On the day of the crash he had expected only two passengers for the flight, which was part of a 40th birthday celebration in the city for Ms Marra, but four turned up and he went ahead, said the report.
Investigators estimated the helicopter was between 12.7kg and 118.4kg overweight.
"The investigation determined that the helicopter was loaded to an overweight condition, likely because the pilot did not anticipate having two additional passengers onboard the helicopter and because he did not perform weight-and-balance calculations.
"The front-seat passenger stated in a postaccident interview that the pilot did not ask for anyone's weight or perform any calculations before takeoff," it is reported saying.
Witnesses described the helicopter as descending in an "uncontrolled spin" before hitting the water, said the report.
Mr Dudley refuted the determination.
"We disagree with their assertions and guesstimates. In 30 years of flying, I never scratched the paint on an aircraft.
"I take it very seriously. I am still mourning the loss of my three friends," he told the Wall Street Journal.
At the time of the crash, the Tamaki family thanked Mr Dudley for his actions.
"This was a tragic accident and we are grateful for the prompt action and bravery of the pilot, Paul Dudley, who recovered Helen and Harriet from the scene," said a family statement.
