K i just started trying this flip.
When I do this i do not think about doing a cartwheel. I think more about going tip over tail. So when im initiating the trick I try to flip directly over the front of my board and let my tail follow.
Keep both hands on the rope! I have a thread on here with my youtube video of my first attempt. I let off my edge and moved the handle up to my head during the rotation, you can see the crash for yourself.
As for the crashes. They hurt. Bad. If you look at the video I posted, when I hit the water my ear drum cracked. It felt like i had an ear ache when I came back up.
I stress this:
Edge hard into the wake, make sure you dont let off, keep the handle at your waist.
Im sure if you do as i suggested, you will complete the rotation, and the crashes will be not as bad!