Diamonds in Black Sand — Ann Marston

Iain dreams of sailing beyond the treacherous Barrier Reefs to the tumultuous Wildesea, to become an Outsider like his father before him. But he is bound in service to his uncle Durstan for raising him after the death of his parents, and may not go until he has paid back the time he owes.

The new King of Celyddon bans the magic that keeps the Out-ships safe on the demanding Wildesea where Iain longs to be, and makes outlaws of those who work that magic. Neither the ships nor the men and women who sail them are allowed in the Realm. Iain has no means of escaping his bondage.

He is almost resigned to his fate and trying to make the best of it when he himself develops some of that banned magic, and becomes an Outlaw on the run from the authorities.