KenzFigee’s new subsea crane focuses on maximising operability and crew safety and has been designed to use either wire or synthetic rope
KenzFigee vice president sales Sietse Gerssen says the development process for the company’s new subsea knuckle-boom crane began following the delivery of two new knuckle-boom cranes that were built for marine construction company Heerema Marine Contractors. “The unveiling of the new cranes gave KenzFigee an opportunity to showcase the equipment for a number of our subsea clients,” says Mr Gerssen. “The specialist cranes incorporated a number of design innovations, such as wire routing below the jib instead of over it, enabling quick re-reeving over the knuckle and over the main boom.”
KenzFigee surveyed its major clients to better understand the future demands of subsea installation projects. “There seems to be common opinion that requirements will generally exceed 400 tonnes,” says Mr Gerssen. “This meant we had to focus on a scalable concept to cover a full range, exceeding the practical limits of a traditional cylinder-actuated knuckle boom crane.”
“This capacity is easily reached with traditional tower cranes or rope luffing lattice boom cranes,” says Mr Gerssen, “but we had to incorporate industry concerns regarding operability and crew safety. Where most attention in tender specifications is typically focused on meeting the maximum lifting capacity, our discussions focused on the daily challenges, such as operability and safety of crew and these were ultimately captured in two tangible design aspects: hook weight and pendulum length.”
Explains Mr Gerssen: “Looking at the operational profile of a typical subsea vessel, most lifts for a typical subsea crane, whether 600 or 1,000 tonnes SWL, are still within the 50- to 100-tonne range, covering more than 75% of their utilisation, while operating at their maximum SWL covers much less than 5%.”
This understanding resulted in a functional specification in which common lifts were prioritized, while not compromising the crane’s maximum lifting capacity or reach. “This sounds very much like the benefits of a knuckle-boom-type crane,” says Mr Gerssen. “However, scaling up on the traditional knuckle-boom crane design has its limitations, especially for longer boom and jib lengths in combination with large lifting capacities. Our focus was to develop a new generation knuckle-boom crane, combining the best of both worlds: the rope-actuated knuckle-boom crane.”
With an SWL of up to 2,000 tonnes, the rope-actuated knuckle-boom crane range is employed as a rope-luffing box boom crane for its heavy lifts. The boom is relatively short and tailored to handle the maximum load. The jib is stored completely folded within the main boom structure, to avoid obstructing the rigging.
The rope-actuated knuckle-boom crane can be retrofitted onto most existing assets, or designed into newbuilds.
The hoisting winch and active heave compensation (AHC) systems are the heart of a subsea crane. To optimise operability and limit risk to personnel and construction, KenzFigee has focused on improving control over the hook and load as much as possible.
“While being suitable to incorporate synthetic ropes on the crane and AHC geometry,” says Mr Gerssen, “our development has focused on applying commonly accepted technology.” Taking the example of twin crane dual lift operations, he says: “Our design features two main winches and applies proven, widely used and accepted technology.”