© 2020 Elsevier LtdGate Rudder® system is a new type of energy-saving and manoeuvring device to provide additional thrust, similar to an accelerating ducted propulsor. Individual control of the twin rudder blades aside the propeller also provides enhanced manoeuvrability. Based on the first full-scale application on a domestic container vessel in Japan, the Gate Rudder® system improved the propulsive efficiency (by ~14% fuel saving in sea trials) as well as manoeuvring, noise and vibrations characteristics of this vessel. More power saving in-service condition was also reported as high as 20–30%. In summary, the power-saving measured with the ship system was more than the predictions based on the CFD analyses and model tests. This has prompted the authors with further investigations on the Gate Rudder® system by detailed CFD analyses and new model tests with a larger size model of this container ship conducted at the Ata Nutku Ship Model Testing Laboratory of Istanbul Technical University (ITU). This paper investigates the influence of the Gate Rudder® on the ship performance by using two different scales of models for the same container ship and the full-scale data which are complemented by the RANS based CFD analyses. The results from the study are discussed to shed light on the scale effect as well as providing further information on the powering performance prediction of vessels with the Gate Rudder® system.