(1) Whenever a question arises whether the wages of any seaman or apprentice are forfeited for desertion from a ship, it shall be sufficient for the person insisting on the forfeiture to show that the seaman or apprentice was duly engaged in or belonged to the ship, and either that he left the ship before the completion of the voyage or engagement or, if the voyage was to terminate in India and the ship has not returned, that he is absent from her and that an entry of his desertion has been duly made in the official log book.
     (2) The desertion shall thereupon, so far as relates to any forfeiture of wages under this Part, be deemed to be proved, unless the seaman or apprentice can produce a proper certificate of discharge or can otherwise show to the satisfaction of the court that he had sufficient reasons for leaving his ship.