GB2190055A

GB2190055A - Mooring system

Info

Publication number: GB2190055A
Application number: GB08607957A
Authority: GB
Inventors: Robert Colin Pearson
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-04-01
Filing date: 1986-04-01
Publication date: 1987-11-11
Also published as: GB8607957D0

Abstract

A mooring system comprises a mooring means (7) for mooring a mooring line (9) to a structure (1) and a resilient retrieval line (12) attached between the mooring means (7) and the structure (1). The mooring means (7) has a first portion (6) attached to the structure (1) and a second portion (8) spaced from the first portion (6) to which the mooring line (9) is attached. The system is such that if the mooring line (9) breaks when connected between a vessel (11) and the second portion (8) of the mooring means (7) the retrieval line (12) pulls the mooring means (7) and that part of the broken mooring line (9) attached to the mooring means (7) towards the structure (1). <IMAGE>

Description

SPECIFICATION A mooring system The present invention relates to a mooring system and more particularly to a mooring system for mooring a vessel to a waterbound structure such as an offshore platform.

Known vessel mooring systems at offshore platforms comprise a rope shackled to a pad-eye on a leg of the platform some 10 ft. above sea level. The end of the rope is stowed at upper deck level and passed to the vessel to be moored.

An access deck, known as a spider deck, is constructed on the platform some 15-20 ft. above sea level, giving access to the leg at the level ofthe pad-eye but as the pad-eye connection is necessarily on the seaward side ofthe leg, it is often a difficult and hazardous operation to connect a new rope to the pad-eye in event of breakage of a mooring rope by fretting or by excess loading. The problem is rendered more difficult when tidal conditions sweep a broken rope end into the platform structure below the spider deck, necessitating cutting away of rope to enablethe old ropeto be disconnected beforethe new rope can be installed.

An object ofthe present invention is to reduce and possibly eliminate these difficulties and to render the operation of rope changing simple and safe.

According to the present invention there is provided a mooring system comprising mooring meansformooring a mooring linetoastructureand resilient retrieval means adapted to be attached undertension between the mooring means and the structure,the mooring means having a first portion adapted to be attached to the structure and a second portion spaced from the first portion to which the mooring line is adapted to be attached, the system being such that ifthe mooring line breaks when connected between a vessel and the second portion ofthe mooring means the retrieval means pullsthe mooring means and that part ofthe broken mooring line attached tothe mooring meanstowardsthe structure.

Also according to the present invention there is provided a mooring system comprising mooring meansformooringa mooringlinetoastructureand a resilient retrieval means attached between the mooring means and the structure, the mooring means having first portion attached to the structure and a second portion spaced from the first portion to which the mooring line is attached, the system being such that if the mooring line breaks when connected between a vessel and the second portion ofthe mooring means the retrieval means pulls the mooring means and that part ofthe broken mooring line attached to the mooring means towards the structure.

The retrieval means may comprise a rope which is able to stretch by IO%to 15% of its length.

The retrieval rope may be arranged to pass around a pulley attached to the structure above the mooring means and be attached to the structure below the pulley so that if the mooring line breaks the retrieval rope pullsthe mooring means upwardsandtowards the structure.

The mooring means may comprise a wire rope comprising a shackle at its first portion to attach the mooring means to the structure and a shackle at its second portion by which the mooring means is attached to the mooring line.

Further according to the present invention there is provided a method of mooring a vessel to a structure, comprising connecting a mooring line between a vessel and mooring means attached to the structure and connecting resilient retrieval means undertension between the mooring means and the structure such that if the mooring line breaks the retrieval means pulls the mooring means and that part of the mooring line attached to the mooring means towards the structure.

The present invention will now be described by way of example and with reference to the accompanying drawings in which Figure 1 schematically shows part of an offshore platform with a vessel moored to the platform by a mooring system according to the present invention, and Figure 2 shows a situation in which the mooring line of the system shown in Figure 1 has broken.

Referring to the drawings, Figure 1 shows an offshore platform a having legs 2, an upper deck 3 and a spider deck 4. On the seaward side of one ofthe legs 2 below the spider deck 4 is a pad-eye 5and attached to the pad-eye 5 by means of a shackle 6 is mooring means in the form of a wire rope 7. The opposite end ofthe wire rope 7 is attached by means of a shackle 8 to a mooring rope 9 which is attached to a bollard 10 of a vessel 11. A resilient retrieval rope 12which can stretch by 10%to 15% without excessive loading is attached to the wire rope 7 at its end remote from the leg 2 ofthe platform and passes around a sheave 13 mounted to a pad-eye 14which is fixed to the platform below the upper deck 7. The end of the retrieval rope 12 is secured to a cleat 15 mounted to a leg 2 of platform 1.

Although the mooring means is shown as a wire rope 7 it is possible to be in the form of a link. Also the retrieval means maycomprisea spring and/ora resilient rope.

When the vessel 11 is not being moored to the platform 1, the mooring rope 9 is stowed on the deck of the platform 1 with its lower end attached to the wire rope 7. The wire rope 7 will be in the position shown in Figure 2 since the tension in the retrieval line pulls the wire rope 7 upwards and towards the platform 1.

When a vessel 11 is to be moored, the mooring rope 9 is lowered by crane and attached to the bollard 10 ofthevessel 11 againstthetension in the retrieval rope 12. Since the retrieval rope 12 is light-weight in comparison with the vessel mooring rope 9 the tension in the retrieval rope 12 does little to deflect the ropes 7 and 9 from a straight line between the pad-eye 5 and the bollard 10 when the mooring rope 9 is undertension.

If the mooring rope9 should break, asshown in Figure 2, the resilience of the retrieval rope 12 pulls the outer end ofthe wire rope 7 and the broken length of mooring rope 9 upwards and towards the platform above the spider deck 4 before the broken length can drift and become fast upon the platform structure belowthe spider deck 4. The broken length of mooring rope9isthen disconnected attheshackle 8 and a new mooring rope connected to the shackle 8.

Claims

1. A mooring system comprising mooring means for mooring a mooring line to a structure and resilient retrieval means adapted to be attached undertension between the mooring means and the structure, the mooring means having a first portion adapted to be attached to the structure and a second portion spaced from the first portion to which the mooring line is adapted to be attached, the system being such that if the mooring line breaks when connected between a vessel and the second portion ofthe mooring means the retrieval means pulls the mooring means and that part ofthe broken mooring line attached to the mooring means towards the structure.

2. A mooring system comprising mooring means for mooring a mooring line to a structure and a resilient retrieval means attached between the mooring means and the structure, the mooring means having a first portion attached to the structure and a second portion spaced from the first portion to which the mooring line is attached, the system being such that if the mooring line breaks when connected between a vessel and the second portion ofthe mooring means the retrieval means pulls the mooring means and that part ofthe broken mooring line attached to the mooring means towards the structure.

3. A system as claimed in claim 1 or claim 2, wherein the retrieval means comprises a rope which is ableto stretch by 1 0%to 15% of its length.

4. Asystem as claimed in claim 3, wherein the retrieval rope is arranged to pass around a pulley attached to the structure above the mooring means and be attached to the structure below the pulley so that if the mooring line breaks the retrieval rope pulls the mooring means upwards and towards the structure.

5. A system as claimed in any one ofthe preceding claims, wherein, the mooring means comprises a wire rope comprising a shackle at its first portion to attach the mooring means to the structure and a shackle at its second portion by which the mooring means is attached to the mooring line.

6. A method of mooring a vessel to a structure, comprising connecting a mooring line between a vessel and mooring means attached to the structure and connecting resilient retrieval means under tension between the mooring means and the structure such that if the mooring line breaksthe retrieval means pulls the mooring means and that part of the mooring line attached to the mooring means towards the structure.

7. A mooring system substantially as hereinbefore described with reference to the accompanying drawings.

8. A method of mooring a vessel, substantially as hereinbefore described with reference to the accompanying drawings.