In a situation when a rig's conventional catenary mooring system is not sufficient for a proposed water depth, the length of the mooring legs can be increased with the addition of extension wires in each mooring leg. This enhancement extends the length of the mooring legs for the rig, thus allowing the rig to operate in greater water depths.Recovery of the mooring leg is the reverse of the installation. With this enhanced operation, the time required to set or recover the extension wire mooring leg is minimized in extreme water depths with multiple extension wires. This allows two anchor handling vessels to complete this operation.
The process of accomplishing this economical upgrade requires two anchor handling vessels (AHVs). One vessel installs the extension wire onto the mooring leg while the other vessel deploys the mooring leg.
The process begins with one AHV receiving the rig chaser and holding the anchor while the rig deploys chain to a predetermined length. The second AHV catches the mooring chain with a J-lock chaser and brings the mooring chain on deck. The rig chain is taken apart at a designated point and the wire is inserted and connected back to the rig chain. The anchor is then pulled out to the proposed anchor drop point and lowered to the seabed.
The rig tensions the mooring leg to apply the required tension for returning the chaser to the rig. With the exception of inserting additional wire, the mooring operation remains the same as conventional catenary mooring.
Influences from water depth, weather, and rig operation are similar to the conventional catenary mooring operation. Delmar has a large inventory of certified wire available to extend the water depth of any rig.