Operational Guide · Registers & Logbooks

# Draft Survey and Determining Cargo Quantity

The method that determines, from the draught readings, how much cargo is actually on board: the basis of every commercial dispute over shortages or excess quantities.

draft survey cargo quantity commercial disputes

## Operational Explanation

The draft survey is the standard method for determining the quantity of cargo loaded or discharged by reading the draughts at the load line marks, corrected for trim, list, hull deflection (hog/sag) and water density, comparing the displacement before and after the operation.

Although it is a commercial method rather than a regulatory one, the draft survey is at the centre of a significant share of disputes between shipowner, charterer and cargo receiver: small reading or calculation errors, multiplied across the entire cargo, generate significant economic differences.

## Regulatory Reference

The draft survey is not governed by any single specific convention, but follows established technical standards (typically ISO/NMSA guidelines or equivalent) and the contractual clauses of the individual charter party, which often specify the detailed procedure and the acceptable tolerances.

## Scope of Application

Mainly dry cargo ships (bulk carrier, general cargo) where the cargo cannot be measured by other methods (e.g. flow meters as for liquids); applicable to every commercially significant loading/discharging operation.

## Procedure / How to Complete It

1. Read the draughts at the bow, stern and midships (on both sides if possible), before and after the loading/discharging operation.
2. Correct the readings for trim, list and hull deflection (hog/sag).
3. Determine the water density at the berth by direct sampling.
4. Calculate the corrected displacement before and after the operation, subtracting the changes in ballast, fuel, fresh water and stores (constants).
5. Compare the result with the quantity declared by the terminal/shore figures, documenting any significant discrepancies.

## Practical Example

Example: a pre-loading draft survey shows a displacement of 12,450 t; post-loading, 24,680 t; after correcting for changes in ballast and fuel during the operation, the quantity of cargo loaded works out at 12,180 t, with a 0.3% discrepancy against the terminal's shore figures, within the contractual tolerance.

## Real Cases

Significant commercial disputes between shipowners and charterers frequently arise from discrepancies between the ship's draft survey and the terminal's shore figures that exceed the contractual tolerance, often traceable to systematic errors (imprecise draught readings, approximate density corrections, outdated constants) rather than to real differences in quantity.

## Common Mistakes Mistake Library

Mistake | Consequence | How to avoid it
--- | --- | ---
Imprecise draught readings, or readings taken by untrained personnel | A systematic error that propagates through the entire displacement calculation | Ensure the draft survey is conducted by experienced personnel, ideally with an independent surveyor present for commercially significant operations
Water density estimated rather than measured directly at the berth | Displacement calculation error, especially in areas with salinity variations (river mouths, port areas) | Always measure density by direct sampling at the specific location
Constants (ballast, fuel, fresh water, stores) not updated to reflect the actual situation | Inaccurate calculated cargo quantity | Verify and update all constants before every significant draft survey

## PSC Observations

The draft survey is not typically subject to direct PSC verification, being a commercial procedure; it can, however, take on indirect relevance in disputes that also involve aspects of the ship's stability or structural stress.

## Operational Tips

- For commercially significant operations, always request an independent surveyor for the draft survey, not just the ship's own personnel.
- Always measure the water density directly rather than estimating it, especially in areas with variable salinity.
- Precisely document all the constants used in the calculation, so the result can be defended in case of a dispute.

## Checklist

- Draughts read at bow, stern and midships, before and after the operation
- Corrections applied for trim, list and hull deflection
- Water density measured directly at the berth
- Constants verified and updated
- Result compared with the shore figures and discrepancies documented

## FAQ

Is the draft survey required by law?
It is not imposed by any specific international convention, but is often contractually required by the charter party as a method for determining cargo quantity, especially when no other measurement methods are available.
What is a typical accepted tolerance between the draft survey and shore figures?
It varies according to the charter party, but tolerances of around 0.5% are commonly considered acceptable in many contracts; larger discrepancies typically require an investigation into the causes.
Who should conduct the draft survey for operations of high commercial value?
It is good practice to request an independent surveyor, not just ship's or terminal personnel, to ensure a result recognised by both parties in the event of a subsequent dispute.
🎬 Additional photos, videos and interactive diagrams for this topic will be available in a future version of the platform.

## Related Topics

Loading/Discharging Plan

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