The Wells inshore lifeboat team was called out to help check on the welfare of a 64-year-old sailor in Brancaster Harbour.
He had not responded to calls from his family and worked with a coastguard team in an operation to ensure the man was OK.
Fortunately, the yacht was found and the man had gone to sleep not realising his phone battery had run out of charge.
Lifeboat Operations Manager, Chris Hardy, said: “We are very relieved that this incident had a happy conclusion. It is important that people know that we are here 24 hours a day, 365 days a year, ready to respond to any eventuality of potential danger from the sea. Any concerns people may have regarding possible incidents on our coastline are always a valid reason to phone 999 and ask for the Coastguard.”