The challenging nature of subsea operations means that load handling cannot always be undertaken by cranes, and in these circumstances the only alternative are module-handling systems of the type pioneered by Hydramarine, and now offered by MacGREGOR’s Offshore division. The module handling system’s great advantage is that it can undertake the kind of guided load handling that a crane cannot, thus eliminating many of the risks of non-guided lifts.
The system designed for Edda Fauna is a fully integrated system where the load carrying structures are part of the vessel structure and even skid beams are fully integrated into the vessel’s deck. The advantages with this solution compared with a ‘modularised add on’ system are a better working environment, more space and better overall safety under all operation conditions. The entire tower system is in this case located inside a large heated work hangar and the system is well suited for arctic operations.
Precise load-handling is critical when mating subsea units on the seabed, and precision becomes even more critical in rough seas or bad weather, so MacGREGOR’s Offshore division has used its experience in offshore cranes and winches to develop solutions that can compensate for the movement of suspended loads in harsh conditions. MacGREGOR’s Offshore division is one of the leading suppliers of subsea cranes and load-handling systems for the offshore market, and specializes in systems that are tailor-made to suit individual customer requirements, including a range of flexible moonpool-based module-handling systems incorporating deck skid systems with pallets and push/pull units, cursor system and moonpool doors.
Such a module handling system has been installed on a Skipsteknisk-designed ST255L inspection, maintenance and repair (IMR) vessel, Edda Fauna, which Aker Yards Brattvåg delivered to Norwegian operator Østensjø Rederi in February. The vessel has been long-term chartered by IMR specialist DeepOcean ASA and will work for Statoil in the North Sea.
Specially designed for operation in northern waters and with a high focus on excellent maneuverability and station-keeping capabilities, Edda Fauna’s capabilities include:
* ROT (‘remotely operated tool’) operations using its module handling system
* Inspection and ROV (‘remotely operated vehicle’) operations
* Light construction works
* Scale squeeze and pumping operations
* RFO (‘ready for operation’) work.
Edda Fauna can handle modules of up to 60 tons with dimensions of 6m x 6m x 8m to a maximum depth of 2,000m in sea states with significant wave heights of up to 5m. The system consists of a rail skid arrangement on the main deck for horizontal transportation of loads, and a cursor system, liftline and guideline winches for vertical transportation through the ship’s moonpools. Horizontal movement of modules is achieved by sliding pallets which are moved by hydraulic tractors or ‘pushers.’ The module handling system has four different types of pallets with their own tractors: a 60 ton pallet, two different sizes of 30-ton pallets, and a 3-ton/10m crane pallet.
The 7.2m x 7.2m main moonpool is amidships. It has hatches, guiding cursor and active heave-compensated winch system for vertical movements. The main moonpool is also fitted with four active heave-compensated guideline winches to guide the modules from deck level, and the system has a separate active heave-compensated liftline winch.
The two smaller 4.8m x 4.8m moonpools are in the ROV hangar, and can each handle a work-class ROV. To the port side of the hangar an A-frame is located for vertical handling of an observation-class ROV.
The Hydramarine electric driven, active heave compensated ROV umbilical winches and Guide Line Winches greatly improve the performance in many ways. First of all, the simplicity and reduced number of critical components increase the overall system reliability. Accuracy in position and force control are at highest level and adjustments possible with exceptional performance. Comfort onboard vessel is improved as the electrical winches have a very low noise and vibration level. There are no requirements for high performance HPU system and advanced critical servo valves, which often are a source for vibration, noise and technical problems. The risk for oil spillage is eliminated improving the vessels environmental factor.
MacGREGOR’s Offshore division designs and manufactures a wide range of load-handling and intervention technology that meets the needs of the market for offshore support and related vessels such as construction and subsea intervention types. The company also offers a complete range of active heave-compensated winches. These are equipped with complete power and control systems, resulting in equipment that is flexible and easily mobilized. Conventional over-side load-handling systems remain in demand, and MacGREGOR’s Offshore division has a range of over-side systems, either as A-frames or standard/special cranes, in its delivery program. Combined with its active heave-compensated winches and pendulum dampened systems, these systems are the standard for many remotely operated vehicle (ROV) operations.
Complete load-handling package
MacGREGOR’s Offshore division is the only supplier able to deliver complete shipset equipment packages for subsea intervention vessels, and its package for Edda Fauna includes:
* a complete 60-tonne module handling system, fully integrated into the vessel
* active heave-compensated main offshore crane
maximum lift, single fall: 130 tons at 15m
depth main hook: 2,000m
maximum outreach: 25 tons at 35m
auxiliary hook: 10 tons at 37m depth auxiliary hook: 1,000m
* a 3.2-tonne fast rescue craft (FRC) davit system
* two heavy-work-class ROV handling systems for moonpool operations
* an over-side observation-class ROV handling system.