There were many changes of ways of operation of low-speed long-stroke marine Diesel engines powering ships introduced last years. Their range of continuous low load operation has been significantly extended. That changes exerted a great influence on operating condition of equipment connected with engines, particularly waste heat boilers. The bellow paper deals with adjustment of water level in smoke – tube exhaust gas boiler depending on real operating condition of the ship powered by the marine slow-speed longstroke Diesel engine operated under the “Super Slow Steaming” program