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Draft, Trim and Heel - Container Stowage Plan affecting hull strength & stability of ship

When considering acceptability of a container cargo stowage plan, the following procedures/guidelines concerning hull strength & stability shall be taken into account:

Draft restrictions at berth, approaches, passage and next port shall be taken into consideration and vessels maximum draft must be maintained within the applicable restriction.

In no case shall the midship draft exceed the loadline. Also requirements of the vessels Loading manual regarding limitations of Draft and Trim must be complied with. Forward draft shall be maintained equal to or more than the limiting figure mentioned in the Loading manual to avoid Slamming.

Vessels trim must always be maintained within reasonable limits so as not to adversely affect cargo operations or vessels safe operation. Excessive trim may result in difficulty in Loading / Discharging containers especially Under Deck in cell guides. Excessive trim may also have adverse effects on ships mooring ropes, on smooth running of machinery and be hazardous during bunkering.

Trim is an important factor affecting Visibility from the Bridge. Slight change in vessels trim may bring the visibility within compliance limits or cause visibility to exceed requirements.

Besides the obvious, an adverse or excessive trim will also affect vessel Speed / Consumption and Performance during the passage.

Stowage plan must be checked to confirm vessels heel at the end of cargo operations. This value of heel must be such that it can be corrected using vessels heeling tanks or additional ballast tanks as required.

In case vessel cannot be kept upright in the final condition, Terminal planner / Central planner is to be informed and cargo stow plan appropriately modified.

Unequal distribution of weights on board including cargo and ballast will result in Torsional forces. Such final stability condition (excessive Heel) corrected by Ballast Water Re-distribution, will likely result in torsional stresses exceeding limits.

Anti-heeling systems – During loading and discharging the ship’s heel has to be kept to minimum to avoid jamming of containers in cell guides, twisting of ramps or damage of rolling cargo. Anti-heeling systems are pump or air blower activated systems developed to compensate ship’s heel.

For vessel passing Panama Canal or entering rivers, Master must be well aware of the changes in draft and trim when passing from seawater density to tropical fresh water density and vice-versa. Corresponding drafts at new density shall be calculated and noted for reference as applicable.

Related Topics

IMO Intact Stability Criterion for containership

Corrected GoM for Hull Strength and Stability of containership

Severe Wind and Rolling criterion affecting Hull Strength and Stability of containership

Visibility from Bridge affecting navigation of containership

Propeller immersion affecting navigation of containership

Shearing forces, Bending moments and Torsional moment affecting Hull Strength and Stability of containership

Other factors affecting Hull Strength and Stability as necessary

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