The mystery of the Robben Island ferry's bumpy ride into port has been solved.
An underwater survey by the Council for Geoscience has detected a rocky outcrop inside the harbour at the World Heritage Site.
The discovery resolves debate about damage to the R26-million flagship Sikhululekile ferry, which has been out of service for almost a year, causing tourist bottlenecks.
The harbour survey included the first detailed picture of what ferry skippers have been complaining about for years - a bumpy ride into port at low tide.
"It was disturbing that the damage to Sikhululekile tended to happen during the time of the year when the tide was low," said Sibongiseni Mkhize, the chief executive of Robben Island Museum.
"We suspected the damage was caused by the rocks. The study ... demonstrates that Sikhululekile's draft is too deep, particularly during low tide."
The study raises questions about why a detailed survey was not conducted prior to spending taxpayers' millions on a fancy new ferry too big to safely navigate the harbour.
Sikhululekile was brought into service amid much fanfare several years ago to operate alongside the two long-serving ferries, Dias and Susan Kruger.
The new boat immediately ran into trouble when it was "attached" by manufacturer Farocean due to non-payment. It was damaged twice previously before being pulled out of service.
The vessel's propulsion system has now been fixed, but it must undergo sea trials before the museum assesses the total cost of repairs.
The new evidence explains why a tender for a new tourist ferry specified shallow water capability.
Robben Island spokesman Quinton Mtyala said the museum decided in October to sell Sikhululekile.
"All three boats are worth R31.6-million. The market will determine the price of Sikhululekile when it is put on sale."
Michael Machutchon, the project leader at Geoscience, said the survey identified two rocky outcrops, one in the middle of the harbour at 2.5m and another near the entrance.
"There is no "gap" in this outcrop [at the entrance] and all vessels need to pass over it," Machutchon said.
The survey also i dentified an old pipeline and a 7.8km underwater "land bridge" between the harbour and Blouberg, with an average depth of 15m.
Adventurer Matt Silver-Vallance is planning to "walk" the route next year to raise funds for charity.
Additional reporting by Roxanne Henderson and Farren Collins
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