The experimental ship Sea Shadow was developed in total secrecy by the United States Navy and its contractors, Lockheed Martin Corporation and the Advanced Research Projects Agency, during the 1980s. The Navy finally unveiled the stealth ship to the American press and public in 1993, nearly a decade later. Sea Shadow moves through the water almost silently, and stealth technology renders it virtually undetectable to radar, sonar, and the infrared sensors used by heat-seeking missiles. The ship measures 50 m (164 ft) long, 21 m (68 ft) wide, and has a 4-m (14-ft) draught.
Although the ship remains the most economical way to transport bulk cargoes over the world's oceans, naval architects recognize that room for improvement remains
Most of today's cargo vessels travel at a speed of about 20 to 23 knots, limited by their hull design. Naval architects are exploring the use of multiple hulls-instead of having one large hull, ships might have two or three hulls connected to each other. These designs are prominent in small- to medium-sized boats but have not been applied to bulk carriers. The catamaran (two hull) or trimaran (three hull) offers great stability with much less water resistance.
Concerns about applying such designs to bulk cargo carriers persist, however. Some question the potential strength of large, multiple-hulled ships in rough seas. Others argue that multiple-hulled cargo carriers would not have adequate carrying capacities to make them economical
Naval architects are also exploring the use of narrower hulls in single-hulled cargo vessels. Military vessels throughout history have used slender hulls, which enable ships to travel faster because they experience less drag in the water. Many question the potential stability of the slender-hulled cargo ship, which will undoubtedly make transoceanic crossings with containers stacked high on its decks. Moreover, a narrow-hulled ship cannot carry as much cargo as a modern freighter of equivalent length.
The solution may lie in the semiplaning monohull. This hull design has a sharp V-shaped bow for cutting the waves and a wide, shallow rear with a slightly concave profile underwater. This design creates waves that help lift the vessel and reduce drag in the water. These hulls, similar to those used in many modern pleasure boats, would become more efficient as the ship goes faster.
New designs in ship propulsion will also increase the efficiency of ship transport. When compared to marine diesel engines of the same weight and volume, gas turbine engines produce far greater amounts of power without using more fuel. They also burn cleaner, emitting only 4 percent of the sulfur oxides and 5 percent of the nitrogen oxides emitted by diesels of the same power. Gas turbine engines currently power small passenger and car ferries, but they have been prohibitively expensive for use in bulk cargo transport.
In the future, water jet drive may replace the screw propeller. Both of these propulsion systems spin and push water to move the vessel. But while the screw propeller becomes less efficient at high speeds, the water jet drive gains efficiency as speed increases.
Such changes will undoubtedly make the ships of tomorrow faster and more efficient. Naval architects and engineers predict that a ship with a semiplaning monohull, gas turbine engine, and water jet drive will easily reach a speed of 45 knots. These and other innovative ship designs will cut the cargo crossing time between Europe and North America from 14 to 35 days to a week or less.