Sunday, September 16, 2007

The fish loading hatches on the Gaul

In 1999, in the year following their first underwater survey of the wreck of the Gaul, the MAIB produced their Marine Accident Report no. 4/99.
Amongst other things, this report put forward the MAIB’s hypothesis as to why the two large fish loading hatches on the Gaul had been found open during the survey. This stated that, at the time of the loss, the hatches had been unsecured and that they had therefore fallen open during the vessel’s capsize and sinking ’by the stern’.
As we have attempted to demonstrate in the document published at this LINK, the MAIB analysis, taken as read by the 2004 RFI panel, appears to have been seriously flawed.
The error it contains relates to one of the possible mechanisms that could have opened the fish loading hatches, namely, an increase in pressure of the air trapped between the water that was flooding into the vessel and the under side of the closed hatches.The MAIB report stated that the maximum lifting pressure on the underside of the fish loading hatches was only 478 N/m² (49 kg/m²), and that this would occur, for some unknown reason, when the vessel was exactly 80m below the sea surface. (!?)

A simple calculation can show, however, that if the Gaul had had a trim by the head of only 5ยบ [1] and had been submerged to merely two metres below the sea’s surface, the lifting pressure on the underside of each fish-loading hatch could have been of the order of 900 kg/m² (i.e. approximately 3.5 tonnes per hatch), while the self-weight of each hatch was approximately 0.9 tonnes.

This ‘error’ meant that one plausible scenario for the opening of the hatches was incorrectly eliminated from the formal investigation, while another similarly plausible hypothesis – the possibility of the hatches having been opened by the force of internal floodwater acting on the hatches from inside the vessel – was not even mentioned.

Here again, as in the case of the duff and offal chutes, the preferred explanation was crew error.


[1] Although both the MAIB and RFI experts have concluded that the Gaul sank initially and sedately by the stern, this theory cannot be relied upon with any degree of certainty, as it does not take into account the dynamic loads and ship motions that the vessel would undoubtedly have experienced, whilst at or near to the sea’s surface and following the redistribution and loss of buoyancy that would have occurred, as it flooded and sank. At the time of the loss the weather was extreme, with a significant wave height of circa 10m and with infrequent individual waves of up to 19m in height.

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