 6 shows a vessel moored by the system of Figure 3 to a piled structure such as a jacket.

Figure 7 shows an embodiment of the invention in which the stiff link is in the form of a ram and the means to tension the link and to resist tilting of the outrigger is another ram.

Figure 8 shows an embodiment of the invention in which the stiff link is in the form of a strut and the tensioning means is a ram located between the outer end of the outrigger and a pylon on the vessel.

Figure 9 shows an embodiment of the invention in which the means to tension the link and to prevent tilting of the outrigger is a counterweight.

Figure 10 shows an embodiment of the invention in which the means to tension the stiff link and prevent the outrigger tilting is a counterweight coupled to a ram.

Figure 11 shows an embodiment of the invention in which the stiff link is a ram and a cable and which prevents the outrigger from tilting.

Figure 1 shows a vessel 10 and a mooring point 12 with a turntable 13 on top of it. An outrigger structure 14 is mounted on the vessel at a pivot point 15. A stiff link 16 extends between the end of the outrigger 14 and the turntable 13. The attachments are made such that the turntable 13 cannot assume a heading substantially different to that of the vessel 10. A means 17 is also provided to resist downward tilting of the outrigger 14.

The stiff link 16 is put in tension by suitable means such that, when the stiff link 16 takes up an angle of inclination with the vertical, a horizontal force component acts on the turntable 13. The direction of the horizontal force component is such that it keeps the vessel 10 nominally in the vicinity of the mooring point 12, in other words the vessel 10 is moored to it, while it also prevents the vessel 10 and mooring point 12 colliding with each other.

Obviously the length of the stiff link 16, the height of the outrigger 14 above the turntable 13 and the tension load introduced in the stiff link 16, contribute to and determine the overall behaviour of system.

The pretension load may be generated by various means and at various locations in the system. These various means may be hydraulic, pneumatic or consist of a counterweight.

These various locations may be in the stiff link 16, in the outrigger structure 14 itself or between the outrigger 14 and the vessel 10.

For example, the stiff link 16 may be in the form of a ram with a strut 17 between the outrigger 14 and the vessel 10 resisting tilting of the outrigger 14, as shown in Figures 1 and 2.

In Figures 3 and 4, the stiff link 16 is a strut whereas a ram connected between the outrigger 14 and the vessel 10 provides both tension in the link 16 and means 17 for tilt resistance for the outrigger 14.

Figure 5 shows different possible relative positions of the vessel 10, mooring point 12 and stiff link 16.

All these diagrams show the mooring point 12 as an anchored buoy. However, it may also be in the form of a piled structure as shown in Figure 16, with the same mooring system as Figures 3,4 and 5.

In the system of Figure 7, the stiff link 16 is in the form of a ram. Further tensioning in link 16, as well as means 17 to resist the outrigger 14 tilting, is provided by a second ram attached between the outrigger 14 and the vessel 10.

In Figure 8 the means 17 to prevent the outrigger 14 tilting and to tension the stiff link 16 is provided by a ram connected to the end of the outrigger and to a pylon 18 mounted on the vessel.

In Figure 9 the means 17 to prevent the outrigger 14 tilting and to provide tension in the link 16 is in the form of a counterweight. In Figure 10 it is in the form of a counterweight and ram in combination and in Figure 11 in the form of a winch and cable.

The system may also be arranged such that the vessel draft position may be compensated for, such that always an optimal overall geometry may be achieved. Furthermore, the mooring system may be made disconnectable, preferably by providing a coupling in the stiff member.

Claims

1. A vessel having a mooring structure at one end thereof comprising an elongate outrigger pivotally mounted about a horizontal axis on the vessel to project from the end of the vessel, a relatively stiff link for connecting the projecting end of the outrigger to a mooring, means to tension the link to provide a force which restrains the vessel against movement towards or away from the mooring when the link is non-vertical and means to resist downward tilting of the outrigger.

2. A vessel as claimed in Claim 1 wherein the stiff link comprises a ram.

3. A vessel as claimed in Claim 1 or Claim 2 in which the means to resist downward tilting of the outrigger includes means to tension the link.

4. A vessel as claimed in Claim 3 in which the combined resisting and tensioning means comprises a ram connected between the outrigger and the vessel.

5. A vessel as claimed in Claim 3 in which the combined resisting and tensioning means comprises a counterweight mounted on the outrigger.

6. A vessel as claimed in Claim 5 in which the counterweight is attached to a ram and the other end of the ram is attached to the vessel.

7. A vessel as claimed in Claim 3 in which the combined resisting and tensioning means comprises a cable attached to the outrigger and running through a winch attached to the vessel.

8. A vessel as claimed in Claim 3 in which the combined resisting and tensioning means comprises a ram attached at one end to the outer end of the outrigger and at the other end to a pylon mounted on the vessel.

9. A vessel as claimed in Claim 1 or Claim 2 in which the means to resist downward tilting of the outrigger comprises a strut attached at one end to the outrigger and at the other end to the vessel.

10. A vessel substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.