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October 11, 2002

The efficiencies of contra-rotating propellers are well known and have been proven in many different applications.Steerprop unit tested at Krylov Institute Finnish azimuthing propulsor specialist Steerprop is now introducing a dual-ended azimuthing propulsor whose propellers contra-rotate..

As a part of its ongoing research and development , Steerprop Ltd. recently conducted a series of model tests at Krylov Shipbuilding Research Institute in St. Petersburg, Russia. The Steerprop dual-end contra-rotating propulsor configuration was tested in both the towing tank (open water tests) and in the cavitation tank.

"The test series clearly showed the benefits of the dual-ended configuration and thus also proved the claims for high efficiency of Steerprop CRP. The efficiency of the forward propeller was measured to be close to 0.9!" said Hannu Jukola, hydrodynamist at Steerprop Ltd. This is mainly a result of the interaction between the pulling propeller and the underwater-body, a phenomenon utilized in the dual-end CRP concept.

The dual-end CRP concept combines the advantages of a pulling propeller to that of contra-rotating propellers. The efficiency of the pulling propeller is further improved by the use of a bluntly shaped lower body.

"The pod geometry is designed to create a pressure wave in front of it, which acts like an additional wake for the forward propeller. The increase in propeller thrust due to this unique interaction between pod and pulling propeller practically cancels the pod drag", explains Hannu Jukola.

During the cavitation tests conducted at the Krylov Institute it was proved that, thanks to the wide non-cavitating operating range, offered by the good inflow quality of the pulling propeller, the propellers of a Steerprop dual-end CRP easily can be designed to be free of cavitation in all normal operating conditions.

The performed model test series was also used to validate the accuracy of the design method newly developed by Steerprop. "The thrust and torque coefficients were found to be within 2% of their design values, thus showing an extremely good accuracy of the calculation and design methods" ends Hannu Jukola.

Steerprop CRP Propulsors in Operation

Dual-ended CRP propulsor used in river cruise vessel

Steerprop dual-end CRP propulsors are already in successful operation in two river cruise vessels operating on the European inland waterways. Both vessels are equipped with Steerprop SP 10 CRP units, with an input power of 2 x 808 kW.

Steerprop SP 35 CRP

A pair of Steerprop SP 35 CRP propulsors is currently under construction for an ROV survey vessel for Østensjø Rederi AS in Norway. The vessel is designed by Skipsteknisk AS and is being built by Myklebust Verft, a part of Kleven Maritime. These units have an input power of 2,200 kW, using propeller diameters of 3500 mm (forward propeller).

CRP Technology

The concept of having two consecutive propellers behind each other, rotating in different directions is very old – as old as the screw propeller itself, as John Ericsson's patent of 1836 included single, twin, as well as a contra-rotating propellers!

Although the high efficiency obtained with contra-rotating propellers has long been known, until fairly recently material technology and the need for long concentric shafts running in different directions, made the concept both technically and economically unfeasible.

However, in the mid 1980's contra-rotating propellers were successfully introduced in azimuth thrusters, utilizing the short propeller shaft and bevel gear.

The engineers now working with Steerprop were part of that development . They are now taking the concept one step further with the state-of-the-art dual-end solution, which was chosen for mechanical reliability and superior hydrodynamic efficiency.

Steerprop Ltd.

Steerprop Ltd. is the centre of azimuth propulsion technology. The company markets, sells, designs, engineers, supplies, and services azimuth propulsors globally, for the maritime industry as well as for the offshore oil and gas industries.

The strategic objective of the company is to develop azimuth propulsors offering a superior life cycle economy.

Steerprop Ltd. is a privately owned company - shareholders are the working management as well as domestic and foreign institutional investors. The company commenced operation in September 2000.

For more information email [email protected]