Section 1.4 Holds: Construction, Numbering, Capacity, Preparation for Cargo

The cargo holds are the very reason for a bulk carrier’s existence. Their design, capacity, and condition are central to the vessel’s commercial purpose and operational safety. The Master must have an intimate knowledge of the vessel’s holds, from their structural layout to their suitability for the myriad of cargoes they might carry.

1. Construction of Cargo Holds:

Bulk carrier holds are typically large, box-shaped (though often with hoppered bottoms and topside wing tanks modifying the “box” shape) compartments designed for ease of loading, discharge, and, in many cases, cleaning.

1. Boundaries:
   1. Bottom: The tank top (inner bottom plating) forms the floor of the hold. This plating must be strong enough to withstand the pressure of dense cargoes and the impact of grabs or other cargo handling equipment. Beneath the tank top lies the double bottom, which is divided into ballast tanks and sometimes service tanks (e.g., fuel oil, fresh water, though fuel in double bottoms under cargo holds is increasingly restricted by regulation).
   2. Sides: In single-hull vessels, the side shell plating with its internal framing (side shell frames, stringers, brackets) forms the vertical boundaries. In double-hull vessels, a smooth inner hull plating forms the hold boundary, with the structural framing located in the void or ballast space between the inner and outer hulls.
   3. Ends: Transverse bulkheads separate adjacent cargo holds. These are typically corrugated (vertically or horizontally) or flat plate with stiffeners to provide strength. Some bulkheads may be designated as “cargo-hold-to-cargo-hold” bulkheads, while others might be “hold-to-sea” (e.g., the collision bulkhead forward or the engine room bulkhead aft) or “hold-to-ballast tank” bulkheads, each with specific strength and inspection requirements.
   4. Top: The hatch opening, surrounded by the hatch coaming, forms the primary access. The underside of the main deck plating and the lower plating of topside wing tanks (if fitted) form the “roof” of the hold around the hatch opening.
2. Internal Structures:
   1. Framing: As mentioned, side shell frames are prominent in single-hull holds. Double-hull holds have smooth surfaces.
   2. Ladders: Access ladders, typically recessed or protected, are provided for entry into the hold. Their condition is critical for safety.
   3. Bilge Wells: Located at the aft (and sometimes forward) low points of each hold, these are sumps designed to collect any accumulated water (from cargo sweat, minor leakage, or washing). They are covered by perforated plates (rose boxes or strum boxes) to prevent debris from entering the bilge lines.
   4. Ventilation Ducts/Openings: Some holds are equipped with natural or mechanical ventilation systems, with ducting or openings at deck level.
   5. Piping: Various pipes (bilge lines, ballast lines if holds are used for ballast, sounding pipes, air pipes for double bottom tanks) may pass through or adjacent to the holds. These must be protected from cargo and grab damage.

2. Numbering of Cargo Holds:

Cargo holds are numbered sequentially, typically starting from the bow and moving aft.

1. Example: On a vessel with five cargo holds, they would be designated as Hold No. 1, Hold No. 2, Hold No. 3, Hold No. 4, and Hold No. 5.
2. Consistency: This numbering is used universally in stowage plans, loading computer inputs, stability calculations, and communication with shore personnel (stevedores, agents).

Analysis for the Master (Construction & Numbering): A clear mental map of the hold layout, including the location of critical components like bilge wells, ladders, and piping, is essential for the Master and deck officers. Understanding the structural differences between, for example, a forward hold near the collision bulkhead and a midship hold is important for assessing risks and planning operations.

3. Capacity of Cargo Holds:

Understanding hold capacities is fundamental for stowage planning, commercial calculations, and ensuring the vessel is not overloaded. Two main capacity figures are used:

1. Grain Capacity (Cubic Capacity – Grain):
   1. Definition: The total internal volume of the cargo hold, measured from the tank top to the underside of the deck (or hatch cover if it protrudes into the hold), and from side to side, including all spaces into which free-flowing “grain-like” cargo can penetrate. This includes the volume within hopper sides, between frames (in single-hull ships), and into any recesses.
   2. Usage: Used for light, free-flowing cargoes that will fill all available voids (e.g., grains, some light minerals, wood chips). It gives the maximum volumetric capacity.
2. Bale Capacity (Cubic Capacity – Bale):
   1. Definition: The internal volume of the cargo hold available for stowing “bale-like” or packaged cargo, measured from the tank top to the underside of deck beams (or other obstructions like protruding frame brackets), and between the innermost surfaces of frames or cargo battens (if fitted). It excludes spaces where bales cannot practically be stowed, such as the narrow gaps between frames or deep recesses.
   2. Usage: Used for cargoes that do not flow freely and cannot utilize all the small voids (e.g., bagged cargo, pulp, steel products, project cargo). Bale capacity is always less than grain capacity for the same hold.
3. Other Capacity Considerations:
   1. Deadweight Cargo Capacity (DWCC): The maximum weight of cargo a vessel can carry, determined by subtracting the weight of fuel, water, stores, crew, and constants from the vessel’s deadweight at the summer load line. This is often the limiting factor for dense cargoes.
   2. Tank Top Strength (Maximum Permissible Load Density): The tank top is designed to withstand a certain maximum pressure, usually expressed in tonnes per square meter (t/m²). For very dense cargoes (e.g., iron ore, steel concentrates), it’s possible to exceed this limit even if the hold is not volumetrically full. The Master must ensure the tank top strength is not exceeded.
   3. Stowage Factor (SF): The volume occupied by one tonne of a specific cargo, typically expressed in cubic meters per tonne (m³/t) or cubic feet per long ton (ft³/LT). This is crucial for calculating how much of a particular cargo can fit into a hold or the entire vessel, and whether the vessel will be “volume full” or “deadweight full.”

Analysis for the Master (Capacity): The Master, usually assisted by the Chief Officer, uses these capacity figures daily.

1. Stowage Planning: Accurate grain/bale capacities and stowage factors are essential for creating efficient and safe stowage plans.
2. Loading Computer Input: These capacities are programmed into the loading computer.
3. Commercial Voyage Estimation: Chartering departments use these figures for voyage calculations. The Master may need to confirm or clarify these based on the vessel’s specific plans (e.g., if some space is unusable due to repairs).
4. Preventing Overloading: Ensuring neither volumetric capacity, DWCC, nor tank top strength is exceeded is a primary safety responsibility.

4. Preparation of Cargo Holds for Cargo:

Before any cargo can be loaded, the holds must be prepared to a standard suitable for that specific cargo. This is a critical step to prevent cargo contamination, damage, and claims. The required standard of cleanliness can vary significantly.

1. Levels of Cleanliness:
   1. Normal Clean / Swept Clean: After discharging cargoes like coal or ore, holds are typically swept to remove loose residues. This might be acceptable if the next cargo is similar or less sensitive (e.g., another type of ore).
   2. Grain Clean: A very high standard required for grain and other food-grade cargoes. Holds must be thoroughly swept, all previous cargo residues removed (from frames, ledges, underdeck areas), and often washed with fresh water. They must be dry, free of insects, odors, and any loose rust or paint scale. Often requires certification by a surveyor.
   3. Hospital Clean / Super Clean: An even higher standard, sometimes required for very sensitive cargoes (e.g., kaolin, mineral sands, certain chemicals). May involve multiple washings, chemical cleaning, and meticulous inspection.
   4. Shovel Clean: A basic level where only loose material easily removable by shoveling is cleared. Usually only for rough cargoes where contamination is not an issue.
2. Preparation Steps:
   1. Removal of Previous Cargo Residues: Sweeping, blowing with compressed air, using scrapers. For some cargoes, high-pressure water washing is necessary.
   2. Washing: With seawater (for initial cleaning of robust cargoes) or freshwater (for final cleaning, especially for sensitive cargoes). Sometimes detergents or specialized cleaning chemicals are used (ensure they are compatible with the cargo and MARPOL regulations for disposal).
   3. Drying: Holds must be thoroughly dried, usually by natural or mechanical ventilation, before loading moisture-sensitive cargoes.
   4. Inspection: Visually inspect all areas, including behind frames, under deck beams, access ladders, and bilge wells, for any remaining residues, loose rust/paint, or odors.
   5. Bilge Well Preparation: Bilge wells must be clean, dry, and the strum boxes/rose boxes clear. Bilge suctions should be tested. For some cargoes, bilge wells may need to be specially sealed or protected.
   6. Testing (if required): For example, silver nitrate test for chloride residues after carrying salt or certain fertilizers if the next cargo is sensitive to chlorides.
   7. Dunnage (if required): For some cargoes (e.g., steel products to prevent contact with tank top, or bagged cargo to aid ventilation), dunnage (planks of wood, bamboo, etc.) may need to be laid.

Analysis for the Master (Preparation):

1. Charter Party Requirements: The charter party will often specify the required standard of cleanliness. The Master must ensure this is met to avoid delays, off-hire, or claims.
2. Cargo Sensitivity: Understanding the nature of the next cargo is crucial. Loading grain into a hold that previously carried coal and was only swept clean would be a recipe for disaster.
3. Resource Management: Hold cleaning is labor-intensive and time-consuming. The Master and Chief Officer must plan this work effectively, especially on tight port schedules.
4. Safety: Ensure proper PPE is used during cleaning (dust masks, eye protection, chemical suits if using chemicals) and that enclosed space entry procedures are followed if holds have been sealed for fumigation or have poor ventilation.
5. Environmental Compliance: Disposal of cargo residues and wash water must be strictly in accordance with MARPOL Annex V.

The cargo holds are the heart of the bulk carrier’s operation. A Master’s thorough knowledge of their construction, capacities, and the meticulous standards required for their preparation is fundamental to the safe, efficient, and commercially successful employment of the vessel.