Draft Survey and Determining Cargo Quantity

No universal international draft-survey tolerance or general independent-surveyor duty exists: protocol, tolerance and appointment depend on contract, cargo, risk and applicable procedures.

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

UNECE — Uniform Code of Draught Survey (1992), coal cargoes; Britannia P&I — Draft Survey Calculation. The UNECE code concerns coal; use for other bulk cargoes should be stated and agreed. Check the contract and applicable provisions for method, appointment and tolerances. A dispute may also involve legal duties and the evidentiary value of documents; it is not necessarily purely contractual.

The UNECE code, ECE/ENERGY/19 (3 February 1992), Part 1, page 2, describes accuracy within 0.5% conditional on suitable approved ship information and work by qualified, experienced surveyors. This technical statement does not establish a universal contractual tolerance for differences against shore figures. Keep method accuracy, actual survey uncertainty and the agreed acceptance criterion separate. UN Digital Library — ECE/ENERGY/19, Part 1, p. 2.

Scope of Application

Operations where the charter party or other contract, Company procedure or agreement uses a draft survey to determine quantity. The UNECE Code is specific to coal cargoes; use by analogy must be agreed and stated.

Procedure / How to Complete It

1. Identify the agreed contract, method, protocol and tolerance.
2. Document drafts, density, constants, ballast, fuel and consumables with the associated uncertainty.
3. Compare results on the agreed basis, not against a universal threshold.
4. Investigate discrepancies against contract, conditions and documented uncertainty.
5. Assess an independent surveyor by contract, cargo value, dispute risk and Company procedure.

Practical Example

Illustrative loading example: corrected displacements are initially 12,450 t and finally 24,680 t, a difference of 12,230 t. If total non-cargo weights increase by 50 t, with unchanged lightship and constant, cargo = 12,230 − 50 = 12,180 t. Against a hypothetical shore figure of 12,217 t, the difference relative to that figure is about −0.30%. Acceptability requires the agreed tolerance; the number alone does not establish contractual compliance.

What Typically Goes Wrong

Common Mistakes Mistake Library

• Confusing the ship’s constant with variable ballast and consumables: measure the latter at initial and final surveys and check lightship and constant separately.
• Changing weights during readings: coordinate operations and suspend ballast and bunker transfers during the survey.
• Using assumed densities or wrong correction signs: document samples and instruments and verify ship-table conventions.

What the PSCO Checks

PSC checks safety and applicable statutory requirements, including stability, loading and ship limits. It does not normally certify commercial quantity or resolve a discrepancy between draught survey and shore figures.

Operational Tips

• Do not use 0.5% as an international default.
• Agree method, joint readings and discrepancy handling before the operation.
• Independent appointment is mandatory only where required by contract or another applicable procedure; otherwise it is a risk-management choice.

Preparation checklist

• Charter party/contract checked
• Protocol and tolerance agreed
• Uncertainty and conditions documented
• UNECE applicability to coal or analogous use stated
• Surveyor appointment checked against contract and risk

FAQ

Related Topics

Last substantive revision of this page: 16 September 2026 · page fingerprint e8be5f1de66b