Calculator Inputs
Example Data Table
| Vessel Type | Length (m) | Beam (m) | Draft (m) | Block Coefficient | Water Density (kg/m³) | Estimated Displacement (t) |
|---|---|---|---|---|---|---|
| Patrol Boat | 38 | 7.2 | 2.4 | 0.58 | 1025 | 386.04 |
| Tug Vessel | 28 | 9.5 | 3.8 | 0.69 | 1025 | 716.71 |
| Cargo Vessel | 120 | 22 | 8 | 0.72 | 1025 | 15594.24 |
Formula Used
Displaced Volume from Main Dimensions
Displaced Volume (m³) = Length × Beam × Draft × Block Coefficient
Displacement Mass
Displacement (kg) = Displaced Volume × Water Density
With Margin
Adjusted Displacement = Base Displacement × (1 + Margin% / 100)
Unit Conversions
Metric tons = kg ÷ 1000
Long tons = kg ÷ 1016.0469088
Short tons = kg ÷ 907.18474
This approach estimates the vessel mass equal to the water mass displaced. It follows Archimedes’ principle and is widely used for preliminary marine design checks.
How to Use This Calculator
- Enter a case name for easy identification.
- Select whether you know hull dimensions or displaced volume.
- Choose meters or feet for dimensional input.
- Enter length, beam, draft, and block coefficient when using dimensions.
- Use a known displaced volume if hydrostatic data already exists.
- Select freshwater, saltwater, brackish, or a custom density.
- Add an optional margin percentage for reserve loading.
- Choose your preferred output unit and press calculate.
- Review the result cards, comparison table, and graph.
- Download the summary as CSV or print it as PDF.
FAQs
1. What is displacement tonnage?
Displacement tonnage is the mass of water displaced by a floating vessel. It is numerically equal to the vessel’s actual mass under the same loading condition and water density.
2. Why does water density matter?
Saltwater is denser than freshwater, so the same vessel displaces a slightly smaller volume for the same mass. Using the correct density improves tonnage accuracy.
3. What does the block coefficient represent?
The block coefficient compares the underwater hull volume to a rectangular block made from length, beam, and draft. Fuller hulls have higher values, while finer hulls have lower values.
4. Can I use feet and pounds-based density?
Yes. The calculator converts feet to meters and lb/ft³ to kg/m³ internally. This lets you work with familiar units while keeping the underlying calculations consistent.
5. Is displacement the same as deadweight tonnage?
No. Displacement is the vessel’s total mass. Deadweight tonnage covers cargo, fuel, crew, stores, and consumables carried between lightship and loaded conditions.
6. When should I use known displaced volume mode?
Use it when you already have hydrostatic or model-test volume data. It avoids estimating underwater volume from dimensions and can improve design-stage accuracy.
7. What is the margin percentage for?
The margin lets you add a reserve allowance for uncertainty, loading growth, or design conservatism. It is applied after the base displacement is calculated.
8. Is this suitable for final certification?
It is best for estimation, planning, and engineering checks. Final certified values should come from approved hydrostatic data, inclining tests, and class or regulatory procedures.