When the Celebrity Solstice will put to sea for her maiden voyage at the end of 2008, she will also have highly sophisticated bearing technology from Schaeffler Group Industrial aboard. Equipped with one radial spherical roller bearing and two spherical thrust roller bearings from FAG, the drives will make it possible to accelerate the ship to a speed of 24 knots (45 km/h) and to perform safe steering and precise decelerating maneuvers. Moreover, the special coating of the bearings decisively contributes to efficient drive operation. The luxury liner, worth nearly half a billion euros, is the largest ship that has ever been built in Germany. Its length measures 315 meters – this means it is about as long as three soccer fields. The XXL vessel accommodates nearly 2,900 passengers in 1,430 cabins and features an array of amenities, including a huge theater, a casino and genuine lawn for playing golf.
Propulsion and steering of the ship are combined in a freely rotatable vertical pod outside the hull. These so-called POD drives feature particularly low vibration and quiet operation, thereby enhancing the travel comfort for the passengers. They significantly improve the ship’s maneuverability and thus its safety, and offer higher efficiency which results in both lower fuel consumption and lower levels of emission. The power output per drive unit is 20 megawatts.
Thrust block unit with a strong bearing trio
The FAG 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 the propeller. The large spherical thrust roller bearing, which has an outside diameter of 850 mm, serves to accommodate the main thrust and is subjected to thrust loads of up to 150 tons at maximum speeds of 135 rpm. Under extreme conditions, the bearing can even support loads of 430 tons for a short time. The smaller counterbearing, which is also a spherical thrust roller bearing, has an outside diameter of 620 mm and serves to accommodate the forces under reverse thrust and during maneuvering operations. It is designed for loads of up to 20 tons; in extreme cases, it can accommodate loads of up to 200 tons maximum for brief periods. Finally, the radial spherical roller bearing accommodates the radial loads resulting from the engine and propeller’s weight 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 are thus able to compensate for misalignment of the drive shaft.
Low-friction bearings ensure higher efficiency
Bearings from the Schaeffler Group make a decisive contribution to improved drive efficiency. In order to optimize the kinematic conditions in the bearing system and reduce friction, the outer ring of the radial spherical roller bearing and the housing washers of the spherical thrust roller bearings carry a Durotect® Z coating. Developed by Schaeffler, this coating reduces the coefficient of friction and tendency to adhesion and increases the resistance to corrosion and fretting corrosion. In addition, the outer diameter of the 7.5 ton thrust block unit (flange connection) is equipped with a 14 mm thick synthetic compound coating which possesses excellent damping properties in addition to providing desirable electrical insulation. This coating prevents the rolling contact zone being damaged by leakage current or downdraft. It provides reliable protection up to 15,000 volts.
The bearing and the oil bath of the thrust block unit are monitored by temperature sensors. In addition, the individual bearings are fitted with a condition monitoring system which detects damage at an early stage so that maintenance activities can be planned well ahead. This prevents unexpected failure and the high costs incurred.
