Introduction
Stern
tube is located at the aft end of the ship and is that part which
connects the engine inside of the ship to the propeller outside of the
ship. The propeller shaft from the engine passes through the stern tube
and is connected with the propeller. A critical part of the ship, the
stern tube can be a soft area for the sea water to seep inside the ship.
In order to prevent the water ingress stern tube bearings are used
inside the stern tube. We will learn about stern bearing housing and its
arrangement in this article
Thus, the two main purposes of a stern bearing are:
Thus, the two main purposes of a stern bearing are:
- To prevent the entry of sea water into the machinery spaces
- To support the tail shaft and a considerable proportion of propeller weight.
Stern Tube Bearings
The
stern tube gland should be such that it allows a free movement of the
propeller shaft without causing any harm. In the ancient days, lignum
vitae - a dense form of timber, was used as bearing material. The timber
was continuously lubricated by sea water. However, with the advent of
higher tonnage steel ships, the size and weight of propellers increased
and timber bearings became outdated.In most of the modern ships, an oil
lubrication system with a white metal lined stern tube bearing is used.
Construction and Working of Stern Tube Bearing
The
arrangement of a stern tube with oil lubrication system has been shown
in the figure. The bush of the white metal bearing has grooves made into
it. Oil is pumped in though this external axial groves into the bush of
the bearing. The oil then passes through the internal axial passages
through the holes made on each side. A return line, at the end of the
bush facilitates the flow of the oil back to the pump. A pump attached
with a cooler, continuously pumps oil into the bearings to maintain the
required pressure. In case the pump fails,of the two header tanks under
gravitational pressure, provide the required oil with a back pressure to
the bearing system. Thus, it is imperative that the level of hydraulic
oil is well maintained in each header tank. Moreover, both the tanks
should also be fitted with low level alarms.
The pressure in the system should be maintained at a level higher than that of the static sea water head to prevent the water from seeping inside in-case of the seal failure. A low pressure alarm is also provided to the system to prevent any kind of accident.
The pressure in the system should be maintained at a level higher than that of the static sea water head to prevent the water from seeping inside in-case of the seal failure. A low pressure alarm is also provided to the system to prevent any kind of accident.
Image Credits
http://www.ship-technology.com/contractor_images/thordon/3-thordon.jpg
http://www.vesconite.com/industry/marine/images/ocean2b.jpg
White Metal bearing for diesel engine compressor, pumps, turbines are manufactured according to the design or sample. White Metal Bearings up to 1000 mm are manufactured.
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