Imagine a mile-long floating structure so massive that it sneers down at an aircraft carrier. The U.S. Navy is mulling just such a craft-a Joint Mobile Offshore Base (JMOB) that could move under its own power anywhere on the ocean and withstand the most violent conditions.

The JMOB is not alone in its giant ambitions. Plans are also being developed for a cargo-ship port, airport and even a floating city. Researchers presented engineering analyses of several of these projects at the June meeting of the International Society of Offshore and Polar Engineers in Stavanger, Norway.

None of the so-called Very Large Floating Structures has been built. Confident in the technical feasibility of each, designers and supporters of these titanic craft face the most challenging task of all-finding someone to pay for them.

One Military Base, to Go

If you want deep pockets, start with the U.S. military, which is finding that it’s increasingly difficult to secure space for military bases overseas and to protect them from attack. The JMOB idea is that the giant floating base-the largest floating object ever built-could be deployed throughout the globe while remaining in international waters.

The plan calls for five 985-foot sections each with their own propulsion system, but connected when on site. Each section would resemble the semi-submersible platforms common in oil drilling. The section would have two pontoons, each shaped like a ship’s hull. Empty, the pontoons would ride on the surface like a ship for travel. On location, the sections would be filled with water, and their massive weight would make the platform almost as stable as land.

“It wouldn’t be a standard project,” says Ronald Riggs, a civil engineer at the University of Hawaii at Manoa, who was involved in the feasibility studies, “but I think it could be done.”

Heavy Hinges

The greatest engineering challenge was figuring out how to deal with the incredible pressure on the joints between sections, says Bat LaPlante, manager of Department of Defense business development with New Orleans-based McDermott, the main commercial partner on the studies.

The team designed a new hinge scheme that includes a central universal joint at the middle and city bus-sized units on either end with massive rubber cones inside that absorb the bulk of the stress. This design is now being used during the construction of some floating offshore oil platforms; the hinges attach barges delivering major pieces of the platforms.

Of course, the studies also identified a financial challenge-an estimated cost of $5 to $10 billion. That makes commitment to a full-scale JMOB unlikely in the near future.

The Navy is considering building a floating platform in the 1,300-foot range to use as a training tool for pilots, who would practice carrier landings designed from results of the JMOB studies. LaPlante says this could even be a single modified section of the JMOB.

SeaHub: Offshore Port

SeaHub would bring the JMOB technology to an offshore port for deep-draft container ships. (Image courtesy of Coastal Operations Institute)

JMOB may spin off a civilian version. A modified JMOB section could act as a floating cargo-ship port called SeaHub, where cargo from huge ships could be transferred to smaller ships for distribution to existing harbors.

Many shipping companies plan to cut costs by building ships that carry up to 18,000 containers-compared to 1,500 in typical ships today. Unfortunately, such giant vessels would draw as much as 60 feet and would not fit into almost any U.S. port. Some harbors could be dredged to sufficient depths, but dredging would be extremely expensive and would require severe environmental regulations.

SeaHub is promoted by the Coastal Operations Institute, based in Panama City, FL, a consortium that includes federal and state agencies as well as private companies and universities. Two possible locations include the Gulf of Mexico, south of New Orleans, and the mid-Atlantic, perhaps off Georgia.

Jim Smith, the institute’s operations manager, estimates SeaHub’s cost at around $500 million. Given that Savannah, Georgia, is considering spending over $200 million dollars to dredge its port for larger ships, Smith says that figure would not be unreasonable if several ports get involved. Currently the group is seeking state and federal funding. Smith says a SeaHub could be completed around 2005-2006 if all goes well.

Floating Airports

In Tokyo, the Technological Research Association of Mega-Float has been pushing for floating airports, built behind breakwaters. A 1,000-foot prototype was completed in 1995, and in 1998 the association finished building a second prototype in the 3,000-foot range.

Earlier this year Japanese researchers finished successful tests to prove planes could land safely without the huge volume of steel impeding navigation equipment, and then dismantled the prototype. It is not clear if the association will find funding for a full-scale version.

Freedom Ship

The controversial Freedom Ship would put high-rise apartments on a gigantic barge. (Image courtesy of Freedom Ship)

And now for something completely different: Freedom Ship International, based in Palm Harbor, FL, aims to create a unique lifestyle. It envisions a Freedom Ship that is 4,500 feet long, 750 feet wide and 25 stories high. This astonishingly large vessel will include all the elements of a functioning city such as businesses, schools, a hospital and homes up to 5,100 square feet.

The dream is to sail Freedom Ship around the world on a two-year cycle stopping for extended stays at interesting ports. Actually, the ship will never fit in any port, so passengers will travel between ship and shore via boats, helicopters or airplanes that land on the top deck.

Norman Nixon, CEO of Freedom Ship, says the company has signed a lease for property in Honduras and hopes to begin setting up construction facilities by yearend. His firm is working on funding for the $10 billion price tag, he says.

Saving on Structure

The greatest challenge in Freedom Ship’s design, says Nixon, was making it relatively economical. Initially the company investigated building what was essentially an over-sized cruise ship, but that proved prohibitively expensive. Freedom Ship decided to sacrifice speed and switched to a much less expensive barge design. As the company’s Web site describes it, the ship is “basically a flat bottomed, bolt-up barge with a conventional high-rise built on top.”

With a height roughly half its width, Nixon says, flipping the ship will be as impossible as making a two-by-four float on its side. And he claims that such a mass will stop even a 100-foot wave dead in its tracks.

University of Hawaii’s Riggs is a little skeptical of the project. “It would be an engineering challenge to make a single structure that long and in the ocean environment,” he says, but adds that it is possible.

Many experts take the gargantuan Freedom Ship with an equally gargantuan grain of salt. And plenty of skepticism and towering financial hurdles remain for all of these monster projects.

But advocates emphasize the ever-growing maturity of underlying ocean engineering technologies and the ever-dwindling supply of open land in many locations. At least one of these mega-projects will go from computer screen to saltwater, predicts McDermott’s LaPlante: “It’s just coming.”