A retrofit 3D motion compensator can enhance the precision and flexibility of a wide range of cranes
As vessels and assets age, many are pushed to work at far different specifications than may have been originally envisioned. With advances in new equipment, however, retrofitting is often an economical and practical way of expanding the operational envelope. In that vein, offshore engineering firm MacGregor has developed a 3D motion compensator (3DMC) for offshore cranes. The device can be retrofitted to the company’s crane range – either on vessels or platforms – and is designed to enhance load-handling precision. The result is an increase in the accuracy and flexibility with which the vessel can operate, even in rough seas. MacGregor senior vice president for Technology and R&D, Alexander Nürnberg, explains: “The 3DMC can be fitted to the knuckle jib of a broad spectrum of new or existing MacGregor subsea/offshore cranes. It compensates for the roll, pitch and heave motions of the vessel to minimise any movement of the load in relation to a fixed point in space.” MacGregor explained to InnovOil that the unit is designed with a safe working load (SWL) of 5 tonnes and is designed to compensate for a significant wave height of 4 metres, although this will vary based on the vessel’s stability. While the standard AHC – supplied through a crane’s winch – compensates for a vessel’s vertical movements, more accurate positioning is sometimes required. The 3DMC therefore allows ship-owners to expand the load-handling capabilities of a crane far beyond its original limitations.
Flexible friend According to the company, the unit can be easily installed and integrated into the crane, connecting to the existing hydraulic power unit and control system. So straightforward is this, in fact, that MacGregor suggests that a fleet of vessels could share a one (or a number of) units, equipping them for specific missions whenever necessary. The 3DMC is fully incorporated into the crane's control system, so that all operations are managed from the existing interfaces in the crane cabin. When the user needs to transfer equipment to or from offshore wind turbine structures or fixed platforms, the operator can opt to use the 3DMC. When not required, the 3DMC simply remains fixed to the side of the crane's knuckle jib allowing normal lifting operations using the main and whip winches. The company’s director of Advanced Offshore Solutions and Global Lifecycle Support, Gaute Sjusdal, adds: “This means that the crane and therefore the vessel can be used for more assignments and owners will be able to bid on a wider range of contracts.” At a cost of around 800,000 euros (US$850,000), it seems a fair proposition for increased versatility. Renewables appear to be the target market for the innovation, with a particular focus on using the 3DMC to supply and transfer equipment accurately from vessels to wind turbine platforms. As more supply vessels aim to diversify operations, or at least to split time more evenly between renewables and oil and gas, innovations such as this are likely to have a major impact on working fleets. Indeed, in an emailed reply to InnovOil, the company added: “The reception and interest from the offshore industry has been very good. The benefit of adding specific operation capabilities to existing equipment has a noticeable high appeal to owners.”