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Friday, June 21, 2019  (Comments: 1)

Lloyd’s Register has reported a number of ships having technical issues with spade rudder neck bearings made from reinforced polyester resin.

In the latest edition of the classification society’s in-house publication Horizons, LR reports that it is investigating several incidences where the bearings had shifted down in the housing of the rudder trunk extension and were resting on top of the rudder blade. During investigations by its Technical Investigation Department (TID), the rudder blades themselves were found to have weld defects.

While several ships had the same issue, all of the affected vessels were built at the same yard.

After carrying out finite element model tests of the assembly with the rudder stock, neck bearing, and rudder trunk extension, analysis found the stresses in the neck bearing were mainly around the knuckle on the rudder stock journal.

Analysis of the bearings indicated that radial direction stresses and axial elongation resulted in local movement of the bearing in the rudder trunk housing, with continued operation resulting in the bearing “being ratcheted out of the housing”.

“As bending of the rudder trunk results in compressive axial strain in way of the contact area on the bearing, then rudder trunk bending may also be a contributory factor, in the movement of the neck bearing,” reports Horizons

LR says non-metallic bearings should have substantial retaining rings.

Reader Comments (1)

This is an interesting piece. I was recently involved in the neck bearing renewal on a 64000dwt bulk carrier. Initial symptoms had been a loud 'groaning' noise form the rudder assembly. The stock was also found bent. Would be interesting to know the shipyard referred to in the article.

By Vincent Muscat on Monday, June 24, 2019

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