GB2166398A

GB2166398A - An improved mooring system

Info

Publication number: GB2166398A
Application number: GB08426113A
Authority: GB
Inventors: Baan Jacob De
Original assignee: Bluewater Terminals S A
Current assignee: Bluewater Terminals S A
Priority date: 1984-10-16
Filing date: 1984-10-16
Publication date: 1986-05-08
Also published as: GB2166398B; GB8426113D0

Abstract

A mooring system in which a vessel (20) is attached to the rotating member of a single point mooring by means of a rigid arm having one end attached to the rotating member comprises a receiving member (3) for mounting for rotation on the vessel about a vertical axis. Resilient means (4) acts between the receiving member and the vessel to resist rotation of the member about the vertical axis. There is a mounting member 26 attached to the vessel end of the mooring arm and there is means to attach the mounting member to the receiving member 3 so that there is no relative rotation between the members about the vertical axis. <IMAGE>

Description

SPECIFICATION An improved mooring system The present invention relates to a single point mooring system with a vessel semi-permanently moored to it. The SPM can be any type of mooring such as a CALM (Catinary Anchor Leg Mooring), fixed or articulated tower or SALM (Single Anchor Leg Mooring) anchored to the seafloor, whilst the vessel is coupled to the SPM by a rigid arm which serves to hold the vessel away from the SPM. There are a large number of known technical solutions to keep the vessel away from the SPM via a rigid arm, but most solutions provide a rigid shear connection which results in very high forces in the rigid arm system. Such solutions are either not suitable to disconnect a vessel from the mooring in the event of adverse weather conditions, or do not provide a satisfactory solution to limit yaw of the vessel.

The invention provides a mooring system in which a vessel is attached to the rotating member of a single point mooring by means of a rigid arm having one end attached to the rotating member in which there is a receiving member for mounting for rotation on the vessel about a vertical axis, there is resilient means for acting between the receiving member and the vessel to resist rotation of the member about the said axis, there is a mounting member attached to the vessel end of the mooring arm and there is means to attach the mounting member to the receiving member so that there is no relative rotation between the members about the said vertical axis.

Preferably the mounting member is attachable to the receiving member by a readily releasable connection.

Two specific examples of mooring systems according to the present invention will now be described with reference to the accompanying drawings in which: Figure lisa side view of a mooring system; Figure 2 is a plan view of the mooring system; Figure 3 is an enlarged vertical cross-section through part of the system; and Figure 4 is a side view of a second mooring system.

As may be seen from Figures 1 and 2, a buoy 01 is connected to a tanker 20 at a single point which allows pitch and yaw motions through a pitch hinge 02 and a yaw bearing 03. However, the yaw motions are restricted by an elastic element 04 (weight cable system) which exerts a restoring force on the lever arm 05 over the deck of the tanker. This lever arm 05 forms an integral construction with the yaw bearing assembly 03. Disconnection is achieved at the rigid arm interface with the tanker through the use of a connector 06 which locks the rigid arm via the pitch hinge 02 to the yaw bearing assembly 03, whilst the restoring moment system remains with the tanker after disconnection.

The buoy 01 is connected to the sea bed by a catenary mooring system; however, other moorings would also be applicable.

The specific embodiment will now be described in more detail.

The buoy 01 comprises a lower portion 21 which is secured to the sea bed by means of catenary chains 22 and an upper portion 23 which is mounted for rotation on the lower portion 21 about an axis 24.

Extending upwardly at an angle from the portion 23 and rigidly connected thereto is a truss 25 which forms a rigid mooring arm. At the extreme end of the rigid mooring arm there is a vertically extending connecting member 26 which is connected to the member 25 by means of the pivot joint 02. Thus the connecting member 26 is rotatable relative to the member 25 about a horizontal axis.

Referring now to Figure 3 the tanker 20 carries at its bows a rigid extension 30 having a through hole 31. Mounted in this through hole by means of a bearing 03 is a rotatable annulus 32. Attached to the upper end of the annulus is the arm 05 which has already been described and the end of the arm remote from the annulus is attached to a rope 04 which passes over a pulley 36 and is connected at its free end to a weight 37 (see Figure 1). The weight is arranged so that rotation of the lever arm 05 will raise and lower the weight and the weight tends to keep the lever arm in its central position.

The connecting member 26 is arranged to be rigidly connected to the lever arm 05 for rotation therewith. The connecting member 26 has at its upper end a rope attachment 40 which is attached to a rope 41 which passes over a pulley 42. The member 40 is attached to the member 26 by means of a universal joint 43 which allows movement in all directions. This means that when the rope 41 is being moved to the right in Figure 3 the member 26 is drawn into the annulus 32 but the joint 40 allows the rope to untwist preventing any unnecessary wear on the rope 41.

The member 26 is first engaged by a locking bolt 44 which not only prevents the member rotating relative to the lever 05 but also holds the member 26 located vertically. There is an additional locking means for holding the member 26 in position namely the provision of a pair of locking pins 45 and 46 which engage the member 40.

A wedge device 47 is also provided to prevent lateral movement of the member 26 relative to the annulus 32.

It will be appreciated that the embodiment provides a very simple apparatus whereby the member 26 can be quickly uncoupled from the tanker or more strictly from the lever 05 when bad weather conditions are expected and the member 26 is simply uncoupled and allowed to fall vertically downwardly out of engagement. Furthermore the embodiment provides a simple arrangement whereby the yaw of the vessel is resisted by the weight and rope system attached to the lever 05 so that the weight and lever act almost as a spring.

In fact it would be possible to replace the weight connected to the rope and the lever by a simple hydraulic device.

Figure 4 is an alternative SPM system according to the present invention. The SPM consists of a jacket 60 fixed to the seafloor 61, with a rotating part 62 fitted to the upper section of the jacket 60. The rigid arm 63 is fitted to this rotating part 62 via a hinge construction 64. This hinge construction 64 allows vertical pitch motions of the vessel 20.

The mounting member 65 having a ballast weight 70 is connected to the other side of the rigid arm 63.

This mounting member 65 is fixed to the receiving member 66, and the receiving member 66 is connected to the tanker structure 20 via a yaw bearing 03. A lever arm 05 is fitted to the receiving member 66 with the resilient spring system 04 acting upon it.

It will be seen that there are universal joints at both ends of the member 65.

A wedge device 47 fixes the mounting member 65 to the receiving member 66 and prevents any movement between those parts in a similar manner to the wedge device of Figure 3.

Claims

1. A mooring system in which a vessel is attached to the rotating member of a single point mooring by means of a rigid arm having one end attached to the rotating member in which there is a receiving member for mounting for rotation on the vessel about a vertical axis, there is resilient means for acting between the receiving member and the vessel to resist rotation of the member about the said axis, there is a mounting member attached to the vessel end of the mooring arm and there is means to attach the mounting member to the receiving member so that there is no relative rotation between the members about the said vertical axis.

2. A single point mooring system as claimed in claim 1 in which the mounting member is attachable to the receiving member by a readily releasable connection.

3. A single point mooring system as claimed in claim 1 or claim 2 in which the resilient means comprises a lever arm connected by a cable to a weight.

4. A single point mooring system as claimed in claim 1 or claim 2 in which the resilient means comprises a hydraulic device.

5. A single point mooring system substantially as herein described with reference to and as shown in the accompanying drawings.