OA11308A

OA11308A - Double point mooring system.

Info

Publication number: OA11308A
Application number: OA1200000001A
Authority: OA
Inventors: Charles O Etheridge; Martin J Kraft; Brent A Salyer
Original assignee: Fmc Corp
Priority date: 1997-07-08
Filing date: 2000-01-06
Publication date: 2003-10-24
Also published as: AU7984698A; EP0994803A1; WO1999002394A1; CA2293328A1; EP0994803B1; BR9810562A; EP0994803A4; CN1261311A

Abstract

A spread mooring arrangement is provided for use in deep water (greater than 200 meters) when it is advantageous to maximize the clearance between shuttle tankers (20) used for product off loading and the anchor legs associated with a spread mooring of the permanently moored tanker (10). Mooring insert tubes are provided at the bow and stern of the vessel. Bow mooring lines (30) extend from the sea floor through an opening of the bottom of the hull of the vessel and via a bow mooring insert tube (100) for securement on a chain pull-up deck (15). Stern mooring lines (40) extend from the sea floor through an opening in the bottom of the hull of the vessel and via a stern mooring insert tube (120) for securement on a chain pull-up deck (15). Space is available on one side of the vessel for a porch (65) for securement of production risers (70), work over risers and control umbilicals, thereby providing flexibility of the use of the vessel for the circumstance where production methods for the oil field change during its leftime or where other fields need to be coupled to the vessel with risers.

Description

-1- 011308

PATENT APPLICATION 15

TITLE: DOUBLE POINT MOORING SYSTEM

BACKGROUND OF THE INVENTION

Cross Référencé To Related Application

This application daims the priority filing date of U.S. Provisionalapplication 60/051,959 filed 07/08/97.

Field of the Invention 5 This invention relates in general to mooring arrangements for vesseis and in particuiar to a spread mooring arrangement for a permanentiy mooredstorage vessel to which a shuttle tanker is tied up along side during product transfer.

Description of the Prior Art 10 A shuttle tanker tied up beside a permanentiy moored storage tanker needs clearance between its hull and the anchor legs of the storage tanker.

There are many permanent mooring arrangements for storage tankersyet, a possibility exists for shuttle tanker entanglement with anchor legs of thepermanentiy moored vessel, especially if anchor legs are secured mid-waybetween its stem and its bow or if anchor legs are secured mid-way betweenits stem and its bow or if anchor legs extend from the deck via the side of the -2- 011308 vessel.

Identification of Qbjects of the Invention

It is an important objective of the invention to provide a mooringarrangement for permanently mooring a storage tanker in deep water 5 (greater than 200 meters) which substantially prevents the possibility of entanglement of the shuttle tanker with the anchor legs of the storage tanker.

Another object of this invention is to provide a spread mooring at thebow end and the stem end of the vessel to allow large shuttle vessels to betied up alongside the storage vessel in moderate environments for offloading 10 of hydrocarbon product without the potential to entangle the permanently installed anchor legs of the storage vessel,

Another object of this invention is to provide a double point mooringSystem for large vessels to be tied up together in moderate environments foroffloading product from one vessel to another while providing space on the 15 side of the storage vessel for the securement of production risers, work over risers or control umbilicals.

SUMMARY OF THE INVENTION

In shallow water, spread mooring Systems hâve been used. Theanchor legs of such spread mooring Systems hâve normally been deployed 20 from a top deck of the vessel from its sides, bow or stern. Placement of such spread anchor legs is likely to cause entanglement of a shuttle tanker when -3- 011308 it is maneuvered for tying up the side of the storage vessel.

According to the invention, a double spread mooring System is provided, one at the stem, the other at the bow of the storage vessel for deepwater (greater than 200 meters) applications. Such placement of anchor legs 5 away from mid-way between stern and bow provides a certain level of clearance of a shuttle tanker tied up to the side of the storage vessel. Thebow and stern anchor legs enter the vessel not from the deck of the bow orstern or from its sides, but rather from beneath the vessel via a mooringinsert tube through which anchor chains are pulled in from winches on the 10 deck of the vessel. Because the anchor legs approach the vessel from the bottom of its keel, a further level of clearance is provided for deep waterapplications, which substantially insure that a shuttle tanker will not becomeentangled with the anchor legs.

BRIEF DESCRIPTION OF THE DRAWINGS 15 The various objects and advantages of this invention will become apparent to those skilled in the art upon an understanding of the followingdetailed description of the invention, read in light of the accompanyingdrawings which are made a part of this spécification and in which:

In the Drawings: 20 Figure 1 is a plan view of a permanently moored vessel with a double point mooring arrangement according to the invention with a shuttle tanker -4- 011308 tied up along its side;

Figure 2 is a cross sectional view taken along sections fines A-A ofFigure 1 which illustrâtes anchor legs at the stern of the vessel entering amooring insert tube of the vessel; and 5 Figure 3 illustrâtes the mooring insert tube of the mooring arrangement of the invention.

DESCRIPTION OF THE PREFERRED

EMBODIMENT OF THE INVENTION A plan view is presented in Figure 1 of a permanently moored storage10 vessel 10 having a shuttle tanker 20 (shown fully loaded) tied up along its side for loading of product. Rubber fenders 50 protect the vessels fromdamage while being tied to each other. Flexible hoses 60 provide productflow paths from the permanent storage vessel 10 and the shuttle tanker 20.

The storage vessel 10 is moored to the sea bed by a double spread15 mooring arrangement comprising anchor legs 30 at the bow and anchor legs 40 at the stern rather than a single anchor leg pattern connected mid-waybetween bow and stem. The anchor legs are terminated at the sea floor byanchors. Such anchors may be of any of several known types in the art ofmooring Systems. Anchor legs 30 may include lengths of chain and wire or 20 synthetic rope as well known in the art of mooring Systems.

Anchor legs 30 at the bow are secured to vessel 10 by entering at a -5- 011308 bottom end of a bow insert tube 100 which is placed on the longitudinalcenter line of the hull of the vessel and extends from the vessel deck 15 (ora Chain pull-up deck) to the keel of the vessel. Each anchor leg 30 is pulledin and secured to the chain pull-up deck 15 of the vessel 10 by a double 5 drum winch 17. Likewise, anchor legs 40 at the stern are secured to vessel 10 by entering at a bottom end of a stern insert tube 120 which is similar inconstruction to tube 100. Each anchor leg 40 is pulied in and secured to thechain pull-up deck 15 of the vessel 10 by a double drum winch 19. Differentchain pull-up decks may be used under certain circumstances. 10 Figure 2 illustrâtes the two vessels 10 and 20 in a cross-section view along lines A-A of Figure 1. Because-anchor legs 40 enter the insert tube120 from beneath the permanently moored vessel 10, rather than from itsside or the top of its bow or stern, and because the anchor legs 30 and theanchor legs 40 are connected to storage vessel 10 at its bow and stern, not 15 mid-way between bow and stern, the shuttle tanker 20 has sufficient clearance from anchor legs 40 and anchor legs 30 to insure that there will notbe entanglement.

The section view of Figure 2 further illustrâtes a riser porch 65 providedalong the side opposite that to which the shuttle tanker 20 is tied up. Riser 20 porch 65 provides a structure where production risers and contro! umbilicals 70 may be run and secured to the permanently moored vessel 10. Such riserporch 65 may be provided mid-way between stern and bow. -6- 011308

Advantageously, the riser porch placed to the side of the permanentlymoored vessel 10 provides a large area for the combination of risers forproduction, re-injection or control umbificals. This allows great flexibility andadaptability for the installation of such equipment in the event that production 5 methods for the oil field were to change during its lifetime or in the event that adjacent production wells were to be required to be serviced by the vessel 10.

Figure 1 illustrâtes that a large deck space 16 is available forproduction Processing equipment even where two mooring insert tubes 100, 10 120 are provided.

Figure 3 illustrâtes an anchor leg 30 being spooled onto the vessel bya drum winch 17. Each mooring insert tube assembly 100,120 is welded intoan existing tanker 10 structure, typically at an intersection of longitudinal andtransverse bulkheads. The internai diameter of the mooring tubes may be 15 three meters, for example. Typically four anchor legs per tube are provided as illustrated in Figures 1 and 2. This arrangement maintains the integrity ofthe tanks of the vessel and provides a way to introduce mooring loads into the tanker.

The drum winches 17, 19 are preferably double drum winches to

20 facilitate the hook up of the anchor legs 30 or 40 as the case may be. A chain-wire-chain anchor leg arrangement is illustrated in Figure 3, but ofcourse other arrangements may be provided. 011308 -Ί-

Although, the preferred embodiment of the double point mooringarrangement of Figures 1-3 is for a shuttle tanker 20 to be tied up along theside of the permanently moored vessel 10, the arrangement may be used foroffloading Systems at the bow and or stern of the vessel to better faciiitate off 5 ioading. The same advantages of providing large clearance distances between the anchor legs 30,40 and the off Ioading shuttle vessel réservoirs are achieved.

Claims

1. A storage vessel (10) having a huII with mooring arrangementsat a bow end and at a stem end comprising, a bow mooring insert tube (100) disposed in said hull at said bowend, said bow mooring insert tube (100) extending from a bow chain pull-up 5 deck of the vessel to the open sea at a bottom end; a plurality of bow mooring iines (30) extending between said bow chain pull-up deck of the vessel, through the bow mooring insert tube (100) and to the sea floor; a stem mooring insert tube (12) disposed in said hull at said stem end,10 said stern mooring insert tube extending from a stern chain pull-up deck of the vessel to the open sea at a bottom end; and a plurality of stern mooring Iines (40) extending between said stern chain pull-up deck of the vessel through the stern mooring insert tube (120) and to the sea floor.

2. The storage vessel (10) of claim 1 further comprising, a riser porch (60) secured to a first side of said vessel and spaced between said bow mooring insert tube (100) and said stern mooringinsert tube (120), said riser porch (60) arranged and designed for securementto said vessel of risers running between sub sea wells and the vessel. -9- 011308

3. The storage vessel of claim 1 wherein,said risers include production risers.

4. The storage vessel of claim 1 wherein, said risers include work over risers and control umbilicals.

5. The storage vessel (10) of claim 2 further comprising, an offloading vessel, (20) secured to a second side of saidstorage vessel (10) wherein securement of said offloading vessel is placedbetween said bow mooring insert tube (100) and said stern mooring inserttube (120).

6. The storage vessel (10) of claim 1 further comprising, a drum (17) which is mounted on said vessel and is arrangedand designed for pulling in said bow mooring lines (30).

7. The storage vessel (10) of claim 6 further comprising, a drum winch (19) mounted on said vessel and is arranged anddesigned for pulling in said stern mooring lines.

8. A storage vessel (10) characterized by a bow and a stern andfloating on a body of sea water of a certain depth and having a huit with -10- 011308 mooring arrangements at a bow end and at a stern end comprising, a plurality of bow mooring lines coupled to said vessel via a first opening in the bottom of the hull at said bow end of said vessel, said bowmooring fines extending to the sea floor; s a plurality of stern mooring fines coupled to said vessel via a second opening in the bottom of the hull at said stern end of said vessel, saidstern mooring lines extending to the sea floor.

-8- 011308 WHAT IS CLAIMED IS:

9. The storage vessel (10) of cfaim 8 wherein, said first opening is the termination of a bow mooring insert tube Q (100) which extends from a bow chain pull-up deck of the vessel to the open sea at its bottom end; said second opening is the termination of a stern mooring inserttube (120) which extends from a stern chain puli-up deck of the vessel to theopen sea, and wherein; 5 said bow mooring lines (30) extend through said bow mooring insert tube (100) and are secured to said vessel at said bow chain pull-updeck of the vessel; and said stern mooring lines (40) extend through said stem mooringinsert tube (120) and are secured to said vessel at said stern chain pull-up 20 deck of the vessel.