Limit the number of bunches the vine produces will help with this problem.

I also remove a third of the small grapes after they have set and then again mid july. This was the way i was told to do it by an eldery gent who kept a vine in one of the NT vinerys. I only ever get about 10 bunches of grapes. I tend to prune it harshly at christas :o)

thank you for your help lets see what i can do now