Since being stationary at Ahuriri, there had been electricians and engineers on board checking it over, and he had been waiting for a hard stand to get it up for a thorough inspection, he said.
"As a boat owner it's probably one of the things you do not want to see, when I got the call I thought maybe the stern had got hooked.
"The stern was down at about 5.30am, and in a matter of about 20 minutes the whole thing was under."
A fisherman of more than 20 years experience, he said he had not encountered anything like it before, and would be interested to see why it had gone down.
The insurance inspectors were due to assess it today, he said.
Salvage efforts took the whole day yesterday, with the boat hoisted up by a 100-tonne capacity crane, and Hawke's Bay Regional Council staff acting for Maritime New Zealand on hand to contain the diesel and oil leaking from the boat.
Acting for Maritime New Zealand, on-scene commander marine oil spills Ian Lilburn said he was first alerted at 7.15am on Monday that the vessel had sunk.
"Along with a team of trained responders from the regional council we acted quickly to contain the oil and diesel - our main priority being to minimise the impact on the environment," he said.
This involved setting up an inflatable boom around the boat to contain the spill, and using absorbent pads and booms to soak up the oil on the surface of the water.
By about 4pm most of the boat was out of the water, but Mr Lilburn said there were still some logistics to be worked through to get it out of the water completely.
"It's going to take a few more hours yet," he said.