The first hulls sticked to the mould a little bit and ther was some damage. I repaired the damage but I got a hint to use other gelcoat. The gelcoat is the first layer applied to the mold. The outher layer of the hull when de-moulded.
Now I used transparant gelcoat with
pigmentpaste for colour. Everythin went oke now and I could demould the
hull without any problems.