Mooring tensioning arrangement and a method for longitudinal cross tension of a mooring system

Abstract

Mooring tensioning arrangement (10) on a vessel (60), comprising a moonpool (20) having a through miming vertical channel with an upper moonpool opening (22) in proximity to a deck (62) of the vessel (60), and a bottom moonpool opening (24) open to surrounding sea (30). A winch (14) is located above the moonpool (20), wherein a first anchor wire pennant (42) runs from the winch (14), over a stern (64) of the vessel (60) and into sea (30), and a second anchor wire pennant (46) runs from the winch (14), through the moonpool (20) and into the sea (30). A wire/chain stopper (18) securing the second anchor wire pennant (46) is placed in the moonpool (20), and the bottom moonpool opening (24) is curved to match bending 0radius and to provide a transition in direction of the second anchor wire pennant (46).

Claims

1. A method for longitudinal cross tension of a mooring system, wherein a vessel comprises: a mooring tensioning arrangement with a moonpool having a through running vertical channel with an upper moonpool opening in proximity to a deck of the vessel, a bottom moonpool opening open to surrounding sea, a winch located above the moonpool, wherein a first anchor wire pennant runs from the winch, over a stern of the vessel and into the sea, and a second anchor wire pennant runs from the winch, through the moonpool and into the sea, and a wire/chain stopper securing lines in the moonpool, wherein the mooring arrangement is centrally placed and in or close to a centerline of the vessel, and wherein said method comprises the steps: connecting the vessel to a first anchor wire using the first anchor wire pennant, said first anchor wire pennant runs from aft of the vessel to the first anchor wire, sailing the vessel to a second anchor wire, while paying out the first anchor wire pennant, lowering a pick-up line through the moonpool of the vessel for connection to the second anchor wire, and pulling the second anchor wire through the moonpool onto the deck of the vessel, connecting the second anchor wire to a second anchor wire pennant, lowering the second anchor wire and the second anchor wire pennant through the moonpool, paying out the second anchor wire pennant to a predetermined length, securing the second anchor wire pennant in the wire/chain stopper in the moonpool, and pulling the vessel to a central location by hauling in the first anchor wire pennant.

2. The method according to claim 1, wherein said method further comprises the step of pulling the vessel in to the central location until desired tension in the anchor wires and/or anchor wire pennants is reached.

3. The method according to claim 1, wherein said method further comprises the step of optionally connecting auxiliary anchor lines to the vessel in a conventional manner.

4. The method according to claim 1, wherein said method further comprises the step of connecting the pick-up line lowered through the moonpool to the second anchor wire using a ROV.

5. The method according to claim 1, wherein said method further comprises the step of connecting the pick-up line lowered through the moonpool to the second anchor wire using a guide rope through the moonpool.

Description

DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, wherein:

(2) FIG. 1 shows a mooring arrangement according to the invention.

(3) FIG. 2 shows a set up for a typical transverse cross tensioning mooring.

(4) FIG. 3 shows a set up for a longitudinal cross tensioning mooring according to the invention.

(5) FIGS. 4-11 show a procedure for performing the longitudinal cross tensioning of a mooring system according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

(6) FIG. 1 shows a mooring tensioning arrangement according to the invention. The mooring tensioning arrangement 10 is placed on a vessel 60, however preferably partly integrated and partly placed on a deck 62 of the vessel 60.

(7) The mooring tensioning arrangement 10 comprises a winch 14 placed on the deck 62 of the vessel 60. A moonpool 20 runs in vertical direction through the hull of the vessel 60, i.e. the moonpool 20 has a through running vertical channel with an upper moonpool opening 22 in proximity to the deck 62 of the vessel 60, and a bottom moonpool bell end 24 open to surrounding sea 30. The bottom bell end 24 of the moonpool 20 can shaped and curved to match bending radius of pennant and mooring system elements.

(8) A first mooring line, such as an anchor wire pennant 42, runs from the winch 14, over a stern 64 of the vessel 60 and into the sea, and a second mooring line, such as an anchor wire pennant 46, runs from the winch 14, through the moonpool 20 and into the sea 30. The winch 14 is equipped with several winch drums, i.e. a first winch drum 14a and a second winch drum 14b. The first anchor wire pennant 42 running over the vessel stern 64 and the second anchor wire pennant 46 running through the moonpool 20 can be wound on a mutual winch drum, 14a or 14b. Alternatively, the second anchor wire pennant 46 running through the moonpool 20 can be wound on the second winch drum 14b, and the first anchor wire pennant 42 running over the vessel stern 64 can be wound on the first winch drum 14a. The references “xx” and “yy” indicates any of the mooring lines, or pick-up line, in case a different configuration is chosen regarding which drum to use.

(9) The mooring lines can be a pennant, wire, rope, chain, anchor wire, anchor wire pennant, or similar, for mooring purposes.

(10) The moonpool 20 also comprises a wire/chain stopper 18 for securing the second anchor wire pennant 46 in the moonpool 20. The wire/chain stopper 18 is preferably arranged to enable inline load transfer into the vessel 60, and makes it possible to avoid additional 90 degrees bend under full tension.

(11) Further, a turning block 16 is placed above the moonpool 20. The turning block 16 can be a roller/sheave arrangement guiding the second anchor wire pennant 46 to the winch 14, in order to lower or haul in the mooring system.

(12) The upper moonpool opening 22 may further be equipped with a hatch 28 to close the deck 62 of the vessel 60, thereby creating an undisturbed cargo deck.

(13) FIG. 2 shows a typical transverse cross tensioning set up, in where a vessel 60′ is at aft connected to two mooring lines, i.e. the first mooring lines 40, 42 on port side and the second mooring lines 46, 44 on starboard side. The vessel 60′ is thus perpendicular to the mooring system. Additional mooring lines 70 can be used.

(14) FIG. 3 shows a longitudinal cross tensioning mooring set up according to the invention. As shown, first mooring lines 40, 42 are (near) longitudinal with the vessel 60 and connected to the aft of the vessel. The second mooring lines 46, 44 are also (near) longitudinal with the vessel 60 and connected through the moonpool 20 to the vessel 60. Additional mooring lines 70 can also be used in this case.

(15) The method for performing the longitudinal cross tensioning mooring according to the invention shall now be described in relation to FIGS. 4-11.

(16) Starting from FIG. 4, the vessel 60 is connecting to a first anchor wire 40 in a conventional way using a first anchor wire pennant 42 (first mooring line) running from aft of the vessel 60. The vessel 60 in FIG. 5 is sailing towards a second anchor wire 44, paying out the first anchor wire pennant 42. In FIG. 6, a pick up wire or line 48 is lowered through the moonpool 20 to connect to the second anchor wire 44.

(17) Connection to the second anchor wire 44 can be established by means of a ROV 50, as shown in FIG. 7, or otherwise.

(18) The second anchor wire 44 is pulled onto deck 62 and can be secured in the wire/chain stopper 18, as shown in FIG. 8. At least the connection shackle is pulled on deck to connect the vessel's pennant wire, i.e. the second anchor wire pennant 46 (second mooring line). The second anchor wire pennant 46 is preferably a chain. Thereafter, as shown in FIG. 9, the second anchor wire 44 is lowered and the vessel's moonpool pennant, i.e. the second anchor wire pennant 46, is paid out to a predetermined length and secured in the wire/chain stopper 18. The second anchor wire pennant 46 can then be disconnected from the winch 14.

(19) As shown in FIG. 10, the vessel 60 is thereafter pulled to a desired center location by hauling in the first anchor wire pennant 42 and pulled in until test or desired tension is reached.

(20) FIG. 11 shows that after bedding, the tension is released from the first anchor wire 40 and the vessel is sailed to the second anchor wire 44 location where this one is released as well. Hence, the procedure is reversed and both systems are released.