MacArtney's latest supply to the new Skandi Acergy, one of the world's best equipped offshore construction vessels, brought launch and recovery systems into an entirely new dimension. 2 complete twin systems of 3 harmonised winch arrangements operate work class ROVs through the middle of the vessel, allowing for deployment in very heavy seas.
Beating heavy seas
Normally, 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 that would 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 swell have an enormous effect on the launch, operation and recovery of tethered vehicles from a vessel.
In heavy seas, pitch and roll can alter the position of a vehicle in relation to the water by many metres in seconds, causing 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 in regard to both pitch and roll. It also provides protection from the wind.