A woman and a 5-year-old boy were taken to hospital after they became stranded in a dinghy without lifejackets in Queen Charlotte Sound just before midnight on Sunday.
Emergency services went to Whatamango Bay after the woman, believed to be in her mid-20s, called for help when the outboard motor cut out on the three-metre aluminium dinghy the pair were sailing in without lifejackets or oars about 11pm.
Coastguard staff, police and St John ambulance officers searched the bay for half an hour before they found the dinghy which had drifted to the shoreline, rescued the hypothermic pair and took them to Wairau Hospital.
The woman is believed to have been from the area.
The Marlborough Express can't confirm why the pair were in the boat or if alcohol was involved.
Coastguard president Dick Chapman said the pair had launched the dinghy from the bay in the afternoon and the Coastguard was called in when the engine stopped in the cold and dark.
He declined to comment on whether alcohol had played a key role in the incident.
"People should take lifejackets out on dinghies because they're pretty easily tipped over.
"They were lucky they got away with it, but I wouldn't want to see them try it again."
The New Zealand Maritime website says every boat must have the right-sized lifejacket for each person on board, and for boats under 6m they have to be worn unless the skipper decides that the risk is very low.
St John operations team manager Tony Cronin said the pair suffered chills and were immediately taken to Wairau Hospital.
"They had been out for a fair bit of time, it's very cold on the sea in the middle of winter."
The boy was discharged from hospital later that day.
A police spokesperson said the woman had not been charged with any offence.
"She was out in the dinghy when the motor broke down. It stopped and she got into strife."
- The Marlborough Express