According to Transport Minister Ben Martins, the SA Maritime Safety Authority has investigated how the tuna-fishing vessel Eihatsu Maru came to lose its way in fog.

It got stuck in the sand off Clifton's First Beach in the early hours of May 12.

In a written reply to a parliamentary question, Martins said the authority found that the vessel "was not appropriately manned for the voyage: there was only one watch-keeper, who was not qualified as required by the Japanese state".

And the lookouts had been told that they were "not allowed" to disturb the captain.

"The vessel's bridge was not manned as required by good seamanship; there were lookouts only on the bridge-wing, who were not allowed inside the bridge, where the captain was asleep."

Martins said the captain had not adhered to international maritime regulations, which require that all available means - including the use of radar and depth sounders - be used to keep a look-out when a vessel was in fog or visibility was otherwise poor.

"In addition, the vessel's autopilot repeater was reading about 12° low in comparison to the gyro compass. No regular compass and gyro error readings had been logged in the deck log book.

"If the error had been known, the master could have applied the correct course setting to steer to the anchorage," he said.

In his reply, Martins suggested that the Cape Town Port Authority staff were not sufficiently vigilant when the Eihatsu Maru entered the harbour's shipping lanes, within range of their radar.

Western Cape tourism MEC Alan Winde said it will be "another week or two" before the cause of the charter boat capsizing in Hout Bay can be revealed.

"The final report on the cause of the accident will be revealed once the boat has been taken out of the water and the investigating officers have inspected it," he said in Cape Town.

"According to the SA Maritime Safety Authority the boat had a valid legal safety certificate and was certified to carry 42 passengers and three crew."

The Miroshga, carrying 39 people, capsized near Duiker Island on Saturday afternoon.

British tourist Peter Hyett, 64, and crew member John Roberts, 37, drowned. Three women were rescued from inside the overturned hull and hospitalised with severe hypothermia. Two have since been discharged.