They didn't drop depth charges off the sides of destroyers from the roller storage racks. Actually there was no way to do that because of the way the racks were built. These storage rack contraptions were designed to slide a charge onto a tray that would then place the charge on the launching arbor in the ASW mortar and then the next charge would be rolled down into place for the next loading. As you can see the storage racks didn't overhang the side of the ship. These racks can vary from ship to ship in details, but they never overhung the deck. The drop racks on the fantail did.
A "Mare Island" installed rack

A "New York Navy Yard" installed rack without the charges in place


