Page 64: of Maritime Reporter Magazine (June 1999)

10 Significant Marine Innovations

Ulstein develops pulling propellei

A new propulsion concept using pulling propeller technology is under development at Ulstein Propeller, and units of up to 6 MW are intended for applications including offshore and mer- chant tonnage

Ulstein Propeller has begun a project to develop a pulling propeller design for use with azimuthing and tractor drive units. The maximum rating of the new pulling propeller will be 6 MW and it will utilize a traditional gear wheel transmission. Although this is recog- nized as a significant development in the industry it is not a new concept to

Ulstein Propeller. Previously, the com- pany successfully developed and mar- keted its Speed-Z design of high-speed pulling propeller unit. This latest pro- ject builds on the company's experience in developing the Speed-Z and extends

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Id offer fully pulling with a the propeller, a number of advantages in propeller in pulling mode rather than the conventional pushing mode.

By removing the gear drive or shaft supports from in front of the propeller, the pulling propeller is able to operate in a optimum and near homogeneous water flow. Efficiency is thereby increased significantly.

Locating the propeller forward of the support strut will also contribute to reduced wear and tear, because the dynamic thrust and torque is of a com- pletely different magnitude to the con- ventional pushing propeller's imperfect wake created by the forward support strut. Propeller efficiency is still affect- ed by the strut aft of the propeller. But its effect on total propulsion efficiency can be reduced by taking full advantage of the aft strut by designing its profile to counter rotational losses induced by the propeller. This will utilize the energy in the swirl aft in the propeller slipstream to create thrust in the same direction as the propeller thrust.

By adopting the pulling propeller con- cept, Rune Garen, research and devel- opment manager at Ulstein Propeller, believes that efficiencies can be increased by as much as 10 per cent. "Such an improvement is considerable by any modern day standard," says Mr

Garen. "Already, evidence suggests an eight percent improvement is attainable but, by optimizing the hydrodynamic interactive package of propeller design and aft support strut, close to 10 percent must be a realistic target".

Speed-Z provided Ulstein Propeller with valuable experience in the design of pulling propellers. Ulstein learned that there is a very interesting interac- tion between the slipstream and the ver- tical strut, and that when the propeller is working in an almost homogeneous inflow; noise, vibration and dynamic torque are very low.

Ulstein has already commenced pre- liminary design of the new propulsion system and has begun analyzing the flow around the strut and the pod. Vis- cous CFD calculations will then be car- ried out and verified by model tests. The next phase will be to build and test a full-scale prototype by the end of next year.

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