Ex – Shounen Hyouryuu

From the Animeraider:
Satoshi and a group of his friends are on a lengthy boat ride to Kijijima when the world comes to an end – literally. A huge Tsunami wave 500 meters tall overpowers the boat and he finds himself stranded on an island and alone. Meanwhile the rest of the boat has grounded after being dashed upon the shores and soon Satoshi finds them, and sets off a struggle to survive for the passengers and crew of the ship…