222. The provisions of this Chapter shall apply to a master and an apprentice as they apply to a seaman, except that-(a) a master shall be deemed to be a “serving seaman” during any period commencing the day on which he assumes command of the ship and ending thirty days after the date on which he finally relinquishes such command; and(b) an apprentice shall be deemed to be a “serving seaman” during any period commencing the day on which he joins the ship and ending thirty days after the date on which he leaves such ship.