The Marine Accident Investigation Branch (MAIB) today published its report into two failures in the lifting wire on the starboard Fast Rescue Craft (FRC) davit of the safety stand-by vessel Dea Fighter. The wire failures occurred on the 13 May and 16 July 1999.

SYNOPSIS
Dea Fighter is a safety stand-by vessel operated in the North Sea with a crew of 12. She is equipped with two davit launched fast rescue craft (FRC).

During 1999 the lifting wire of the starboard FRC davit failed twice, once on 13 May when in Aberdeen Harbour, and again on 16 July when on station at an offshore installation. FRC occupants were injured. On each occasion the wire failed about 1 metre from the FRC's lifting eye.

The owners of Dea Fighter carried out their own investigations into the causes of the failures. As the results were inconclusive, the (MAIB) began its own investigation on 17 September 1999.

Shortly before the first failure, an undersized top sheave (pulley wheel) was fitted to the davit arm. Apart from changing the wire geometry, this allowed the wire to be displaced from the sheave's groove and become trapped between the sheave and sideplate boss of the arm. Excessive bending of the wire also resulted. When swinging out the FRC, with the telescopic arm fully compressed, the change of wire geometry caused the wire to be grossly overloaded.

A combination of gross tensile overload, excessive local bending, and crushing caused the wires to fail. The mechanism of failure was similar on each occasion.

The Maritime and Coastguard Agency (MCA) is recommended to publish standards for the FRC launching systems on board safety stand-by vessels.

It is also advised to publish advice in its system of Marine Guidance Notes, Code of Safe Working Practices for Merchant Seamen, and Instructions to Surveyors, on the importance of using replacement parts on davits and lifting gear which comply with the manufacturer's specifications.

The owners of Dea Fighter are recommended to modify their davit operator training and on-board instructions to suit the amendments made by the davit's manufacturer, Caley Ocean Systems. They are also recommended to introduce management procedures, which will ensure that replacement parts for davits comply with the manufacturer's specifications.

The International Association of Classification Societies (IACS), International Chamber of Shipping (ICS), and the International Transport Federation (ITF) are recommended to disseminate the lessons learned from this investigation to their members.

CONCLUSIONS

Findings
1. The lifting wire on the starboard FRC davit of Dea Fighter failed on two occasions during 1999, once on 13 May, when in Aberdeen Harbour, and once on 16 July, with the vessel on station at an offshore installation.

2. Shortly before the first incident, the top sheave of the davit was replaced by an item with incorrect dimensions. It was too small in diameter, and not of the material recommended by the manufacturer.

3. Except for the fitting of an incorrect top sheave, davit maintenance was satisfactory.

4. On each occasion the wire failed about 1metre from the FRC's lifting eye, coincident with the davit's top sheave.

5. Both lifting wires were in good condition before their failures.

6. Both wires failed due to tensile overload.

7. The davit's winch could not have generated sufficient load in the wires to cause simple tensile failure.

8. The winch could not have withstood a wire load sufficient to cause simple tensile failure without slipping.

9. Normal launching procedures resulted in the davit's tele-leg being fully compressed. This has the potential to increase the load in the lifting wire beyond the weight of the rescue boat plus its crew.

10. Normal launching procedures, with a correctly dimensioned top sheave, did not generate a sufficient overload to cause the wires' failures.

11. Normal launching procedures, with correctly dimensioned top sheave but with the tele-leg fully compressed, have the potential to induce wire loads exceeding their Safe Working Load (SWL).

12. The wire geometry was upset by the use of the undersized top sheave.

13. Wire loading can be amplified when using an undersized top sheave.

14. Normal FRC recovery and stowing procedures allow the lifting wire to slacken.

15. Prior to the attempted launchings on 13 May and 1 July, the slack wire slipped between the top sheave and a sideplate, where it was trapped.

16. Wire failure was caused by the trapped wire being overstrained as the davit was swung out.

17. Additional local effects of bending and crushing caused the failure to occur where the wire passed over the top sheave's pin.

18. Failure might not have occurred on these occasions if the tele-leg had not been fully compressed before the davit was swung out. However, it is likely that the eventual wire damage was due to bending and crushing.

19. On-board instructions implied that operating the davit with the tele-leg fully compressed was acceptable.

20. The MCA publishes no standards against which FRC davit systems should be assessed.

CAUSES

Immediate causes
The davit wires failed due to overloads generated by the consequences of the wires having slipped from the top sheave and becoming trapped in the adjacent space.

The wire slipped from the sheave because the sheave's diameter was significantly less than the manufacturer's specification.

Underlying causes
A lack of understanding of the general principles and dangers associated with fitting undersized wire sheaves to lifting plant.

The lack of a vessel management system able to identify the fitting
of a safety related component that significantly deviated from the manufacturer's specification.

RECOMMENDATIONS
The Maritime and Coastguard Agency is recommended to:

1. Publish standards for the FRC launching systems on board safety stand-by vessels.

2. Include advice on the importance of using replacement parts on lifting equipment which comply with equipment manufacturer's specification in: Code of Safe Working Practices for Merchant Seamen A Marine Guidance Notice Instructions to Surveyors

The owners of Dea Fighter are recommended to:
3. Modify their davit operator training and on-board instructions for the operation of these davits to suit the amendments made by Caley Ocean Systems.

4. Introduce management procedures to ensure that replacement parts of davit systems comply with original equipment specifications.

The International Association of Classification Societies (IACS), International Chamber of Shipping (ICS) and the International Transport Federation (ITF) are recommended to:

5. Make the lessons from this investigation known to their members.