Azimuthal working podded drives

The world of azimuthal working thrusters as presented in the May issue would not be complete without a description of the podded drives which is following here. By Hans-Jürgen Reuß

Talking about azimuthal working podded drives most persons involved look at ABB as the main player in this business. But[ds_preview] this part of the world of azimuth thrusters comprises more than large thrusters for cruise liners. Thus, first a look back to the definitions made in the last issue starting with the generic term of »azimuthal thrusters«. The world has been split into two groups, the passive and the active units. In this issue the active units will be covered, generally known as podded drives or in short called »pods«. However, this group comprises not only the classical electrically driven pods, but also the thrusters with a rim drive belong to it.

The biggest advantage podded drives offer is the high degree of manoeuvrability at narrow places. But there are also limitations. That means that the azimuthal movement of the pod must be blocked to angles depending on the speed of the vessel to avoid construction overload. Thus the quality of the electronic control of the pods is of greatest importance. This is not the place to repeat all the technical problems and setbacks, which accompanied more than 20 years of podded drive development. Instead, this item is concentrating on the programmes of the market leaders.

Classical podded drives

Azipod is the trademark of ABB for the 360° azimuthal working podded drives. The company offers them in many variants for the power range from 500 kW to 25 MW. The first idea to develop such ship propulsion system originates from 1987. The first prototype was installed already in 1989 with a transmissible power of 1,500 kW. And in 1993 the first large pod installation followed with an 11,400 kW unit in a tanker. The next milestones were an icebreaker in 1994 and a cruise vessel in 1997. In 2001 ABB introduced the CRP Azipods and presented in 2008 after about 20 years of experience the second generation.

Since 1997 the operative business was in the hands of Azipod Oy, owned 55 % by ABB and 22,5 % each by Kvaerner Masa-Yards and Fincantieri. ABB acquired all shares in 2000 and integrated Azipod Oy in ABB Marine. With the introduction of the second generation Azipods the power range reached 20 MW. To improve maintenance possibilities and reduce operating costs the design had been modified to extend the docking intervals of the vessels. The first new units were available in 2009.

Today’s programme comprises four different series for a wide spectrum of applications including ice-breaking vessels. The two series at the lower end are in full competition with rudder propellers as far as the power range is concerned. At the upper end there is only a competition with the pods of the other manufacturers like GE and Rolls-Royce.

The second large player in the podded drive business is in alphabetical order the division GE Power Conversion of the large American combine General Electric. GE acquired in 2012 the French Converteam Group SAS, which only had been formed from Alstom Power Conversion in 2005. The pod programme consists of two series. The lower end is marked by the Inovelis series with a power range from 1,800 to 5,500 kW. The units were designed to improve dynamic positioning operation. Main applications will be offshore supply vessels, drilling rigs and ships. The second generation of these podded drives was presented at the OTC in Houston this year.

The second series are the well-known Mermaid pods, which range with five models between 6,000 and 27,000 kW. With an improved drive motor technology and improved hydrodynamics »the pods can now be delivered one smaller than previous models,« says GE.

The Mermaid pods are manufactured in co-production by General Electric and Rolls-Royce. RR is responsible for »the hydrodynamic design and mechanical parts« and GE’s part is »the electric motor, drive and control«. Both companies call these pods their »azimuthing electrical podded propulsor» and publish coordinated brochures.

From Rolls-Royce the technical editor received an official statement concerning the co-operation with GE: »Rolls-Royce and GE’s Power Conversion business [i.e. the predecessor of Alstom Power Conversion] have together developed the Mermaid Pod back in 1995. The Mermaid Pod has recently been upgraded and we have together started to commercialize this improved version.« Thus, the standard versions of the Mermaid pods are offered with identical technical data.

Schottel and Siemens started a cooperation to develop podded drives at the end of the 1990s. First vessels installed with Siemens-Schottel-Propulsion (SSP) were the TT Line ferries »Peter Pan« and »Nils Holgersson« put into service in 2001. The big advantage of this pod development was the use of permanent magnetic motors leading to a very compact housing.

Siemens offers the podded drives now –being independent from Schottel after

more than ten years – under the trade name »eSiPOD« in four standard sizes between 5000 and 12,000 kW. The new pods are equipped with two propellers turning in the same direction. With this new development the company claims for »setting new standards as far as manoeuvrability, flexibility as well as service and handling friendliness« are concerned.

Rim driven thrusters

The rim thrusters developed during the last ten to twenty years are not a new idea, but besides others, they could only be realized with the technical knowledge and the availability of special material at a reasonable price in the last two decades. Today on the market there are the products of three companies offered by Brunvoll, Schottel, Van der Velden and Voith.

Market leader is the Voith Turbo Group with a programme covering the power range from 50 to 1500 kW. The development of these thrusters was started by AIR Fertigung-Technologie GmbH in Rostock at the end of the 1990s. The company was taken over by Voith step by step beginning in 2005 (refer to HANSA 12/2012, pp. 26f). Voith offers the rim drives in two versions with identical power ratings as VIT »Inline Thrusters« for manoeuvring aids and as VIP »Inline Propulsers« for ship main propulsion systems. Compared with the VIT thruster units, the propulsor units VIP have not only a larger outer diameter, they also generate a higher thrust.

Before AIR had been taken over by Voith the company had a cooperation contract with Van der Velden in the Netherlands. This company is currently sales partner of Schottel for special pod applications, after Schottel had taken over 2012 the rim drive know-how from Velden and carries on the development using the own know-how concerning thruster development. At SMM 2012 Schottel released a programme of four units for the power range from 200 to 800 kW rated transmissible power. Starting with the 200 kW unit, the 315 kW and 500 kW units will be next.

Brunvoll started development of rim thrusters as »the concept of the future« in 2002. Testing of the first 100 kW unit followed in 2003. In 2007 the company delivered two units as tunnel thrusters serving dynamic positioning. Further deliveries concerned units for a fishery inspection vessel and a mega yacht. Today, the programme comprises five units starting with 200 kW and a 900 kW unit at the top end.