Of the three ways to move outsized, awkward cargoes—wet-transport towing for things that float, dry-transport hauling on towed barges for things that don’t, or the use of specially constructed heavy-lift ships—the heavy-lift ships are the safest, fastest, and most economical means. Also, heavy-lift insurance costs are a fraction of those for towing and barge-shipping.
The first heavy-lift ship, the MV Lichtenfels, was put into service in 1929 by the German company DDG Hansa. She had a 120-ton lift capability. As more ships were constructed or converted for the purpose (heavy lift was defined as loads greater than 100 tons), they looked like conventional break-bulk freighters of the time, distinguished only by larger masts and booms.
By the 1960s there were few such specialized ships operating. Then two changes occurred that led to increased heavy-lift demand. The first was the world maritime shipping industry’s conversion from break-bulk cargo carriage to containers. Despite its advantages—such as accommodation of a wide variety of cargo types and shapes—break-bulk cargo handling was slow, labor-intensive, and costly. The new shipping used pre-packed containers that were in standard sizes so the boxes could be stacked in racks in the holds and on deck. Containerization provides rapid cargo-handling in port, greater safety at sea, and much lower labor costs.
The second change was the rapid expansion of the global offshore oil and gas industry. As exploration and production activity moved into deeper water, the structural components became more massive. In shallow coastal waters, the requisite marine construction had been done using barges and floating cranes. Much of this development had depended on the offshore site being near shipyards where the major oil platform components were manufactured. But if the huge assemblies and entire oil platforms could be manufactured anywhere in the world, then rig owners could take advantage of the lowest construction costs. The question became how to transport such bargains great distances across the oceans—which led to the development of the float-on/float-off (flo-flo) heavy-lift ships, also called semi-submersibles, the largest behemoths of the heavy-lift family. First coming into service in 1979, they are basically self-propelled, floating drydocks.
The flo-flos have a large, clear main deck with the bridge deckhouse set well forward so almost the entire topside area can be used for the load. A very flexible and complex ballasting system lets the ship submerge slightly stern-first so the load can be floated aboard. The largest semi-submersibles can ballast down so that the main deck is 42 feet below the surface, permitting deeper-draft loads to be floated on. When the ballast water is pumped out, the ship is surfaced and the cargo is secured on deck.
For loads that do not float, the ship comes alongside a pier and the cargo can be skidded or rolled aboard. (The process can be a real challenge for the ballast and trim system.)
Today, about 60 flo-flo ships are in operation, with more being constructed to meet expanding operational demands. The largest are the sister ships Blue Marlin and Black Marlin. The former was recently upgraded and can carry loads up to 70,000 tons, the weight of a medium-sized cruise ship. The Blue Marlin has transported several U.S. Navy ships between the Middle East and the United States, including the war-damaged USS Cole (DDG-67) and Samuel B. Roberts (FFG-58).
While semi-submersibles are the largest in the global fleet of heavy-lift ships, several other types are in service, generally more conventional in appearance. Some offer roll-on/roll-off capabilities similar to a super-sized Navy landing craft. Others are equipped with large cranes and oversized (often open) holds. The largest of this type can lift and transport 5,000 tons.
Size does matter, since the weight and dimensions of the heavy loads continue to grow. In 2010 the Dutch company Dockwise, the largest heavy-lift operator, announced its intention to build a semi-submersible that will have a 100,000-ton capacity. So if the USS Missouri (BB-63) needs to get a lift somewhere, such a ship could easily do it. That is, if you could get her aboard.