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In the early hours of 24 February 1994, the Norwegian flag (NIS) off-shore anchor handling and supply vessel Boa Force was engaged in deploying anchors from the off-shore construction barge, Support Station III, about half a mile south of Thevenard Island, 11 miles north-west of Onslow, Western Australia.

Anchor handling vessels do not navigate in the accepted meaning of the term, but are directed to go in directions determined by the person controlling the operation on board the parent vessel, in this case, using a differential global positioning system and monitor.

In the immediate area of Boa Force's operation, there was a pipeline, marked at regular intervals with temporary buoys and an unmarked subsea wellhead, standing about 3m high in a general seabed depth of under 8m of water. The well itself was not active and had been capped and suspended for some time. To the west, and about 70m from the wellhead, a new pipeline had been laid, running from oil production platforms to Thevenard Island.

At about 0220 Western Australian Standard Time, Boa Force recovered the barge's number one anchor from close to the wellhead. Those on the barge were concerned with the proximity of the wire to the wellhead. Boa Force was ordered to go in a northerly direction to ensure that the wire was clear, before the barge recovered the wire prior to repositioning the anchor.

At about 0250, while moving stem first towards the barge, Boa Force hit the wellhead and holed the engine room space in the only area where the vessel did not have a double hull.

Despite efforts by the Chief Engineer, the Second Engineer and an Integrated Rating, the vessel's pumps could not keep up with the ingress of water. A launch was sent from the Support Station III to stand by Boa Force. A little before 0345, the Master ordered the crew to abandon Boa Force and by 0345 the complement of eleven were on board the launch.

The vessel sank, to the seabed partially supported by the wellhead. A boom was deployed to combat any pollution.

An operation to raise and dispose of Boa Force was completed on 6 April. This involved lifting Boa Force clear of the wellhead, patching the breach in the hull, and recovering all oil and other pollutants. The vessel was then towed beyond the continental shelf and scuttled.

The incident occurred in Western Australian State waters, where shipping is administered by the Western Australian Department of Transport, and the general operation, connected with the petroleum industry, came under the provisions of legislation administered by the Western Australian Department of Minerals and Energy. Boa Force was a "declared vessel" under the provisions of the Navigation Act 1912 and its Australian Master and crew held Commonwealth qualifications. Therefore, in addition to the flag State, three Australian administrations had jurisdiction to investigate the incident (Commonwealth Department of Transport, Western Australian Department of Transport and the Western Australian Department of Minerals and Energy), however, by mutual agreement the authorities agreed to conduct a joint investigation in accordance with the provisions of the Navigation (Marine Casualty) Regulations.


These conclusions identify the different factors contributing to the accident and should not be read as apportioning blame or liability to any particular organisation or individual.

The sinking of Boa Force was the result of a series of factors which combined to cause the vessel to make contact with Saladin No.3 wellhead.

These were:

1. The failure to temporarily mark the location of Saladin No.3 wellhead with an adequate buoy.

2. The failure to use adequate and accurate charts, or drawings, or plans to enable the anchor laying operation close to the south of Thevenard Island to be conducted in safety.

3. The provision of bathymetric data which was in error by about 1.6m.

4. The failure to supply a differential global positioning system monitor to Boa Force to provide the Master with a display of the operation upon which known hazards could be plotted.

5. The lack of appreciation on board Support Station III of the problems in manoeuvring an off-shore anchor handling vessel in a relatively confined area for a prolonged period without an effective point of reference.

6. The failure of the job safety analysis to properly take into account the operational safety issues of an unmarked subsea well.

7. The lack of local marine knowledge and expert marine advice in the planning and operational stages to address the above issues.

8. The failure of the Master of Boa Force to check known depths on 20 February, following an apparent bottom contact, particularly as it was known that the vessel would have to operate in the same area to retrieve the anchor at a later time.

9. The possibility of fatigue, resulting from the operational program, cannot be ruled out.

Other Conclusions:

10. Boa Force met the requirements of the Navigation Act 1912 and subordinate regulations and orders. All certificates were valid.

11. The provision of plans and documents in the Norwegian language did not facilitate the effort by those on Boa Force to control the emergency.

12. The Master, Deck Officers and Engineer Officers should have considered trying to restrict the extent of the flooding by closing all doors and hatches, consistent with the safety of the engineers in the engine room. Any decision not to close doors should have been based on known effects of flooding of the vessel.

13. The damage stability characteristics of the vessel met the relevant criteria for an offshore supply vessel under the provisions of Marine Orders Part 46 and IMO Resolution A. 469(XII), but the criteria did not allow for penetration of the hull inboard of the line of the inner bulkheads of the side tanks.

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General details
Date: 24 February 1994 Investigation status: Completed 
Time: N/A  
Location:Thevenard Island Investigation type: Occurrence Investigation 
State: Western Australia  
Release date: 02 September 1994  
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
Vessel details
Vessel: Boa Force 
Flag: Norwa 
IMO: 7625990 
Type of Operation: Anchor handling supply, off-shore support 
Damage to Vessel: Substantial 
Departure point:N/A
Departure time:N/A
Destination:Thevenard Is, WA
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Last update 18 May 2016