Three boozed yachties sailing home after the AC/DC concert were rescued off Wellington's south coast after the skipper was knocked overboard.

The skipper, the only one with sailing knowledge, ended up in the sea after being struck in the head by the boom while trying to return to shore after weather conditions became too treacherous in Cook Strait.

Senior Constable Craig Pickering, of the Wellington Maritime Unit, said the young skipper and two other young men were about 5km from shore when the incident happened.

AC/DC AC/DC performs 'Rock Or Bust' for the crowd in Wellington, despite technical issues at the start.

"The skipper had met the other two and offered them a lift back to the South Island," he said.

"The conditions got rough and the skipper tried to turn the yacht around. While turning the boom swung round and hit him in the head knocking him off the yacht."

The remaining two crew, unable to sail, called emergency services, Pickering said.

However, somehow the pair managed to turn the yacht around and pull the skipper back on board.

By chance, the Wellington Maritime Unit's Lady Elizabeth IV launch was in the area near Sinclair Head and sped to the yacht.

"Two crew from the launch were transferred to the yacht to help provide medical assistance and pilot the skipperless yacht back to Wellington Harbour," Pickering said.

Two paramedics from the Westpac rescue helicopter were also lowered onto the Lady Elizabeth IV and transferred to the yacht.

The skipper, who had remained conscious the whole time, was taken to hospital with a gash to his head and a suspected neck injury.

Pickering said it had been a lucky escape for the trio after they had failed to check the weather forecast and were not wearing life jackets.

They had also been drinking, he said.

It was not compulsory to wear a life jacket on the yacht but when the conditions were rough life jackets could save a life, Pickering said.

Drinking was also not illegal but could impair awareness and judgment, he said.

"It was a lucky escape and it is important skippers should have knowledge of the conditions, carry safety equipment and wear life jackets in severe weather."