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Ballasting by gravity, by water ballst pumps & priming procedure
Ballast is taken on to increase a ships draught, particularly the stern draught, when sailing without cargo. On a bulk carrier, the ballast system is operated from the engine room. Ballast piping is usually made of ordinary mild steel. A ships size determines the capacity of its ballast system.
During ballast water or liquid cargo handling operations, always handle the valves and pumps with care so that there is no sudden change in the pressure or the flow rate of the liquid. On recently introduced larger sized vessels operation hitherto deemed routine, there is a higher possibility of water hammering and/or surging..
AA) Ballasting by gravity
Start the ballasting as per Common Procedures
BB) Ballasting by Water ballast pump (WBP)
- Ensure the Water ballast pump delivery valve is Full shut.
- Confirm the ballast suction line has positive pressure, fill up the line with sea water Common Procedures
- Confirm that the ballast suction line is filled with sea water and Priming of the Water ballast pump is completed; by checking the WBP suction gauge pressure indication corresponds to the water head of the Ships draft and sea water comes out from the Air purge cock on the suction strainer of WBP.
Priming is defined as the process of filling up or the filled-up condition of pumps suction side with liquid, which is the most vital practice for any centrifugal pumps prior to start up. If the priming is insufficient, the pumps may take in vapor which brings about Cavitation and, furthermore, when the Running Dry Condition is continued it may result in the burn-out of the mechanical-seal of the pump.
- Simultaneously, line-up for relevant WBT(s) shall be done. WBP delivery valve should be opened slightly (about 10%) for some time to ensure safe condition of each part, and then proceed to set up Normal running.
In many cases speed adjustment is not available for Electric driven WBP, so delivery pressure are controlled only by opening ratio of the delivery valve, When ballasting a WBT, WBP delivery pressure should be slightly higher than the corresponding maximum height for water head of the WBT from the WBP base line. For example, if the height of the WBT is 30M from the base line of the WBP, the delivery pressure of WBP should be slightly higher than 3 kg/cm2.
Above practice is not necessarily to be followed for De-ballasting through the overboard discharge valve above the sea water; free from any back pressure.
Finishing ballasting by gravity
As per Section Common Procedures / Principle procedure to Stop ballast handling by gravity to close the valves, from the WBT suction filling line valve to the WBP sea chest valve in turn.
Finishing of ballasting using WBP
- Fully shut the WBP delivery valve
- Upon confirming above, stop the WBP
- Shut the relevant WBT suction filling line valve
- Full shut WBP sea chest valve and then shut the WBP suction valve.
Procedures for tank-to-tank ballast water shifting
For adjusting ships list or other reasons, tank-to-tank ballast water shifting becomes necessary. In this case also, you should mind there is a possibility of Surging by an existence of Air Lump: When an Air lump exists in the ballast line between the Supplying WBT and the Receiving WBT, water flow from Supplying WBT rushes into the cavity (air lump), which may damage the downstream valve.
- Confirm that the ballast suction line is at positive pressure and then fill it up with sea water as per Section 1. Common Procedures.
- Close all ballast valves
- Open the Supplying WBT suction filling line valve slightly (about 10%-open).
- Open valves from Supplying WBT side toward Receiving WBT side in turn.
- After confirming the level in the Receiving WBT is rising, open the Supplying WBT suction filling line valve by 100%.
Note-Line-up for ballast operation by gravity
You should always choose the simple and shortest Line-up when shifting ballast water. If possible, the shifting shall be done between 2 tanks with the least difference of water-head to control water flow speed and to complete successful air purging.
All piping systems within cargo holds, saltwater ballast tanks, double-bottom tanks, pipe tunnels, cofferdams and void spaces adjacent to cargo holds, and pipes that pass through the deck or connect to the hull, are examined and tested under working conditions to ensure that they remain tight.
Air pipe A pipe provided to equalize the tank pressure with the atmospheric one while the tank is being emptied or filled. Air pipes terminating on the open deck shall be fitted with approved air pipe heads. However, air pipes from the fuel oil settling and service tanks should be led to the funnel in order to eliminate the risk of water ingress due to a broken pipe or head.
To meet requirements of the International Convention on Load Lines it is enough to arrange 760mm high air pipes on freeboard deck and 450mm height ones on forecastle and poop. However such standard approach is no more valid. Efficiency of many vessels depends on their damage stability characteristics: better damage stability allows higher permissible vertical centre of gravity. In order to improve damage stability of the vessel it is very important to arrange air pipes and vents as far as possible from ship sides and as high as reasonable.
Ballast exchange procedure at sea
Practical method for the control of transportation of harmful marine organisms
Safety precautions during ballast operation
Loading of high density cargo and water ballast distribution for bulk carriers
Regulation of pumping system of bulk carriers
Risk of partially filled ballast tanks
Handling water ingress problems in bulk carrier, investigation and countermeasures
- MARPOL 73/78
- IMO Resolution A.774 (18) Guidelines for Preventing the Introduction of Unwanted Aquatic Organisms and Pathogens from Ships Ballast Water and Sediment Discharged
- Ships Procedure and Arrangements manual (Approved by Class)
- Guide to Port Entry
- US NPDES Vessel General Permit Compliance Manual
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