It was their last refuge — the sea.
Having escaped death at the hands of brain-hungry zombies, these poor people have now had to endure days at sea on this makeshift raft. At first, it was kind of fun. They played “I Spy”, the geography game, and when the seas were calm enough, charades. But then they ran out of food and good spirits. Of the 150 survivors for the zombie apocalypse who got on the raft, only 15 survived the days of madness, starvation, dehydration and an ironic bit of cannibalism.
Then they landed on the coast, where they were eaten by waiting zombies.
Of course, this tale is only a bit less horrible then the historical event it is actually based on. The Raft of the Medusa was painted by the French Romantic painter Théodore Géricault in 1818-1819; he picked this topic because he knew it would be controversial and help to launch his career. The historical event, the scandal it caused, and the painting it inspired are all described in Death and the Masterpiece.