AU702007B2

AU702007B2 - A mooring device for a floater

Info

Publication number: AU702007B2
Application number: AU51644/96A
Authority: AU
Inventors: Dag O. Aavitsland; Espen Lange
Original assignee: Kvaerner Engineering AS
Current assignee: Kvaerner Oil and Gas AS
Priority date: 1995-03-24
Filing date: 1996-03-06
Publication date: 1999-02-11
Anticipated expiration: 2016-03-06
Also published as: NO301157B1; GB9719815D0; GB2314541A; WO1996030253A1; GB2314541B; NO951142L; BR9607636A; AU5164496A; NO951142D0

Description

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1 A MOORING DEVICE FOR A FLOATER The invention relates to a mooring device for a floater, comprising a vertical shaft extending from a deck to a bottom of the floater, a socket, rotatable about a vertical axis in said shaft, for a submerged buoy moored by means of mooring cables and adapted for positioning in said socket, said buoy further being adapted to receive one or more risers in the sea, one or more elongated fastening elements extending from the deck down to the buoy, and tensioning means on deck level for pretensioning said one or more fastening elements, said fastening elements having end heads which during the tensioning process bear against retainers on said buoy.

It is known in the art to have a riser in the sea connected to a submerged buoy moored to the seabed, and, when a vessel has manoeuvred to a position above the buoy, to raise the buoy to a socket in the vessel. The buoy is then connected to the socket and the riser is connected to an arrangement of lines aboard the vessel. The socket may be built as a rotational part, a so-called turret, of a vertical shaft in the vessel, but systems are also known wherein the buoy is in two parts, thus having an outer part which may be connected to the vessel, whereas the inner part may be rotated in relation to the outer part. The socket is generally positioned at such a level aboard the vessel that it is completely submerged. Methods are known which make it possible to carry out couplings of the buoy and of the riser in dry chambers.

As typical examples of prior art, reference is made to NO 175,418 and 176,130 which teach various loading/unloading combinations with respect to vessels and buoys whereby buoys, by means of cables and deck-mounted winches, are hauled into a well with which the vessel is provided.

It would be desirable to enable the buoy including the risers to be raised into and lowered out of the socket by means of equipment accessible on deck level.

"Deck level" is here me, to denote the level above the surface of the water.

4~, 2 According to the present invention there is provided a mooring device for a floater, including a vertical shaft extending from a deck to a bottom of the floater, a socket rotatable about a vertical axis in the shaft for a submerged buoy moored by means of mooring cables and adapted for positioning in the socket, the buoy further being adapted to receive one or more risers in the sea, one or more elongated fastening elements extending from the deck down to the buoy, and tensioning means on deck level for pretensioning said one or more fastening elements, the fastening elements having end heads which during the tensioning process bear against retainers on the buoy, wherein the elongated fastening elements and the one or more risers are gathered in an upper tensioning head.

Such a device makes possible the coupling or locking of the buoy to the socket by means of a tensioning process carried out on deck level. When the buoy is 15 to be released, the upper tensioning head may be connected to a winch and further tension applied, whereafter the tensioning means are relaxed and removed. By means of the winch the buoy may then be lowered out of the socket and down into the sea, The buoy will stabilize in the sea, wit its buoyancy acting against the mooring forces. At a further lowering, the 09t* S 20 fastening elements will leave the retainers on the buoy aid sink further down, eoI until their upper ends bear against the retainers of the buoy. The wire used for ••°099 9i lowering may thereafter be released from the winch and connected to a surface 0 ,buoy for marking the submerged moored buoy. The risers are 'ircluded in the above mentioned lowering and retrieval.

It is particularly expedient that the tensioning head be designed for coupling engagement with a winch cable from a winch aboard the floater.

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The tensioning means may advantageously include hydraulic power cylinders or jacks.

It is particularly advantageous that the buoy comprise an upper part designed for fitting into the socket and a lower part extending down into the sea. The mooring cables may advantageously be connected to the buoy by means of rigid bodies.

The invention shall now be explained further by means of reference to the drawings, wherein 0 0 0 0 0 a C

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P IGo 1 15 FIG. 2 FIG. 3 FIG: 4 FIG. 5 FIG. 6 FIG. 7 is a schematic section of a mooring according to the invention, is a schematic section of another embodiment of the invention, in a state of transport, shows the device of Fig. 2 in a fully connected state, shows a step during the lower ing/haul ing of the buoy, shows the buoy in a fully lowered position, respectively ready for hauling in, shows a third embodiment of the invention, fully connected, and shows a detail variant of the embodiment of Fig.

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In Fig. i there is shown a floater 1 having a vertical shaft 2 extending from a deck 3 downward to a bottom 4.

In the vertical shaft 2 there is disposed a rotational part which is rotationally mounted in the shaft 2 about a vertical axis by means of suitable bearings 6, 7 and 8. The rotational part 5 has a part 9, here f ormed as a pipe, extending from the rotational part 5 itself up to deck level 3. The rotational part 5 has further a conical receiving area 10 for receiving a correspondingly conical buoy 11.

WO 96/30253 PCTINO96/00052 4 The buoy 11 is moored in the sea by means of mooring cables 12, 13.

Fastening cables 14 (only one is shown) extend from the buoy 11 up to deck level 3. The fastening cable 14 has a lower end head 15, bearing against a conical retainers 16 on the buoy 11. and an upper head 17, fastened to a tensioning head 18. Only one fastening cable 14 is shown, but in practice a number of fastening cables are used, all being formed in a corresponding manner and engaging with end retainers 16 on the buoy, as well as being secured to the common tensioning head 18.

On top of the pipe 9 there are positioned a number of hydraulic jacks 19, 20, which bear against the bottom side of the tensioning head 18. By means of these hydraulic jacks 19, 20, the tensioning head 18 and thereby the fastening cables 14 can be tightened, whereby the buoy 1 is tightly secured to the conical socket In Figs. 2-5 there is shown an embodiment which in principle is designed like the device in Fig. 1, but somewhat modified by the buoy being provided with an extension down into the sea. In Figs. 3-5 a pertaining riser is also shown. The buoy in the device of Fig. 2 is, like that of Fig. 1, provided with a conical part 11, mounted in a conical socket 10 in a rotational part 5, but, as shown in the drawing, the buoy 11 is designed with an elongated part 21, extending down into the sea. The end retainers 16' for the lower heads 15 of the fastening cables 14 are here mounted at the end of the buoy extension 21. The end heads 15 of the fastening cables are connected by a common regulation ring.

As seen in Fig. 1, the buoy 11,21 is fixedly secured in the socket 10 by means of fastening cables 14, which are tightened by the hydraulic jacks 19, 20 positioned on top, of WO 96/30253 PCT/N096/00052 the pipe 9, said jacks acting against the tensioning head 18 in which the fastening cables 14 are fastened.

In Fig. 2 there is shown a coupling swivel 23 connected to a loading hose 24. The swivel head 23 may be moved and positioned by means of hydraulic power cylinders 25, mounted in a tower 26 upon which a winch 27 is mounted. The winch cable 28 carries a coupling head 29.

The buoy is in Fig. 2 shown in a transport position. The floater or the vessel 1 moves to the field with the buoy 21 tightly secured within the rotational part 5, as shown in Fig. 2. Attached to the buoy 11ii by means of universal joints are rigid, tubular bodies 31, which in a known manner are used for connecting the mooring cables, as shown in Fig. 1 and in Figs. 3-5. In Fig. 2 these rigid bodies are shown in a transport position, pivoted toward the buoy part 21.

When the floater 1 has entered the field, holding the buy tightly secured therein as shown in Fig. 2, mooring cables 12, 13 and a riser 32 are hauled in and connected thereto.

The floater 1 is now moored and the riser 32, which extends to the tensioning head 18, is connected to the swivel head 23. The loading can now take place through the riser 32 and the swivel head 23 and further through the loading hose 24.

When the floater 1 is to leave the field, the buy is released and lowered into the sea,. This is shown particularly in Figs. 4 and The swivel head 23 is released and the coupling head 29, which is suspended from the winch wire 28, is connected to the tensioning head 18. By means of the winch 27, the winch cable 28 is tightened. The hydraulic jacks 19, 20 are loosened and removed. Now the buoy 11ii, 21 may be lowered out of the socket 10, as shown in Fig. 4.

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WO 96/30253 PCTI/NO96/00052 6 The buoy 11, 21 is lowered further down into the sea and will finally stabilize, with its buoyancy acting against the mooring forces. This state is shown in Fig. 5, wherein it is also shown how the lowering is continued, resulting in the fastening cables 14 leaving their respective positions 16' at the bottom of the buoy, so that the tensioning head 18 finally reaches the top of the buy 11 and remains there. Now the wire 28 may be released from the winch 27 and connected to a surface buoy (not shown).

The submerged, moored buoy is now ready for a new retrieval i by a vessel entering the field.

In Fig. 6 there is shown en embodiment of the device according to the invention wherein the buoy has a somewhat different design which allows the use of a greater number of risers. The buy in Fig. 6 is provided with an upper part 11 and a lower part 21' which, unlike the embodiment in Figs. 2is designed as a conical body. The buoy thus consists of two conical sections, one upper section (upper part) 11 and a lower section (lower part) 21'. The buy has a central bore providing space for a number of risers 32, collected in a circular group disposed about a centrally positioned elongated fastening element 14. Instead of being connected to the ring 22 (Figs. the fastening element 14 is here connected to a body 37 which serves to regulate the risers.

Otherwise the device is in principle designed as the device in Figs. 2-5, and the same reference numerals are therefore used for the same or corresponding components. The swivel head 23 comprises in Fig. 6 a manifold, since there are, as noted, a number of risers 32, here ten. In Fig. 7 there is shown a variant wherein the body 37 is replaced by a regulation ring for the risers.

The advantages inherent in the new device according to the invention are primarily that all arrangements demanding supervision and maintenance will be fully accessible at any -e L 1_ WO 96/30253 PCTIN096/00052 7 time. The mooring cables will be fully accessible from the floater by means of lines extending up through guide tubes 36 in respectively the buy 11 and the rotational part Because of its design the buoy will have a greater potential buoyancy, and auxiliary buoys on the mooring cables can therefore be avoided.

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Claims

1. A mooring device for a floater, including a vertical shaft extending from a deck to a bottom of the floater, a socket rotatable about a vertical axis in said shaft for a submerged buoy moored by means of mooring cables and adapted for positioning in said socket, said buoy further being adapted to receive one or more risers in the sea, one or more elongated fastening elements extending from the deck down to the buoy, and tensioning means on deck level for pretensioning said one or more fastening elements, said fastening elements having end heads which during the tensioning process bear against retainers on said buoy, wherein the elongated fastening elements and said one or more risers are gathered in an upper tensioning head. t

2. A device according to claim 1 wherein the tensioning head is designed o S 15 for coupling engagement with a winch cable from a winch aboard the floater, 009,

3. A device according to claim 1 or claim 2 wherein the tensioning means includes hydraulic power cylinders or jacks. o 9. •o 0° 0*

4. A device according to any one of the preceding claims, wherein the buoy includes an upper part for fitting into the socket and a lower part extending down into the sea. 9 A device according to any one of the preceding claims, wherein the mooring cables are connected to the buoy by means of rigid bodies.

6. A device according to any one of the preceding claims, wherein the fastening element(s) is/are connected to a guiding body for said riser(s) by j means of lower end heads. 7 t i iR i U t e *oe 1 o so o o 'l I* j/J< o 9

7. A mooring device for a floater substantially as herein described with reference to any one of the embodiments illustrated in the accompanying drawings. DATED: 11 December, 1998 PHILLIPS ORMONDE FITZPATRICK Attorneys for: KVAERNER ENGINEERING A.S. i/, p',jC~C 9' d nL" I, al au,