Effects Of Podded Propulsion Bearing Failure

2579 words - 11 pages

Executive Summary:Introduction:Podded propulsion drives have become more and more popular within the maritime industry especially within the cruise industry. The first podded propulsion systems were implemented in early 1990s. Podded propulsion systems can generally provide high efficiency and maneuverability with lower noise generation than traditional shaft-driven rotor systems. They also provide a high degree of layout flexibility because of the relative independence of their location relative to the primary power plant of the vessel. However, since the implementation of the podded propulsion systems aboard cruise vessels, there have been significant malfunctions and failures of the ...view middle of the document...

When entering a port, some vessels employ a stern and/or bow thruster, which aids in maneuvering. Also, a tug may assist in maneuvering depending on the port.Podded Propulsion:The podded propulsion system employs the diesel electric concept as stated previously. However, the rest of the system is completely different. The propulsion unit is fixed outside the ship in a pod, which combines the functions of a propulsion motor, main propeller, rudder, and stern thruster. The pod itself can rotate 360 degrees and provide maximum maneuverability. The pod contains a fix pitched propeller, electric AC synchronous motor, exciter, propeller shaft, propeller shaft thrust support bearings, bilge pumps, and monitoring and control equipment. The steering unit, lubricating oil equipment, and ventilation and air cooling unit are all outside of the propulsion pod and inside the ship.The reliability and effectiveness of podded propulsion has been proven over the last decade in the toughest ocean-going ship application; arctic tankers and ice breakers. In those non-passenger-carrying vessels, propulsion was provided by only one pod; cruise ships have two for additional maneuverability and redundancy. In the wake of the introduction of podded propulsion systems in cruise liners lies the wave of the future.Several advantages of the podded propulsion unit include: an all electric ship, reduced exhaust gas emissions, flexibility in machinery arrangement, reduced number of main components, higher hydrodynamic efficiency, low noise and vibrations with reduced pressure pulses, excellent maneuvering characteristics, space savings in general arrangements, minimized crash stop distance, and easier shipyard logistic and construction. Also, the propeller blades on the pod face forward so as to pull versus push the ship through the water, which is more efficient. With conventional steering, aft-facing propellers need to ensure proper water flow over the rudder, but with podded propulsion, the propellers pull a vessel through the water rather than push it. The disadvantages that come with installing podded propulsion are higher capital costs and maintenance repairs as well as some power losses due to electric propulsion.Bearing Failure:Pod drives implement thrust and support bearings to control axial and radial alignment of the propeller shaft respectively. The pod shaft bearing is a system that consists of the bearing itself, sealing, lube oil, monitoring equipment, operating methods, care and service.Both the thrust and support bearings on the podded propulsion system have failed on numerous occasions. The primary cause of the bearing failures is a combination of many variables such as design, control, and maintenance. Early models of the pod drives were designed with bearings that were insufficient for carrying the types of loads present on the drives. This was due to the thermal expansion of the bearings while under load. The rise in temperature of the shaft, rotor, and...

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