ONS 2016: Cranes deploy braided fiber rope in deepwater
Rolls-Royce has introduced offshore cranes that can install braided fiber ropes in deepwater operations.
The cranes, available in lifting ranges up to 400 tons, are said to offer a key advantage over steel wire cranes, in that they retain their full rated capacity down to maximum working depth.
A wire crane, however, must be de-rated for deepwater installations due to the weight of the steel wire.
At more than 2,500 m (8,202 ft) , a 250-ton fiber rope crane can perform the same work as a 400-ton steel wire crane, Rolls-Royce claims, because the braided fiber rope has a near-zero weight in water.
This means the length of rope deployed does not impact the useful lifting capacity, whereas with wire, the useful lift is said to decrease with depth because of the suspended weight of the heavy steel construction of wire rope.
Reducing the crane size for a set deepwater work capacity brings other benefits, the company adds, notably the fact that the lower crane weight has less of an impact on the ship’s stability.
A smaller crane could also suit deployment from a smaller, lower-cost vessel.
Control is provided from the Rolls-Royce control cabin attached to the crane, which houses the operator chair with touch screens, a writing desk, master cabinet and redundant uninterruptible power supplies, an a co-pilot chair.
Fiber rope handling is managed below decks in a compact system using a cable traction control unit. This is designed to accommodate increased local rope diameter at any sections spliced into the rope, should part of it be damaged or abraided.