"The skipper would have been in the water for at least 18 hours now. The water temperature is no more than 13 degrees Celsius and unfortunately that makes survivability highly unlikely."
The Horizon is thought to have sank about five kilometres off the coast of Foxton.
A 45-year-old man from Levin who was also on board managed to swim ashore near Hokio Beach after several hours in the water. He does not wish to be identified at this stage.
He was picked up by police after he managed to make it ashore near Hokio Beach between 3am and 3:30am, and walked for up to 45 minutes, Mr White said.
"Having spoken to the survivor and having sought advice from the Police Dive Squad we believe the best benefit will be to check the shoreline after high tide tomorrow."
He said searches, including air support, will continue at key times over the coming days to try to find the missing man and boat.
Public using the beaches are advised that there is a potential for him to come ashore in the coming days.
Police are speaking to the survivor to find out as much as they can about the incident and the boat.
- APNZ