A court may in an action for the recovery of any wages order the master of a ship or a person employed in a ship otherwise than under a crew agreement to pay in addition to the sum due, interest on it at the rate of 20% per annum or at a lower rate as the court may specify starting from seven days after the sum became due and ending when the sum is paid; except that where it appears to the Court that the delay in paying the sum due was by mistake not attributable to any default of the master or other agent of the owner, it may refuse to allow payment of interest on the wages.