Four people were on board the craft when they got into difficulties off Shanganagh cliffs between Killiney and Bray. One person swam to shore to raise the alarm, two clung to a buoy while another was reported missing.
The RNLI's all-weather (ALB) lifeboat and inshore lifeboat launched at 14.08pm and proceeded to the scene, arriving 15 minutes later.
Dun Laoghaire RNLI volunteer crew recovered two of the casualties on board the inshore lifeboat while the Irish Coast Guard rescue helicopter 116 located the missing person in the water. All three were transfered to the helicopter and taken to Tallaght Hospital for treatment.
Conditions were described as fresh with force four to five winds.