Fifteen people were rescued from lifeboats after drifting some 300km in strong winds and high waves from their ferry which sank Friday night in a storm in the Java sea.

Armansyah Putra was among 13 others also picked up Wednesday, all clinging to a Conoco Phillips rig after the ferry sank en route from Kumai on Borneo island to Semarang in Central Java.

Apart from a blistered and sunburnt back, Armansyah Putra looked little the worse for his ordeal, after reportedly drinking or eating nothing but a few sips of sea water, saying he survived with the help of others.

"When the ship was sinking, they asked us all to remain calm," he told MetroTV on Thursday from his bed in Soetrasno Hospital in Central Java.

"I tried to grab on to a float but I could not... the ferry was swaying."

"I did not know anything. In the end I was saved by people around me."

Doctors said he was well on the way to recovery.

His mother, Bekti Riwayati, said she had given up hope of ever seeing her two missing sons again as they slipped from her grasp as the ferry went down.

Riwayati was among the first people rescued on Saturday but her youngest son, three-and-a-half-year old Agil Widodo, has still not been found.

She said she was hopeful one of her sons might be alive after her husband, Askuri, received information that a child had been found and was waiting to be evacuated to Surabaya, MetroTV reported.

The family said they would return to their home in Kendal in Central Java and move on with their lives.