Draft Survey Service

Independent Draft Survey for Cargo Quantity Determination

PAMS Pacific Admiralty Maritime Services provides independent draft survey services for vessels involved in bulk cargo loading and discharge operations. The survey determines the change in vessel displacement between the initial and final conditions and converts the displacement difference into the quantity of cargo loaded or discharged.

Draft surveys are particularly important where cargo quantities are commercially significant and an independent technical measurement is required to support cargo documentation, terminal operations, charter-party requirements and commercial settlement.

Technical principle: A draft survey determines cargo quantity from changes in vessel displacement. Accurate results depend on reliable draft readings, correct hydrostatic data, appropriate corrections, accurate density information and proper recording of the vessel's loading condition.

PAMS Draft Survey Methodology

Initial Draft Survey

Recording of the vessel's initial forward, aft and, where applicable, midship drafts before cargo operations or at the agreed survey stage.

Final Draft Survey

Recording of final drafts after loading or discharge and determination of the corresponding final displacement condition.

Hydrostatic Calculations

Application of vessel hydrostatic information, displacement data, draft corrections and relevant vessel particulars to calculate the cargo quantity.

Independent Verification

Cross-checking of drafts, ballast condition, tank soundings, density data and calculation results to improve confidence in the final cargo quantity determination.

Draft Survey Inspection Scope

The survey scope is adapted to the vessel, cargo, port conditions, loading or discharge operation and available technical documentation. Typical survey activities include the following.

Vessel Draft Readings

Forward draft readings on port and starboard sides.
Aft draft readings on port and starboard sides.
Midship draft readings where applicable.
Assessment of draft visibility and reading conditions.
Recording of observed drafts before and after cargo operations.
Application of appropriate trim and draft corrections.

Ballast & Tank Condition

Ballast tank soundings or levels.
Fresh water quantities.
Fuel oil and diesel oil quantities.
Lubricating oil quantities where relevant.
Other liquids onboard affecting vessel displacement.
Comparison of initial and final tank conditions.

Vessel Particulars & Hydrostatics

Deadweight and displacement information.
Hydrostatic tables or curves.
Lightship information.
Trim and draft correction data.
Density and water-plane information where applicable.
Relevant vessel loading documentation.

Cargo Quantity Determination

Calculation of initial displacement.
Calculation of final displacement.
Determination of displacement difference.
Deduction or addition of relevant consumables and liquids.
Calculation of net cargo quantity.
Comparison with shore or terminal figures where available.

Draft Survey Technical Documentation

Accurate draft survey work requires review of the vessel's relevant technical and cargo documentation. Available information is checked against the physical condition and measurements obtained during the survey.

Documentation Area	Technical Review Focus
Hydrostatic Data	Verification of applicable hydrostatic tables, displacement data, draft information and vessel particulars used for the calculation.
Tank Capacity Information	Review of tank calibration information, sounding tables and available capacity data relevant to ballast, fuel, fresh water and other liquids.
Loading Plan	Review of cargo distribution, loading sequence, expected drafts and vessel loading condition.
Cargo Documentation	Review of cargo quantity information, cargo declarations, terminal figures and available cargo documentation.
Vessel Stability Information	Review of relevant stability and loading information affecting the vessel's draft and displacement condition.
Previous Survey Information	Comparison with available previous draft survey records where required for verification or operational continuity.

Draft Survey Calculation Process

1. Initial Condition

The vessel's initial drafts, trim, ballast, consumables and other relevant displacement components are established before the agreed cargo operation stage.

2. Draft Corrections

Observed drafts are evaluated and appropriate corrections are applied in accordance with the vessel's hydrostatic data and established survey methodology.

3. Initial Displacement

The corrected mean draft and relevant vessel information are used to determine the vessel's displacement at the initial survey condition.

4. Final Condition

Following cargo loading or discharge, final drafts, ballast, consumables and other relevant quantities are established.

5. Final Displacement

The corrected final vessel displacement is calculated using the applicable hydrostatic information.

6. Cargo Quantity

The difference between the initial and final displacement is adjusted for relevant changes in onboard liquids and other displacement components to determine the cargo quantity.

Draft Survey Verification Factors

Draft Reading Accuracy

Accurate observation of draft marks is fundamental to the reliability of the survey. Visibility, vessel movement, sea conditions and draft-mark condition are considered.

Water Density

Water density at the survey location can materially affect displacement calculations and is therefore established or verified as part of the survey where required.

Ballast Condition

Changes in ballast water quantities between the initial and final surveys must be accurately identified because they directly affect displacement.

Consumables

Fuel oil, diesel oil, fresh water, lubricating oil and other relevant consumables are considered when determining the cargo quantity.

Trim Condition

Vessel trim is considered in accordance with the available hydrostatic information and applicable correction data.

Cargo Distribution

Cargo distribution and loading condition are reviewed where necessary to ensure that the calculated displacement is consistent with the vessel's actual condition.

Technical decision principle: Draft survey results depend on the quality and accuracy of the measurements and information available at the time of attendance. Independent verification of drafts, tank quantities, water density, hydrostatic data and vessel condition helps reduce avoidable calculation uncertainty.

Draft Survey Applications

Draft surveys may be performed at various stages of maritime cargo operations where independent determination or verification of cargo quantity is required.

Cargo Loading

Determination of cargo quantity loaded onboard following the agreed loading operation and final draft survey.

Cargo Discharge

Determination of cargo quantity discharged through comparison of vessel displacement before and after the discharge operation.

Ship-to-Ship Operations

Independent quantity determination for applicable ship-to-ship cargo transfer operations where draft survey methodology is appropriate.

Cargo Quantity Disputes

Independent technical measurement and verification where differences exist between vessel and shore cargo figures.

Commercial Verification

Independent cargo quantity information supporting commercial documentation, chartering requirements and cargo settlement.

Operational Control

Draft survey information supporting monitoring of vessel loading condition and cargo operation records.

Draft Survey Deliverables

Draft Survey Report

Structured technical report documenting the survey observations, vessel condition, calculations and resulting cargo quantity.

Draft Reading Record

Recorded initial and final draft observations with the relevant survey condition and measurement information.

Calculation Sheet

Detailed calculation record showing the principal displacement, correction and cargo quantity calculations.

Tank Sounding Record

Recorded ballast, fuel, fresh water and other relevant tank quantities used in the survey calculation.

Reporting objective: The final survey documentation is structured to provide a clear technical record of the measurements, calculation methodology and cargo quantity determined during the attendance.

Who Requires an Independent Draft Survey?

Independent draft surveys can provide useful cargo quantity verification for shipowners, charterers, cargo interests, terminal operators and other maritime stakeholders involved in bulk cargo operations.

Shipowners

Independent verification of cargo quantities and vessel loading or discharge conditions.

Charterers

Independent cargo quantity information supporting chartering and commercial operations.

Cargo Interests

Technical quantity verification for cargo accounting, documentation and commercial settlement.

Terminal Operations

Independent vessel-based quantity information for comparison with terminal loading or discharge records.

Technical Reference Standards – Draft Survey

Draft survey calculations are performed using recognized marine surveying principles, vessel hydrostatic information and the technical documentation applicable to the vessel and agreed survey scope.

Vessel Hydrostatic Data Applicable hydrostatic tables, displacement information, draft data and vessel particulars.

Vessel Loading Information Loading condition, trim, ballast condition and relevant vessel loading documentation.

Tank Calibration Data Applicable sounding tables and tank capacity information used to determine onboard liquid quantities.

Marine Survey Practice Recognized technical principles for vessel draft measurement, displacement determination and cargo quantity calculation.

Cargo Documentation Relevant cargo, loading, discharge and terminal documentation available during the survey.

Applicable Contractual Requirements Survey requirements specified by the client, charter-party, cargo interests or other applicable commercial arrangements.

Standards hierarchy: The applicable vessel documentation, hydrostatic data, survey instructions, contractual requirements and established marine surveying practices should be considered according to the specific vessel and cargo operation. The exact survey methodology may vary according to vessel type, port conditions and client requirements.

Independent Technical Survey Oversight

Independent Consultancy

PAMS Pacific Admiralty Maritime Services is an independent Philippine technical consultancy providing marine surveying, marine engineering and technical assessment services.

Technical Experience

Survey activities are led by Gregory Apostologlou, Managing Director, Mechanical Engineer and Marine Technical Superintendent with extensive maritime technical experience.

Measurement-Based Assessment

Draft survey conclusions are based on recorded vessel measurements, available hydrostatic information, tank quantities and documented calculation procedures.

Independent Reporting

Survey findings and calculated cargo quantities are presented in a structured technical report for the relevant stakeholders.

About the Technical Author

Gregory Apostologlou

Managing Director of PAMS Pacific Admiralty Maritime Services. Mechanical Engineer and Marine Technical Superintendent with international maritime experience in marine surveying, vessel inspections, marine engineering, offshore technical consultancy and maritime regulatory compliance.

His technical background includes vessel condition assessment, marine surveying, engineering evaluation and independent technical reporting.

Technical Content Review

Last Technical Review

September 2026

Review Frequency

Content is reviewed periodically to maintain alignment with applicable marine surveying practices, vessel documentation requirements and technical developments.

Technical framework: Draft survey work is based on the applicable vessel hydrostatic information, tank calibration data, survey instructions, recorded vessel condition and recognized marine surveying principles relevant to the agreed scope.

Draft Survey FAQ

What is a draft survey?

A draft survey is a method of determining the quantity of cargo loaded or discharged from a vessel by measuring the change in the vessel's displacement between two survey conditions.

When is a draft survey normally conducted?

Draft surveys are commonly conducted before and after bulk cargo loading or discharge operations to determine the corresponding change in vessel displacement and cargo quantity.

What information is required for a draft survey?

Relevant information can include vessel hydrostatic data, tank calibration tables, draft information, ballast and consumable quantities, loading condition and available cargo documentation.

Why is water density important?

Water density affects the relationship between the vessel's immersed volume and its displacement. An accurate density value is therefore important for reliable draft survey calculations.

Are ballast quantities included in the calculation?

Yes. Changes in ballast water and other onboard liquid quantities can affect displacement and therefore need to be established and considered in the calculation.

Can a draft survey be used for cargo quantity disputes?

An independent draft survey can provide technical measurement evidence for comparison with other cargo quantity figures, subject to the agreed survey scope, available documentation and survey conditions.

Does a draft survey replace shore weighing or terminal measurements?

No. A draft survey is a vessel-based quantity determination method. Where shore scales, terminal measurements or other independent quantity methods are available, the results may be compared as part of the agreed verification process.

Is the draft survey result guaranteed to be exact?

No measurement system can eliminate all uncertainty. Draft survey accuracy depends on draft visibility, vessel movement, water density, hydrostatic data, tank measurements, vessel condition and the accuracy of the information available during the survey.

Draft Survey Technical Notice

This page describes the general scope and methodology of PAMS independent draft survey services. The actual survey procedure depends on vessel type, cargo, port conditions, accessibility, available hydrostatic and tank documentation, client instructions and the agreed attendance. Draft survey results are subject to the accuracy and completeness of the measurements and information available at the time of the survey.