A draft survey is a maritime procedure based on Archimedes’ principle, determining the weight of cargo loaded or unloaded by measuring a vessel’s displacement change.
Surveyors calculate weight by reading draft marks at six points (forward, midship, aft on both sides), accounting for ballast/bunkers, water density, and trim corrections.
Why are Draft Surveys Important?
- Ensure accurate cargo quantity measurement
- Help prevent disputes between shipowners, charterers, and cargo interests
- Support compliance with contracts (e.g., charter parties, sale agreements)
- Provide a practical solution when shore scales are unavailable (common with bulk cargo)
What Does a Draft Survey Involve?
1. Draft Readings
- Measuring draft at:
- Forward (F)
- Midship (M)
- Aft (A)
- On both port and starboard sides
2. Initial & Final Surveys
- Initial survey → before loading/discharging
- Final survey → after completion
3. Displacement Calculation
- Using hydrostatic tables to convert draft into displacement
4. Corrections Applied
- Ballast water
- Fuel (bunkers)
- Freshwater
- Stores and consumables
5. Environmental Adjustments
- Water density (dock water vs seawater)
- Trim and list corrections
- External conditions (waves, swell)
