Freeboard Calculator
Calculate minimum freeboard for a vessel based on its length, depth, and load line rules.
Use the Freeboard Calculator
Vessel Dimensions
Measured from stem to rudder post. Min 24 m for ILLC tables.
Vertical distance keel to upper deck.
Typical range: 0.60 (fine) – 0.85 (full tanker).
0 = no superstructure credit; 100 = full-length superstructure.
Minimum Freeboard
Calculation Breakdown
What This Means
Enter vessel dimensions and click Calculate.
Summary
Freeboard is the vertical distance from the waterline to the top of the working deck, and it determines how much reserve buoyancy a vessel has. This calculator applies a simplified version of the International Load Line Convention (ILLC) approach — scaling a tabular freeboard value by length, block coefficient, depth-to-length ratio, and superstructure deductions — to give an estimate of minimum required freeboard. Use the result as a planning reference and always consult a certified surveyor for regulatory compliance.
How it works
- Enter the vessel's length between perpendiculars (LBP), moulded breadth (B), and moulded depth (D).
- Enter the block coefficient (Cb) — the ratio of displaced volume to the bounding box — typically 0.60–0.85 for most hulls.
- Enter the superstructure effective length as a percentage of LBP (0 if none).
- Select the freeboard type: Type A (tankers / low permeability), Type B (general cargo / others).
- Click Calculate. The tool applies the ILLC tabular baseline, Cb correction, D/L correction, and superstructure deduction to produce minimum freeboard in millimeters.
Use cases
- Preliminary design check for new vessel construction.
- Estimating load line position for stability studies.
- Educational reference for naval architecture students.
- Comparing Type A vs Type B freeboard requirements for a given hull.
- Verifying that a proposed loaded draft meets minimum safety margins.
- Planning cargo loading limits before a full classification society review.