Wind Farm Operational Considerations: Most cable must be laid under a minimum tension to prevent the cable from “hockling” – forming a loop under torsion when there is insufficient tension. Cable must be laid though a plough under tension, this can cause suspensions, especially at the towers where the cable exits the J-tube. Cable under tension here cannot be buried later. It is preferable to lay the cable with slack and PLIB it afterwards.
Controlling the plow operations within a wind farm can be challenging. In addition to the plough tow cable and product cable, there is also a plow umbilical cable. If this is an armored cable, it also requires floats with extra people to put them on and take them off. All these moving parts are difficult to control especially in high currents usually found at OWFs. Alternatively, a trenching ROV will usually have it’s umbilical integral to the lifting cable requiring only one cable to manage during operations and less people required for operations.
Over the course of a project, it is difficult to avoid some periodic recovery of underwater equipment for maintenance or adjustment purposes. If a plough needs to be recovered between towers, it will leave exposed cable or else the entire cable section may need to be recovered and ploughed in again, starting all over, requiring more time cable handling personnel. Any “plough-ups” or anomalies not corrected at the time will require PLIB by a trenching ROV.
A trenching ROV, on the other hand, can be quickly recovered – usually by a single man if needed. This makes it easier to repair or adjust nozzles or jetting arms in mid-operations. The arms of a jetting trencher do not need to be “loaded”. The product cable can then be re-captured by lining up and lowering the jetting arms around the cable.
It’s probable that every wind farm plough job will need some form of PLIB to remedy these unburied situations. Exposed cable, slack, bends and loops are best buried with a jetting ROV while a mechanical cutting ROV would introduce too much risk of damaging the cable.