Bespoke running line monitors for vessel

Dynamic Load Monitoring (UK) Ltd. (DLM) provided the RLMs to monitor the tension on mooring winches aboard Jan de Nul’s 236.8m-long Les Alizés, due to be completed in 2022. DLM delivered the RLMs to NOV’s BLM division, which designs and manufactures ship and offshore equipment products.

The solution is for an eight-point mooring system, that will keep the vessel locked and stable during operations. The original performance criteria was 0-2750 kN, but that was later changed to 3,500kN (approx. 350t). DLM chose a customised solution, based on its standard 200t-rated RLM, adapted to a larger rope diameter and increased safe working load (SWL) and minimum breaking load (MBL) requirements.

Calibration was a challenge

Jamie Woodcock, business development manager at DLM, said: “The initially-quoted working range was up-rated by the client. The calibration was also a challenge due to the high working load and proof load requirements. We tested to a safe calibrated load using wire rope, then proof tested the pin in a compression machine to simulate the resultant load the pin would see when in service. This negated the need for risky and potentially unsafe wire rope tests to this very high tension [5,000 kN].”

Woodcock added: “By enlarging the frame we could use larger wheels to suit the 76mm diameter rope. We also needed to up-rate some components for the higher SWL, but still maintained a high safety factor.”

Other standout features of the RLMs included maximum design speed of 30m/min up to 200t, 15m/min thereafter; proof load 1.5 x SWL, which equalled 5,625 kN line tension; and high repeatable accuracy up to the full working scale. The calibration process required multiple 76mm slings, as each RLM needed to have multiple runs.

By Rebecca Jeffrey