A new Joint Industry Project (JIP) has been initiatedrecently by MARIN, called ESD-JILI (??), lookinginto the working principles and scale effects on EnergySaving Devices (ESDs). Three ESDs have been chosenfor the investigations in the first phase. They were a preductwith a supporting stator in the duct, a pre-swirl statorwith asymmetric blade design and Propeller Boss CapFins (PBCF). Measurements of forces and moments on allcomponents of the ESDs have been carried out in selfpropulsionmodel tests with dedicated sensors. ParticleImage Velocimetry (PIV) technique has been used in theinvestigation of the detailed flow around the ESDs. Inorder to investigate the scale effects in model tests, a fullscalewake field was approximated by a 'smart shipmodel'. Computational Fluid Dynamics (CFD) calculationswere carried out both for designing the smart shipmodel and also for the detailed flow around the ESDs.Some findings and fundamental issues on scale-effects ofthe ESDs are addressed in this paper.