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Subsea Global Solutions Exchanges Retractable Thruster on Semi-Submersible Despite Challenges

Case Study

Subsea Global Solutions Exchanges Retractable Thruster on Semi-Submersible Despite Challenges

A valued client contacted Subsea Global Solutions to exchange a retractable azimuthing thruster for its managed semi-submersible rig stationed in the famous Pearl Harbor of Oahu, Hawaii. As Subsea Global Solutions successfully completed similar thruster overhauls with this same rig two times prior, we attended once again to take on the challenge of exchanging the #4 retractable azimuthing stern thruster with limited clearance between the flat bottom of the rig and the ocean seabed. In conjunction with this service, Subsea Global Solutions tackled a full Class UWILD, full Hull Cleaning, and installation/ removal of blanks on all 16 sea chests to ensure the rig was cleared for its dry dock extension.

Solution 1
Subsea Global Solutions mobilized 2 teams composed of 14 expert diver technicians to execute the various projects in less than 35 days from Long Beach, Port Angeles, and Miami. Once our teams were on site, one team began the UWILD, Hull Cleaning, and Sea Chest blanking operations while the other began installing a custom engineered track beam system to the flat bottom of the rig. The track beam system sits perpendicular to the rigs hull and is designed to carry the load of the retractable azimuthing thruster when disconnected from the steering pipe in the retraction column. Since retractable azimuthing thrusters are NOT DESIGNED for underwater demounting this specialized system is required. Additionally, the engineered track beam system allows Subsea Global Solutions to overcome clearance limitations from the flat bottom of the rig to the ocean seabed. The bottom clearance was insufficient for Subsea Global Solutions' standard thruster exchange protocol using buoyancy control solutions. The track beam system leverages a precision-built thruster cradle—which houses the retractable thruster—and is hydraulically driven on the track beam system under the control of our diver technicians. In general terms, this system is a trolly to get the thruster from point “A” (underneath the rigs hull) to point “B” (a picking zone for the crane to safely retrieve the thruster cradle) and vice versa with the overhauled replacement thruster.

All was going to plan when the project suddenly hit a roadblock—the crane could not safely pick the thruster cradle at the intended position as an obstruction from the rig was interfering with the crane booms required picking position—causing a 3’ lead from the center of the thruster cradle. At this position, the crane could only safely achieve a 20-ton load versus the planned load at 23 tons. After review with the various parties involved, it was decided that Subsea Global Solutions needed to incorporate enhanced buoyancy control solutions to float the thruster to a safe picking zone to avoid delays with the project.

Solution 2
Thankfully, Subsea Global Solutions is always prepared for “Plan B” and installed sufficient buoyancy to allow our dive team to safely float the 23 ton thruster cradle to a position for the crane to retrieve with absolute confidence. Subsea Global Solutions proceeded with the remainder of the project using this methodology for the reinstallation of the overhauled replacement thruster.

Subsea Global Solutions adapted and overcame, as we do with all technical repairs that are bound to invite barricades into the planned work scope. The UWILD, Hull Cleaning, and Sea Chest Blanking operations were finished swiftly. The projects were completed in a safe, professional, and efficient fashion 6 days ahead of schedule to ensure our clients’ expectations were met. We thank all of the parties involved in this project for their professionalism and collaboration, it was our honor to have worked alongside your teams.


Tony Lenzi - USNS SBX-1 Port Engineer - TOTE Services, LLC 

"Having worked with several dive companies in my position as a rig project manager, I can say I've easily seen the most consistent performance from Subsea Global Solutions by far.  They perform their work diligently with a level of commitment & respect from the top down.”

Our goal is to always deliver unrivaled service. From hull maintenance to complex ship repair, there is only one global resource you can truly rely on; Subsea Global Solutions.

Learn more about Underwater Exchange of Demountable Thrusters

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