Marine Occurrence report 232 - Australian Transport Safety Bureau

2 ANALYSIS
2.1 Evidence
On 15 and 16 September 2006, investigators from the Australian Transport Safety
Bureau (ATSB) attended Creciente while it was at anchor off Port Hedland. The
master and directly involved crew members were interviewed and they provided
accounts of the incident. Copies of relevant documents were obtained, including log
book entries, statutory certificates, maintenance records, procedures and permits.
Information relating to the incident was also obtained from the Port Hedland Port
Authority and the Port Hedland pilots. The draught surveyor, the harbour master
and the involved port pilots were also interviewed.
2.2 Breakaway
At about 0245 on 12 September 2006, Creciente’s mooring lines failed to hold the
ship alongside the wharf against a strong ebb tide, which resulted in the ship
breaking away from its berth.
2.2.1 Mooring arrangements
Construction work was being undertaken on the Finucane Island berth C and a
construction barge was positioned close to the berth D number nine berthing
dolphin. To facilitate this, the mooring arrangements for all ships using berth D
were changed from the usual configuration and the new arrangement (Figure 8) was
assessed as equivalent and acceptable by the port pilots.
The effective static load holding capacities of Creciente’s mooring lines was
calculated by the ATSB investigators for the normal berth D mooring arrangement
and compared with the modified arrangement that was used on 10 September 2006.
For this comparison, the pitting on the brake drums was disregarded and the brakes
were assumed to have been applied by tightening fully. The calculations considered
the length of each mooring line and the number of layers of unused line remaining
on each winch drum.
The total athwartships holding capacity using the normal mooring arrangement was
calculated to be 181.2 tonnes and the static load holding capacity in the fore and aft
direction was 642 tonnes. The modified mooring arrangement had a total
athwartships holding capacity of 211.0 tonnes and a fore and aft capacity of 611.9
tonnes.
The modified mooring arrangement provided greater holding athwartships at the
expense of some holding capacity in the fore and aft direction. The comparison
indicates that the modified mooring arrangement is unlikely to have contributed to
Creciente’s stern breaking away from the berth.
2.2.2 Winch brakes
Of the sixteen lines used to hold Creciente alongside Finucane Island berth D, four
of the aft mooring lines parted when the ship broke away from the berth; two
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