Page 217 - Introduction to Marine Engineering

Chapter 11 __
Shafting and propellers

The transmission system on a ship transmits power from the engine to
the propeller. It is made up of shafts, bearings, and Finally the propeller
itself. The thrust from the propeller is transferred to the ship through
the transmission system.
The different items in the system include the thrust shaft, one or more
intermediate shafts and the tailshaft. These shafts are supported by the
thrust block, intermediate bearings and the sterntube bearing. A sealing
arrangement is provided at either end of the tailshaft with the propeller
and cone completing the arrangement. These parts, their location and
purpose are shown in Figure 11.1.

Thrust block

The thrust block transfers the thrust from the propeller to the hull of
the ship. It must therefore be solidly constructed and mounted 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.
The casing of the independent thrust block is in two halves which are
joined by fitted bolts (Figure 11.2). The thrust loading is carried by
bearing pads which are arranged to pivot or tilt. The pads are mounted
in holders or carriers and faced with white metal. In the arrangement
shown the thrust pads extend threequarters of the distance around the
collar and transmit all thrust to the lower half of the casing. Other
designs employ a complete ring of pads. An oil scraper deflects the oil
lifted by the thrust collar and directs it onto the pad stops. From here it
cascades over the thrust pads and bearings. The thrust shaft is
manufactured with integral flanges for bolting to the engine or gearbox
shaft and the intermediate shafting, and a thrust collar for absorbing the
thrust.
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