The individual and three other persons were working to relocate the 30” diverter housing from the main deck to a stump cart inboard of the port side cantilever beam. To facilitate this movement, the cart was placed outboard of the main deck, part way out to the Texas Deck. After placement of the diverter on the cart, it was necessary to secure the diverter with two chains and load binders prior to moving the cart inboard. The first chain was deployed without incident; however, a ‘cheater’ was required to set the load binder on the second chain. A 2” steel tube 40” long, weighing 11 pounds was tossed to the individual. He failed to catch it cleanly and was struck by the tube, causing him to lose his footing and fall to the deck of the cart. While attempting to stand he rolled over the outboard edge of the cart and fell to the sea. Search and rescue efforts were unsuccessful.