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发表于 2011-8-14 10:07
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来自： 中国辽宁大连
请问处置压载水的溢流法怎么解释？什么是溢流法？求解，谢谢!
xiaoyigjg 发表于 2011-8-13 23:27 
OVERFLOW METHOD
Through the continuous overflow of a ballast tank, seawater is exchanged regularly during a ship’s passage.
This method ensures that many of the dangers associated with the sequential system are skipped or become of lesser importance.
For most of the time the ballast water tanks are full, in order to reduce the free surface effects, and they remain full during the whole process. This fact is enough to negate the navigational and structural strength risks related to the sequential method.
On the other hand, the existing non-return overflow ventilation heads on deck have not been designed for continuous flow. In addition, in the case of a malfunctioning valve, the overpressure inside the tank becomes a real and present danger, especially when considering the diminishing local strength of an old ship.
Operational and maintenance-wise having a flooded main deck is definitely not the best environment for the deck outfittings, let alone the people working on deck.
This condition is becoming even more serious on some new container ships. This is particularly so where the WBT (water ballast tank) ventilation outlets are located on the torsion box of the transverse bulkheads on the upper deck, close to the cargo hold ventilation duct outlets, the reefer container sockets, and in fact on the top of the cargo-hold hatch coamings.
Hence, the overflow method is not recommended if the ballast piping system has not been designed to be operated in this way.
COMMON WATER BALLAST OVERFLOW SYSTEM
This is not a very widely known system, although it combines the benefits of both the sequential and flow-through methods, without some of the undesirable aspects inherited by both. To the knowledge of the writer, this system has been employed in the past on some high-quality north European designs and recently in the Korean shipyards, upon the owner’s request.
Some of the merits of the common overflow system are:
• Operational flexibility. As long as the WBTs are treated in full condition, there is no change to the longitudinal strength, stability or any other navigational feature of the ship. This also applies irrespective of the weather conditions.
• Simple/trouble-free system. There are no additional moving parts (except in damaged condition). This aspect gives the operator a great degree of confidence. A chief officer only arranges that the proper valves (as usual) switch on the ballast pump. He then forgets about the process, and returns only after some time to switch off the pump. The ballast exchange takes place as many times as one desires, and maybe nobody on board will notice anything.
• Outfittings. The plethora of big ventilation heads on the upper deck are becoming obsolete. This aspect has been very welcomed by the designers. It reduces the number of outfittings on the already congested main decks, and saves strength from the otherwise inevitable upper deck plate penetrations.
Some of the disadvantages also inherent to the system are :
• Initial capital cost. The system has an initial capital cost, due to the extra piping installed. This cost is in the region of USD 20 to 70 thousand, depending on the size of the ship ranging from small feeder vessels to large post-panamax ones. There is also a small reduction to the deadweight, which ranges from 10MT to 40MT.
• Structural reinforcements. The ship’s structure should be reinforced to compensate for the material loss due to the passage of the two (PORT and STARBOARD) main overflow pipelines. The ballast tanks should also be reinforced to withstand the additional pressure imposed by the head losses of the water travelling towards the fore or aft overboard outlets.
Such a design should elaborate on the pressure losses of the additional piping under different ballast exchange condition and flows, taking into account combinations of tanks used, pump capacities and vessel draught conditions.
The tanks most likely to suffer from the increased pressure are the centre double bottom tanks. One way to get over this, in cases where it becomes a major obstacle especially on standard designs, is to arrange for a locking mechanism. This permits only a certain combination of tanks and pumps to be operated each time, and/or additional flexibility by installing ballast pumps of different capacities. The latter solution minimises the flow rate and consequently the pressure at the bottom of the tank.
• Damage stability. Another matter that requires very close attention from the designer of the system, is for the ship to retain her damage stability characteristics even though the ballast tanks are interconnected through a common system. The main common overflow lines running along the whole length of the ship from both sides should be arranged above the damage water line, and also prevent the uncontrollable flow of water from one tank to another, regardless of the damage condition. To satisfy the class damage stability requirements, depending on the specific design, a number of isolating valves may be installed across the piping to be used only when there are collisions or any other situations that endanger the ship’s stability.
• Operational. The design should be such that the ballast water outflow does not obstruct the ship’s normal operational procedures. The overboard ballast outlets should be constructed well away from the accommodation ladders, and the pier should be out of reach of the ballast water discharge in case the de-ballasting operation takes place in the port during the cargo operation.
The guideline of such design concepts is that the systems that aim to protect life, property and the environment in the maritime industry should be designed in a user- friendly way.
Furthermore, the design should be simple and able to withstand the harsh marine environment.
Such modifications are difficult to implement on existing ships. However, with the correct design during the construction phase, new buildings attain a high degree of safety which is easier to implement.
The port state controls, who police and monitor the implementation of these regulations, should bear in mind that in today’s shipping industry, false log book entries are not the actions of lazy or criminal seamen. These are actions of frustrated people, squeezed in the corner by the law makers on the one side and the charterers/managers/owners on the other side, where their only way of surviving is by breaking the rules.
Ballast water management methods_TSCL 1_2004.pdf
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