Propeller Optimization Brings Efficiency Improvement With the recent announcement by MAN Diesel that as of 2010 the company will be known as MAN Diesel & Turbo, also came the indication that the company will look at an internal synergies strategy to enhance the offer of combined product packages. In the marine business, this will translate into a greater emphasis on marine propulsion packages with gear manufacturer Renk (partly owned by MAN), as MAN Diesel looks at enhancing its propeller line with more involvement in the vessel’s initial design stage.
The company already offers its Alpha Controllable Pitch (CP) propellers for the complete power range of its mediumspeed four-stroke engines, as well as the two-stroke units, where the utilization of CP propellers is very relevant. Karsten Borneman, MAN’s senior sales manager for medium-speed sales propellers and aft ship systems, said that the company has recently registered an increased number of projects for very large propellers beyond 30 000 kW and a propeller diameter of more than 8 m. “Considering this market trend, we developed two new propellers, the VBS2080 and VBS2240, with hub diameters of 2080 and 2240 mm, respectively,” said Borneman.
The basic design of the new large propellers is very similar to the existing smaller hubs and focuses on reliability, low wear rates and easy serviceability. In fact, these large hubs are even serviceable from the aft end without dismantling from the shaft. “Some minor changes have been introduced, mainly because of the propeller dimensions and weight,” said Borneman. “For example, the largest propeller hubs can be delivered separate from the propeller tail shaft to facilitatetransport and installation at the shipyard. “The Alpha hub series is also the first CP propeller on the market that can operate on biodegradable oil, not only in the stern tube system, but also in the propeller hub,” added Borneman. He also emphasized how propellers and aft ship optimization have a great potential in improving propulsion efficiency, thus reducing fuel consumption and environmental impact.
With increased research and development resources, MAN Diesel has launched an internal CP propeller program aimed at improving total propulsive efficiency by 8 to 10% within the next three to five years. To this extent, the company’s engineers have two main tools at their disposal. One is a new software program by MAN Diesel called Computer Optimization of Propulsion Systems (COPS), which combines several calculation programs into one tool. This software allows MAN Diesel to study the preliminary parameters involving hydrodynamic and strength issues, statistical data, PTO layout and gearboxes, among others.
Borneman said it is important to address the issue of propeller efficiency at an early project stage. “Often a poor basic layout is difficult to compensate for in a later stage as the main components have already been selected. It is very important to design a propulsion plant in a comprehensive manner,” he said. “Considering all the parameters and selecting the right combination of components, we can improve propeller efficiency by 2 to 3%.” Another tool MAN Diesel utilizes is computational fluid dynamics (CFD), which is used mainly for research on specific phenomena, rather than in order-specific studies for propeller optimization.
The CFD tool was also used at MAN Diesel to develop a new propeller nozzle, the Alpha High Thrust (AHT) nozzle. It is mainly used for offshore support vessels where bollard pull is a key element, but also for tugboats, dredgers and fishing boats. “Research with the CFD showed that the AHT nozzle has superior performance than the 19A nozzle that is widely used in the marine industry,” said Borneman. “A changed nozzle profile with double curve on both the inner and outer diameter, and an optimization concept involving nozzle suspension, aft ship lines and rotation directions allowed achievement of an increased bollard pull by more than 8 to 12% compared to solutions with the 19A nozzle.” As far as propeller blades, MAN Diesel signed an agreement with J.J.
Kappel for the supply of their tiploaded propeller blades, including their own calculation hydrodynamic model, which allows MAN Diesel to optimize the effect of tip loading on every project. The company expects improvement in efficiency compared to conventional propeller blades in the range of 4%, but said that model testing indicated even higher efficiency. The potential efficiency improvement from the propeller blades and nozzle design has a great position in retrofitting projects. Borneman cited the example of the Scandlines’ Sassnitz, a 1235 LM RoPax vessel with a total propulsion power of 18 200 kW, recently equipped with newly designed propeller blades. At the same time, it was possible to increase the propeller diameter for existing propeller speed, thus not changing the gearbox reduction ratio. The first reports from the crew mention a fuel oil consumption reduction of 12.5%, with consequent engine load reduction of 60 to 65% at service speed. Scandlines, one of Europe’s largest ferry companies, has already announced it will also retrofit the M/S Ask and M/S Urd ferries with new propeller blades in the near future.
Considering the difficult worldwide financial situation, owners and operators do not need to worry and struggle to fund a retrofit project. In fact, MAN Diesel has launched its PrimeServ Trident, a financial product that helps customers invest in retrofit technology. “PrimeServ Trident is a retrofit financing package, where saved expenses cover the investment,” said Borneman. “The financing program is directly linked to a two-year payback period, which we have calculated to be the average with the indicated efficiency improvements. The payment is spread over the payback period and balanced by the savings created by the retrofit itself.