(1) Anchor cables may be wires, chains or wire/chain combinations. Anchor wires offer greater flexibility in anchor handling operations especially in pipeline areas and shallow waters.
It is recommended to use only Regular or Ordinary Lay wires with Independent Wire Rope Core (IWRC). Wires should be galvanised.
Length and size of wires vary with the type and size of the rig/barge, typically the minimum length being 915 metres.
Pipe-lay barges, installation barges, semi-submersible rigs, drill-ships and vessels with self-anchor laying capability usually have longer wires.
The anchor end of the wire shall be fitted with a closed type Spelter Socket or Gold Nose socket. Experience has shown that this type of socket is more robust, easier to handle and can be replaced onboard the barge. It is also specified for the purpose of standardising anchor handling equipment.
The use of bulldog grips for making terminations is not acceptable.
The drum end of the anchor wire shall be connected to the drum in such a manner that it can be released easily in an emergency.
Chains and wire/chain combinations are not commonly used except in semi-submersible rigs and drill-ships. Chains used shall be of Oil Rig quality. In wire/chain combinations a length of chain is fitted to the wire just before the anchor.
This chain serves as part of the ground cable and it enhances the holding power of the anchor.
Towing, Moving and Anchor Handling Guideline WW ALL S 04 012
(1) High holding power in varying soil conditions;
(2) Possess good stability in its buried position and when it is dragged through the seabed when tensioning;
(3) Capability to quickly engage and penetrate the seabed upon dropping;
(4) Have a low breaking out force;
(5) Lightweight and easy to handle;
(6) Not prone to being damaged or causing damage to 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 metres 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.
1.8.1 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 + 25 metres) but should not be less that 45 metres.
To effectively lay a piggyback anchor, the intermediate
Towing, Moving and Anchor Handling Guideline WW ALL S 04 012
Mooring Equipment Rev. 0, April 2012
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PETRONAS CARIGALI SDN BHD
SECTION 6Page 6 Piggyback anchors may be required under one or a combination of the following circumstances:
(1) Where the seabed condition offers poor anchor holding ground;
(2) Where prerequisites tension cannot be achieved within a reasonable time; and
(3) Where there is insufficient ground wire owing to limited anchor wire length or anchor pattern being restricted by pipelines or structures.
Since laying 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 minimise 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 6.1 Piggy Back Anchor
Towing, Moving and Anchor Handling Guideline WW ALL S 04 012
Mooring Equipment Rev. 0, April 2012
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1.8.2 Pennants 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. 1/4 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.
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 metres for hard sea bed and water depth + 30 metres 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.