The South African Maritime Safety Authority (Samsa) released the findings of its investigation into the Miroshga Hout Bay boat accident on Wednesday morning.
Tourist Peter Hyett and crewman John Roberts died when the boat capsized near Duiker Island nearly two weeks ago.
Several of the 37 passengers, including several foreigners on board, were injured, but have all since been released from hospital.
According to the report, "a sequence of events occurred which resulted in the vessel capsizing".
The investigation found that the capsizing "occurred as a result of water ingress into the aft port and starboard fuel tank compartments combined with incorrect wiring of the port bilge pump, which resulted in the pump not operating when activated by the water level float switch".
"Water ingress continued with the vessel trim increasing by the stern which resulted in progressive flooding into adjacent compartments at a rate faster than the capacity of the remaining bilge pump," read the report.
"The increased trim by the stern together with prevailing wind and waves coming from the aft quarter resulted in intermittent submergence of the outboard engines and flooding of the aft deck. The port outboard engine stopped first as a result of loss of electrical power and the starboard outboard engine suffered catastrophic failure a short time later due to flooding through the engine air intakes.
"With all propulsion power lost, the vessel subsequently drifted into shallow waters in a partially flooded condition, where it was eventually capsized by wave action," the report concluded.
Samsa said that while the Miroshga's skipper held a basic certificate, it "was not endorsed to allow him to act as skipper of a small passenger boat as prescribed by regulation".