Andreas,
The subject of polar diagrams has always been a source of wonderment and confusion. People often are dismayed that a manufacturer does not provide polar diagrams for a particular model. The reason is, there are so many different configurations, shoal keel, deep keel, standard mast, furling mast and more they they could not provide accurate polars in a single sheet. As well, it also depends on how each individual boat is loaded. Accurate polars require that the freeboard measurements be taken, stability test and sails be measured. Even then, the Velocity Prediction Program cannot take into account sea state and such. If useful polar diagrams are to be obtained, it can be done by contacting US Sailing or the governing body in your area. A certified measurer will obtain the aformentioned data and apply that to the VPP. Though they can be very useful, I know highly successful racing skippers that disregard polar data.