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Stability calculations & Stability and hull strength check item - operational guideline for cargo ships

CMA CGM Lamartine at sea passage

Masters are reminded of the dangers that inaccurate estimating of cargo centres of gravity can present to the stability of the vessel. Crew members must advise masters when similar cargoes of differing densities are being loaded so that a proper estimate of weights and positions of centres of gravity can be determined.

They should also provide the master with accurate stowage factors of different parcels of cargoes. Care must be taken to ensure that stowage factors used for cargoes are accurate. Cargoes such as scrap metal should not be assumed to be homogeneous.

The Master should ensure that terminals are instructed on the correct order of shipment to ensure that the vessels minimum stability criteria can be exceeded throughout loading and the voyage. Sufficient time must be allowed for the master to ascertain the vessel's stability and allow for any necessary ballasting operations to be undertaken before proceeding to sea.

Stability calculations and assumptions should err on the side of caution. Incorrect estimates can have serious consequences as the voyage progresses with reducing stability margins.

When ballasting care must be taken not to unduly stress or overload the vessel. When correcting angles of heel, care is necessary to avoid the danger of inappropriate ballasting, especially when the vessel has an angle of 'loll' caused by a negative metacentric height. The effect of free surface and the vertical and transverse movement of centre of gravity must be considered.

The conditions of stability, hull strength, draft and trim of the vessel at sea and on arrival / departure at / from port and during loading / unloading cargo, bunkering and water ballast exchange, should be worked out, ensuring safety of the vessel. Safety of the cargo vessel depends on proper GM, stress calculation and other factors as being within appropriate Limits.

Following are the check item confirming stability and hull strength of cargo ship:

1. Is the GM value within limits specified in the loading manual and in compliance with IMO rules upto arrival next port?

2. Are GZ curves of the vessel fully understood, and their characteristics confirmed?

3. Have expected weather and sea conditions, been taken into consideration when confirming stability & hull strength?

4. Have free surface effects and any sloshing effects for the planned passage, been taken into consideration?

5. Are other items mentioned in the loading manual taken into consideration?

6. Are values of bending moment, shearing force and torsional stress at sea within acceptable limits upto arrival next port?

7. If applicable, has the “Auto” mode for heeling pump been changed over to “Manual” mode prior sailing?

8. Is the draft within applicable loadline or port/passage limits/restrictions?

9. Is stack weight / cargo density in accordance with maximum permissible values and have precautions as per the loading manual been followed?

10. Has forward draft limit (per loading manual) to prevent slamming been confirmed?

11. Is a proper propeller immersion ratio assured?

12. Have trim and draft changes during voyage in fresh or brackish water such as rivers, canals and lakes, been taken into consideration?

13. Is squat due to shallow water effect taken into consideration?

14. Is proper under keel clearance assured as per company policy

15. Are fuel oil and fresh water consumptions taken into consideration?

16. Have air draft limitations due to bridges, cargo handling equipment or other obstructions been assessed as necessary?

17. Is the navigation bridge visibility restriction in compliance with requirements of SOLAS chapter V and other applicable requirements (Panama Canal, Suez Canal etc)?

18. On tankers, is the Marpol (Reg 18) minimum criteria for draught and trim complied with? And has the departure condition been forwarded to office for use in case of emergency?

NOTE: Attach loadicator stability & hull strength summary

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