OK that explains it then at least now when I see which side the damage is I will know if I am placing the tube to high or low on the show. I was thinking zipper side towards water. That explains my confusion. I was noticing I was hitting the shell close to the zipper so I was thinking I was not off setting the tube enough when in fact I should of been going the other direction.

That is one of the nice things about the tubes fp sells they transmit contact with the shell very well so you know right away to stop pushing.

This post almost sounds like porn. Clams, zippers, pushing ,breaking it lol.