Floating on Air Could Lend Ships Speed and Fuel Efficiency

Tiny bubbles...great in champagne, but could a blanket of bubbles be the next technological leap in eco-efficient shipping? The question of how to overcome water's drag and build a "slippery ship" is being studied by government and private concerns in the US, Russia, Japan and Europe, which suggests it is understood as a potentially valuable technology for both traditional defense and for defending positions in the global market. A good assessment, since 90% of goods travel around the globe by ship. That is 6 billion tons of cargo*, and growing. Naval architects must battle three types of drag when designing ships: wave drag, pressure drag and frictional drag. Wave resistance is significant when moving at high speeds, and can be largely addressed by good bow design. Pressure drag is a backwards tug which develops due to the pressure difference in the water at the bow and the stern of a boat as the seas are split and come together again behind a moving ship. It can be significantly reduced by streamlined hull design. But frictional drag is a problem which has bedeviled boat designers since British engineer William Froude formulated principles of fluid dynamics in the 19th century. The prospect of using tiny air bubbles was proven when Michael McCormick and Rameswar Bhattacharyya showed that a cylinder generating hydrogen bubbles by an electrolytic process moved through the water with significantly reduced frictional drag in work done at the US Naval Academy at Annapolis, Maryland. But the ability to produce this effect on an actual ship has proven elusive.

An article in the New Scientist reviews the state of the art in the technology and the obstacles that researchers are facing. For example: how do you create a blanket of bubbles around the ship but keep the propellers in undisturbed water where they can create thrust efficiently? How do you keep bubbles in place at high speeds? And can the gains from drag reduction outweigh the energy costs of creating the bubbles?

One promising solution derives from the work of Yoshiaki Kodama, director of the Advanced Maritime Transport Technology Department at Japan's National Maritime Research Institute (NMRI) in Tokyo. Kodama's team proposes to shoot a layer of bubbles from slots near the bow of the ship. The bubbles will travel along the hull of the ship, with enough bubbles trapped under the ship's surfaces so that the constant replenishment is sufficient to maintain the blanket of bubbles.

For the sports fan or the gambler, the field appears to offer the race of the century: Will the Japanese team led by Kodama succeed to create a "Super-eco Ship", which will include propulsion, control and design changes in addition to drag resistance technology? Will researchers in the US get an advantage from computer models being developed in competition by Stanford University in California and researchers from the defence contractor General Dynamics? Has the concept of air cavitation, invented by the Russians for super-speedy torpedoes, given Russian shipyards a step ahead? (They are already turning out low speed ships which benefit from up to 40% reduction in drag.) Can naval architect Knud E. Hansen and Rotterdam-based DK Group deliver on the promise of a high-speed freighter that can cross the Atlantic in two-and-a-half days? We will watch with great anticipation for the next big break-through.

*2003 data

Via ::New Scientist Tech