A bundle of new 3-1/2” drill pipe was being lifted by crane from a workboat to a rig’s main deck. There were nine joints of pipe in the bundle measuring approximately 30’ in length. The crane rigging consisted of a 10’ spreader bar with a 30’ single leg wire rope cable sling on each end. Each sling was single wrapped around the bundle on each end and then attached to itself with a shackle. There was a slight angle on the sling lines that made up the difference between the length of the spreader bar and that of the tubulars. Once the load swung clear of the boat, one of the cable slings slipped toward the center of the load, causing the load to become unbalanced and eventually allowed the whole bundle of 3 ½” drill pipe to shift and slip out of the rigging. The drill pipe fell to the sea bottom. No injuries resulted.