Kokako Rescue then accompanied the yacht to Ōpua, arriving at 4am.
Armitage said treatment was also provided to two other sailors on the yacht, who had sustained moderate injuries.
“Our thoughts are with the whānau of the sailor, and their fellow crew members, who were on board at the time,” he said.
Armitage said the volunteer crew on Kokako Rescue had been training at the time of the incident, allowing them to respond quickly.
However, they had planned to coincide their training with the race so they could be on-hand to assist if needed, the Coastguard said.
More than 140 yachts started this year’s Coastal Classic.
Hosted by the New Zealand Multihull Yacht Club, it is an annual 119-nautical-mile race from Auckland to Russell.
First run 41 years ago, the event is one of the biggest events on the yachting calendar in New Zealand.