I thought it worked like HOI, where they go into the same area that under-construction units do, and then become available again once fully repaired.
(I tried this, and it works, *except* that the ships can only be redeployed at their original home port province - not even connected provinces, and not where they were when you sent them in, either. This can be quite troublesome when you don't control that province anymore, and as home ports are not visible in-game except when the ship is in the force pool....)