Barge Draught Survey Calculator
Calculate the weight of cargo loaded or discharged from a barge using the draught survey method.
Initial Survey
Draft Readings (m)
Density & Displacement
Look up this value from hydrostatics using the Mean of Means draft below.
Deductibles (Tonnes)
Final Survey
Draft Readings (m)
Density & Displacement
Look up this value from hydrostatics using the Mean of Means draft below.
Deductibles (Tonnes)
Final Cargo Calculation
Enter valid data in both surveys to see the final cargo weight.
**Disclaimer:** This tool is for estimation and educational purposes. It performs standard draught survey calculations based on your inputs. The accuracy of the result is highly dependent on the accuracy of your draft readings, density measurements, and the hydrostatic data you look up from the barge's official tables. Trim and deflection corrections on displacement are not applied here for simplicity. Always rely on a certified marine surveyor for commercial and safety-critical calculations.
About Barge Draught Survey Calculator
Commercial Cargo Measurement
A draught survey is a method used to determine the weight of cargo loaded on or discharged from a vessel by measuring the change in displacement. This process is critical for bulk carriers and barges where weighing cargo via scales is impractical. It relies on Archimedes' Principle: the weight of the water displaced by the vessel is equal to the weight of the vessel itself.
Key Calculation Steps
- Draft Averaging: Measure drafts at Port and Starboard (Fwd, Mid, Aft) to find the mean drafts.
- Mean of Means Draft: The final "working draft" used to look up displacement in hydrostatic tables.
- Density Correction: Adjusting for the difference between the actual water density (e.g., brackish) and the table density (usually 1.025).
- Deductibles: Subtracting ballast, fuel, and fresh water from the gross displacement.
Primary Formulas
Density Correction:
Disp_Corr = Disp_Table × (Density_Obs / 1.025)
Net Displacement:
Net_Disp = Disp_Corr - Total_Deductibles
Cargo Weight:
Weight = Net_Final - Net_Initial
Surveyor's Checklist
- Density: Always take a water sample at the exact time of draft reading and at the vessel's mid-draft depth.
- Draft Marks: Ensure marks are clean and readable. Use a transparent tube (stilling well) if there are ripples or waves.
- Tank Soundings: Conduct a full sounding of all ballast, fuel, and fresh water tanks simultaneously with the draft reading.
Limitations
While effective, draught surveys have an inherent error margin of 0.5% to 1.0%. Accuracy is affected by hull fouling, calculation of "Mean of Means" (this tool uses a linear average), and the accuracy of the barge's hydrostatic scales.