on propeller noise and blade vibratory stresses. The Gannet was particularly suitable because the independently-driven propellers provided a comparison between counter and single rotation. Ultralight applications An Austrian company, Sun Flightcraft, distributes a contra-rotating gearbox for use on Rotax 503 and 582 engines on ultralight and microlight aircraft. The Coax-P was developed by Hans Neudorfer of NeuraJet and allows powered hang-gliders and parachutes to develop 15 to 20 percent more power while reducing torque moments. The manufacturer also reports reduced noise levels from dual contra-rotating props using the Coax-P gearbox. Use in water Torpedoes such as the Bliss-Leavitt torpedo have commonly used contra-rotating propellers to give the maximum possible speed within a limited diameter as well as counteracting the torque that would otherwise tend to cause the torpedo to rotate around its own longitudinal axis. Recreational Boating: in 1982 Volvo Penta introduced a contra-rotating boat propeller branded DuoProp. The patented device has been marketed since. After the Volvo Penta patents ran out, Mercury has also produced a corresponding product, MerCruiser Bravo 3. Commercial ships: In traditional machinery arrangement contra-rotating propellers are rare, due to cost and complexity. In 2004 ABB produced a product for large-power installations: the forward propeller is on a traditional shaftline, while the aft propeller is in an ABB Azipod. At lower power levels, contra-rotating mechanical azimuth thrusters are one possibility, convenient for CRP due to their inherent bevel gear construction. Rolls-Royce and Steerprop have offered CRP versions of their products. See also Coaxial rotors Contra-rotating Marine propulsion References External links Luftfahrtmuseum.com – Further information and pictures of contra rotators for the Fairey Gannet and Shackleton A History of Aircraft Using Contra-Rotating Propellers (Part 1) – Aircraft Engine Historical Society A History of Aircraft Using Contra-Rotating Propellers (Part 2) – Aircraft Engine Historical Society A History of Aircraft Using Contra-Rotating Propellers (Part 3) – Aircraft Engine Historical Society A History of Aircraft Using Contra-Rotating Propellers (Part 4) – Aircraft Engine Historical Society Aircraft engines Aircraft configurations Propellers