Ten peoples, including five children, were ferried to safety after the speedboat they were travelling in ran aground on rocks off the North Down coastline.
Five adults were also rescued when the vessel got into difficulties close to Millisle on Saturday afternoon.
It is understood the group had been fishing close to rocks when the engine failed.
The drama unfolded shortly before 3.30pm on Saturday, and the Bangor lifeboat was on the scene within 30 minutes.
One man who had got out of the stricken vessel was standing on rocks - and was quickly plucked to safety by the crew.
Attention then turned to rescuing the other people who were stranded on the speedboat.
Bryan Lawther, from Bangor Lifeboat, said mechanical failure is thought to have caused the incident.
"They were fishing close to the rocks and, for whatever reason, the engine failed," he said.
"As they drifted to the rocks, some of the adults got out to try and push it clear.
"Another one of the adults climbed over the rocks and got cut off from the rest.
"When we arrived they had to get him into the lifeboat, while another of our volunteers entered the water with a tow-line and we towed them back to Millisle slipway."
According to Mr Lawther the group had a lucky escape.
"They had put themselves in a certain amount of danger," he added.
"Sometimes even the least likely scenario can turn into an absolute disaster.
"There were five adults and five children - when you see the crowd that was on board, it could have been very serious."
According to Jude McNeill, of the Belfast Coastguard, the quick reaction by rescuers had been crucial.
"Had the boat been left for too much longer being bashed against the rocks, it could have been badly damaged," she said.
"Fortunately, they were all wearing lifejackets, but things could have been a lot different if we hadn't been able to give such a swift response."
North Down MLA Peter Weir said the incident underlined the importance of retaining the coastguard station at Bangor.
"The first few minutes of any emergency situation are critical, and once again we have shown how vital the decision to retain the coastguard centre was," he said.
"This weekend's close shave should act as a wake-up call to all of us about the dangers of the sea.
"We cannot be complacent, and in the month that we commemorate the centenary of the Titanic, this is a timely reminder that the risk from the sea is not just an historic threat.
"This weekend, tragedy was averted thanks to this Bangor lifeboat. We may not be so fortunate in the future."