Aircraft carrier rear bumpers?

Anyone know why the US Navy started putting steel I beam assemblies on the stern of aircraft carriers, ibelieve beginning with CVN-72, and retro fitting them to older carriers? What is their purpose? Could it really be that they simply are bumpers?

Could you point out what you are referring to?

http://www.1000pictures.com/aircraft/carrier/041108-n-0780f-088_1280x1024.jpg

Screw Guards?

When a carrier “anchors out” in the harbor during a port visit, they use that fan-tail area to get on and off the ship.

The port authority will tie up a barge or pontoon, with a stair/ladder attached. The crew will use that to get into small chartered ferries to get rides to the port/pier.

Those guards may keep the barge/pontoon from smacking the hull too much (due to wave or wake action).

photo