Chemical Tanker Safe Stability & Stress Limitations

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A chemical tanker must always maintain a sufficient level of stability whether being loaded, unloaded, or ballasted as reported by Chemical Tanker Solutions. 

Voyage remains manageable 

Chief Officer must plan for safe loading or ballasting of the vessel so that stability, stress and trim are acceptable throughout the voyage and that the ship remains manageable in a seaway without excessive shear forces, bending moments, pounding, or vibration.

Damage stability requirements as per the IBC code are to be complied with.

Complete and effective use must be made of the ship’s loading computer for both cargo and ballast operations and voyages.

During cargo and ballast operation stability and stresses are to be checked hourly and printed records maintained on board.

At sea, the ship must never be loaded to a deeper draft than that permitted by the Load Line Regulations.

A vessel must at all times be ready to sail for sea during cargo operations in port in case of emergencies.

Stress monitoring system

Some vessels may be equipped with strain/stress gauges, which may sound an alert automatically when certain levels are reached. Despite the fact that this equipment offers useful information, it is crucial to calculate the cargo/ballast plan accurately and ensure that stresses stay within reasonable bounds. It is not permitted to load or discharge the vessel only based on the strain or stress gauges.

All activities must halt until the situation is assessed if the stress alert rings while carrying out cargo or ballast operations.

Loss of stability

The following actions are taken if loss of stability is discovered or suspected at any point during loading or discharge. It should be emphasised that each vessel is unique, necessitating the adoption of various plans or crucial checklists for each one.

This is particularly crucial in double-hull ships without centre line bulkheads but nonetheless, is required for all vessels.

  1. Immediately stop cargo and all other operations such as ballast and bunkers.
  2. Advise terminal operator;
  3. Advise the office who will declare a contingency
  4. Ensure all mooring ropes are tight;
  5. Carefully check levels in all and verify the number of slack tanks (ballast, cargo and bunker);
  6. Determine the cause (e.g. incorrect or deviation from loading/discharging plan or technical cause such as valves or other cause of cargo/ballast internal transfer);
  7. Enter data into loading computer in order to check GM; and check for angle of loll and investigate preventive action accordingly.
  8. The company is to be kept fully advised on the situation. The majority of tankers have contracts with damage stability providers e.g. LR SERs and assistance from them will be sought in most cases. They will require accurate data on the vessels tank status in order to perform these calculations.
  9. Create a draft plan for correcting the situation. No action is to be taken without permission from the company who will be obtaining advice the damage stability provider. The only exception to this is when the master considers it essential to for the purpose of saving the vessel and he considers immediate action is required.
  10. When loss of stability has occurred, on no account is any ballast or cargo to be pumped out. Where ballasting is required only split double bottom tanks are to be filled, starting with the side which the vessel is listed over to, before making the ship upright with double bottom tanks on the opposite side. On no account are DB tanks that run the full width of the ship to be ballasted as this could increase free-surface with disastrous results.
  11. Before attempting to correct the stability, the plan must be carefully checked using the ship’s loading computer in order to check the criteria at every stage of the plan. The plan is to be agreed with the terminal operator before commencing the operation and hoses disconnected.
  12. Once stability is correctly restored, further checks should be made in order to ensure that adequate stability is maintained for the remainder of the cargo operation.

 

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Source: Chemical Tanker Solutions

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