Why does an oil tanker have less freeboard?

flowchart LR
    A[Slack tank] -->|Heel| B[Liquid shifts]
    B --> C[Virtual rise of G]
    C --> D[Loss of GM]
    D --> E[Reduced stability]
    E -->|Mitigation| F[Longitudinal subdivision]
    F --> G[Smaller free surfaces]
    G --> H[Lower freeboard]

• Reason: extensive longitudinal subdivision minimizes free surface effect
• Mechanism: slack tanks create virtual loss of GM; subdivision reduces breadth cubed of free surfaces
• Instrument: International Convention on Load Lines — Type A freeboard for oil tankers
• Classification: IACS UI LL23, UI LL77 on freeing arrangements and load line application
• Chief Engineer: verify subdivision, minimize slack tanks, maintain valid Load Line Certificate