Elodie Plough Recovery
“Briggs Marine employed UTROV on a complex salvage task off the Isle of Skye in 150 meters of water, utilising UTROV with the MFE and other specifically designed tooling. The equipment and particularly the team, worked hard to make this operation a success. The versatility of UTROV and attitude of their personnel ensure that Briggs look forward to working with them on future projects and have full confidence in recommending UTROV to other employers”
“We were very impressed with the teams commitment to get the job done in the pre planning and on-site stages resulting in a successful project. Quick turnaround with design and build of equipment”
Late in 2014 Utility ROV Services were employed by Briggs Marine to provide subsea support for the recovery of a 29t plough that was partially buried in 105 metres of water. When laying cable between the isles of Uist and Harris on the west coast of Scotland the plough had sunk into the seabed, causing the tow wire to break.
Approximately 110 meters of tow wire and umbilical were still attached to the plough potentially hindering attempts to grapple the draw bar.
The plough was to be hooked and lifted, relocating it to a site approximately 3 miles away with a water depth of 20 metres. Here it would be positioned on the sea bed for divers to replace the lifting harness prior to recovery.
The method of recovery initially proposed by the client was to dredge around the plough to reduce the suction action being caused by the mud. It was then proposed that two work class ROV’s would be used to put a large sling around the draw bar hooking this onto a vessel main crane or winch.
This approach would require three full systems, three sets of operators and three mobilisations. Either a very large vessel (to accommodate all three systems) or multiple vessels would be necessary in this situation. It was also uncertain whether work class ROV’s would have the payload capacity to handle a sling cable of transferring the force required to free the plough.
It was when discussing this problem that the advantages of the Utility ROV (UTROV) system became apparent. The adaptability of the system made it possible to quickly engineer solutions for the various problems associated with the project. The fact that the UTROV has the ability to hydraulically and electrically power implements meant that multiple solutions with differing release or grapple mechanisms could be considered.
The Utility ROV Solution
A timber grab was purchased and modified to interface with the UTROV. This was fitted whilst carrying out the survey of the plough to allow the immediate removal of the tow wire and umbilical should it be hindering access to the plough draw bar. This also acted as the means of releasing the buoyant spreader bar.
Upon completion of the survey the MFE was attached and deployed. Two acoustic cameras were fitted onto the UTROV allowing the operator to closely monitor the excavation site at all times.
The mass flow excavation lasted for approximately two hours and during this time mud was cleared from around and on top of the plough.
A two wire grab was designed for latching onto the stranded plough and lifting it without damaging it. This was designed, manufactured, tested and delivered in 10 days. Key factors in the design of the two wire grab were that it would grip hold of the plough without causing damage and that it would be able to release the grab from the plough should the need arise due to deteriorating weather.
The two wire grab (weighing 2.5t) was suspended in the open position from the UTROV using the timber grab to hold a buoyant spreader bar. Once in position the timber grab was released transferring the load onto the main winch wire of the vessel. An additional buoy provided a constant tension on the winch wire preventing the grab from being unintentionally released with the vessel movement in the swell.
The UTROV was recovered to the surfaceand the plough was successfully lifted and repositioned using the ships main winch. Below, the plough can be seen lifted to the surface during re positioning.
The UTROV was deployed again to grip the spreader bar releasing the two wire grab from the plough.
This was a very successful operation all carried out from Briggs Marine’s relatively small (61.2m x 13.5m) anchor handling vessel The Kingdom of Fife, with a crew of 11 and a 4 man UTROV team.
Read more about the operation:
Wind Energy Network Magazine – Issue 26 – March 2015 – Page 54