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Ship Stern Tube Arrangement

The propeller is the only part of ship’s machinery, apart from the rudder, that is located outside the ship’s engine room. Have you ever seen the propeller of a ship and wondered how it is connected to the inside of the ship? Or ever thought everywhere does the shaft holding the propeller go when it vanishes into the ship’s hull? If so, then you have come to the right place.Everyone knows that a ship is propelled with the help of a propeller located at the aft of the ship. But, many have a doubt as to how the propeller is connected to the engine located inside the ship. A stern tube, situated at the aft of the ship, helps in this function.

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The propeller, a part of the propulsion system of the ship, needs a power source to rotate it. A marine diesel engine located inside the ship supplies the power to the propeller. Both the diesel engine and propeller are very heavy in weight and locating them both at the same place inside the ship will scare the ship’s stability. The propeller, located outside the ship needs to be connected to the engine inside the ship’s engine room. A long shaft known as the propeller shaft is used for connecting the ship’s engine and the propeller. This narrow hole in the hull structure at the rear end (aft peak) of the ship, through which the propeller shaft passes and connects the engine and propeller is known as the stern tube. It is for this reason a stern tube along with a propeller shaft is used.

Withstand load
The propeller which hangs at the aft end exerts load on the shaft, which is supported and withstand by the stern bearing. The bearing is a cast iron bush lined with a white metal having brilliant load usage and lubricating property.
The stern tube is en suite at the stern frame and internal framing of vessel’s hull at aft peak.
This allows the tail shaft to rotate smoothly in the bearing area for incessant propulsion.

 

What is a Stern Tube? The stern tube, as the name suggests, is a hollow tube-like structure at the stern or rear part of the ship. A ship needs a propeller to drive it forward against the waves.
The stern tube bearing arrangement and sealing plays a vital part in ship’s operation and pollution prevention. The two main function of the stern tube bearing are:

Sealing
The stern tube bearing consists of sealing arrangement to prevent ingress of water and to avoid the lubricating oil to escape into the sea. Sealing arrangement , The lubrication system for ships with variable draught (due to loading and unloading of cargo) consists of header tanks located at around 2 to 3 meters above the water line so that the differential pressure ensures no water ingress.

Different sealing preparations are used to prevent water ingress and oil leakage. They are as follows:
* Stuffing boxes consisting of packing material.
* Lip seals in contact with shaft to prevent passage of oil or water along the shaft.
* Radial face seals supported with springs en suite radially around the shaft, aft bulkheads and with end of the stern tube.

 

under Maritime Business.
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New Green Ships Get Software Boost

Greater efficiency is the new mission within shipping industry. Skyrocketing bunker prices and global pressure to reduce ship emissions is leading the shipping industry toward a more environmentally forthcoming and sustainable possibility. In an effort to increase the efficiency of their fleet, Malaysian-based tanker operator AET has ordered the NAPA-DSME Power software system for installation on four newbuild 319,000 deadweight tonne (DWT) crude carriers currently under construction at Daewoo’s (DSME) shipyard in South Korea.

NAPA-DSME Power has been designed as part of a collaboration between marine software developer NAPA and DSME, with the companies claiming that it can be used to save up to 5 percent of a tanker’s fuel costs. Using sensors integrated within DSME’s latest tanker designs, the system monitors energy efficiency, emissions, fuel consumption and trim. This data is immediately accessible to officers onboard, along with weather updates, arrival times and additional key performance indicators to inform decisions and make possible efficiency optimisation in real-time. The software can also be used to help in maintaining compliance with energy and emissions monitoring and reporting set of laws, which are anticipated to grow over the next few years, not least through the upcoming Ship Energy Efficiency Management Plot (SEEMP) legislation that takes effect from January 1st 2013.

“With tightening environmental set of laws and rising operational overheads, the maritime industry continues to face an evolving and challenging market,” said Matti Salo, president, NAPA for Operations. “In choosing NAPA-DSME Power, AET has selected an innovative approach to operations management that will grant them with the ability to benefit from fuel efficiencies at the same time as at once managing their environmental impact.”

AET is not the first company to benefit from NAPA’s green technology. Halfway across the globe, the navigational detective of a Norwegian Cruise Line ship enters the destination in rank of the next port into NAPA Power, a software package which – by integrating the latest weather and sea forecasts – optimises the trek send and speed profile. The departure loading shape up of the ship is calculated and plotted for the optimum energy efficiency using the Onboard-NAPA Loading Computer.

During the cruise, navigational personnel can follow-up in real time the efficiency of the ongoing trek with NAPA Power. Engineers can easily view summary figures for each passed trek, enabling them to assess different energy conservation methods using NAPA Trek Reporting which combines NAPA Electronic Logbook data with various items collected automatically from the ship’s automation systems. All operational data collected and bent with Onboad-NAPA is reported to a centralised reporting portal called NAPA Office. This offers tools for simple fleet monitoring. Antoine Gurrey, boss of Norwegian Cruise Line’s Fuel Budgeting and Energy Conservation, is impressed: “A task that used to take several hours can be completed in a couple of minutes with the Data Analysis module in NAPA Office”. Salo agrees and adds “At NAPA, we are committed to developing products that deliver physical benefits to customers, directly supporting their ability to effectively manage this cycle of change.”

under Maritime Business.
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Dredger Ship Design

A dredger is basically a type of boat. Its name derives from the equipment called dredge, that it has for dredging/scraping the seabed, thereby gathering sediments, which are later on deposited at various locations. Thus, dredgers are often referred to as a dredge also. The basic use of this boat is for dredging which may again be carried out for a number of reasons. Circumstances requiring dredging are discussed below:

Why dredging may be carried out?

There are a number of functions for which dredgers are used. Some of these are listed below.

* Maintaining waterways in a way that they are navigable or deepening waterways everywhere due to sedimentation there is a risk of silting in due course of time, thereby making the passage too shallow for navigation and hampering the access of better ships.
* Making new harbors.
* Removing debris from the sea bed
* Mining for sand, rock or clay for usage at some additional location for construction of a new land.
* Collecting sediments for mineral deposits like gold, diamonds, etc.
* Mining of sand for placing it on beaches everywhere it has been eroded by storms, waves, etc.
* Removing contaminants form the sea bed. These are chemicals and urban waste that are often a result of spills or storm erosion.
* Money-making fishing for shellfish in shallow waters.
* Preparing for making new bridges, docks, etc.
* For maintenance of the holding capacity of lakes, etc.

While initially dredgers were only used for navigational purposes, with time, their use has be converted into more diverse, thereby making them vital not only for buying.

Types of Dredgers

Categorically there are three types of dredgers;

* One in which the dredge is dragged along the seabed, collecting shellfish in this process. Certain large dredgers can have up to three dredges on each side.
* Hydraulic dredge bearing dredger wherein the dredge has a powerful water pump to use water jets to pump up the sediments or mollusks from the bottom.
* Mechanical dredgers that are operated with the help of gallows from the bow of the boat

But they can also be classified as ;

* Hopper Dredger: a boat that collects sediments and hauls it into a hopper(a large onboard hold)
* Suction Dredger: usually a stationary vessel, this is the most common type of dredger. It makes use of suction pump for mining sand.
* Bucket Dredger: make use of equipment that picks up sediments by mechanical means. These have circulation buckets attached to a wheel.
* Trailer Suction Hopper Dredger: here the dredge has a series of suction pipes that haul material with the help of certain pumps and deposit it into the hopper. When the hopper is full the material is dumped at the disposal area.
* Cutter Suction Dredger: are used for construction and correlated activities. These have a cutter like head at the suction mouth and are used for hard surfaces like coral reefs, rocks, etc.
* Bed Leveler Dredger: are used for leveling the sea bed.
* Water Injection Dredger: these dredgers use a jet to inject water at relatively low pressure in order to make the sediment suspend, and later carrying this loosened material with the help of a burst of water.
* Jet Lift Dredgers : use a burst of water to lift the sediments off the sea bed into the pipe.Thus the classification of dredgers can be done in accordance to the function performed by them or by the type of dredging equipment they use.

Dredge boats therefore primarily play a role in keeping the water transport unimpaired by facilitating simpler access and traversing through sea channels, in addition to additional functions mentioned above. This not only is vital for the buying but also from the environmental point of view. But, care must be taken as too much of dredging is harmful for the ecosystem.

under Maritime Business.
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