Possible sea condition link to sinking of fishing vessel Lindsay on Eastern Agulhas Bank
May 16, 2005
Author: Ian Hunter : Manager Maritime Services, South African Weather Service
On Sunday May 8 at approximately 01.30 the Ouro do Brasil (18 600 dwt) collided with the Mossel Bay-based fishing trawler Lindsay. The reefer was en-route to Brazil from Singapore and in ballast. It appears that her exposed bulbous bow lifted the fishing vessel almost clear of the water. The trawler sank in less than a minute, roughly 15 n.miles southwest of Cape Recife.
The collision resulted in the tragic loss of 14 fishermen who were below deck, sleeping. Only the skipper and one crew member survived.
Both of the global wave prediction models available to the South African Weather Service (one from the United States' National Weather Service and the other from the Met Office in the United Kingdom) predicted a heavy southwesterly swell for early Sunday 8 May. In fact they were predicting this event over four days ahead - and within a half-a-metre of the maximum measured height (5.7m was measured at the offshore 'FA' gas production platform located 170 n.mls southwest of the disaster).
Although the heavy southwesterly swell probably had nothing directly to do with the collision it did impede the rescue teams. On the other hand the wind is estimated to have been about 25 knots and radar clutter due to the combination of wind and swell may have been a factor with the relatively small target presented by the trawler. There was no indication of the presence of fog.
The attached time series shows the rapid fall in atmospheric pressure recorded by a drifting weather buoy late on Thursday 5 May. The buoy was approximately 2000 km southwest of Cape Town and the reason for the extreme decline in pressure was a case of 'explosive cyclogenesis' (a low pressure system intensifying much faster than normal). Just over 48 hours later - i.e. early on Sunday morning - the swell generated by this system reached the area where the collision took place.
The above weather buoy has a particularly interesting history. It was deployed by the French research vessel Marion Dufresne in November 2002 northwest of Kerguelen Island in the South Indian Ocean. It is now on the Greenwich meridian.
Thus it has drifted almost right around the world and continues to operate after two-and-a-half years in the mountainous seas of the Southern Ocean.
These buoys provide invaluable information, particularly in the data-sparse ocean regions of the Southern Hemisphere. Without them the accuracy of the initial and predicted wind fields would decrease, which would in turn reduce the accuracy of the wave models.
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