Marine Occurrence report 232 - Australian Transport Safety Bureau

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move off the wharf and this resulted in these brakes slipping at less than their rated load. 2.2.6 Combination of brake factors On 10 September, Creciente was berthed using 16 mooring lines, all of which were secured using the winch brakes. The ship was totally dependent upon the winch brakes to hold it alongside the wharf. The mooring forces for each of the mooring lines can be calculated using the geometry of the ship’s mooring arrangement. The effect of all of the limiting factors affecting Creciente’s winch brakes on 12 September can then be calculated (Table 3). Table 3: Creciente’s winch brake effective holding strength on 12 September Mooring line P - S holding capacity F - A holding capacity Overall holding effect Max. brake capacity Hinge effectiveness (estimate) Drum area (as inspected) Tightness (estimate) Layer effect (Table 2) Headline outboard 6.6 26.5 27.3 67.4 100% 60% 80% 84% Headline outboard 5.0 20.2 20.8 67.4 100% 60% 80% 64% Headline inboard 6.7 19.7 20.8 67.4 100% 60% 80% 64% Headline inboard 6.7 19.7 20.8 67.4 100% 60% 80% 64% Fwd Breast 2.6 17.1 17.4 67.4 100% 50% 80% 64% Fwd Breast 2.6 17.1 17.4 67.4 100% 50% 80% 64% Fwd Spring 0.7 8.6 8.7 67.4 50% 50% 80% 64% Fwd Spring 0.7 8.6 8.7 67.4 50% 50% 80% 64% Total Fwd (tonnes) 31.6 137.4 141.9 Stern line (#7 dolphin) 1.5 9.1 9.3 67.4 50% 60% 80% 58% Stern line (#8 dolphin) 0.9 11.8 11.8 67.4 50% 60% 80% 73% Aft breast (outboard) 16.4 10.6 19.6 67.4 100% 70% 80% 52% Aft breast (outboard) 16.4 10.6 19.6 67.4 100% 70% 80% 52% Aft spring 5.4 27.0 27.6 67.4 100% 70% 80% 73% Aft spring 4.8 23.8 24.3 67.4 100% 70% 80% 64% Aft breast (inboard) 12.6 10.9 16.8 67.4 100% 60% 80% 52% Aft breast (inboard) 14.7 12.8 19.6 67.4 100% 70% 80% 52% Total Aft (tonnes) 72.5 116.5 148.8 Combined total (tonnes) 104.1 253.9 290.7 - 19 -
For these calculations, the brakes were assumed to have an effective tightness of 80 per cent, although it could conceivably be lower. The drum area was estimated from an inspection of the brake drums and the hinge loss was estimated from the ability of the brake band to clamp onto the drum. As can be seen from the table, the effective total athwartships holding capacity of Creciente’s winch brakes on 12 September 2006 was about 104 tonnes, far less than the 211 tonnes that was theoretically possible using the modified mooring configuration (Section 2.2.1) and the aft winches only had an effective holding capacity of 72.5 tonnes. 2.2.7 Environmental forces Creciente’s mooring winches were required to hold the ship alongside the wharf against the wind and tidal forces that were acting on the ship. The size of the wind force acting on the exposed area of the ship’s hull and superstructure can be calculated. Given that the wind in the early morning of 12 September was about four knots from the north, the maximum force from this wind would have been about 6 tonnes if the wind was acting directly on the ship’s beam, which it was not. In this instance, with the ship laying on a heading of 018° (T), the wind had negligible effect on the ship. Figure 15: Tidal flow affected by build up under the loader belt Buildup under loader belt - 20 -
Page 2 and 3: ATSB TRANSPORT SAFETY INVESTIGATION
Page 4 and 5: CONTENTS DOCUMENT RETRIEVAL INFORMA
Page 6 and 7: DOCUMENT RETRIEVAL INFORMATION Repo
Page 8 and 9: THE AUSTRALIAN TRANSPORT SAFETY BUR
Page 10 and 11: ATSB INVESTIGATION REPORT TERMINOLO
Page 12 and 13: EXECUTIVE SUMMARY On 8 September 20
Page 14 and 15: 1 FACTUAL INFORMATION 1.1 Creciente
Page 16 and 17: Each mooring winch consists of two
Page 18 and 19: 1.2.1 Tidal flow A drying sand spit
Page 20 and 21: Figure 7: Normal mooring arrangemen
Page 22 and 23: The second mate walked aft, along t
Page 24 and 25: Figure 10: Creciente aground in Por
Page 26 and 27: 2 ANALYSIS 2.1 Evidence On 15 and 1
Page 28 and 29: holding capacity of the ship’s wi
Page 30 and 31: ake’s strongest holding direction
Page 34 and 35: The spring tides in Port Hedland ar
Page 36 and 37: Figure 16: Port Hedland hydrographi
Page 38 and 39: While the port emergency plan did n
Page 40 and 41: 3 FINDINGS 3.1 Context At about 024
Page 42 and 43: 4 SAFETY ACTIONS 4.1 Safety action
Page 44 and 45: APPENDIX A: EVENTS AND CONDITIONS -
Page 46 and 47: APPENDIX B: SHIP INFORMATION Crecie
Page 48 and 49: APPENDIX C: SOURCES AND SUBMISSIONS

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