Ships and even small boats are a major source of noise and other pollution, a growing concern along today's crowded coasts. One solution: a waterjet technology being developed by Rolls-Royce Naval Marine in Walpole, MA. The waterjets propel ships by shooting water out their sterns, allowing them to maneuver in water that would be too shallow for comparably sized vessels that rely on propellers and rudders. And unlike the waterjets used in personal watercraft and some ferries, which expel water above the vessels' waterlines, the new design discharges the propulsive stream underwater, thereby reducing wake and lowering noise. The Rolls-Royce waterjet operates at 30,000 to 50,000 horsepower-suitable for propelling fast ships like naval destroyers, which would benefit from the underwater jets' stealth. Smaller boats also may benefit from similar technology, though; a 2,000-horsepower version is scheduled for testing in spring 2003.