A transverse section through the cargo hold of a bulk carrier consists of the following principal structural members (as shown in the given sketch):

At the top, the strength deck plating forms the upper boundary of the hull girder. It is stiffened by deck longitudinals and connected to the hatch coaming, which increases deck strength around the hatch opening.

Below the deck on either side are the topside tanks (wing tanks). These are formed by:

• Topside tank sloping plating
• Topside tank longitudinal plating (vertical strake)
• Topside tank sloping plate longitudinals
• Topside tank transverse ring webs

The topside tanks taper inward toward the cargo hold and provide structural continuity between the deck and the side shell.

The side shell plating forms the vertical boundary of the hull and is supported by:

• Side shell frames (transverse framing)
• Side shell longitudinals

At the lower corners of the hold are the hopper tanks, consisting of:

• Hopper tank sloping plating
• Hopper tank sloping plate longitudinals
• Hopper transverse ring webs

These sloping structures connect the side shell to the inner bottom and help direct cargo toward the centreline during discharge.

At the bottom of the hold is the inner bottom plating (tank top), supported by:

• Inner bottom longitudinals
• Double bottom floors
• Double bottom girders

Below this lies the double bottom tank space, bounded externally by the bottom shell plating and centrally by the keel plate and duct keel.

The curved transition between bottom and side shell is formed by the bilge plating, which ensures smooth stress distribution between vertical and horizontal structures.

1. Hull Girder Strength (Longitudinal Strength)

• The ship behaves like a beam subjected to wave-induced hogging and sagging. The strength deck plating forms the upper flange of the hull girder, while the bottom shell plating and keel structure form the lower flange.
• The large vertical distance between deck and bottom increases the section modulus, enabling the hull to resist high longitudinal bending moments. Continuous deck, bottom, and side shell longitudinals further increase the moment of inertia and efficiently carry longitudinal stresses along the ship’s length.

2. Double Bottom Structure

• The double bottom forms a rigid box girder at the base of the hull. The inner bottom plating supports cargo loads directly, while floors and girders distribute these loads to the side shell and keel.
• This arrangement:
  • Resists vertical cargo pressure
  • Strengthens the lower flange of the hull girder
  • Provides protection against grounding damage
• The double bottom tanks also contribute to structural stiffness by forming a closed cellular structure.

3. Side Shell and Transverse Framing

• The side shell plating, supported by transverse frames and longitudinals, resists sea pressure externally and cargo pressure internally.
• Transverse framing prevents local buckling of plating between stiffeners, while longitudinals ensure effective distribution of stresses along the ship’s length. This combined system balances local rigidity with overall flexibility.

4. Hopper and Topside Tanks (Box Structures)

• The hopper tanks at the lower corners and topside tanks at the upper sides form strong triangular and trapezoidal box sections.
• These structures:
  • Reduce unsupported plate spans
  • Transfer cargo loads smoothly to the side shell and double bottom
  • Minimize stress concentration at sharp corners
  • Increase torsional and transverse stiffness
• By converting flat plate regions into closed box sections, they significantly enhance both local and global hull strength.

5. Transverse Ring Webs and Bulkhead Effect

• The topside and hopper transverse ring webs act as deep transverse beams. They reinforce the sloping plates and maintain structural shape under heavy cargo loading.
• In addition, transverse bulkheads (at hold boundaries) act as strong web frames, dividing the ship into rigid compartments and improving resistance to racking and shear deformation.