Going to AC for the first time in a couple of weeks. Have some questions about the beaches that the hotel and other web sites don't seem to address very well.

How are the beaches for swimming? Some of the hotel sites mention swimming from the piers... is the bottom sandy or rocky (or coral)? what's this thing about sea walls?

Also what about walking up and down the beach for a real stroll or jog? Seems like they are all touting their private beaches, which doesn't seem that cool to me...

Any places for shelling?

Thanks for any insight.