GB2185950A - A mooring system - Google Patents

Abstract

A mooring system comprises a hook (3) adapted to be attached to a platform (1). A link (10) is adapted to sit in the eye (4) of the hook (3) and to be attached to a mooring rope. Guide rope (16) has one end adapted to be attached to the platform (1) above the hook (3) and the other end is adapted to be located rearwardly of the eye (4). Retrieval ropes (17) have one end attached to the link (10) and the other end slidable upwardly along the guide rope (16) when an upward pull is exerted on the retrieval ropes (17) to cause the link to be pulled out rearwardly from the eye (4). The forward region of the eye (4) extends rearwardly of the hook (3) to allow the mooring rope to be upwardly inclined without the link (10) being pulled over said region of the eye (4). Means are provided to prevent the link (10) rotating in the eye (4) of the hook (3) beyond a predetermined point towards the underside of the hook (3). <IMAGE>

Description

SPECIFICATION A mooring system The present invention relates to a mooring system and more particularlyto a mooring system for mooring vessels to an offshore platform.

It is known to moor a vessel to an offshore platform by attaching a mooring rope forthe vessel to a hookfixed to a leg ofthe platform and to run a guide wire down to thetip ofthe hook. Thewire extends through an attachment ring or link connected to the mooring rope so that on lowering the linkaround the guidewire,the link is abletofall into the eye of the hook. This procedure may be termed "front loading".

This arrangement is advantageous when it is required to recoverthe inner end ofthe mooring rope backto the deck of the plafform. In this operation the ring or link is lifted by a retrieval line attached to it or near to it. However, difficulty can be experienced in removing the linkfrom the hook, particularly ifthetip ofthe hook points backwards towards the platform, as is necessary to avoid disengagement ofthe ring or linkfrom the hook when the rope loads are oscillating from tightto slack conditions in conjunction with vessel heave.

A hook having a tip which points upwards rather than backwards towards the platform may be usable in light weather conditions or if the hook is above the splash zone when there is no risk of wave action forcing the linkoutofthe hook, butsucha configuration makes the removal of the mooring rope and linkfromthehookanecessarypartof unmooringthevessel, as the upward pull ofthe mooring rope when it is secured at the top; for stowage, to the upper deck, pulls the bottom end out ofthe hook attachment.

Preferably the mooring rope may be stowed in the customary manner after mooring by lifting its end fromthevessel and attaching the ropeatthedeckof the platform while the bottom of the rope remains in its hook as is the case when a pad-eye and shackle is used on the platform leg; such an arrangement permitting upward pull on the mooring rope without risk of its lower end being withdrawn from the hook also.

This also enables the use of a system inwhichthe mooring rope is connected to a further rope attached to vertically spaced points on the leg of the platform in which the lower part ofthefurther rope extends upwards from the lower attachment of the leg of the platform.

When a vessel is not being moored to the platform the end ofthe mooring rope which during a mooring operation is attached to the vessel is preferably stowed on the deck of the platform and the other end remains connected to the hook. This is not possible when using a hook having a tip with a configuration which allows lifting out bysimplevertical pulling sincethelinkwould be pulledfrom the hook.

Afurther disadvantage occurs when a standard link or ring is used to engage a hook of standard contour in that should a rope breakandthe linkor ring fall to a position at the bottom ofthe hook, removal of the link by a retrieval line attached to it becomes aimost impossible whatever point of attachment is used.

An object of the present invention is to avoid the above disadvantage, and allow normal stowage of the mooring rope at the upper deck while the lower end of the mooring rope remains secure in the hook.

It is another object of the present invention to enable a vessel to be moored by the use of resilient rope means extending downwardly from a structure According to the present invention there is provided a mooring system comprising a hook adapted to be attached to a structure, a link adapted to sit in the eye of the hook and to be attached to a mooring rope, guide means having one end adapted to be attached to the structure above the hook and the other end adapted to be located rearwardly ofthe eye, retrieval means having one end attached to the linkand the other end slidable upwardly along the guide means when an upward pull is exerted on the retrieval means to cause the linkto be pulled out rearwardlyfrom the eye, the forward region of the eye extending rearwardly of the hookto allow the mooring rope to be upwardly inclined without the link being pulled over said region ofthe eye, and there being provided means to prevent the link rotating in the eye of the hook beyond a predetermined point towards the underside ofthe hook.

The means to prevent the link rotating beyond the predetermined point may comprise a front surface of the hook, which surface is inclined upwardly towards the rear ofthe hook and a bar extending across the link, the predetermined point being that at which the bar of the link engages the inclined surface of the hook.

When loading the link into the hook, this front surface,which mayextendabovetheeyeofthe hook, may co-operate with the front and/or bar surfaces ofthe linkto guide the rearofthe linkinto the eye ofthe hook.

The hook may comprise an upwardly facing surface which extends from the base of the eye towards the rear of the hook and which is upwardly inclined towards the rear of the hook. The link may be provided at its outer end region with means to at least reduce longitudinal sliding friction between a resilient rope when connected between a moored vessel and the structure ata portion above the hook and when the length of rope above the hook is substantially horizontal. When such a system is used for the mooring of a vessel, the link is inclined substantially above the horizontal and the upward component of the pull on the link must not cause the linkto disengage from the hook.

Preferably the means to at least reduce the friction comprises a roller.

The forward region of the eye may comprise a surface which faces the surface extending from the lower side of the eye and which is inclined in generally the same direction.

The link may comprise an elongate ring having two facing parallel straight sides joined at each end by a semi-circular portion.

In an adaptation suited for close-in mooring of vessels (when sufficient resilience cannot be provided in the short distance from the platform leg to vessel bollard and musttherefore be provided in the vertical length from link to the top of the platform leg orfirstdeck) an outer portion ofthe linkmay comprise roller means to enable rope movement without chafing.

The bar may extend between the straight sides.

The guide means may comprise at least one wire to be attached to the platform between the deck and the rearofthe hookorthe leg of the platform adjacentthe rear of the hook or between the deck and a structure adjacent the rear of the hook.

The retrieval means may comprise a wire having one end attached to a ring which is free to slide along the guide means, the ring being attached to the link by means of a line.

The present invention will now be more particularly described by way of example and with reference to the accompanying drawing in which: Figure 1 shows a side view of an embodiment of a mooring system according to the present invention, Figure2 shows a plan view of a hook and link of the system shown in Figure 1, Figure 3 shows a side view of another embodiment of a mooring system according to the present invention, Figure 4shows a front view of the embodiment shown in Figure 3, Figure 5shows a side view ofthe mooring system shown in Figure 1 in which a resilient mooring rope extends downwardly from a deck an offshore platform, and Figure 6shows a plan view of the link used in the embodiment shown in Figure 5.

Referring to the accompanying drawing, Figure 1 shows a leg 1 of an offshore platform. Mountedto the leg 1 is the rear2 of a hook3. The hook is inthe form of a solid body and has an eye4,afrontsurface 5which is upwardly inclined towards the rear ofthe hook,-a surface 6 which extends from the eye 4 and which is also upwardly inclined towards the rear of the hook and a forward region in the form of a tip7 which comprises a surface 8 generally parallel to the surface 6. The eye has a surface 9 between the surfaces 6 and 8, which is generally circular in cross-section.

Hooked around the eye 4 is a link in the form of an elongate ring 10 having two parallel sides 11 joined at each end by a semi-circular portion 12 (Figure 2).

Extending between each side 11 is a bar 13. Attached to that partofthe ring 10 hooked around the eye 4 is one end of a strop 14. The opposite end ofthestrop 14 is attached to a circular ring 15through which extends a pair of taut guide wires 16. The lower end of the guide wires 16 is attached to the rear of the hook 3 and the upper end to the deck region ofthe platform. Attached to the ring 15 is the lower end of a retrieval wire 17, the upper end of which is alsd attached to the deckofthe platform orto awinch on the deck. Attached to the semi-circular portion 12 of the ring 10 opposite that hooked around the eye 4 is a mooring rope (not shown) which extends to a vessel moored to the platform.

To lower the mooring rope for attachment to a vessel, the mooring rope and the retrieval wire 17 are lowered simultaneously from the deck. The retrieval wire 17 can be lowered manually or by means of a winch and the mooring rope by a platform crane situated on the deck and connected to the portion 12 of the ring 10 attached to the mooring rope so keeping the ring 10 generally horizontal, or at least the portion 12 connected to the mooring rope above the opposite portion 12 of the ring 10.

Should the ring 10 be inclining downwards during loading due for example to excessive lowering ofthe mooring rope, the front ofthe ring 10 and the bar 13 across the parallel sides 11 ofthe ring 10 slide down the surface 5 while the rearend ofthe ring 10 is held backwards by the wire 14 such that the rear end of the ring 10 enters the opening ofthe hookandfalls intotheeye4ofthehook3.

Afterthe opposite portion 12 ofthe ring 10 falls on to the inclined surface 6 of the hookthe ring 10 slides down the surface 6 into the eye 4 ofthe hook 3.

Should a mooring rope break the remains ofthe old rope attaching to the linkwill need to be removed and a new rope fitted. In such event, the outer end of the ring 10 will fall only until the bar 11 contactsthe surfaceS. To retrieve the ring 10 in such an eventthe retrieval wire 17 is pulled upwards raising the ring 15 on the guide wires 16. The ring 15 reacts on the guide wires 16 to apply a line pull on the strop 14 substantially parallel with slope 6 which raises the portion 12 ofthe ring 10 attached to the strop 14 backwardly up to the inclined surface 6 of the hook 1, while the bar 13 of the ring rides up the inclined front surface ofthe hook 3.

The inclination of the surface 5 and the position of the bar 13 across the ring 10 are such thatthe bar 13 does nottouch the surface 5 atthe mooring rope angles applying when the vessel is moored to the hook3.

Should large changes of horizontal angle of pull on the mooring rope be envisaged owing to the vessel being required to move in widely different positions, the rear end of the hook may be hinged to the leg of the platform.

The ring 10 is able to remain in the hook 3 both when a vessel is being moored and when the mooring rope is being stowed on the deck ofthe platform. The ring 10 can, however, be removed from the hook 1 when necessary e.g. for replacement on inspection of the rope, or for safety if storm conditions are expected. Removal ofthe ring 10 is easily achieved because the inclined surface 5 ofthe hook3 and the bar 13 of the ring co-operate to preventthe ring 10 rotating to a position where it hangs vertically down from the hook3.

In another embodimentshown in Figures 3 and 4 two guide wires 20 are used which are reaved at 21 to either side ofthe hook3 to the rear of and below its eye 4.

Aring 22 runsoversuch guidewire 20andis connected by a strop 23 to the semi-circular portion 12 ofthe link (one each side) adjacent the region where the link 10 engages the eye 4. This means of attachment to the strops 23 is advantageous because it is awayfrom the bearing surface ofthe link 10 in the hook. Both rings 22 are connected to a common retrieval line 17 which serves to centralize the link 10 when engaging and disengaging the linklOfrom the hook.

Figures 5 and 6 showa system forclose-in moorings in which a link 50 incorporates at its outer end a roller.

A resilient rope 52 is attached to the underside of the upper deck 53 of a platform buy a pin 54, the lower end of the rope 52 is joined to a fiexible wire 54which contacts the roller 51 to change its direction from substantially vertical to substantially horizontal and the end 55 of the wire 54 connects with a mooring rope 56 attached to the vessel (not shown).

The angular position of the link 50 with tension in the mooring rope is therefore substantially at 45' from horizontal. The link has no tendency to be lifted out of the eye of the hook 3 in spite of the vertical componentbecausetheupperarcofthehook3 continues round to a substantially horizontal angle.

Withdrawal ofthe link 10 from the hook3 by pulling backwards enables this full circle of the eye 3 to almost horizontal to be used.

Claims (12)

1. A mooring system comprising a hook adapted to be attached to a structure, a linkadaptedto sitin the eye ofthe hook and to be attached to a mooring rope, guide means having one end adapted to be attached to the structure above the hook and the other end adapted to be located rearwardlyofthe eye, retrieval means having one end attached to the linkand the other end slidable upwardly along the guide means when an upward pull is exerted on the retrieval means to cause the linkto be pulled out rearwardly from the eye, the forward region ofthe eye extending rearwardly of the hookto allow the mooring rope to be upwardly inclined without the link being pulled over said region ofthe eye, and there being provided means to prevent the link rotating in the eye ofthe hook beyond a predetermined point towards the underside of the hook.

2. A system as claimed in claim 1,wherein the means to prevent the link rotating beyond the predetermined point comprises a front surface ofthe hook, which surface is inclined upwardly towards the rearofthe hookand a bar extending acrossthe link, the predetermined point being that at which the bar of the link engages the inclined surface ofthe hook.

3. Asystem as claimed in claim 1 or claim 2, wherein the hook comprises an upwardly facing surface which extends from the base of the eye towards the rear of the hook and which is upwardly inclined towards the rear of the hook.

4. A system as claimed in any one ofthe preceding claims wherein the link is provided at its outer end region with means to at least reduce longitudinal sliding friction between a resilient rope when connected between a moored vessel and the structure at a portion above the hook and when the length of rope above the hook is substantially horizontal.

5. A system as claimed in claim 4, wherein the means to at least reduce the friction comprises a roller.

6. A system as claimed in any one ofthe preceding claims, wherein the forward region of the eye comprises a surface which faces the surface extending from the lower side ofthe eye and which is inclined in generallythe same direction.

7. A system as claimed in any one of the preceding claims, wherein the link comprises an elongate ring having two facing parallel straight sides joined at each end by a semi-circular portion.

8. A system as claimed in claim 7, wherein the bar extends between the straight sides.

9. Asystemasclaimedin anyoneofthe preceding claims wherein an outer portion ofthe link comprises roller means to enable rope movement without chafing.

10. Asystemasclaimed in any one of the preceding claims, wherein the guide means comprises at least one wire to be attached to the platform between the deck and the rear of the hook orthe leg of the platform adjacentthe rearofthe hook or between the deck and a structure adjacent the rear of the hook.

11. Asystem as claimed in anyone ofthe preceding claims, wherein the retrieval means comprises a wire having one end attached to a ring which is free to slide along the guide means, the ring being attached to the link by means of a line.

12. A mooring system substantially as herein before described with reference to Figures 1 and 2 or Figures 3 and 4or Figures Sand 6 ofthe accompanying drawings.