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Bearings improve efficiency and safety of marine drives

Bearings improve efficiency and safety of marine drives

 

Luxury cruise liner 'Celebrity Solstice', which was put to sea for her maiden voyage at the end of 2008, uses drive technology that incorporates sophisticated bearing technology from Schaeffler. The ship's propulsion and steering drives utilise one FAG radial spherical roller bearing and two FAG spherical thrust roller bearings, which enable the liner to accelerate to a speed of 24 knots (45km/h). The bearings ensure that steering and precise deceleration manouvres are performed smoothly and safely. Special coatings on the bearings are critical to the efficient operation of the drives.

Worth almost half a billion euros, Celebrity Solstice is the largest ship ever constructed in Germany. The vessel measures 315m in length - the length of three football pitches. The ship accommodates around 2,900 passengers in 1,430 cabins and features an array of amenities, including a huge theatre, a casino and a real lawn for playing golf.

Propulsion and steering of the ship are combined in a freely rotating vertical pod outside of the hull. These so-called 'POD drives' provide extremely low vibration and noise levels during operation, therefore enhancing passenger comfort. The drives significantly improve the maneuverability, and therefore the safety, of the ship, as well as offering higher efficiencies, resulting in both lower fuel consumption and reduced emission levels. The power output per drive unit is 20MW.

Schaeffler's bearings support the drive shaft on the locating bearing side in each of the two engine pods, accommodating thrust forces and loads from the engine and propeller.

The large spherical thrust roller bearing, which has an outside diameter of 850mm, serves as the main thrust bearing and is subjected to thrust loads of up to 150 tonnes at maximum speeds of 135rpm. Under extreme conditions, the bearing can even support loads of up to 430 tonnes for short periods.

The smaller counter bearing, which is also an FAG spherical thrust roller bearing, has an outside diameter of 620mm. The bearing withstands reverse thrust loads during maneuvering operations. The bearing is designed for loads of up to 20 tonnes, although in extreme cases, it can withstand loads of up to 200 tonnes for short periods.

The FAG radial spherical roller bearing, also supplied by Schaeffler, is designed to accommodate radial loads from the engine, the weight of the propeller and dynamic forces. The bearings in the Schaeffler thrust block unit are arranged in such a way that they align via a common point and so are able to compensate for any misalignment of the drive shaft.

<b>Low friction bearings provide greater efficiencies</b>
Schaeffler's bearings play a pivotal role in improving the efficiency of the drive. In order to optimise bearing system kinematics and reduce friction, the outer ring of the radial spherical roller bearing and the housing washers of the spherical thrust roller bearings are coated with Durotect Z.

Developed by Schaeffler, this special coating reduces the coefficient of friction and adhesion properties, while increasing the bearing's resistance to corrosion and fretting. In addition, the outer diameter of the 7.5 tonne thrust block unit (flange connection) is equipped with a 14mm thick, synthetic compound coating, which offers excellent damping properties, as well as providing electrical insulation. This coating prevents the rolling contact zone from being damaged by leakage currents or downdraft. The coating provides reliable protection up to 15,000V.

The thrust block unit's bearing and oil bath are monitored using temperature sensors. The individual bearings are also fitted with a condition monitoring system that detects damage at an early stage, enabling maintenance tasks to be planned well in advance. This eliminates costly, unexpected bearing failures.

 

 
Schaeffler (UK) Ltd

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