One of the men was found clinging to a mooring buoy. RNLI spokesman Vic Booth said: "He was able to speak to the Coastguards on his mobile phone and said he had lost sight of his friend who had been in the dinghy with him."
Both rescue boats battled through near gale-force winds and torrential rain to reach the men and arrived at 11.05pm. By then the missing man had made it safely back to shore.
Mr Booth said: "The casualty was immediately spotted by the inshore lifeboat crew after they had been given precise details that the man was clinging to the first mooring buoy east of Gillingham Marina.