Inshore lifeboat tasked to report of craft aground near Martello Tower, Isle of Grain. ILB launched at 1440 and advised by Medway VTS, that the yacht had re-floated and was proceeding up the harbour. ILB located the said Yacht, two occupants all okay, owner reported that all was well onboard and he was returning to his mooring. ILB released and returned to station at 1515. Estly 3.