MacArtney supplies visionary launch and recovery system
MacArtney’s latest supply to the new Skandi Acergy, one of the world’s best-equipped offshore construction vessels, has brought launch and recovery systems into an entirely new dimension. Two complete twin systems of three harmonised winch arrangements operate work-class ROVs through the vessel's middle, allowing for deployment in heavy seas.
Beating heavy seas
Typically, ROV systems are launched from the aft of a vessel or over one of the sides using Active Heave Compensation winches that allow them to operate in heavy seas. When Acergy acquired the Skandi, they envisioned a system that could go beyond the current limit and designed a launch and recovery system to launch ROVs through a fully automated moon pool system in the centre of the vessel.
Protecting the ROV
Often, the most risky part of an ROV dive is the launch and recovery. Winds and sea swells enormously affect the launch, operation, and recovery of tethered vehicles from a vessel.
In heavy seas, pitch and roll can alter a vehicle's position about the water by many metres in seconds, potentially damaging snatch loads.
Strong winds can also cause unwanted movement of suspended equipment, and very strong winds can even render launching impossible.
Launching the vehicle from the centre of the vessel minimises the effect of sea conditions as the centre is the most stable place regarding both pitch and roll. It also protects from the wind.
This ingenious winch and control system allows ROV launch and operation in sea states far out of the reach of ordinary vessels. Combined with AHC, the launch and recovery system provides the ultimate protection for the ROV during the launch and recovery period. Each twin system installed on the Skandi is designed for sea states equivalent to significant wave heights of 6 metres [Hs 6]. The protected launch and recovery significantly extend the operational window, reducing costly downtime.
A precise and complex system synchronises ROV launch
The system of winches and sheaves used to launch the ROV through the centre of the vessel employs three types of winches that run at different speeds. The control system includes functions such as opening and closing the moon pool doors, automated ROV orientation, and emergency recovery features. Making this design work together as a fully automated system required precise, advanced engineering and project management.
Amazingly simple to operate
This MacArtney-made system synchronises the functions and performance levels of the entire system while integrating a host of non-MacArtney supply features. The easy-to-use interface proves that even complex systems with sophisticated launch and recovery sequences can be user-friendly. Once the parameters have been set on the Graphic User Interface, the fully automated launch and recovery sequences can be set in motion with just a few button presses.
From the initial contact with Acergy, engineers and experts at MacArtney recognised that this system was destined to perform like no other. Months later, the system has been performing excellently, and Acergy is very happy with its performance.
