Loss Of Steering – Rudder Flange Bolts Missing

Incident:

A 23,400 GRT  Bulk Carrier,  built in 1982 was on a ballast voyage when the Master noticed a loss of steering.  Fortunately, the vessel was close to a port.  Once in port, a survey revealed that although the balanced rudder was still in place, seven out of eight fitting bolts between the rudder stock and the rudder flange were missing.

The nut on the remaining bolt was found to be secured to the rudder stock flange with a flat bar and not to the bolt (Fig.1). Apparently the bolts were loosened, turned off and were lost because they had been fitted upside down.  The securing should have been between the bolt and the nut as indicated in Fig.2. Securing nuts and bolts by welding are generally considered to be the most reliable solution; however, the materials and the nuts must be weldable.  If such welds crack, the securing is lost.  Other securing arrangements such as washers with locking screws, specially designed nuts with split pins etc, are also used but are not considered equally good.  When securing devices of rudder flange bolt and rudder pintles are not functioning or missing, the result may be loose flange bolts, loose pintles, loose or damaged bushes, and consequently, possible loss of the rudder.

Lessons Learnt:

1. When refitting rudders, make sure that fitted bolts are used and proper securing arrangements are employed.
2. Always secure the nut to the bolt.  This is especially important where, for practical reasons, bolts are fitted upside down.
3. Make sure that the weld has been carried out properly and that both the bolt and the nut materials are weldable.
4. If screws are used in the securing arrangements, the material used is to be carefully selected with a view to avoid galvanic corrosion of the nuts and bolts. Such screws are to be secured as well.
5. Nut/bolt connections should be checked when available for inspection.
6. Whenever damage is experienced, a thorough permanent repair should be carried out the first time.
7. Similar procedures as above are also applicable to rudder pintles.

Additionally:

1. The tapered part of the pintle is to be properly adjusted, the pintle must be properly tightened and the nuts must not reach the end of the threads.
2. The pintle pull-up distance should be checked.

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Source: DNV exchange

Disclaimer: This case study is to highlight the importance and throw light for the safety awareness.

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