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
The draft survey is governed by no IMO convention, and this page until now pointed to “ISO/NMSA guidelines or equivalent”: there is no ISO standard on draft surveys, and the abbreviation NMSA designates no standard-setting body in this field. The citation had no referent and is replaced.
The written standard that does exist is the Code of Uniform Standards and Procedures for the Performance of Draught Surveys of Coal Cargoes of the United Nations Economic Commission for Europe (UNECE), 1992: it addresses coal cargoes and remains the reference text even where it is applied by analogy to other bulk cargoes. For everything else what governs is the charter party clauses, which typically fix the procedure, who appoints the surveyor and the acceptable tolerances, together with the documented practice of independent surveyors. Whoever disputes the result of a draft survey is disputing a contractual arrangement, not a rule.
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
- Identify the agreed contract, method, protocol and tolerance.
- Document drafts, density, constants, ballast, fuel and consumables with the associated uncertainty.
- Compare results on the agreed basis, not against a universal threshold.
- Investigate discrepancies against contract, conditions and documented uncertainty.
- Assess an independent surveyor by contract, cargo value, dispute risk and Company procedure.
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.
What Typically Goes Wrong
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 |
What the PSCO Checks
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: 31 August 2026 · page fingerprint 7f35fd57a4dc