The Robben Island Museum has said it needs to make use of chartered vessels as it alone cannot cater to the number of tourists it attracts.
"We do not have the capacity in house to meet the tourist demand," the museum's chief executive officer Mava Dada told News24 on Thursday.
"Robben Island Museum will not be eliminating chartered ferries. In order for [the museum] to maintain their vessels and carry out statutory safety surveys, we need to partner with the chartered ferries."
Dada said this after News24 on Wednesday reported that the museum appeared to have overlooked a warning contained in one of its own reports that a ferry, the Thandi, which last Friday partially sank in choppy seas and high wind with more than 60 passengers aboard, "only be used in fine weather conditions".
Asked about the report earlier this week Regine le Roux, speaking on behalf of the museum, on Tuesday said: "We [are] not aware of this."
The report is a proposal request for a new high-speed passenger ferry and is available on the government online tenders site and is dated 2016.
Dada on Thursday, in an emailed response to the News24 article, did not directly address this report.
It contained a section about the Thandi which said: "This vessel was joined for a return trip from Robben Island during which time no passengers were carried due to adverse weather (wind 40 knots and swell 2 meters)," the proposal request said.
"This vessel was found to not be suitable for operating with non-seafaring personnel on board during that sort of weather conditions and is [recommended] to only be used in fine weather conditions."
Last Friday, September 15, the Thandi started to sink about 3km from the V&A Waterfront with 64 passengers and five crew members aboard.
A dramatic rescue operation ensued and everyone was brought safely ashore.
Investigations are underway to determine what caused the incident.
The Democratic Alliance has also called for an independent probe.
At the moment, only one ferry - the Dias - is in operation, which belongs to the Robben Island Museum.
The four other vessels in operation are hired from other companies.
"Through this, we have created business opportunities for ferry owners to help share the load," Dada said on Thursday.
"This allows us to have sufficient infrastructure in place while at the same time ensuring that all the vessels are maintained and safety surveys conducted.
"This ensures that the vessels are always in perfect running condition as well as ensuring all safety matters are fully addressed."
Dada said the museum would never jeopardise the safety of passengers.
"Masters of the ferries are trained to assess the water and weather conditions, and they are the best placed to know their ferries' capabilities."
News24 on Wednesday reported that a weather warning for heavy winds along the Cape coast was issued about two hours after the ferry started sinking.
Dada on Thursday said Robben Island Museum monitored the weather and checked each vessel to see if it could be used in specific weather conditions.
"If the weather conditions are not suitable to safely transport our passengers they inform the Robben Island representative and all tours are cancelled," he said.
A chartered ferry needed a maintenance plan to do business with the museum.
"They are also required to have all the safety certificates for the vessels. Robben Island Museum also has a maintenance plan for all their vessels," Dada said.
The ferries, he said, were an important part of the museum's operations.
"As the demands in capacity to the island increased, we were necessitated to increase the number of trips and thus the fleet of ferries."
The Thandi is owned by Yacoob Yachts, which is run by Esa Yacoob.
A statement issued by Yacoob Yachts to News24 on Wednesday said that the Thandi was surveyed by the South African Maritime Safety Authority on September 12 "and obtained the necessary certificates in order to operate". This was three days before the incident.
"On the morning of the incident, all vessels were operating as weather conditions were favourable. All vessels, including the other Robben Island ferries, were operating," it said.