Enter Ship Dimensions and Loading Data
Example Data Table
| Scenario | Length (m) | Beam (m) | Draft (m) | Cb | Density (kg/m³) | Estimated Displacement (t) |
|---|---|---|---|---|---|---|
| Coastal cargo vessel | 95 | 16 | 5.8 | 0.71 | 1025 | 6,405.32 |
| Medium tanker | 180 | 32 | 10.2 | 0.80 | 1025 | 48,200.45 |
| River operation vessel | 72 | 13 | 3.6 | 0.68 | 1000 | 2,289.60 |
Formula Used
1. Underwater volume: V = L × B × T × Cb
2. Geometric displacement: Δg = V × ρ / 1000
3. Deadweight: DWT = Cargo + Fuel + Ballast + Stores + Crew
4. Operating weight: W = Lightship + DWT
5. Margin-adjusted weight: Wm = W × (1 + Margin/100)
6. Estimated draft from weight: Test = (Wm × 1000) / (L × B × Cb × ρ)
7. Waterplane area: Aw = L × B × Cwp
8. Tonnes per centimeter immersion: TPC = Aw × ρ / 100000
These are standard first-pass engineering approximations. Detailed design work still needs hydrostatic curves, trim data, stability checks, and hull form tables.
How to Use This Calculator
- Enter the vessel’s length at waterline, beam, and operating draft.
- Provide the block coefficient and waterplane coefficient.
- Choose water density for seawater, brackish water, or freshwater service.
- Enter lightship, cargo, fuel, ballast, stores, and crew weights.
- Add a design margin if you want a conservative loading check.
- Press Calculate Displacement to show the result above the form.
- Review geometric displacement, weight-based draft, TPC, and loading difference.
- Use CSV for spreadsheet analysis and PDF for reporting or sharing.
FAQs
1. What does ship displacement mean?
Ship displacement is the weight of water displaced by the hull. Under floating equilibrium, it matches the vessel’s actual weight at that draft.
2. Why does water density matter?
Seawater is denser than freshwater. A ship therefore displaces the same weight at a slightly smaller draft in seawater than in freshwater.
3. What is the block coefficient?
The block coefficient compares the underwater hull volume to a rectangular block with the same length, beam, and draft. Fuller ships have higher values.
4. What is TPC?
TPC means tonnes per centimeter immersion. It estimates how many tonnes are needed to change mean draft by one centimeter.
5. Why compare geometric and weight-based displacement?
The comparison helps detect whether the assumed draft and the entered loading condition agree. Large gaps can indicate unrealistic inputs or a needed draft change.
6. Can I use this for final stability approval?
No. This calculator is a preliminary engineering estimator. Final approval requires stability booklets, loading manuals, hydrostatic particulars, and class or flag compliance checks.
7. What should I enter as lightship weight?
Use the vessel’s weight without cargo, fuel, ballast, stores, passengers, or crew consumables. It usually comes from lightweight surveys or design documentation.
8. What does fresh water allowance indicate?
It estimates draft change when moving between water densities. It is useful when a vessel sails from saltwater to freshwater ports.