About 11.30am, two men, aged 29 and 30, were on board the catamaran when it overturned off Seven Mile Beach.

They were thrown into the water and let off two marine flares.

Members of the public observed the flares and contacted emergency services.

Volunteers from Marine Rescue Shoalhaven were called to assist the crew, battling strong north-easterly winds which caused difficult conditions offshore.

One of the men was able to cling to the upturned vessel, the other drifted away.

Rescue vessel Shoalhaven 30 responded joined the Westpac Rescue and Ambulance NSW helicopters in the search for the catamaran.

Marine Rescue Shoalhaven volunteers found the vessel and its crew member, taking him aboard.

The other man drifted towards the beach where he was spotted and rescued by a member of the public on a surf ski.

Marine Rescue Regional Controller for Illawarra Bruce Mitchell, said the man rescued by Shoalhaven 30 was taken to Greenwell Point.

“He is reported to be safe and well, although shaken,” Mr Mitchell said.

“He did not require ambulance attention.

“We understand that the man rescued by the surf ski is also safe and well with no reported injuries.”

The catamaran was unable to be rescued due to the conditions and is still capsized and adrift offshore. It is expected to wash up on Seven Mile Beach in coming days.

“Sunday’s sunny weather attracted a lot of people onto the water, but the strong winds caused difficulties,” Mr Mitchell said.

“Marine Rescue NSW urges all boaters to take extra care and to always log on with their local marine rescue base or use the Marine Rescue NSW App for smartphones to ensure that their boating plans are known in case of any emergency.”