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Purpose of Ballast Water Management System onboard cargo ships

Ballast water is carried by ships to maintain stability and seaworthiness, especially when it is not carrying cargo. It is estimated that 7000 species of plants, animals, and other organisms are transported every day in ballast water.

Scientific research has now proven that the discharge of ballast containing certain species can have a serious effect on the ecological balance of the environment in which the ballast is discharged. The introduction of foreign species can impact local biodiversity and ecological systems, human health, and the local economy. This has been recognized by the IMO and the World Health Organisation. The ballast water and sediments carried by ships have been identified as a major pathway for transporting harmful invasive aquatic organisms and pathogens.

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Oil Tanker Safety Guide
The purpose of the Ballast Water Management System is to minimize the transfer of Non-indigenous harmful aquatic organisms and pathogens from one area to another (arrival port) through the ship's ballast water system. Invasive marine species are one of the four greatest threats to the world's oceans.

Unlike other forms of marine pollution, such as oil spills, where ameliorative action can be taken, and the environment will eventually recover, the impacts of invasive marine species are often irreversible. The objectives can be safely met through the use of prescribed ballast water management practices, standard operating procedures, and training.

Each vessel should be supplied with a ship-specific "Ballast Water Management Plan." This Plan gives general guidance and requires additional input from the ship to take into account the vessel’s unique arrangements. Ship specific pages spread in various sections to be filled as accurately as possible. It also includes a log for all ballast handling and is to be presented to port state inspectors when required as a means of proof that correct procedures have taken place.

Micro organism category
Micro organism category

Even if a ship is trading in an area where ballast water information is not required, this Logbook is still required to be completed to maintain a history of ballast source. The ship’s safety during ballast handling supersedes any other requirement. There is vast importance for ship details, calculations and plans provided to be as accurate as possible.

Within the plan, the following pages/sections are expected to be filled with all relevant data, drawings, calculations, etc., before submission to any class or flag representative. The vessel is required to fill only for methods that are going to be used on-board. Ballast Water Management Methods, not included in a plan are NOT allowed to be used unless they have been class or flag approved.

Micro organism

At any case, Master should ensure that the following points have been taken into account when providing ship specific data:

Longitudinal Strength

The longitudinal strength for each step should be within the allowable sea-going limits. This should be demonstrated by printouts for each step as developed by the approved loading program or by the method of the approved Loading Manual. The approved Test Loading Conditions (at least one) should be available for the engineer to compare, as a minimum, the format of the output to determine whether the approved program has been used. In any case, a statement of the submitter to that effect is required.

If in any step the sea-going limits are not met, and cannot be met due to the vessel 's/tank configuration (this must be demonstrated by the designer) consideration may be given in meeting the allowable with the Total Bending Moment resulting by adding 50% of the Wave Bending Moment to the SWBM.


Ship-specific intact stability criteria under assessment are expected to be met in all steps of the Exchange. Accurate calculations need to be prepared to demonstrate compliance. When calculating stability, the maximum free surface of all tanks should be taken into account.

Propeller Immersion - Drafts

a) Bulk Carriers contracted after 01 July 2003 and Oil Carriers: The propeller should be 100% immersed at each step of the exchange process. MARPOL Annex I, Reg. 13(2), 13(7), 13(10), and IACS UR S25 4.4.1(a) should be complied with, as applicable for the particular vessel. If these requirements are not or cannot be met, the BWMP should identify which steps of the Exchange do not meet the requirements and a footnote is to be assigned to the relevant steps to refer to the following statement which is to be included in the review letter and the BWMP:

"At some stages of the indicated ballast water exchange operations, the vessel's draft amidships, trim, and/or propeller immersion are not in compliance with the requirements in MARPOL 73/78 I/13(2) and IACS UR S25 4.4.1(a). It may be considered satisfactory provided the ballast water exchange operations are undertaken in fair weather and sea conditions. The master must be satisfied with the control of the vessel's maneuverability. There should be sufficient segregated ballast capacity available at all stages of the voyage to enable compliance with the applicable draft, trim, and propeller immersion requirements in a reasonably short period should weather, and sea conditions begin to worsen."

Ballast water discharging

b) Vessels other than those covered by a): For such vessels where there is no requirement for propeller immersion or the bulk carrier was built before the date indicated in (a) above and was not designed to comply with MARPOL I/13 considering BWE and the propeller is not fully immersed, the BWMP should identify which steps of the Exchange do not meet the requirements, and a footnote is to be assigned to the relevant steps to refer to the following statement which is to be included in the review letter:

"The master should be aware of the fact that the propeller of the vessel is not fully immersed in steps ... and accordingly the vessel's maneuverability will be adversely affected while operating in these conditions."

c) Draft at the forward perpendicular The Loading Manual and Shell Expansion of the vessel should be checked as to whether there is any note concerning the forward ballast draft. If not, IACS UR S25 4.4.1(b)(v) should be checked. In case that the above requirements are not satisfied, the BWEP should identify which steps of the Exchange do not meet the requirements. A footnote is to be assigned to the appropriate steps to refer to the following statement, which will be included in the review letter: "Exchange of ballast in tanks should be carried out in favorable sea conditions such that the risk of forwarding slamming is minimized…."

Bridge Visibility

For vessels designed to achieve visibility limit of 2 times the vessel's Freeboard Length or 500m whichever is less, each step of the exchange process is to be checked to verify compliance with that criteria. (Note: For vessels built before 1998, this visibility limit was not mandatory and should not be invoked simply because BWE is being implemented.) In case that the above requirement is not satisfied, alternative methods that will guarantee adequate surveillance of the seaplane in front of the vessel must be presented.

Acceptance of the proposed method must also have the acceptance of the vessel's flag administration as this requirement comes from SOLAS 74, as amended, V/22(c).

For example, an Owner may propose including instructions to the master for conducting the particular stages of ballast water exchange (BWE) when the visibility criteria from the bridge are not met under the conditions of daylight hours, in fair weather and sea conditions, with lookouts stationed forward and in radio communication with the bridge to have the required visibility forward available to the bridge.

The BWE operation sequence should identify the particular exchange operation stages and their durations during which visibility forward from the conning station would not comply so that the lookouts could be posted. Depending on the period the lookouts would have to be posted and the ship's trade pattern, this may be a reasonable solution and one that classification society or flag administration could support on a case-by-case basis.

5. Sloshing For vessels like oil carriers and for the ballast hold of Bulk Carriers, sloshing must be considered where there is resonance or whether the width of the tank is more than 0.56 B or if its length is more significant than 0.10 L. In such cases, either sloshing calculations must be submitted, or the BWEP should identify which steps of the Exchange are not met and a footnote is to be assigned to the relevant steps to refer to the following statement which is to be included in the review letter:

"Exchange of ballast in tanks may impose significant structural loads generated by sloshing action when the water level in the tank is between ...% and ...%. Accordingly, the procedure should be carried out only in favorable sea and swell conditions such that the risk of structural damage is minimized. "

Related info :
  1. Marine environment protection recommended guideline

  2. Ballast water management convention recommended guideline for environmental protection

  3. Ballast water treatment system components

  4. Pollution by ballast water

  5. Impact of ballast water at marine environment

  6. Ballast water management USCG final rules

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