Section 9.3 Preventing Cargo Shifting: Precautions and Actions

One of the most significant dynamic forces that can jeopardize a bulk carrier’s safety at sea is the shifting of its cargo. When a large mass of bulk material moves transversely or longitudinally within a hold due to the ship’s motion, it can lead to a dangerous list, a critical loss of stability, severe structural stress, and, in worst-case scenarios, capsize. The propensity of a cargo to shift depends on its physical characteristics (angle of repose, particle size, cohesiveness), how it is stowed and trimmed, and the severity of the vessel’s motion. Preventing cargo shift through meticulous pre-voyage planning and diligent cargo handling is a primary responsibility of the Master and Chief Officer. This section will explore the mechanisms and consequences of cargo shifting, the regulatory framework, preventative measures, and actions to be taken if a shift is suspected or occurs.

1. Understanding the Hazard of Cargo Shifting:

A. Mechanism of Cargo Shift:

Angle of Repose: This is the steepest angle, measured from the horizontal, at which a piled bulk material will remain stable without slumping or sliding. Cargoes with a low angle of repose (e.g., many grains, some fine ores, dry sand) are more prone to shifting than those with a high angle of repose.

Ship’s Motion: The rolling, pitching, and heaving motions of the vessel at sea, especially in heavy weather, provide the energy to overcome the inter-particle friction within the cargo, causing it to move.

Void Spaces (Ullage): If a cargo hold is not completely filled (“slack hold”) or if the cargo settles during the voyage creating void spaces (ullage) under the deckhead and in the wings of the hold, the cargo has room to shift into these voids.

Surface Collapse/Sliding: An untrimmed or poorly trimmed cargo surface, forming a steep cone or cliff, can collapse or slide when subjected to ship motion.

Liquefaction (A Special Case of Shifting): For Group A cargoes, liquefaction results in the cargo behaving like a fluid, leading to a very rapid and often catastrophic shift (as discussed in Chapter 4 and Chapter 8). This section primarily focuses on the shifting of non-liquefiable (Group C) or Group B cargoes that are not properly secured.

B. Consequences of Cargo Shifting:

Development of a List: A transverse shift of cargo moves the vessel’s overall center of gravity (G) towards the side of the shift, causing the vessel to develop a list.

Reduction in Stability (GM): The list itself can reduce the righting levers (GZ values). More significantly, if the cargo shifts and creates a large void on one side and a pile on the other, the effective VCG of the cargo rises, reducing the metacentric height (GM) and thus the vessel’s initial stability. For cargoes like grain, the IGC quantifies this as a “volumetric heeling moment.”

Progressive Shifting: Once an initial list develops, it can exacerbate further shifting, as the lower side of the hold presents a downward slope for the remaining mobile cargo.

Structural Stress: A significant shift of dense cargo can impose abnormal stresses on the hull structure, particularly on transverse bulkheads and side shell framing.

Difficulty in Steering and Maneuvering.

Risk of Capsize: If the list becomes excessive and stability is critically impaired (e.g., GM becomes negative, or the angle of list exceeds the angle of vanishing stability), the vessel can capsize.

Damage to Cargo: Shifting can cause abrasion and breakage of friable cargoes.

Difficulty in Discharge: Shifted cargo can make discharge operations more difficult and time-consuming.

C. Cargoes Prone to Shifting:

Grains: The classic example, due to their free-flowing nature and low angle of repose. Governed by the International Grain Code.

Other Agricultural Products: Seeds, some pellets, if not stowed correctly.

Fine Mineral Cargoes (Group C): Even if not Group A (liquefiable), fine, dry mineral cargoes with a low angle of repose can shift if not well-trimmed (e.g., some types of sand, fine ores not meeting Group A criteria).

Any bulk cargo loaded with significant void spaces and not adequately trimmed, especially if it has a tendency to settle and compact during the voyage.

2. Regulatory Framework:

SOLAS Chapter VI (Carriage of Cargoes):

Regulation 3 (Stowage and securing) places a general obligation on the Master to ensure cargo is stowed and secured so as to prevent damage or hazard to the ship and persons on board.

Regulation 5 (Stowage and securing) refers to the Code of Safe Practice for Cargo Stowage and Securing (CSS Code), which, while primarily for unitized cargoes, contains principles applicable to preventing movement.

Makes the International Grain Code mandatory.

Makes the IMSBC Code mandatory.

International Grain Code (IGC):

Provides specific, detailed requirements for the stowage, trimming, and securing of grain in bulk to prevent shifting and ensure adequate stability. (Key aspects covered in Section 8.3).

IMSBC Code:

Section 5 (Trimming Procedures): Mandates trimming “reasonably level, as necessary” to minimize the risk of shifting, with specific attention to cargoes with low angles of repose.

Individual Cargo Schedules: Many schedules provide specific advice on trimming or shifting precautions for particular cargoes.

3. Preventative Measures (Pre-Voyage and During Loading):

Prevention is the most effective strategy for dealing with cargo shifting.

A. Meticulous Stowage Planning:

Filling Compartments: Whenever possible, compartments should be substantially filled to minimize void spaces. The IGC defines “filled compartment, trimmed” and “filled compartment, untrimmed.”

Minimizing Ullage: Reduce the empty space above the cargo as much as practicable.

Considering Angle of Repose: For cargoes with a low angle of repose, ensure the stowage plan allows for thorough trimming.

Stability Calculations (Accounting for Potential Shift):

For grain, stability calculations must account for the grain heeling moments as per the IGC and the ship’s approved Grain Loading Stability Booklet.

For other cargoes prone to shifting, while not as formally quantified as for grain, the Master should consider the potential for a surface shift and ensure a good margin of stability.

B. Proper Trimming of Cargo:

This is a critical preventative measure, discussed in detail in Chapter 7, Section 3.

“Reasonably Level”: Ensure the cargo surface is leveled to reduce peaks and fill voids in the wings and ends of holds, especially for cargoes with an angle of repose ≤ 35°.

Supervision: The Chief Officer must closely supervise trimming operations to ensure they meet IMSBC Code/IGC requirements.

C. Securing Partly Filled Compartments (Especially for Grain): If a compartment is only partly filled with a shifting-prone cargo like grain, the IGC mandates that the cargo surface must be secured against shifting, unless detailed stability calculations prove the vessel can withstand the maximum assumed heeling moment from an unsecured surface (this is a high bar to meet). Methods of securing include:

Overstowing with Bagged Grain (Saucers): Constructing a “saucer” of bagged grain (or other suitable bagged cargo) over the surface of the bulk grain. The bags must be stowed compactly and interlocked.

Strapping or Lashing: Using timber shores, wire mesh, or tarpaulins secured by lashings over the grain surface. This is complex and less common now.

Shifting Boards: Longitudinal bulkheads or divisions (permanent or temporary) to reduce the transverse width of the free grain surface. More common on older, smaller general cargo ships than modern bulk carriers.

Other Approved Methods: Any method used must be detailed in the ship’s approved Grain Loading Stability Booklet.

D. Use of Dunnage:

For some cargoes (though less common for typical bulk commodities prone to shifting like grain or fine ores), dunnage (planks of wood) might be used to create a more level stowage base, fill large voids, or help restrain movement of specific types of bulk items (e.g., some forms of scrap or logs, though these have their own securing challenges).

E. Ensuring Adequate Intact Stability:

Maintain a good positive GM throughout the voyage.

Ensure compliance with all relevant IMO intact stability criteria, including the specific, more stringent criteria of the IGC when carrying grain.

A vessel with robust stability characteristics is better able to withstand the heeling moments caused by a minor cargo shift.

4. Precautions During the Voyage:

A. Weather Routing and Heavy Weather Seamanship:

Avoidance: Where possible, plan routes to avoid areas of predicted heavy weather that could cause severe vessel motions.

Seamanship: If heavy weather is encountered:

Reduce speed.

Alter course to minimize rolling and pitching (e.g., heading into the sea or wind, or running with it, depending on the specific conditions and vessel type).

Secure everything on deck.

Ensure all hatch covers and access points to holds are weathertight.

B. Monitoring for Signs of Cargo Shifting:

Unexplained List: The most obvious sign. If the vessel develops a persistent list that cannot be attributed to wind, uneven consumption of consumables, or known asymmetrical loading, a cargo shift should be suspected.

Unusual Vessel Motion: A sudden change in rolling period or character of roll, or sluggish recovery from rolls.

Noises from Cargo Holds: Rumbling, sliding, or thumping sounds from within the cargo holds, especially during heavy rolling.

Cracking Sounds from Structure (Extreme Cases): Indicates severe stress due to cargo movement.

Difficulty in Steering.

C. Regular Inspection of Securing Arrangements (if applicable):

If partly filled compartments have been secured with lashings, shifting boards, or bagged cargo, these should be inspected (if safe access is possible, e.g., through hatch manholes without entering the hold) periodically during the voyage, especially after periods of heavy weather, to ensure they remain intact and effective.

5. Actions if Cargo Shift is Suspected or Occurs:

If a cargo shift is suspected or has clearly occurred, the Master must take immediate and decisive action, prioritizing the safety of the crew and vessel.

A. Raise Alarm and Muster Crew (if situation is serious).

B. Assess the Situation:

Determine the angle of list. Is it increasing?

Assess the vessel’s stability. Does it feel tender or stiff? Is the rolling period changing?

Try to identify which hold(s) might have experienced the shift (e.g., by observing trim changes, or if one hold was known to be more slackly loaded).

Check bilge soundings for any associated water ingress.

C. Maneuver the Vessel to Reduce Motion:

Reduce speed immediately.

Alter course to minimize rolling and pitching. This might involve heading into the predominant sea/swell or, in some cases, running with it if that provides a more stable platform. The aim is to prevent further shifting.

D. Ballast Operations (To Correct List – WITH EXTREME CAUTION):

High Risk: Using ballast to correct a list caused by a cargo shift is potentially very dangerous and must be approached with extreme caution and only after careful consideration and calculation.

Why it’s Risky:

If stability is already compromised, adding ballast (especially filling double bottom tanks on the high side) can further reduce GM due to the free surface effect of the slack ballast tank, potentially making the situation worse or even leading to capsize.

It can induce significant torsional (twisting) stresses on the hull if a large list is corrected purely by asymmetrical ballasting.

When it Might be Considered (after thorough assessment):

If the initial stability was very good and the list is moderate.

If calculations (using the loading computer, accounting for the shifted cargo VCG/TCG if estimable) confirm that counter-ballasting will improve the overall stability condition (GM, GZ curve) and not overstress the hull.

It should be done slowly and incrementally, continuously monitoring the effect on list and vessel behavior.

It is often safer to accept a moderate list and focus on preventing further shift and seeking shelter, rather than risking capsize through improper counter-ballasting.

Consultation: If time and communications permit, the Master should seek urgent advice from the company (DPA, technical support) and P&I Club before undertaking significant counter-ballasting for a cargo shift.

E. Attempting to Re-trim Cargo at Sea:

For bulk cargoes, this is generally not feasible or safe at sea. Entering a hold with shifted cargo is extremely dangerous due to the risk of further sudden movement, unstable surfaces, and potentially hazardous atmospheres. Trying to manually shift thousands of tonnes of bulk cargo in a rolling ship is impractical.

F. Seek Shelter and/or Assistance:

If the list is severe, stability is doubtful, or the situation is deteriorating, the Master should make for the nearest port of refuge or sheltered waters.

Transmit appropriate safety or urgency messages if the vessel is in grave danger.

G. Communication:

Inform the company (DPA) immediately of the situation, actions taken, and current status.

Notify charterers.

If the vessel is in immediate danger, follow GMDSS distress procedures.

H. Damage Assessment: Once the immediate situation is stabilized or shelter is reached, assess any damage to the cargo or ship’s structure.

I. Log All Events: Meticulously record all observations, decisions, actions taken, communications, and changes in the vessel’s condition.

6. Master’s Overall Responsibilities for Preventing and Managing Cargo Shift:

Ensuring Full Compliance: With the IGC (for grain) and IMSBC Code (for all other bulk cargoes) regarding stowage, trimming, and securing.

Diligent Stowage Planning: Personally reviewing and approving all stowage plans to ensure they minimize shifting risks.

Supervision of Loading: Ensuring the Chief Officer effectively supervises trimming and loading operations.

Prudent Seamanship: Exercising good seamanship in voyage planning (weather routing) and vessel handling in heavy weather.

Crew Training: Ensuring the crew is aware of the dangers of cargo shifting, can recognize the signs, and knows the initial emergency actions to take. Drills should include scenarios involving unexpected list.

Decisive Action in Emergencies: If a shift occurs, the Master must make calm, informed, and decisive judgments to protect the vessel and crew.

Preventing cargo shift is a fundamental aspect of safe bulk carrier operation. It requires a thorough understanding of cargo properties, meticulous adherence to regulatory requirements and best practices during loading, and prudent seamanship during the voyage. The Master’s leadership in all these areas is critical to ensuring the cargo stays put and the vessel arrives safely.