UK-based provider of engineering analysis, Integrated Design and Analysis Consultants (IDAC) has performed structural integrity assessment of a new thimble design, by carrying out non-linear structural analyses of the thimble design.

During the test, the thimble was subjected to the minimum breaking load (MBL), a fatigue load case and a stern roller load case through a synthetic fibre rope.

IDAC had conducted the test as structural static analyses with nonlinear contact behavior.

To define the direction of the pull load, a short section of the cylindrical rope, after leaving the thimble geometry, was included in the actual model.

The company has divided the assembly into two identical halves, as only a half symmetric model was required for the test, while model was used for the MBL and fatigue load cases.

It included the thimble (half), the retaining pin, two representative retaining nuts, the shaft and the fibre rope.

IDAC created another half-symmetric geometric model with an angled fibre rope and used for the stern roller load case.

The test result showed that when the thimble was subjected to the rope failure load (MBL) of 1905 tons, it did not fail under the load condition, despite localised plastic yielding around the top and bottom edges of the pinhole.

A larger fillet area than the current value of 5mm would help to alleviate the high stresses in these areas.

The fatigue evaluation of the thimble design, using the maximum mean operating current load of 1024 kips with a range of 592 kips showed that the design can survive for an indefinite period.