Murray Kayes and his crew were heading to a new fishing spot near Manukau Peninsula when they spotted two men waving at them from the ocean.
The stricken pair were visible in their bright yellow life jackets, while the third man who had died was floating face down in the water without a life jacket.
"The boat sank straight away. They had actually tried to go out across the bar and realised they shouldn't have been there and tried to turn and it got them," Kayes said.
The first man they rescued had been clinging onto the body of his deceased friend, who had turned blue in the face.
"The first chap we picked up. He had been holding on to the deceased until he passed away and he had hypothermia very badly."
The second survivor had tried to swim for help, but had become disorientated and was swimming in the wrong direction before he was pulled aboard.
Those that were rescued were taken to hospital and the boat later sank.
Police Senior Sergeant Ross Hunter praised Kayes and his companions at the weekend for their professionalism and said he "couldn't thank them enough".
Police said Williams' death had been referred to the coroner.
The Manukau Bar claimed two more lives in 2014, with three others taken to hospital after their boat was swamped trying to cross it.
TIPS TO SAFELY CROSS A BAR
• Seek local advice on the bar and channels • Check the weather, tide and bar conditions • Ensure your boat has adequate stability • Check your boat and make sure hatches and equipment are adequately secured • Make sure everybody is wearing a lifejacket and is awake • Ensure you are carrying two forms of communication that work even when wet • A call sign is vital for bar crossings to ensure positive identification and efficient communication Source: Coastguard NZ