Flooded Generators have been proposed as a possible solution to eliminate the risks due to the seal failure, and improve cooling in tidal stream turbine generators. In a flooded generator, the stator-rotor gap is filled with the seawater; this poses a serious corrosion risk to the material inside the generator. For this reason, a can or a protective shield is used on the stator and the rotor surfaces in the watergap. This paper compares different rotor-can materials based on the eddy current losses in the rotor-can, and its impact on the temperature inside the generator. Due to the flooded gap, the temperature rise in magnets, because of rotor-can eddy current losses is much lower than in a corresponding airgap machine. Thus from the thermal point of view, the choice of the rotor-can material is less critical in a flooded generator than in an airgap generator.@en