Contra-rotating propeller Aircraft equipped with contra-rotating propellers (CRP) coaxial contra-rotating propellers, or high-speed propellers, apply the maximum power of usually a single engine piston powered or turboprop engine to drive a pair of coaxial propellers i ...

s have benefits when providing thrust in marine applications. Contra-rotating propellers are used on

torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, such ...

es due to the natural torque compensation and are also used in some motor boats. The cost of boring out the outer shafts and problems of mounting the inner shaft bearings are not worth pursuing in case of normal

ships A ship is a large vessel that travels the world's oceans and other navigable waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research and fishing. Ships are generally distinguished from boats, ...

Advantages and disadvantages

Advantages

*The propeller-induced heeling moment is compensated (negligible for larger

). *More power can be transmitted for a given propeller radius. *The propeller efficiency is increased by recovering energy from the tangential (rotational) flow from the leading propeller. Tangential flow does not contribute to thrust, conversion of tangential to axial flow increases both thrust and overall system efficiency.

Disadvantages

*The mechanical installation of coaxial contra-rotating shafts is complicated and expensive and requires more maintenance. *The hydrodynamic gains are partially reduced by mechanical losses in shafting.

Applications

Torpedoes A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, such ...

such as the

Bliss-Leavitt torpedo The Bliss-Leavitt torpedo was a torpedo designed by Frank McDowell Leavitt and manufactured by the E. W. Bliss Company of Brooklyn, New York. It was put into service by the United States Navy in 1904 and variants of the design would remain in i ...

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 also found applications: in 1982

Volvo Penta Volvo Penta is a Sweden, Swedish marine and industrial engine manufacturer, a joint stock company within the Volvo, Volvo Group. Volvo Penta evolved from a foundry in Skövde 1907, when the first marine automobile engine, marine engine, the B ...

introduced a contra-rotating boat propeller branded DuoProp. The patented device has been marketed since. After the Volvo Penta patents ran out,

Mercury Marine Mercury Marine is a marine engine division of Brunswick Corporation headquartered in Fond du Lac, Wisconsin. The main product line is outboard motors. It also produces the MerCruiser line of sterndrives and inboard engines, as well as a li ...

has also produced a corresponding product, MerCruiser Bravo 3. However, in commercial ships and in traditional machinery arrangement, contra-rotating propellers are rare, due to cost and complexity.

ABB ABB Group is a Swedish-Swiss multinational electrical engineering corporation. Incorporated in Switzerland as ABB Ltd., and headquartered in Zurich, it is dual-listed on the Nasdaq Nordic exchange in Stockholm, Sweden, and the SIX Swiss Excha ...

provided an

azimuth thruster An azimuth thruster is a configuration of marine propellers placed in pods that can be rotated to any horizontal angle (azimuth), making a rudder redundant. These give ships better maneuverability than a fixed propeller and rudder system. Type ...

for ShinNihonkai Ferries in form of the CRP ''Azipod'', claiming efficiency gains from the propeller (about 10% increase) and a simpler hull design.

have launched the IPS ( Inboard Performance System), an integrated diesel, transmission and pulling contra-rotating propellers for motor yachts. At lower power levels, contra-rotating mechanical

s are one possibility, convenient for CRP due to their inherent bevel gear construction. Rolls-Royce and Steerprop have offered CRP versions of their products.

References

{{reflist Propellers Marine engineering