blind 180--two concussions

Need some help. I have a really consistant ollie to blind and can throw them off rollers, but when I try to take them wake to wake it always ends bad. Out of my maybe 12 attempts at the blind 180 w2w I have had two concussions. Both falls were to the back of the head. My friends said that I rotated properly, but that the boat pulled me out the back. How do I keep this from happening? Any help would be great.