Over the next five years, more subsea installation work will be performed in deeper water, requiring a new generation of energy-efficient and cost-effective offshore cranes
Forecasts predict that over the next half decade, more subsea tree installations and subsea umbilical, riser and flowline (SURF) work will be performed on average annually in deep waters than has been the case over the previous two decades. This, combined with tighter cost controls and stricter emissions requirements put in place by oil companies, are driving the development of a new generation of energy-efficient offshore cranes.
“What would an offshore lifting and subsea lowering system look like today if we started with a blank sheet of paper?” asks Imeca offshore business development manager Mattijs Faber.
Mr Faber explains that as a whole, the industry has been developing its equipment in an evolutionary manner, making changes in small, incremental steps. “There are good reasons to develop in small steps,” he notes, “but it is also good to ask ourselves at each step, ‘what do we need and what can we do without?’”
As part of the development process for a new offshore subsea crane, Imeca, a unit of Reel SAS, gathered feedback from industry stakeholders, marine contractors, vessel owners, ship designers and shipbuilders on product design and performance, operation and how an offshore crane impacts and integrates with vessel design and construction.
The result from that feedback and several years of development was the Imeca Agilis knuckle-boom crane, unveiled at the Annual Offshore Support Journal Conference, Awards and Exhibition in London in February. While knuckle-boom cranes have been around for a long time, the Agilis offshore crane incorporates several innovations aimed at improving reliability, efficiency, safety and environmental performance.
Designed to be incorporated into a newbuild or retrofitted on an existing vessel, the crane uses fibre rope instead of steel wire rope. Mr Faber says the weight of steel wire consumes 50% of the offshore crane’s safe working load (SWL) at 3,000 m. “This means that in order to place a certain weight at 3,000 m, you need to have a crane of at least twice the capacity of the load. This translates into a larger crane, with more weight and a higher centre of gravity, requiring a vessel with a wider beam and increasing fuel consumption,” he says. “This is a very significant cost driver for a certain capability, both in capex and in opex.”
Since fibre rope is neutrally buoyant in water, it can facilitate large subsea lifts from smaller vessels. Additionally, the low weight and centre of gravity of the Agilis offshore crane reduces the required vessel size further, says Mr Faber. “The Agilis Subsea Crane can deliver its SWL at practically unlimited water depth,” he says.
Agilis has an electric drive and control system for all its winches and slewing. Supercaps are used for peak shaving to reduce the generator load. Additionally, regenerated power from subsea lowering operations is captured and stored in a battery pack or fed back to the vessel grid. “The energy efficiency is considerable,” he says, “but we believe that the Agilis could be a net energy generator for the vessel, instead of a consumer.”
Limited moving parts also make the electric drive system less susceptible to failures and demand lower maintenance requirements.
“Analytics on our equipment are performed and digitisation is used to provide information about the actual condition of parts in the system, predict where and when failures will occur and advise the operator how to avoid a predicted failure,” says Mr Faber.
A high degree of digitisation also enhances the flexibility of the Agilis, allowing remote operation of the crane using an augmented reality environment on the bridge. Other digital safety benefits include motion reference unit real-time information and forward-looking information to predict wave heights and patterns.