III. METODOLOGÍA
3.5. Procedimientos
A wide variety of anchors are used in mooring rigs and barges offshore. An ideal anchor shall have the following characteristics:
i. High holding power in varying soil conditions.
ii. Possess good stability in its buried position and when it is dragged through the seabed when tensioning.
iii. Capability to quickly engage and penetrate the seabed upon dropping.
iv. Have a low breaking out force.
v. Lightweight and easy to handle.
vi. Not prone to being damaged or causing damage to anchor handling vessels.
vii. Must have no moving parts, which may be clogged or jammed in operation. Anchors fitted on the barge/rig must be of the type and size mentioned in the specifications.
The 'FLIPPER DELTA' type is most commonly used in our operations. They
have been found to be efficient and reliable,
and therefore highly recommended. High holding power anchors e.g. Stevpris and Bruce anchors are acceptable.
All anchors must be fitted with a chain pigtail (about 4 meter long) at the crown end. This is to provide for safer handling and avoid chafing of pennant wire, which commonly occurs if they are fitted directly to the anchor.
Some anchors, e.g. FLIPPER DELTA and STEVIN, have a provision for changing fluke angles to suit the soil conditions. This provision shall be made use where necessary.
7.8.1 Piggy – Back Anchor
A back-up anchor, which is connected to and laid in line with the main anchor, is referred to as a piggyback anchor. The distance between the main and the piggyback anchor is determined by the pennant wire length (water depth + 25metres) but should not be less than 45metres.
To effectively lay a piggyback anchor, the intermediate pennant must be well stretched and the anchor must be laid in the same direction as the main anchor.
Piggyback anchors may be required under one or a combination of the following circumstances.
i. Where the seabed condition offers poor anchor holding ground.
ii. Where prerequisites tension cannot be achieved within a reasonable time.
iii. Where there is insufficient ground wire owing to limited anchor wire length or anchor pattern being restricted by pipelines or structures
Since lying of piggyback anchors is time consuming and requires additional equipment, the practice should be discouraged and carried out only as a last resort.
The use of high efficiency anchors, like the 'Flipper Delta', will minimize the need for piggybacks. Despite their high initial cost, experience has shown that these high efficiency anchors are beneficial on the long run.
When preparing for a rig or barge move, the need for piggyback anchors shall be considered so that prior arrangements can be made to acquire and transport the additional anchors and fittings to the location.
In laying piggyback anchors the requirements for anchoring in pipeline areas shall be complied with.
Figure 7.1 Piggy Back Anchor 7.9 PENNANT WIRES
Pennants wires are used for laying and retrieving the anchor.
Pennant wire used shall be similar in size and type to the anchor wires. Occasionally where the anchor wire is small (e.g. 1-1/4 inch) then a slightly bigger pennant wire (e.g. 1-1/2 inch) may be used. This is because the wear on the pennant is usually greater than that of the anchor wire. If the anchor digs down deeply into the seabed, it is recommended to use bigger pennant wires to avoid losing the deeply penetrated anchor.
The length of the pennant wire varies with water depth, expected anchor penetration, tide and sea conditions, and type of anchor handling tug. As a practice pennant length for crucifix type buoy shall be water depth + 15 meter for hard sea bed and water depth + 30 meter for soft mud conditions.
Pennant wire arrangement depends on the type of anchor buoy. For a suitcase type buoys the pennant consist of a single length of wire. The main disadvantage of this
system is the need to constantly change out the pennants to suit the locality. For a crucifix type buoy the pennant may consist of a combination of different lengths.
Then it is only a matter of putting together the correct length with minimum joints.
Pennant ends shall be fitted with Gold Nose wire termination. For the suitcase buoy arrangement, the buoy end may be spliced. In order to avoid excessive load at this end, sufficient turns should be taken up on the work drum of the anchor handling tug before lifting the anchor.
When a barge/rig is on tow it is important that the pennants are properly hung off or stowed.
7.10 ANCHOR BUOYS
Anchor buoys serve to hold the pennant wire and as a marker for the anchor position. They come in varying shapes and sizes. An ideal anchor buoy shall have the following characteristics:
1) Required Buoyancy - this is directly related to the weight of the pennant. There should be sufficient reserve buoyancy to ensure that the buoy is always visible above the water.
2) A good balance to keep the buoy upright.
3) Consist of several compartments.
4) Foam filled.
5) Have rounded corners with minimal sharp edges.
6) Have flat sides for better stability when placed on anchor handler deck.
7) Connected to anchor by pennant wire of suitable size and length. The length of pennant wire should be equivalent to the water depth plus maximum of 20m.
8) Be painted with highly visible and luminous colour.
7.10.1 Crucifix Type Buoy
This type of buoy is used commonly on rigs and maintenance barges. The advantages of this system are:
No need for a complete change out of pennant in varying water depths.
Piggyback anchors can be laid without having to change the pennant system.
No chafing of pennant with the buoy as in the case of the suitcase type buoys.
Convenient for bringing anchor on the anchor handler deck.
Figure 7.2 Crucifix Buoy
7.10.2 Suitcase Type Buoy
This type of buoy is commonly used on installation, pipe-lay and construction barges, which move frequently. With this type of buoy, anchor-handling operation is much faster and work on the anchor handler tug is minimized.
However it lacks the advantages of the crucifix type buoy.
Another disadvantage of this system is that most of the joints and fittings remain underwater during anchor handling. It is therefore important that the whole anchor / pennant / buoy system be lifted on the barge for inspection regularly
Figure 7.3 Suitcase Buoy
7.11 SPRING BUOY
Spring Buoys are buoys that are connected to anchor wires for the purpose of giving the latter a vertical lift. They are used when there is insufficient vertical clearance between pipelines and anchor wires crossing them
Figure 7.4 Spring Buoy
7.12 BUOY CATCHER
Buoy catchers are used to retrieve anchor pennant buoys. The buoy catcher sling is attached to a tugger winch on deck to enable it to pull the buoy clear of the water.
The recommended assembly for the buoy catcher sling should consist of the following:
1. One x 2 feet x 1/2 inch diameter chain 2. Two x 20 feet x 3 inch circumference wire 3. One connecting ring
All buoy catcher slings shall be colour coded in accordance with the Company's procedure for the registration, inspection and maintenance of slings and lifting tackle.
Figure 7.5 Buoy Catcher
7.13 OTHER FITTINGS
The various connections between wires, chain, pennants and buoys shall have a compatible Safe Working Load (SWL) with the items they connect. Suitably sized shackles / Baldt links should be used to ensure slightly loose fitting for ease of connecting and disconnecting.
Drilling tenders and work barges, which remain in position for a period of more than 6 months, shall use Baldt links for connections. Proper split pins shall be used and sufficient spares are made available during anchor handling operations.
Shackles must be Safety Type Shackles i.e. with hexagon head pin, nut and split pin.
Figure 7.6 Baldt Link and Safety Shackles
8.0 ANCHOR PATTERN
8.1 DRAWING OF ANCHOR PATTERN
In drawing anchor patterns, the following procedures shall apply:
i. Draw on an updated 1:5,000 scale survey chart. The 1:10,000 scale charts shall only be used if the 1:5,000 scale charts is not available for the field. If other barges are in the field, or are expected to be in the field, then the chart used shall show their anchor patterns. The PETRONAS project owner shall ensure that correct charts are given to the contractors. These charts are to be obtained from PETRONAS through Marine Coordinator and relevant parties for International operations ii. Draw to the correct scale.
iii. Show the barge, the anchor position with their numbers, direction and distance from the barge. Additionally distance from obstruction and/or pipelines.
iv. Where anchor cable/s cross pipeline/s, show the touchdown TENSION (kips) at the crossing and the touchdown POINT at 9.1 MT (20kips) and 27.3 MT (60 kips) respectively. (2.2 kips = 1 MT)
8.2 FACTORS TO CONSIDER FOR ANCHOR PATTERN
i. Keep the pattern symmetrical to maintain even load distributions ii. Scope of work of the barge
iii. Barge position - it is recommended to keep to leeward side of the platform, head into predominant swell and/or weather, and crane reach.
iv. Amount of cable required - depends on water depth, nature of the bottom of the site.
v. Gangway positions and access to the platforms.
vi. Expected weather, tide and current.
vii. Time of move and duration of stay.
viii. Helicopter access.
ix. Presence of other barges in vicinity.
x. Minimal use of soft moorings.
xi. Supply vessel and crew boat access.
xii. Comply with the anchoring restrictions requirements specified in Section 9, paragraph 1.
8.3 ANCHOR PATTERN APPROVAL
All vessels that are required to anchor within the vicinity of platform, pipeline or installation shall seek anchor pattern approval from PETRONAS Marine Coordinator or any other assigned person prior to carrying out anchor deployment.
8.3.1 Early Submission of Request
All anchor patterns request shall be submitted well (minimum 14 days prior to mobilisation) in advance to PETRONAS Marine Coordinator to avoid any delays in approval.
8.3.2 Supporting Document
Request shall be submitted with the following supporting documents:
i. Approach to Location ii. Sequence of anchoring iii. Anchor touchdown catenaries iv. Anchor wire size/tension
v. Spring buoy location (parachute/Damage protection buoy) vi. Type of anchor/weight
vii. Anchor handling boats Brake Horse Power (BHP) viii. Working winch capacity/Date last tested
ix. Type of seabed x. Mooring procedures
xi. Contingency Plan/Emergency Pull Out due to a. Adverse Weather
b. Emergency situation on platform
9.0 ANCHOR HANDLING OPERATIONS 9.1 ANCHORING RESTRICTION
1. Positioning of anchor shall conform to the following mandatory distances requirements.
2. Minimum distances shall be met after allowing the anchor to set in until it reach the ultimate holding capacity or after pre tensioning of anchor has been performed.
3. If it is necessary to run an anchor wire over a pipeline/under water telecommunications cables, the anchor wire catenary calculation should be consulted and appropriate anchor support i.e. parachute buoy to be used.
4. In preserving the environment, coral communities shall be avoided. In scattered coral area the following mandatory distance requirement shall also be followed
9.1.1 Anchor Position Crossing Pipeline
i. Distance between anchor and closest pipeline not less than 150m (figure 9.1)
ii. Distance along anchor wire from crossing point of closest pipeline to anchor not less than 220m. ( figure 9.1)
Figure 9.1 Anchor Crossing Pipeline
9.1.2 Anchor Position between Barge and Pipeline
i. Distant between anchor and closest pipeline not less than 100m (figure 8.2)
ii. If water depth more than 100m the distance is equal to depth of the water.
Figure 9.2 Anchor position between barge and pipeline
9.1.3 Anchor Wire Parallel to Pipeline
Distant between anchor and pipeline not less than 150 m (figure 8.2)
9.1.4 Anchor Positioning in the Vicinity of Structures
i. When anchors are positioned in the vicinity of existing marine structures, a minimum of 150m horizontal clearance from the structures shall be maintained. (figure 9.3)
ii. A minimum of 5m shall be provided between anchor wires and any part of a platform or associated structures at all times.
Figure 9.3 Clearances from Structures
9.1.5 Anchor Wires Crossing Existing Pipelines
i. Anchor wires crossing pipelines within the elevated section of the catenary shall at all times maintain a vertical clearance of not less than 5m ( figure 9.4)
Figure 9.4 Vertical Clearances from Pipeline
In the event above requirements cannot be achieved, clarification and approval shall be obtained from the marine Coordinator
9.2 ORIENTATION OF ANCHORS
1. The barge shall be equipped with a minimum number of eight anchors. (During operation, the number of anchor to be deployed shall be subjected to anchor pattern approval).
2. For a self propel vessels that are able to maneuver to avoid endangering the structure in the event of a drift or emergency, a four points mooring is sufficient (including soft moor).
3. The orientation of the anchors relative to barge during operation is determined using the following:
a) The bow anchors provide the main forward pull during barge advances. They will be positioned forward and slightly out from the barge route.
b) The bow breast anchors are for lateral control and for forward pull during barge advances. They will be positioned somewhat further out from the bow anchor.
c) The stern breast anchors are for lateral control of barge stern. They will be positioned only slightly forward from the barge stern.
d) The stern anchors are positioned to bring the barge to a stop forward movement. The orientation of all anchors will be such that adequate back up is provided during anchor re-location.
9.3 CONTINGENCY PROCEDURES
Contingency procedures for every foreseeable anchoring difficulty shall be included as part of the anchoring procedure;
1. For retrieval of anchor when anchor wire has parted.
2. For retrieval of anchor when pennant wire has parted/entanglement.
3. For retrieval of drifting (runaway) pennant buoy.
4. To ensure safe mooring of vessel in bad weather.
5. In the event of anchor (s) drags.
6. For escape in the event of emergency. The barge shall be able to
clear the location of the platform independently.
9.4 EXTENDED HOURS ANCHORING OPERATIONS
1. Ideally anchoring operations is carried out during daylight with 1 set of crew. However it can also be carried out in 24 hrs operation if 2 sets of independent crew are available on board the barge and AHT.
2. For the case of 1 shift crew it is allowed to work a maximum of 16 hrs to avoid fatigue issues. CSR to conduct risk assessment which includes adequacy of lighting and safety of the crew.
3. Should anchoring in non-daylight hours be necessary, the following additional requirements shall apply
The Barge and AHT to be equipped with Barge Management System (BMS), where location of all pipelines is charted and the location of Barge and AHT in relation to the existing pipelines are continuously shown. Anchor handling operation outside 1000m from coordinate of anchor position to the structures/pipelines does not require BMS
Pennant buoys used are large enough to act as radar reflections.
The anchor buoys are continually monitored in reference to the marker buoys or Barge Management System.
9.5 ADVERSE / MARGINAL WEATHER PRECAUTIONS
1. Mooring / anchoring during bad weather is NOT PERMITTED, especially in areas within the vicinity of existing pipelines and platforms. As a guide, weather is considered bad when significant sea / swell is more than 2.5 meters or wind speed is more than 25 knots (This criteria may differ according to different locations where local requirements shall apply)
2. The criteria generally used for determining limiting conditions are the maximum tension allowable in the anchor wires. The rig/barge shall only remain alongside an installation, whilst all the anchor wire tensions are within the acceptable working range.
3. During initial setting up at new location, barges are required to carry out tensioning of anchors. Anchors are pretension in excess of their normal working tensions, to allow for expected environmental loads on the mooring system. When anchor wire tensions begin to approach these pre-tension values, the barge should be in the state of readiness to ensure that she is able to suspend operations and pull out in minimum time required, if the weather continues to deteriorate further.
4. The barge may also pull out of location when the sea conditions begin to limit the type of work operations being carried out, although her sea keeping qualities might not be adversely affected.
5. The Barge Master shall continuously monitor all weather forecasts; sea
state conditions and anchor wire tensions, so that he is able to take prompt action as soon as limiting weather conditions are being approached.
6. Every rig/barge shall have their limiting operating conditions clearly stated in their Operation Manuals. The various stages of „Alert‟ and „Required Action‟
shall also be clear.
9.6 TRANSFERRING ANCHOR FOR RUNNING
All works involving decking/ lowering and connection/ disconnection of anchor from the AHT, AHT vice versa Barge/ work boat/ rig must be carried out at least 100m from pipelines or subsea installation.
i. Crucifix Type Buoy
If the anchor is detached to the anchor wire:
1) The anchor, its pennant wire (secondary and primary) and the buoy are transferred to the AHT by barge crane.
2) Connect secondary pennant wire (length depending on water depth) to the work wire and spool it into the drum. The last set being the primary pennant which will be connected to the anchor at the chain pigtail.
3) Once connected take up the slack on the pennant.
4) The barge then will pass the end of anchor wire and the AHT will pick up by means of tugger wire and align and secure its socket at the shark jaws.
5) Connect the anchor to anchor cable.
6) The AHT takes the anchor on its deck or secure it against the stern roller for running.
If the anchor attached to the anchor wire:
1) The secondary anchor pennant wire (length depending on water depth) and the buoy is transferred to the AHT barge crane.
2) Connect the secondary pennant wire to the work wire and spool them into the drum.
5) The barge will slack away the anchor cable gradually.
6) The AHT/AHTS takes the weight of the anchor.
7) The AHT/AHTS takes the anchor on its deck or secure it against the stern roller for running.
ii. Suitcase Type Buoy
1. The buoy is transferred to AHT/AHTS by using barge crane.
2. The buoy then lowered next to the AHT stern roller. AHT deck crew pick
up the end of the pennant wire and connect it to the work wire.
3. The barge slack away the anchor wire gradually while the AHT crew spool in the pennant wire and takes the weight of the anchor.
4. The AHT takes the anchor on its deck or secure it against the stern roller for running.
Figure 9.5 Transferring Anchor for Running
9.7 RUNNING ANCHOR
1. The AHT will proceed to approved anchor coordinate while maintaining slight tension on the anchor wire so as to ensure no bight is formed on the anchor wire. This is also to ensure the belly of the anchor wire is not being dragged on the seabed especially when subsea facilities are present.
2. Barge should constantly check on the wire tension by means of remote winch tension meter and advise AHT accordingly.
3. Position of the barge is monitored using survey management system i.e. BMS.
Anchor foreman instruct AHT to adjust her course and speed if needed.
Anchor foreman instruct AHT to adjust her course and speed if needed.