According to Official Guinness Records,
The longest known time which anyone has survived adrift at sea is approximately 484 days, by the Japanese Captain Oguri Jukichi and one of his sailors Otokichi. Their ship was damaged in a storm off the Japanese coast in October 1813 and they drifted in the Pacific before being rescued by an America ship off California on 24 March 1815.
Jukichi's cargo ship was carrying several hundred bags of soy beans between Toba and Edo in Japan, when a strong wind led the captain to order the mast cut down. The crew lived off the beans and distilled seawater, but by the time of their rescue, 12 of the crewmembers had died of scurvy.
For a complete list of 1815 records, please visit 1815 Guinness Records in Japan.