ANCHOR DEPLOYMENT PROCEDURE
Anchor and Mooring Line Installation
AHTS will sail to Field with all mooring system equipment and installation equipment on-board for the pre-lay of the anchors.
Anchor Deployment
AHTS sails to the drop anchor point, and then slowly pays out the mooring line to drop the anchor into the target box.Target box is a small area around target point where anchors are supposed to be installed.
Mooring Line Deployment and Pull Test
AHTS sails forward and deploy the mooring line along the designed corridor. After mooring chain and mooring wire are deployed, connect the towing wire to mooring wire and continue sailing forward to pay out the towing wire to a sufficient length for pull test.Perform the pull test with the required amount for line out. Tension in the mooring line is brought to 40% of the design load and shall be holded for some time. Then tension shall be increased to design load and and to be held for 20minutes.
Pennant Wire Deployment and Abandonment
After pull test, AHTS recovers the towing wire, and then continues paying out the chain and pennant wire. The installation of first line is completed after abandoning the marker buoy and Norwegian buoy into water.
Contingency Procedures
Anchor Dragging
If the anchor drag is significant, the anchor shall be recovered and dropped again. New drop location and target boxed are shifted 10m side-way from the initial drop position. The overall installation procedures are unchanged. Excess of dragging may be caused as well by an incorrect anchor fluke angle. The fluke angle may be changed if necessary.
Chain Twist
Chain twisting shall be avoided and swivel forerunner can be used in between the chain and the wire.
Loss of Marker Buoy
AHTS uses the grapnel to catch the mooring chain or mooring wire.Once recovered, the mooring lines and chains are recovered on deck or in chain lockers and AHTS drums.
Existing Platforms,Existing Jacket,Pipelines and other existing vessels shall be considered while anchor and mooring line laying.
The drilling vessels or other production vessel in the vicinity during the anchor deployment its 8-own mooring system, which limits the mooring line deployment.
Equipment Storage and AHTS Deck Lay-out
Equipment for the anchor and mooring line installation normally requires Anchors, Marker Buoys, Norwegian Buoys,chain segments, swivels ,PP rope,Mooring Chains, Steel wires.
Bulky equipment (anchors, penant buoys, short chains, swivels, PP rope and Norwegian buoys) shall be stored on deck.Mooring Chains shall be stored in the AHTS chain lockers or on the deck based on space requirement. The volume of each chain segment shall be estimated to know required chain locker volume.Steel wires and pennant wires shall be stored on the Anchor Handling Drum, and/or on the storage drum if available.The wires will be inter connected with shackles, which shall be fitted on the wires.After storage length computation extra chain shall be stored on deck.
Installation Sequence
If cable length for the different mooring lines are different and there are presence of other moored vessel on site during, the installation sequence shall be pre decided. When mooring wires are wrapped on AHTS drums, it come out in reverse order and therefore the installation sequence must be followed.
Anchor Deployment Location
Anchor deployment location shall be made within a box of 10m long (+/-5m) and 10m wide (+/- 5.0m):- +/- 5.0m in line with the mooring line is defined to ensure a minimum drop precision before dragging the anchor and exceeding the allowable drag length.- +/- 5.0m transverse to the mooring line is leading to a variation in the final mooring line bearing angle of less than +/-0.3 deg. Such small variation of angle in mooring line heading is deemed negligible.
Mooring Line Installation Path
Mooring line shall be laid in a limit around the targeted path, in order to avoid incorrect pretensioning during hook-up.
Final Anchor Location and drag length
In any case, the anchors must not drag more than limit values from their drop position target boxes.The minimum anchor radius should be kept for each line, as well as allowable drag length:
Any anchor dragging exceed the maximum allowable (leading the anchor radius less than minimum required) can be considered improperly deployed and shall be redeployed.
Pull Test
Pull Test Tension for Drag Anchors
Anchors shall be pull-tested at 80% of the maximum intact design load for 15min, as recommended in API RP 2SK. In addition, the test tension applied to the system shall be kept during 15min above this load. A tension of 25% of the maximum intact design load (horizontal tension) is first applied and once stabilized it must be kept for 10min to confirm anchor is digging in the mud. Then, the tension is increased to 80% and maintained for 15min once stabilized (anchor will drag a bit more).
Stern Roller to Anchor Distance during Pull Test
Pull test is performed after all the chain, plus all the wire of single mooring line and an extra towing wire are paid out of the stern roller.This extra length is used to ensure no uplift at the anchor during pull test. Position of the anchor directly from the stern roller shall be computed.During pull test,horizontal distances between the stern roller and the anchor shackle for the two tensions will be different because of different elongation in the system.
Mooring Line and Anchor Recovery
AHTS sails to recover the marker buoy and pennant wire on-board.PP rope shall be disconnected from marker buoy, Connect Anchor handling wire to the pennant wire. AHTS sails backwards towards the anchor and recover the pennant wire, chain and mooring wire on deck.Lock the mooring wire in shark jaw.Disconnect the 15 m chain from both ends.Re-connect the pennant wire to the mooring wire.
AHTS sails backwards while pay-in the pennant and mooring wire, until AHTS stern is above estimated anchor position.
Swivel forerunner is on-board and passed the shark jaw.Lock the mooring chain in the shark jaw.Disconnect swivel forerunner from both ends. AHTS pay-in the anchor chain and breaks out the anchor from mud and bring it onboard. Disconnect the anchor from mooring chain and store it aside.Pay in the mooring chain in the chain locker until the end of mooring chain is close to the windlass.The recovery of one mooring line and anchor is complete. AHT sails to the next buoy location for the recovery of other lines.
Anchor and Mooring Line Installation
AHTS will sail to Field with all mooring system equipment and installation equipment on-board for the pre-lay of the anchors.
- Mobilization
- AHTS deploy and pull test first anchor and mooring line
- AHTS recover working wire on-board, connect the marker buoy and pennant wire, then abandon the mooring line
- Repeat the Step 2&3 above for remaining anchor and mooring lines
- Survey final position of the anchor using survey system
- In case the pull test cannot be done during the deployment due to the existence of drilling vessel ,the alternative installation procedure shall be adopted.
Anchor Deployment
AHTS sails to the drop anchor point, and then slowly pays out the mooring line to drop the anchor into the target box.Target box is a small area around target point where anchors are supposed to be installed.
Mooring Line Deployment and Pull Test
AHTS sails forward and deploy the mooring line along the designed corridor. After mooring chain and mooring wire are deployed, connect the towing wire to mooring wire and continue sailing forward to pay out the towing wire to a sufficient length for pull test.Perform the pull test with the required amount for line out. Tension in the mooring line is brought to 40% of the design load and shall be holded for some time. Then tension shall be increased to design load and and to be held for 20minutes.
Pennant Wire Deployment and Abandonment
After pull test, AHTS recovers the towing wire, and then continues paying out the chain and pennant wire. The installation of first line is completed after abandoning the marker buoy and Norwegian buoy into water.
Contingency Procedures
Anchor Dragging
If the anchor drag is significant, the anchor shall be recovered and dropped again. New drop location and target boxed are shifted 10m side-way from the initial drop position. The overall installation procedures are unchanged. Excess of dragging may be caused as well by an incorrect anchor fluke angle. The fluke angle may be changed if necessary.
Chain Twist
Chain twisting shall be avoided and swivel forerunner can be used in between the chain and the wire.
Loss of Marker Buoy
AHTS uses the grapnel to catch the mooring chain or mooring wire.Once recovered, the mooring lines and chains are recovered on deck or in chain lockers and AHTS drums.
Existing Platforms,Existing Jacket,Pipelines and other existing vessels shall be considered while anchor and mooring line laying.
The drilling vessels or other production vessel in the vicinity during the anchor deployment its 8-own mooring system, which limits the mooring line deployment.
Equipment Storage and AHTS Deck Lay-out
Equipment for the anchor and mooring line installation normally requires Anchors, Marker Buoys, Norwegian Buoys,chain segments, swivels ,PP rope,Mooring Chains, Steel wires.
Bulky equipment (anchors, penant buoys, short chains, swivels, PP rope and Norwegian buoys) shall be stored on deck.Mooring Chains shall be stored in the AHTS chain lockers or on the deck based on space requirement. The volume of each chain segment shall be estimated to know required chain locker volume.Steel wires and pennant wires shall be stored on the Anchor Handling Drum, and/or on the storage drum if available.The wires will be inter connected with shackles, which shall be fitted on the wires.After storage length computation extra chain shall be stored on deck.
Installation Sequence
If cable length for the different mooring lines are different and there are presence of other moored vessel on site during, the installation sequence shall be pre decided. When mooring wires are wrapped on AHTS drums, it come out in reverse order and therefore the installation sequence must be followed.
Anchor Deployment Location
Anchor deployment location shall be made within a box of 10m long (+/-5m) and 10m wide (+/- 5.0m):- +/- 5.0m in line with the mooring line is defined to ensure a minimum drop precision before dragging the anchor and exceeding the allowable drag length.- +/- 5.0m transverse to the mooring line is leading to a variation in the final mooring line bearing angle of less than +/-0.3 deg. Such small variation of angle in mooring line heading is deemed negligible.
Mooring Line Installation Path
Mooring line shall be laid in a limit around the targeted path, in order to avoid incorrect pretensioning during hook-up.
Final Anchor Location and drag length
In any case, the anchors must not drag more than limit values from their drop position target boxes.The minimum anchor radius should be kept for each line, as well as allowable drag length:
Any anchor dragging exceed the maximum allowable (leading the anchor radius less than minimum required) can be considered improperly deployed and shall be redeployed.
Pull Test
Pull Test Tension for Drag Anchors
Anchors shall be pull-tested at 80% of the maximum intact design load for 15min, as recommended in API RP 2SK. In addition, the test tension applied to the system shall be kept during 15min above this load. A tension of 25% of the maximum intact design load (horizontal tension) is first applied and once stabilized it must be kept for 10min to confirm anchor is digging in the mud. Then, the tension is increased to 80% and maintained for 15min once stabilized (anchor will drag a bit more).
Stern Roller to Anchor Distance during Pull Test
Pull test is performed after all the chain, plus all the wire of single mooring line and an extra towing wire are paid out of the stern roller.This extra length is used to ensure no uplift at the anchor during pull test. Position of the anchor directly from the stern roller shall be computed.During pull test,horizontal distances between the stern roller and the anchor shackle for the two tensions will be different because of different elongation in the system.
Mooring Line and Anchor Recovery
AHTS sails to recover the marker buoy and pennant wire on-board.PP rope shall be disconnected from marker buoy, Connect Anchor handling wire to the pennant wire. AHTS sails backwards towards the anchor and recover the pennant wire, chain and mooring wire on deck.Lock the mooring wire in shark jaw.Disconnect the 15 m chain from both ends.Re-connect the pennant wire to the mooring wire.
AHTS sails backwards while pay-in the pennant and mooring wire, until AHTS stern is above estimated anchor position.
Swivel forerunner is on-board and passed the shark jaw.Lock the mooring chain in the shark jaw.Disconnect swivel forerunner from both ends. AHTS pay-in the anchor chain and breaks out the anchor from mud and bring it onboard. Disconnect the anchor from mooring chain and store it aside.Pay in the mooring chain in the chain locker until the end of mooring chain is close to the windlass.The recovery of one mooring line and anchor is complete. AHT sails to the next buoy location for the recovery of other lines.