A hydrofoil unit for attaching to the stern of the hull of a boat. The unit includes a mount that mounts to the stern of the hull of the boat, a hydrofoil that is pivotally attached to the mount, a pivot assembly that pivotally attaches the hydrofoil to the mount, and apparatus for pivoting the hydrofoil relative to the mount. In one embodiment, the apparatus is automatic and includes an hydraulic cylinder that is pivotally attached to the transom of the boat and a strut that is pivotally attached to the hydraulic cylinder and the hydrofoil. In another embodiment, the apparatus is manual and includes an upper threaded rod that is pivotally attaching to the transom of the boat, a turnbuckle that is attached to the upper threaded rod, and a lower threaded rod that is attached to the turnbuckle and the hydrofoil.