A Nelson yatchsman's near miss is one of several rescues over the past week, prompting police and the coastguard to urge boaties to take care.
The man, 27, was more than 5km from shore when his 3.6-metre catamaran capsized on Wednesday, police said.
"He then spent about two hours in the water trying to right the yacht - which, due to their design, are very difficult for one person to right," said Sergeant Malcolm York, who ran the rescue operation.
"After two hours, one of the hulls of the catamaran had filled with water and the weight of the water allowed the yachtsman to right the small yacht.
"He then attempted to sail the yacht, but due to having one sunken hull the catamaran kept capsizing."
Mr York said the sinking yacht was eventually spotted by a member of the public using a telescope, and was found by helicopter about 12.30am, about seven and a half hours after the sailor set out.
He said the only safety equipment the man had was a lifejacket, with no way of communicating.
He urged those considering taking a boat out to remember the boating safety code, consider the weather, ensure they had the right equipment, and behave responsibly.
"If weather and tide conditions had not been so favourable, the outcome could have been tragic," Mr York said.