ShaftBearing.ppt

Thrust Bearing The thrust block transfers the thrust from the propeller to the hull of the ship. It must therefore be solidly constructed onto a rigid seating or framework to perform its task. It may be an independent unit or an integral part of the main propulsion engine. Both ahead and astern thrusts must be catered for and the construction must be strong enough to withstand normal and shock loads. Thrust Bearing It can limit crankshaft end play. Thrust flanges are formed on the main bearing sides, almost touching the thrust surfaces machined on the crankshaft. Absorb axial forces Shaft Bearing Shaft bearings are of two types, the aftermost tunnel bearing and all others. The aftermost tunnel bearing has a top and bottom bearing shell because it must counteract the propeller mass and take a vertical upward thrust at the forward end of the tail shaft. The other shaft bearings only support the shaft weight and thus have only lower half bearing shells. Sterntube Bearing The sterntube bearing serves two important purposes. It supports the tailshaft and a considerable proportion of the propeller weight. It also acts as a gland to prevent the entry of seawater into the machinery space. Sterntube Bearing Early arrangements used bearing materials such as lignum vitae (a very dense form of timber), which were lubricated by seawater. Most modern designs use an oil lubrication arrangement for a white metal lined sterntube bearing. Shafting There may be one or more sections of intermediate shafting between the thrust shaft and the tailshaft, depending upon the machinery space location. All shafting is manufactured from solid forged ingot steel with integral flanged couplings. The shafting sections are joined by solid forged steel fitted bolts. Propeller The propeller consists of a boss with several blades of helicoidal form attached to it. When rotated it ‘screws’ or thrusts its way through the water by giving momentum to the column of water passing through it. The thrust is