Marine Survey Reveals Secret Of Robben Island

The Robben Island Museum (RIM) currently has a fleet of four ferries to transport tourists to and from Robben Island; the Sikhululekile, the Susan Kruger, the Dias and the cargo ferry Blouberg. Sikhululekile, the newest ferry, was purchased in 2008.

Unfortunately, this R26 million flagship ferry has been out of service for almost a year because of repeated damage to the ferry’s hull during low tides.

The museum management had been worried about the possibility of rocks in the harbour for some time and asked the South African Navy and police divers to survey the harbour in February and May last year. These surveys showed submerged obstacles, but no more detail could be provided.

In June 2014, the Council for Geoscience approached Robben Island Museum for permission to survey the seafloor from the harbour at Murray Bay to Blouberg. The acquired data would be used as part of an endeavour to walk on the seafloor between these two localities to raise funds for the Nelson Mandela Children’s Hospital. Information on the area within the 1 nautical mile (exclusive zone) around the island and the harbour floor would then be provided to RIM should they grant said permission.  Marine geoscientists, under the leadership of Michael MacHutchon,  determined the presence of two rocky outcrops, one in the middle of the harbour at 2.5 m and another near the entrance to the harbour. There is no gap in the outcrop at the entrance and all vessels need to pass over this outcrop. The rock outcrops cannot be removed because they are in the sensitive environment of a World Heritage Site. In addition, the survey identified an old pipeline and a 7.8 km underwater land bridge between the harbour and Blouberg, at an average depth of 15 m.

The rocks posed no problems to the other two ferries used by the museum as these have shallower draughts. However, the draught of the Sikhululekile is too deep, particularly during low tide. At the time of the survey, a tender had been issued to replace the ferry with a new one of similar draught.  Owing to the findings of the CGS investigations, the tender specifications were amended for a shallower draught vessel with a shallower water capacity. The study raised questions as to why a detailed survey had not been conducted prior to spending money on a new ferry which ultimately proved to be too big to safely navigate the harbour.

A detailed account of this survey will follow in the next issue of GEOclips. An adventurer is planning to “walk” this route to raise funds for charity.

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