propulsors
Testing times pay off for Danish ferries
Investment in model basin testing enabled optimised propulsion systems to be delivered by Schottel to two double-ended ferries
TWO double-ended ferries, delivered last year by the Sietas yard in Germany, feature an interesting propulsion system developed by Schottel. The 99.9m long, 600 passenger-capacity Langeland and Lolland were handed over to the Danish shipping company Faergen, which operates the pair between the ports of Spodsbjerg and Tårs. The company supplied a total of four diesel-electric driven Schottel Twin Propeller STP 550 units, each with 850kW input power, which provide a service speed of around 16 knots. Schottel points out that the optimum balance of the fore and aft drives was determined in model trials in a test tank in the Potsdam model basin operated by SVA. In addition, the best positioning angle of the drives was the subject of a number of trials before the final solution was adopted. Furthermore, cavitation tests were carried out to find the optimum design
The Danish double- ended ferry Lolland
for the twin propeller system regarding efficiency and pressure variation. According to Schottel, the four-drive
propulsion concept gives the double- ended ferry design very good sailing properties and impressive manoeuvring capabilities, along with high levels of safety and efficiency. A possibly unique feature is that these ferries have no engine control room. Instead the machinery controls are located in the bridge allowing captain and engineer to always be in close contact, a big plus in safety terms. Another notable project for Schottel involves propellers for a train-ferry roro passenger vessel for the Italian railways, which is due to start operations later this year in the straits of Messina. The 147m long, 18.7m wide ferry will be equipped with three STP 1515 units, rated at 2,040 kW each, driven by Wärtsilä diesel engines. Because the service speed of the vessel is above 18 knots, heavy duty
twin disc Marine Control Drives (MCDs) have been incorporated into the propulsion trains. Schottel has developed special control software for these MCDs, giving the vessel the same operational and manoeuvring flexibility as CP rudder-propellers while also maintaining the hydrodynamic advantages and high levels of efficiency of the STP system. Three 35m long hollow shaft lines have been designed for the train ferry using completely new technology. The shaft lines consist of hollow steel shafts with one fixed and one loose shaft bearing alternating with carbon shafts of the Centalink CL type. Schottel points out that this innovation has enabled the number of shaft line bearings to be cut by 50 per cent, facilitating both the installation of the shaftlines by the shipyard and future maintenance by the operator. Adopting this approach should also lead to improved operational safety. Schottel is also working on a number of other passenger ship contracts at the moment, for both its twin propeller and rudder-propeller systems. In particular the company notes that two 123m long, LNG- powered double ended ferries building at the Remontowa yard in Poland for Norled of Norway will be equipped with two STP1515 units, rated at 1,850kW each, providing a service speed of 16 knots. Propulsion systems for vessels
under construction in Germany for Viking River Cruises’ Longship class will also feature Schottel technology. The ships will be equipped with enhanced Schottel Combi Drives, the SCD 200, in a twin propeller arrangement designed to increase space available for passenger facilities. Other benefits are expected as a
result of using this latest generation SCD system. The resiliently mounted electric motor that is installed on top of the drive is part of the thrusters and is designed to reduce noise levels, while the permanent electric motor has an efficiency level of 97 per cent. The lower gear is a single rather than a double bevel type, resulting in fewer mechanical parts and has been designed to deliver higher levels of reliability. Schottel also pointed out that the
twin propeller system allows for lower propeller diameters than a single propeller, decreasing the draught of the vessel, a characteristic that is especially useful for shallow, inland waterways. PST
54 I Passenger Ship Technology I 2nd Quarter 2013
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