The Cannibals — Iain Lawrence

As Tom Tin nears Australia, where he's to serve a lengthy sentence for a murder he didn't commit, he and his fellow convict, Midgely, plot their escape. No matter that the ship carrying them and the other juvenile criminals is captained by Tom's father. Tom knows his father can't help him clear his name and regain his freedom -- not as long as Mr. Goodfellow, a man who wants the ruin of the Tin family, wields power back in London. So Tom and Midgely decide to go overboard! So do other boys who seize their chance at liberty -- boys who aren't so innocent, and who have it in for Tom.
To make things worse, the islands in the Pacific look inviting, but Tom remembers his father's warnings: headhunters and cannibals lurk there! The boys go anyway. And as conflict among them mounts, as they encounter the very dangers Captain Tin spoke of, Tom must fight to keep himself and Midgely alive.