PROCEDIMIENTO PARA LA CONSTRUCCIÓN DE LA HERRAMIENTA EVALUATIVA DE REQUERIMIENTOS DEL

It is of paramount importance that permissible limits are always observed, and the Master should be advised if at any time if the vessel is likely to be subject to stress, stability or draft conditions outside those limits.

The calculations must be attached to the cargo or ballasting plan. The Chief Officer must ensure that all other Deck Officers are aware of the cargo plan and the attached stability calculations, and of what action to take should there be any deviations from the cargo plan which might significantly affect stability. Where there is a deviation from the original plan then a new calculation must be performed.

5.3 Damaged Stability

5.3.1 The Calculation of Damaged Stability

The Master must take into account damaged stability and satisfy himself that on a loaded voyage the vessel complies with the damaged stability requirements of MARPOL, or the IBC or IGC Codes, as applicable. Masters may be required by port authorities to demonstrate that damaged stability has been taken into account for all parts of a voyage.

Most Stability Information Books contain a statement to the effect that the stability is approved for the stated loading conditions only and a deviation from any of those conditions is only permitted as long as the stability complies with the IBC or IGC Codes or MARPOL. In effect this means that if the actual loading condition deviates from one of the loading conditions in the SIB by more than 1% then an additional calculation for damaged stability must be made.

5.3.2 Cargo Loading Computers Provided with Damaged Stability

Most loading computers have now been provided with a damaged stability programme. On such vessels the damaged stability must be assessed for the actual loaded conditions and a printed copy, signed by the Master, must either be included in the stability calculation or appended to it.

This procedure must be complied with for all loaded conditions, including departure, arrival and if necessary, an intermediate condition.

5.3.3 Cargo Loading Computers not Provided with Damaged Stability

The vessel should be loaded as close as practically possible to one of the loading conditions provided in the Stability Information Book taking into consideration the cargo quantity and draft restrictions provided in the voyage orders.

The following must be taken into consideration:

1. The vessel should normally loaded in accordance with the conditions in the Stability Information Book;

2. If an alternate loading condition is used, has written authority been obtained from either the class or flag administration?

3. The Master must verify any alternate loading condition by assessing the condition against the critical damage KG data which is included in the approved stability information.

The Master must check the actual loaded condition against the closest conditions provided in the approved Damage Stability Booklet in order to verify compliance with damage stability criteria.

This condition should be copied, signed by the Master, and attached to the intact stability calculation.

5.4 Comparisons during Cargo Operations

During cargo operations comparisons are to be made between the pre-calculated data at 25%, 50% and 75% of the operation and the actual data obtained from the loading computer.

Should significant differences be noted then consideration must be given to stopping the operation until the cause has been found. If there is a difference of more than 0.2 metres or 20% of the pre-calculated GM, the cargo operation must immediately cease. An investigation must be carried out as to the reasons for the difference and operations must not be resumed until the Master is satisfied that the cause has been identified and adequate corrective action, as required, has been taken.

At the completion of cargo operations and periodically, the actual draft is to be compared with that calculated and any significant differences must be investigated and dealt with.

5.5 Revisions to the Original Cargo Plan

During cargo operations it may be necessary to revise the discharge plan due to unexpected circumstances, for example to accord with the requests of the receivers or shippers. If necessary, stability must be re-calculated and this may result in delay. Under no circumstances must cargo operations proceed if there is any doubt as to whether or not stability and stress can be maintained within the desired limits. If problems arise then the company is to be immediately informed.

5.6 Slack Tanks

Every effort is to be made to avoid slack cargo and ballast tanks in order to keep free surface effect to a minimum.

Particular attention must be paid to the effect slack ballast tanks can have on stability, particularly those which do not have a centreline bulkhead and which extend across the width of the vessel.

5.7 Loss of Stability

Loss of stability or an excessive list is caused by:

• The loss of buoyancy on one side of the vessel; or

• A minimal or negative GM.

The result of instability will either be capsize or the vessel attaining an angle of loll.

For vessels with a negative GM, any external force applied will result in the vessel heeling. As the vessel heels, the centre of buoyancy will move outwards and provided it can move sufficiently outboard then it will result in stability being re-established and it will come to rest at an angle of list, known as the angle of loll. At that point, the centres of gravity and buoyancy are in the same vertical line and any further external forces applied will result in a righting lever developing which will return the vessel to the angle of loll when the applied force is removed.

The vessel has effectively capsized to an angle of loll. Angles of loll generally are of the order of between 5 and 10 degrees.

A vessel at an angle of loll is in a potentially dangerous condition. It would take little to cause the vessel to roll through the vertical and come to rest at an opposite angle of loll. Apart from the obvious physical results of a vessel moving quickly through what can be a large angle, there is also a possibility that the momentum will cause the vessel to roll to a larger angle, lose stability and capsize.

If a vessel assumes an unexpected angle of inclination the following actions must be taken:

• If the vessel is in port all cargo, ballast, bunkering and storing operations must immediately cease;

• Check that stability calculations were correct and that an error has not been made;

• If at sea, alter course to put the head into the weather;

• Check that there is not an obvious reason for the list, such as an unplanned movement of cargo, bunkers, water or ballast. If there are no such listing effects then it should be assumed that the vessel is unstable and is lying at an angle of loll;

• Check for slack tanks – free surface effect will have a significant effect on stability;

• Inform the company as soon as circumstances permit.

Masters must ensure that before taking any action to correct stability, such action will in fact improve the situation and not compromise it. External forces, such as wind and tide, must be considered, and it might be necessary to take immediate action to prevent a deterioration of the situation.

If the vessel is at a terminal they should be informed. If considered prudent cargo hoses must be disconnected.

The company subscribes to a class Ship Emergency Response Service for all tankers in the fleet. The service may not necessarily be provided by the same society as the vessel is classed under. The SERS may be contacted at any time to provide emergency assistance.

5.8 Loading Computers

A loading computer is provided to supplement the Trim and Stability Booklet to those vessels in the fleet where one will be of benefit. Its primary function is to facilitate the pre-calculation of conditions of loading with respect to draft, trim, shear force and bending moments. Officers are expected to know how to manually calculate draft, trim and stress using the Trim and Stability Booklet in case of a malfunction of the loading computer, and to be able to manually calculate damaged stability using the Damaged Stability Booklet.

The loading instrument will be approved by a regulatory body, usually the class society, and a copy of the approval certificate should be lodged in a certificate file and shown to those who have the authority to ask for it.

The output data is only as good as the input data, and that care should be taken in ensuring that the quantities entered are correct, particularly with respect to slack tanks where free surface may be an issue. Data on stores, fuel and ballast must be updated regularly where necessary.

The loading computer must be tested monthly for operational accuracy against both the approved test data supplied by the manufacturer or class and against the conditions in the Trim and Stability Book. The load computer results must also be checked at least monthly where practicable against visually observed drafts. The record ECF40 - Cargo Load Computer Test must be maintained. If there are any significant differences the company must be informed.

Records of stability calculations must be retained on board. It is recommended that upon sailing, a copy is taken to the bridge and left available in the event of an emergency situation. Upon arrival at the next port, this stability record should then be removed to the Cargo Office and filed.

5.9 Free Surface Effect

The two issues with free surface are the effect on transverse metacentric height, and thus stability, and sloshing, which can cause structural damage. The effect on stability will be most

severe with tanks which have a large transverse width, such as ballast tanks that extend the full width of the vessel.

The most critical stages of any operation will be while filling and emptying double bottom ballast tanks and whilst the liquid level is below the double bottom tank top. If sufficient cargo and ballast tanks are slack simultaneously, the overall free surface effect could well be sufficient to reduce the transverse metacentric height to a point at which the transverse stability of the ship may be threatened. This could result in the ship suddenly developing a severe list or angle of loll.

It is imperative that personnel involved in cargo and ballast operations are aware of this potential problem, and that all cargo and ballast operations are conducted strictly in accordance with the ship’s loading manual.

5.10 Sloshing

The movement of liquid with a free surface within a cargo tank when the vessel is pitching or rolling at sea is called “sloshing”.

There are several negative effects of sloshing:

• The slamming effect of the liquid may cause damage to the tank structure and fittings;

• A rolling and pitching motion can generate a source of ignition – an electrostatic charge;

• The effect of free surface reduces the ship’s GM and may lead to a loss of stability.

Although none of the Columbia vessels is subject to restrictions, in order to avoid any potential problems slack tanks should be avoided wherever possible whilst the vessel is at sea.

5.11 Maximum Density Restrictions

Most, if not all, vessels have density restrictions. Such restrictions must be complied with and if necessary a reduced volume of cargo loaded in order to ensure that the restrictions are not exceeded.

If the vessel is requested to load a cargo, the density of which is in excess of the maximum density it is approved to carry, the company must be informed and approval sought before commencing loading.

The maximum permitted cargo density must be recorded on the notice CCR29 - Cargo System Maximum Capacities.

6. Gas Detection and Personal Protective Equipment