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Ballasting / deballasting guideline for bulk carriers
Seagoing bulk carriers when not carrying cargo or is lightly loaded, sufficient ballast must be carried to ensure that the ships stress, stability, draft, trim and propeller immersion is within permissible limits to guarantee the safe handling of the vessel in the prevailing or expected conditions.
Following are basic guideline for De-ballasting at sea:
AA. Commencement of de-ballasting by gravity : Follow the Common Procedures ...
BB. Commencement of de-ballasting by water ballast pump (WBP)
- Ensure Full shut position of WBP delivery valve
- Confirm the ballast suction line is under positive pressure, fill it up with sea water as per Common Procedures .
When starting de-ballasting of WBT(s) distantly located from the WBP, below procedures shall be taken additionally to above steps, to prevent the Surging.
Surging with existing Air lump in the WBP suction line
In the process of de-ballasting, once a cavity is created in the WBP suction line by extraction of Air lump which has a blocked water movement, water flow rushes from the WBT into the hole (cavity) like floodwater. This is called Surging.
i). Shut all ballast related valves
ii). Open the relevant WBT suction filling line valve slightly (less than 10% opening ratio) and then open valves toward the WBP in turn.
Prevention of water flow acceleration in the suction line
By the following method the minimum time interval for opening the next valve on downstream side after slight opening of the WBT suction filling valve should be calculated.
Distance between the ScFl V. & Next V. [mtr] ÷ Standard water flow speed 6[mtr/sec]
Especially, in case no block valves are provided between the WBT ScFl V. and the WBP suction valve, water runs long distance. Therefore, the common procedure should be followed strictly, or the closer WBT to the WBP shall be given priority when starting de-ballasting.
Confirm the ballast suction line is filled up with sea water, by checking that the WBP suction gauge indicates a pressure corresponding to the water head of the Ships draft and sea water comes out from the Air purge cock on the suction strainer of WBP, then open the WBT ScFl valve 100%.
(4) The Line-up to relevant WBT(s) shall be conducted simultaneously, then WBP Delivery valve is to be opened slightly (about 10%) to ensure each part is in order, and then proceed to Normal running stage.
CC. Finishing de-ballasting by gravity
As per Common Procedures / Principle procedure to Stop de-ballast handling by gravity, valves shall be closed from the WBP sea chest valve (or WBP over discharge valve) to the WBT ScFl valve in turn.
DD. Finishing de-ballasting by WBP
- (1) Fully shut the WBP delivery valve
- Stop the WBP after ensuring above (1).
- Shut the WBT ScFl valve
- Fully shut WBP sea chest valve or WBP overboard discharge valve.
EE. Change-over of tanks from a lower water head tank to higher one, while the ballast pump in operation
This procedure is to be applied where the water level of the WBT(s) became too low to continue de-ballasting by BWP and the tank should be stripped by WBED, while WBP in operation can be used continuously for de-ballasting, changing over to a WBT(s) with higher water level.
In such case, where a WBT level reaches to the stripping level, suction pressure will surely indicate Negative, thus its required to offset Negative pressure to neutral prior to a changeover for avoiding Water Hammer in the relevant suction line.
(1) Close the WBP delivery valve to about 10%-opening to recover the WBP suction pressure from negative to approximate to atmospheric pressure (Zero on gauge).
(2) After the process in (1) above, open the suction valve of high-level tank slowly and then close the same of low-level tank.
How to assess the effect of valve open / shut operation?
Any valve operations (shut or open) are reflected as the change of pressure on the gauges, both suction and delivery. In other words, if those pressure indications are unchanged, the valve operations have no effect on the pump. Therefore, when the WBP suction pressure shows Negative after the operation above EE-(1), stop the WBP and then back to the procedures mentioned above Commencement of de-ballasting using WBP
Stripping (or Draining) with WB Eductor
aa. Basic operation of WBED
Basic operating method of WBED is; (1) Line-up the discharging side of the WBED.
(2) Line-up the driving side, then start the driving pump (usually WBP) at low speed rate (or with the delivery valve slightly open), then increase the pressure up to the required driving pressure.
(3) Open the WBED suction valve and confirming the pressure of the WBED suction line negative, open the WBT ScFl valve of the relevant tank to be stripped.
bb. Releasing the negative pressure in suction line after stripping by WBED
Normally, WBED is used for draining water from WBT(s) after the pumping-out by WBP, therefore, even if the suction line is left in negative pressure, there may not be a high risk of Water Hammer.
However, as almost all vessels are not provided with an exclusive in-tank stripping line, and in-tank water ballast main line is used for both Filling or Discharging water ballast to/from WBTs, and the suction line is common for both WBP and WBED as well.
Consequently below procedure shall be followed to prevent the great negative atmosphere left in the suction line, in assumption that the WBP is used continuously for de-ballasting a higher water-head tank after completion of stripping another WBT by WBED.
The procedure for Change-over of tanks during stripping by WBED
(1) Close the ballast pump discharge valve to about 10%-open, and lower the WBED driving pressure as much as possible to offset the suction pressure of WBED from negative to approximate to atmospheric pressure (Zero on the gauge).
(2) After the process (1) above, change over the WBT. Close WBT ScFl valve of the stripping tank and open the ScFl valve of the next WBT to be stripped.
Stopping WBED (at the completion of all stripping operation by Eductor)
(1) Close the ballast pump discharge valve to about 10%-open, and lower the WBED driving pressure as much as possible, in order to offset the WBED suction pressure from negative to approximate to atmospheric pressure (Zero on the gauge).
(2) After the process (1) above, close WBT ScFl valve on the final stripping WBT.
(3) After the process (2) above, close the suction valve of WBED.
(4) After stopping the driving pump (WBP), open both suction and delivery valve of WBED to let all the suction/delivery lines be released from negative pressure.
How to prevent water hammer and surging during regular ballast operations ?
Ballasting by gravity, by water ballst pumps & priming procedure
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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