ship handling

Home page|| Tanker Notes || Container Ship Operations || Ocean Navigation ||

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

Ship stability is the ability of a ship to float in an upright position and, if inclined under action of an external force, to return to this position after the external force has ceased acting. Stability is not connected with a defined direction. However, ship inclination in transverse direction is most common and easiest to achieve and in practice transverse stability is the most critical to ship safety. Stability of a loaded ship depends on her shape and dimensions and on the actual location of her centre of gravity. Small ships with low freeboard are more prone to stability accidents than other seagoing vessels.

After a ship is constructed, an operator has no influence on shape, dimensions, as well as mass and location of the centre of gravity of an empty vessel. Still, he has an influence on the final mass of the loaded vessel and the location of the centre of gravity defining amount of cargo, stores and ballast water as well as their locations.

A number of ship operations can adversely affect stability. Such effects must be understood and, where possible, mitigated. When liquid is consumed or removed from tanks than a free surface is created which decreases stability. When a weight is lifted and suspended, its centre of gravity rises to the point of suspension. When a quantity of loose dry bulk cargo moves transversely across the ship, it will list to one side with some lost of stability. Phenomena such as absorption of moisture by timber or similar deck cargoes, ice accretion on decks and accumulation of shipped water will rise the vertical centre of gravity VCG reducing the righting arm GZ.

Damage stability – Stability of the ship in flooded condition. This stability is attained by installing a number of watertight compartments. If one of these compartments is breached, then the watertight bulkheads surrounding it will prevent the inflow of seawater from spreading to the rest of the ship.

CMA CGM Lamartine at sea passage
Fig: 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

See also Damage stability calculations. Further reading: “Ship Stability in Practice”

Related articles

Hull stress and Torsional moment in Container Ship Operation

Larger wind area in Container Ship Operation

Fore-ward Visibility in Container Ship Operation

Container Ship navigation - Meeting with Heavy weather

Basic guideline for Container Ship Operation

Ship Encountering Parametric Roll In A Seaway

Action by vessels navigating in congested water

Action by vessels navigating in an area of restricted visibility
How to confirm stabilty condition ?

How to maintain watertight integrity?

Guide to watch officer for ships navigation ?

Heavy weather countermeasures for prudent navigator

How to navigate vessel safely in heavy seas ?

Meeting rough sea conditions by containerships

Checklist for calculating stability and hull strength for cargo ship

Container Ship navigation - passage planning guideline

Navigation in cold districts and countermeasures

More shipboard operation and safety matters

Safe anchoring - planning and operational guidance for cargo ships

Anchor watch check item - deck officers guideline ....

How to deal with a damaged anchor? ....

How to recover a lost anchor ? ....

What is stranding ? Investigation of possibility of self-refloating and urgency of danger ....

What are the emergency procedures for loss of anchor and chain? ....

In case of damage to anchor and chain when to claim for '' general average"? ....

Ships arrival in ports - check item prior entry

Ships navigation in restricted visibility check items

Rules of ships navigation in restricted visibility

Ships navigation in confined water - matters that require attention

Securing your vessel for sea passage - when to check and what to check

Collecting Information and Data for Passage Planning

Shipping industry recognizes environmental protection as one of its highest priorities and that every effort should be made to conserve and protect the environment from marine, atmospheric and other forms of pollution.
Our articles are based on various shipboard activities,prevention of pollution,safe operation & maintenance procedure. We welcome any feedback from our visitors. For any comments or suggestions please Contact us

Site Use and Privacy - Read our privacy policy and site use information.
Terms and conditions of use

Copyright © 2010 All rights reserved.


Oil tanker golden victory at sea is merely an informational site about various aspects of ships operation,maintenance procedure, prevention of pollution and many safety guideline. The procedures explained here are only indicative, not exhaustive in nature and one must always be guided by practices of good seamanship. User feedback is important to update our database.For any comments or suggestions please Contact us

Other info pages !

Basic guideline for Container Ship Operation
Tanker vessel safety guideline Check items in oil tankers operation
Questions from user and feedback Read our knowledgebase
Cargo care at sea Precautions to be taken
Reefer cargo handling Troubleshoot and countermeasures
DG cargo handling Procedures & Guidelines
Cargo securing Check items prior departure port
Safe navigation Various factors affecting ships navigation at sea
Hull strength & stability Prior loading how to ensure hull strength & stability of ship
stevedores injury How to prevent injury onboard
Environmental issues How to prevent marine pollution
Safety in engine room Standard procedures
Site Map Page listing for this site.
Questions from user and feedback Read our knowledgebase

Cargo ships procedures for securing for sea

Related articles

How to confirm stability & hull strength in containership

Affects of Shearing forces, Bending moments and Torsional moment for containership

Risks of heavy weather with containerized cargo onboard

Ships motion in heavy weather

More info pages:

Home page