Volunteer crew member Stephen Crowley was giving one of his fellow volunteers, helm David Knight, a lift ashore from his own boat shortly after 5pm when the pagers were set off.
As they made their way to the slipway at the back of the harbour to get to the lifeboat station, they encountered a man in the water who had become separated from his personal watercraft and was struggling to stay afloat.
They managed to get a rope around the man and help him onto the side of their boat and began bringing the man to shore, where they were joined by two more volunteers, helm Philip Ferguson and crew member Emma Wilson, who were already fully suited up and preparing the boat for launch when they saw the situation unfolding from the lifeboat station.
The man was helped ashore and was assessed for any first aid requirement.
Speaking after the callout, volunteer lifeboat press officer Gerry Canning said: "Fortunately our volunteers were on hand almost instantly. It is important to remember that whatever your activity, wearing a well-fitted and suitable lifejacket or buoyancy aid could save your life."