Thank you very much for your explanation Michael,

yes, i should better try to do this shape in sub-d. However, prior reading your reply i tried also Andrei's example which worked nicely, but imho did not matched the tail right, like getting very thin at the end. So i tried to model the profiles and the curves in MoI again and tried the "Cover Surface" function out in an old copy of ViaCAD. My humble approach one can see here, how the tail (were it's getting thinner at the end) should imho look like. After that i imported the cover surface and mirrored it in MoI and made also a solid out of it. But i'm not sure if this would represent a good smooth surface model...

Best regards
Stefan