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Bulk carriers ballast exchange requirements at sea

Ships ballast tanks allow her to maintain adequate trim, propeller immersion and sufficient stability to proceed safely on a ballast voyage. This is usually between 30 - 45% of the carrier's deadweight carrying capacity.

The nature of their trade usually means that bulk carriers spend half of their life travelling large distances in ballast.

It is estimated that billions of tonnes of water, along with thousands of species of plants, bacteria and othe marine organisms, are transported on ballast voyages each year. Anything that can pass alive through a ship's ballast system can be loaded in the ballast tanks and then transported to another country's territorial waters where that particular organism may not yet exist.

Cape size bulk carrier underway

The IMO adopted the International Convention for the Control and Management of Ships' Ballast Water and Sediments (BWM Convention)8 in February 2004. According to this Convention, maritime nations are required to take joint measures to ensure prevention, reduction or elimination of transportation of harmful marine organisms by appropriate management of ships' ballast water and sediments. These measures include rules for the design, control and construction of:

In addition, the following guidelines are also given in the Convention:

While the BWM Convention is not fully implemented, countries such as the USA, Australia, Ukraine and Brazil already have similar requirements for ships to exchange ballast by either the flow through, sequential or dilution method.

It is recommended that approval of a procedure for exchanging ballast water at sea be obtained from the ship's classification society.

A major hazard when carrying out ballast exchange at sea is the sloshing of seawater in ballast tanks and holds. The variability of the sea and swell conditions in a short period of time is an important factor in deciding whether to exchange ballast water at sea. Responsibility for deciding on whether to exchange ballast at sea must rest with the ship's Master, taking into account the permissible limits in respect of structural strength and stability and the sea and weather conditions prevailing at the time.

Where the exchange of ballast water at sea is to be carried out, that the following guidelines be followed;

a) The ship's Master must ensure that the necessary calculations are carried out at each intermediate step so that:

i) Adequate intact transverse stability is maintained.

ii) The permissible seagoing SWSF and SWBM are not exceeded.

iii) For each cargo hold and block of cargo hold(s), the combined weight of the cargo in the hold(s) and the water ballast in the double bottom and hopper wing ballast tanks directly in way of that hold(s) does not exceed the allowable Seagoing limits for all intermediate draught conditions.

iv) The present and forecast sea and swell conditions must be favourable to ensure that significant sloshing loads, which could cause structural damage to holds or tanks, cannot be generated.

b) If the ship has been provided with a ballast exchange sequence and procedure approved by the classification society, it should always be used and followed.

c) To minimise the risk of structural damage, the exchange of water ballast at sea should always be carried out in calm weather conditions. All available weather forecasting should be utilised to determine that the weather condition is likely to stay calm within the 'weather window' of the ballast water exchange operation. This 'weather window' should be determined based upon the ballast water exchange sequence and the achievable ballasting/deballasting rates. A sufficient time margin should always be included to allow for any unexpected circumstances such as the breakdown of ballast pumps.

d) Ballasting and deballasting of each pair of symmetrical port and starboard wing and double bottom ballast tanks should always be carried out simultaneously, such that the amount of water ballast carried in each tank is always the same, to avoid the introduction of twisting and torsional loads into the hull girder.

e) The progress of the ballast/deballast operation and the weather and sea condition should be closely monitored throughout the ballast exchange operation.

f) The practice of continuously pumping in new ballast water from the sea and allowing the old ballast water in the tank to overflow through the tank's ventilation pipes may be considered. However, caution should be exercised as over pressurisation of the ballast tank could result if one or more of the vent lines are obstructed and lead to structural damage.

g) If there is any difficulty in establishing a safe ballast exchange sequence, or if there is any doubt in the interpretation of an approved procedure or the stress limits imposed on the ship, no attempt should be made to exchange water ballast at sea.

Related articles:

  1. Practical method for the control of transportation of harmful marine organisms

  2. Safety precautions during ballast operation

  3. Loading of high density cargo and water ballast distribution for bulk carriers

  4. Regulation of pumping system of bulk carriers

  5. Risk of partially filled ballast tanks

  6. Handling water ingress problems in bulk carrier, investigation and countermeasures

  7. Various categories of garbage and management onboard

  8. Bulk carrier types - Ore carriers, OBO ships, forest product carrier , self unloader and more

  9. Loading of high density cargo and water ballast distribution for bulk carriers

  10. Regulation of pumping system of bulk carriers

  11. Risk of partially filled ballast tanks

  12. Handling water ingress problems in bulk carrier, investigation and countermeasures

  13. Survival and safety procedure for bulk carriers

  14. Procedure for exchanging ballast at sea

  15. Preparation for ships carrying bulk cargo & standard loading condition

Our detail pages illustrated many safety aspects of Bulk carrier

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Operation of sea going bulk carriers involved numerous hazards . Careful planning and exercising due caution for all critical shipboard matters are important . This site is a quick reference to international shipping community with guidance and information on the loading and discharging of modern bulk carriers so as to remain within the limitations as specified by the classification society.
It is vital to reduce the likelihood of over-stressing the ship's structure and also complying with all essential safety measures for a safe passage at sea. Our detail pages contain various bulk carrier related topics that might be useful for people working on board and those who working ashore in the terminal. For any remarks please Contact us

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