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Heavy Weather Ballast .1 General Provisions

In document DCOM Petroleum & Chemical (Page 179-183)

Annex V Garbage I Air Pollution

9. Pump Rooms

10.8 Heavy Weather Ballast .1 General Provisions

10.6 Discharge of Dirty Ballast

Ballast which has been loaded into cargo tanks which have not been cleaned, on either crude oil or product tankers, must be treated as dirty ballast. Any clean or segregated ballast which has been contaminated with oil from any source must also be treated as dirty ballast.

Where there is any doubt as to whether ballast should be treated as clean or dirty, then it should be considered dirty ballast and must dealt with in accordance with this section.

Dirty ballast must be discharged in accordance with MARPOL and either discharged to a shore facility, or discharged overboard using an ODME.

The following must be observed when disposing of dirty ballast overboard at sea:

• Lines and associated pumps to be used must have been cleaned and must be free of all oil prior to the discharge commencing;

• The initial discharge of dirty ballast should be internally to a slop tank;

• The requirements of MARPOL with respect to the discharge of ‘oil or oily mixtures’

(Annex I - Regulation 34) must be complied with;

• The ODME must be fully operational, and the instantaneous rate of discharge – the rate of discharge of oil in litres per hour at any instant divided by the speed of the ship in knots at the same instant – must be less than 30 litres per nautical mile;

• Upon commencement of discharging dirty ballast, a visual watch should be established to observe the ballast as it discharges into the sea. The operation should be stopped immediately in the event of any oil sheen being observed;

• Pump speeds should be reduced during the latter stages of discharge in order to avoid vortices developing and oil being drawn into the suctions prematurely;

• If the vessel is moving in a seaway then it will be necessary to transfer more residues to a slop tank than when the weather is calm;

• Decanting should not be undertaken if the vessel is rolling or pitching in a sea because of the likelihood of turbulence and the loss of a satisfactory interface between any oil on the surface and the water beneath;

• A full record of the discharge must be maintained in the Oil Record Book Part 2.

Retained slops on board after de-canting should either be loaded on top, discharged to shore reception facilities, or retained on board.

It is extremely important that accurate records are maintained in the Oil Record Book Part 2.

10.7 Ballasting Tanks Adjacent to Solidifying Cargoes

Consideration must be given to the effects on solidifying cargoes when ballasting tanks which have a common bulkhead with such cargo tanks. It should be avoided as problems may be experienced with the cargo solidifying, particularly in pumps and pump wells.

10.8 Heavy Weather Ballast 10.8.1 General Provisions

Severe weather should be avoided if at all possible and consideration should be given to deviation or taking shelter if the Master considers that the safety of the vessel or the cargo might be compromised by severe weather. Use should be made of the company weather routeing systems.

A vessel’s response to heavy weather will depend to a large degree on its statical stability. A vessel can be too stiff (return very quickly to the upright because of a relatively large GM) or too tender (return slowly to the upright because of a relatively small GM). In tankers the change of

GM during a voyage due to the use of fuel and water is generally a lot less than that of fine-lined dry cargo vessels. The main concern with tankers is structural damage in heavy weather, although if there is significant rolling this will invariably result in considerable discomfort to the crew and possibly machinery and equipment damage.

In severe weather, if the forward draft is insufficient the bow will emerge periodically from the water and slamming will result. Excessive slamming can lead to structural damage or even to hull failure and ship loss in extreme conditions.

Deeper drafts forward will generally reduce the tendency for the ship to slam. If the sea conditions are causing regular slamming, then in addition to heavy weather ballast, appropriate measures such as a change in speed or heading may be required in order to avoid structural damage.

If the aft draft is insufficient then in heavy weather the propeller will race when it emerges from the water and will slow down when it re-enters. This may cause engine control problems and increased loading on the propeller shafting and machinery. Increasing the aft draft reduces this tendency.

Accordingly, safe ship operation in severe weather may require the loading of heavy weather ballast into cargo tanks. The decision to initiate heavy weather ballasting procedures lies with the Master when the weather forecast indicates that heavy weather will be encountered. The Chief Officer shall be responsible for carrying out such ballasting and will report regularly to the Master throughout the operation.

10.8.2 Specific Requirements for Crude Oil Carriers

MARPOL Annex 1 Regulation 18(3.1) states: “In no case shall ballast water be carried in cargo tanks, except on those rare voyages when weather conditions are so severe that, in the opinion of the Master, it is necessary to carry additional ballast water in cargo tanks for the safety of the ship. Such additional ballast water shall be processed and discharged in compliance with Regulation 34 – Control of discharge of oil”.

Furthermore, IMO Crude Oil Washing Systems states:

“If it is considered that additional ballast in a cargo tank or tanks may be required during the ballast voyage under the conditions of regulation 35 of Annex 1 of MARPOL, the tank or tanks which may be used for this ballast shall be crude oil washed.”

It is the responsibility of the Master to determine whether or not it is likely that there may be a requirement during the forthcoming voyage to ballast cargo tanks, either because of anticipated bad weather, for draft or trim restriction requirements, or for any other reason. If so then the cargo tanks designated as heavy weather ballast tanks must be crude oil washed prior to departure from the final discharge port.

Under normal circumstances ballast water shall not be put into tanks that have not been crude oil washed. Water that is put into a tank which has been crude oil washed, but not tank cleaned, must be regarded as dirty ballast.

Care should be taken at the completion of crude oil washing that any cargo tank which might be ballasted is stripped as completely as possible. Where such ballast is filled through cargo lines and pumps, these must also be drained and stripped of oil.

10.8.3  Specific Requirements for Product Tankers and Chemical Carriers

If possible cargo tanks and lines should be cleaned into a slop tank prior to the taking of heavy weather ballast. This will result in significantly less dirty ballast than if the tanks were not cleaned. However, the safety of the vessel should not be jeopardised in order to clean tanks, and heavy weather ballast should be loaded if necessary into dirty tanks.

On tankers without an inert gas system, static precautions should be followed when loading ballast into cargo tanks containing a flammable atmosphere.

10.8.4 General Considerations for All Vessels

Normally cargo tanks are ballasted using a cargo pump taking suction from a sea water intake via the suction cross-over. However, some vessels are fitted with arrangements to connect the ballast system with the cargo system and load ballast utilising a ballast pump.

One of the most important considerations when taking heavy weather ballast is that of sheer forces and bending moments. It is important that the sheer forces and bending moments are calculated for at least the initial, intermediate and final stages of the ballasting operation, and the corresponding drafts and trim recorded. If necessary, further stages should also be calculated.

Before loading or discharging heavy weather ballast at sea, the operation should be discussed and agreed between the Master and the Chief Officer.

The following precautions must be taken when taking heavy weather ballast:

• Heavy weather ballast should be loaded well before any heavy weather is expected;

• If the vessel is still alongside a terminal the terminal representative must be informed;

• Any additional ballast must be loaded and discharged in such a way as to ensure that stresses are maintained within the maximum limits at all times during the transfer operation;

• When commencing ballasting, cargo sea suctions must not be opened until the cargo pump is running and there is a vacuum on the line, to avoid any oil escaping overboard;

• The ballast must be loaded through the loading lines;

• If it is necessary to mount special spool pieces to carry out ballasting, the spool pieces are to be removed as soon as the ballasting is completed;

• If ballast is to be loaded into tanks containing hydrocarbon vapour or which previously contained cargoes that required closed operations, closed loading procedures must be followed and the tank ventilation system utilised;

• Reliable communications must be maintained between the officer in charge, the bridge and the crew on deck during the entire operation;

• The operation must be carried out in accordance with good tanker practice in the management of the operation and the checking of it throughout, including the monitoring of ullages and tank pressures;

• Records of the operation must be maintained;

• The Ballast Water Management Plan should be consulted.

10.8.5 Discharge of Heavy Weather Ballast

The discharge of heavy weather ballast must be agreed between the Master and the Chief Officer, and be carried out strictly in compliance with the requirements of MARPOL if the ballast contains any pollutants.

10.8.6 Ship-Specific Heavy Weather Ballast Procedure

Each vessel should develop a ship-specific heavy weather ballast handling procedure. The procedure should identify the following:

• The sequence of which tanks are to be loaded and in which order;

• The maximum loading rate;

• Which pumps and lines are to be used, with alternatives identified in case of unavailability of the first choice;

• The procedure for opening the sea valve, ensuring that pollution prevention methods are adopted;

• The final ullages of the tanks to be loaded;

• Any venting requirements;

• Copies of the initial, intermediate and final stress and stability calculations for a condition with all side ballast tanks full, and bunkers, stores and other consumables at an ’average’

level.

The procedure must be developed and lodged in the CCR Information File in the document CCR27 - Procedure for Dealing with a Contaminated Ballast Tank.

11. Small Craft Alongside

In document DCOM Petroleum & Chemical (Page 179-183)