All weather lifeboat launched at 1250 to report of 34ft Sloop aground on Knock John near Tower, one person onboard, comms between casualty and CG were very poor, so contact was being made via mobile phone. Whitstable Lifeboat also proceeding, on route, advised by Whitstable, they were on scene and no sign of craft. ALB on scene at 1342, nothing visual, info was still being gleaned by the CG and person on casualty craft, reported he can see two red & white sticks with aerials and a seawall, it was believed the casualty was close to Foulness Point. Both lifeboat were stood down at 1350 and CG tasking rescue 163 to carry out shoreline search. ALB back on station at 1455. NW 5/6, rain.