The inshore lifeboat at Shoreham was launched to a 16ft vessel, which had lost its propeller and was drifting.
The boat had three people on board but they had no lifejackets, radio or other means to attract attention.
She had launched from Shoreham Beach at 3am that day and had lost her prop.
Their position was given to the coastguard as 2km south of Shoreham Harbour. The inshore lifeboat searched the area but found no trace.
Eventually the boat was found several miles south west of the harbour. A tow line was set up between the lifeboat and the vessel and she was towed back into the harbour.