Home / Guides / Draft Survey Calculation Guide
Draft Survey Calculation: Formulas, Examples, and Step-by-Step Guide
A draft survey determines how many tonnes of iron ore, coal, or grain a ship loaded or discharged. Get the calculation right, and both buyer and seller pay the correct amount. Get it wrong by just 2 centimetres on a Capesize vessel, and someone is out roughly 120 tonnes of cargo. This guide covers the complete calculation method with a worked example.
Data verified July 2026. Sources include UNECE ECE/ENERGY/19, Britannia P&I Club Loss Prevention Reports (2023-2024), Ships Nostalgia forum archives, and GOTEC field measurements at Chinese ports.
1. What Is a Draft Survey?
A draft survey is a method for determining cargo weight by measuring a ship's displacement before and after loading or discharging. It is based on Archimedes' principle: a floating object displaces its own weight in water. If you know the ship's underwater volume at each stage, and you know the density of the water it sits in, you know the ship's total weight. The difference between the initial and final weights, after accounting for all non-cargo changes, is the cargo weight.
The process runs in two parts. In the initial survey, you measure the ship's draft at all six positions, record all ballast tank levels, and note the quantities of fuel, fresh water, and other consumables onboard. In the final survey, you repeat the same measurements after cargo operations are complete.
The basic equation is:
Where "other weight changes" covers fuel consumed, ballast water pumped in or out, fresh water used, and any stores added or removed between the two surveys. Every tonne of diesel burned between initial and final survey must be accounted for, or it shows up as phantom cargo.
The UNECE Code of Uniform Standards and Procedures for the Performance of Draught Surveys (document ECE/ENERGY/19, 1992) specifies an accuracy standard of plus or minus 0.5% of cargo weight. On a 50,000-tonne shipment, that means plus or minus 250 tonnes. This is not a target to aim for; it is the boundary of what is commercially acceptable. The same UNECE code notes that under proper and favourable conditions, 0.1% accuracy has been demonstrated. A survey that misses the 0.5% tolerance means a dispute between buyer and seller, potentially involving independent surveyors, laboratory testing of cargo samples, or arbitration.
Draft surveys are used for bulk commodities: iron ore, coal, grain, bauxite, fertilizers, steel products, and aggregates. They are not used for containerised or general cargo. Those shipments use weighbridge weights, shipper-declared weights, or, increasingly, the VGM (Verified Gross Mass) system mandated by SOLAS for containers.
The math in a draft survey is not complicated. What makes it hard is doing it accurately in real conditions: wind, swell, poor light, time pressure, and a ship that has been at sea for weeks with hull fouling and deformed ballast tanks. The formulas below give you the theoretical foundation. Applying them well takes practice.
2. The Six Draft Readings
Every draft survey starts with six draft mark readings. You read three positions on each side:
- Forward Port (Fwd P) and Forward Starboard (Fwd S)
- Midship Port (Mid P) and Midship Starboard (Mid S)
- Aft Port (Aft P) and Aft Starboard (Aft S)
You read port and starboard separately because the ship may have a list, even a small one. Averaging each pair cancels out the list and gives you the true draft at that longitudinal position.
Draft marks are read to the nearest centimetre in metric practice, or to the nearest half-inch in imperial practice. A centimetre matters. On a Panamax bulk carrier, one centimetre of immersion at laden draft is roughly 60 tonnes. If you misread by 2 cm on all six marks, you are wrong by about 120 tonnes per mark, potentially several hundred tonnes in total.
At the same time as reading draft marks, you must also:
- Measure water density with a certified hydrometer. Take samples from at least two depths: surface and approximately 2-3 metres below surface. Surface water can be less dense after rain.
- Sound all ballast tanks. Every single one. A missed ballast tank with 50 tonnes of water in it is a 50-tonne error in your cargo figure.
- Record fuel oil, diesel oil, fresh water, and lubricating oil quantities from the ship's soundings or flow meters.
- Note the ship's constant: the weight of stores, crew, spare parts, sludge, and other fixed items that do not change between surveys. This number comes from the ship's records and should be verified periodically.
For detailed instructions on how to read draft marks accurately, including how to handle waves, parallax error, and imperial versus metric marks, see our guide on how to read draft marks.
Experienced surveyors on the Ships Nostalgia forum emphasize one rule: if it can hold liquid, it must be checked. Spaces commonly overlooked include:
- Duct keels (can hold 50-100 tonnes on Capesize vessels)
- Cofferdams and void spaces (often accumulate rainwater or seepage)
- Pipe tunnels and shaft alleys
- Chain lockers (water used for anchor chain washing)
- Swimming pools (drained or filled between surveys = 20-30 tonnes difference)
- Sewage holding tanks
- Bilge wells and sludge tanks
A full duct keel missed on both surveys cancels out only if the quantity is exactly the same -- an assumption that should never be made without verification.
3. The Quarter Mean Formula
This is the core formula in draft surveying. The Quarter Mean (also called the Mean of Means) is a weighted average of the six draft readings that corrects for hull bending. Ships bend. A loaded bulk carrier with cargo concentrated amidships will hog (ends droop down). A tanker with empty midship tanks and full end tanks may sag (midship droops down). If you averaged forward and aft drafts alone, you would miss this deformation and get the wrong displacement.
The Quarter Mean formula weights the midship reading six times more than the forward and aft readings. Why six? Because the midship section of the hull contains the largest cross-sectional area and contributes the most to displacement volume. The formula compresses hog and sag effects by blending the end readings with the midship reading.
Step 1: Forward Mean
Step 2: Aft Mean
Step 3: Midship Mean
Step 4: Quarter Mean
This is the formula you will use on almost every survey. Memorise it. Write it in your survey notebook. The midship reading carries six times the weight of each end reading because the midship section dominates the hull's volume.
When to Use the Simple Mean Instead
If the ship is on an even keel (zero trim) and has no measurable hull deflection, you can use the simple mean:
But in practice, this is rare. Most cargo ships have some trim during surveys. A bulk carrier loading iron ore will typically start with significant stern trim (empty, ballast aft) and finish closer to even keel but still with measurable trim. If trim exceeds roughly 0.5 metres, always use Quarter Mean. The error from using the simple mean grows with trim and with hull deflection.
4. Trim Corrections
What Is Trim?
Trim is the difference between aft draft and forward draft.
If the aft draft is greater than the forward draft, the ship is "trimmed by the stern." This is the most common condition during loading. If the forward draft is greater, the ship is "trimmed by the bow." Trim by the bow is rare and usually temporary during ballasting operations.
Trim matters for two reasons. First, the Longitudinal Center of Flotation (LCF) is not at midships. The LCF is the point about which the ship trims, and its position shifts with draft. Second, for large trims, the hull shape is not linear, and a second-order correction is needed.
1st Trim Correction (LCF Correction)
When the ship has significant trim, the draft at the LCF is not the same as the draft at midships. The Quarter Mean formula gives you an average draft, but we need the draft at the LCF to enter the hydrostatic tables, because the tables assume the ship is on an even keel.
The 1st trim correction adjusts the Quarter Mean draft to the draft at the LCF:
Where:
- QM = Quarter Mean draft (metres)
- Trim = Aft draft minus forward draft (metres)
- LCF = Longitudinal Center of Flotation, distance from midship (metres, from hydrostatic tables, positive if aft of midship)
- LBP = Length Between Perpendiculars (metres, ship constant)
This gives you the corrected draft to enter the hydrostatic tables. Note that LCF is read from the hydrostatic tables at the Quarter Mean draft, not at the corrected draft. Some surveyors iterate once or twice, reading LCF at the corrected draft and recalculating, but the difference is usually a millimetre or two and not worth the effort.
The full 1st trim correction in tonnes (if you prefer to correct displacement directly rather than draft) is:
Where TPC is Tonnes Per Centimetre Immersion. Both LCF and TPC come from the hydrostatic tables at the Quarter Mean draft. For most practical work, correcting the draft and then entering the tables is simpler and less error-prone.
2nd Trim Correction (Nemoto Correction)
For large trims, typically more than about 1% of LBP (roughly 2 metres or more on large vessels), a second correction adjusts for the non-linear shape of the hull.
Where dM/dZ is the rate of change of MTC (Moment to Change Trim) per centimetre of draft. This value is found in the hydrostatic tables. MTC is the moment required to change the trim by one centimetre. dM/dZ tells you how quickly MTC changes as draft changes.
For most practical surveys, the 2nd trim correction is small, typically less than 5 tonnes. Many experienced surveyors skip it when trim is moderate (under 2 metres). The 1st correction does 95% of the heavy lifting. But when trim is extreme, a ship leaving dry dock in ballast, or a VLCC with a 4-metre trim, the 2nd correction becomes material and must be applied.
5. Density Correction
Hydrostatic tables are calculated assuming standard seawater density of 1.025 tonnes per cubic metre. This is the density convention used consistently across all classification societies and in the UNECE Draught Survey Code. The water at your berth is almost never exactly 1.025. River ports can be fresh water (1.000-1.005). Brackish estuaries can be anywhere from 1.005 to 1.020. Even open-ocean ports vary with temperature and salinity.
The correction is:
Here is why this matters, with real numbers.
The density correction affects both the initial and final surveys. If the density is the same for both, the errors partially cancel out, but you cannot rely on this. Density changes with tide, rainfall, temperature, and even the passage of other ships stirring up different water layers.
Measuring Density Correctly
Use a certified glass hydrometer calibrated at 15 degrees Celsius. Take samples from at least two depths: surface and approximately 2 to 3 metres below the surface. The surface can have a layer of fresh or brackish water after rain that is not representative of the water the hull displaces. The deeper sample gives you the density of the water that actually matters.
If the water temperature differs significantly from 15 degrees Celsius, apply the temperature correction factor from your hydrometer's calibration certificate. Most hydrometers include a correction table. In tropical ports with water at 28 to 30 degrees Celsius, this correction can be 0.001 to 0.002 on density, which translates to roughly 0.1% to 0.2% on displacement.
In fresh water ports and river terminals, the density correction is even more important. A ship sitting in fresh water (1.000) has a true displacement about 2.4% less than the table value at 1.025. On a 70,000-tonne displacement, that is roughly 1,700 tonnes.
6. Complete Worked Example
Here is a realistic draft survey calculation for a bulk carrier loading iron ore. Every number is provided. Work through it with your own calculator; the arithmetic should match exactly.
Type: 50,000 DWT bulk carrier
Cargo: Iron ore, loading at Port Hedland, Australia
LBP: 210 metres
Ship's constant: 350 tonnes (from ship's records)
Initial Survey (Before Loading)
Draft readings:
| Position | Port | Starboard | Mean |
|---|---|---|---|
| Forward | 5.20 m | 5.24 m | 5.22 m |
| Midship | 6.55 m | 6.65 m | 6.60 m |
| Aft | 7.78 m | 7.82 m | 7.80 m |
Quarter Mean calculation:
QM = (5.22 + 7.80 + 39.60) / 8
QM = 52.62 / 8
QM = 6.5775 m
Trim = 7.80 - 5.22 = 2.58 m (by stern)
Ship has significant stern trim, as expected for a ballast condition. LCF at 6.58 m draft, from hydrostatic tables: +2.35 m (aft of midship).
1st Trim Correction to draft:
Dcorrected = 6.5775 + 6.063 / 210
Dcorrected = 6.5775 + 0.0289
Dcorrected = 6.6064 m
From hydrostatic tables at 6.606 m: Displacement = 28,450 MT
Dock water density: 1.023 (measured)
Density correction:
True displacement = 28,450 × 0.99805
True displacement = 28,394 MT
Deductibles (initial survey):
| Item | Weight (MT) |
|---|---|
| Ballast water | 12,500 |
| Fresh water | 280 |
| Fuel oil | 1,200 |
| Diesel oil | 85 |
| Lubricating oil | 40 |
| Ship's constant | 350 |
| Total deductibles | 14,455 MT |
Initial lightweight (net displacement):
Final Survey (After Loading)
The ship has taken on approximately 62,000 tonnes of iron ore and now sits much deeper. Most ballast has been pumped out. The trim is much smaller.
Draft readings:
| Position | Port | Starboard | Mean |
|---|---|---|---|
| Forward | 16.82 m | 16.86 m | 16.84 m |
| Midship | 17.14 m | 17.18 m | 17.16 m |
| Aft | 17.40 m | 17.44 m | 17.42 m |
Quarter Mean calculation:
QM = (16.84 + 17.42 + 102.96) / 8
QM = 137.22 / 8
QM = 17.1525 m
Trim = 17.42 - 16.84 = 0.58 m (by stern)
Notice the trim has reduced dramatically from the initial survey. When loaded, the ship sits with only 0.58 m of trim. LCF at 17.15 m draft, from hydrostatic tables: +1.85 m (aft of midship).
1st Trim Correction:
Dcorrected = 17.1525 + 1.073 / 210
Dcorrected = 17.1525 + 0.0051
Dcorrected = 17.1576 m
From hydrostatic tables at 17.158 m: Displacement = 78,880 MT
Dock water density: 1.024 (measured, slightly different from initial survey due to tide change)
Density correction:
True displacement = 78,880 × 0.99902
True displacement = 78,803 MT
Deductibles (final survey):
| Item | Weight (MT) |
|---|---|
| Ballast water | 800 |
| Fresh water | 260 |
| Fuel oil | 1,170 |
| Diesel oil | 80 |
| Lubricating oil | 38 |
| Ship's constant | 350 |
| Total deductibles | 2,698 MT |
Notice the ballast dropped from 12,500 MT to 800 MT. Most ballast was pumped out during loading. Fuel oil dropped slightly from 1,200 to 1,170 MT because the auxiliary engines were running during cargo operations.
Final lightweight:
Cargo Loaded
Cargo = 76,105 - 13,939
Cargo = 62,166 MT
Save time and avoid manual errors. Enter 6 draft readings and get instant Quarter Mean, trim corrections, density correction, and cargo weight. All calculations run in your browser. Open the Draft Survey Calculator →
Walk through this example with your own survey data. The pattern is always the same: six drafts, Quarter Mean, trim correction, hydrostatic tables, density correction, deductibles, subtract initial from final.
7. Common Calculation Errors
After twenty years of surveys, you learn which errors repeat. Here are the ones that junior surveyors make most often, in order of frequency and cost.
| Error | Typical Effect | How to Avoid It |
|---|---|---|
| 1. Forgetting density correction | 0.2-0.3% error. On our worked example: 195 tonnes. | Always measure density. Never assume 1.025. Write "DENSITY CORRECTION" in bold at the top of every survey sheet. |
| 2. Using wrong hydrostatic table entry | Variable, but can be large if you interpolate incorrectly. | Use the nearest tabulated draft or linear interpolation between the two bounding entries. Check your interpolation direction. |
| 3. Missing one ballast tank in soundings | The weight of whatever is in that tank. Could be 50-500 tonnes. | Get the tank arrangement plan before starting. Count tanks. Tick each one off as you sound it. |
| 4. Decimal point errors in Quarter Mean | Can be enormous if you misplace a digit. | Calculate twice. Use a calculator with memory. Check that QM is between Fwd Mean and Aft Mean. |
| 5. Using mean draft instead of Quarter Mean | Variable. On ships with 1m+ trim or visible hog/sag: 100-500 tonnes. | If trim exceeds 0.5m, always use Quarter Mean. If Mid Mean differs from (Fwd+Aft)/2 by more than 5 cm, always use Quarter Mean. |
| 6. Not measuring density at multiple depths | Can be 0.05-0.2% if there is a freshwater layer on top. | Sample at surface and at 2-3 m depth. If the two readings differ by more than 0.002, take a third sample at mid-depth. |
| 7. Forgetting fuel consumed between surveys | Equals the weight of fuel burned. Typically 10-50 tonnes for a loading port stay. | Record fuel at both initial and final surveys. Work the difference into your deductibles. |
| 8. Ship's constant not updated | Accumulates over time. Can reach 50-200 tonnes on older ships. | Verify the constant during dry dock or after a full stores inventory. Do not blindly use the same constant for years. |
The first four errors cause most of the disputes I have seen in practice. Density correction and the Quarter Mean formula are where the math goes wrong. Ballast tanks and fuel accounting are where the recording goes wrong.
Deliberate Manipulation: The Vietnam Case
Not all errors are accidental. Britannia P&I Club and Spica Vietnam reported in 2024 that cargo surveyors at Vietnamese ports (particularly Cai Lan and Phu My/Cai Mep) have been found deliberately misreading draft marks by 2 to 4 centimetres to create apparent cargo shortages of 100 to 150 tonnes on Handymax to Panamax vessels. The pattern is consistent: draft is read slightly higher on the initial survey (making the ship appear lighter) and slightly lower on the final survey (making it appear to have loaded less cargo). Additional tactics include: using non-local-standard hydrometers to dispute the ship's density readings, claiming blocked sounding pipes as a "vessel deficiency" to reject the draft survey result, and refusing to negotiate discrepancies once produced. Prevention: always use your own certified equipment, take timestamped photos of every reading, measure water density independently, and consider hiring an independent surveyor when calling at high-risk ports.
A consignee claimed a cargo shortage using the barge displacement method (a form of draft survey applied to barges). The Philippine Supreme Court dismissed the claim, ruling that because measurements were taken in "slight to slightly rough sea conditions," the resulting figures "may not be accurate and should not be completely relied upon." This case established an important legal principle: a draft survey's reliability depends on the conditions under which it was conducted. Surveyors should document sea state, weather conditions, and water surface quality in every report. Calm water readings and photographic evidence are not just good practice -- they are your legal defense.
8. Draft Survey Equipment
You can do a draft survey with basic tools. A hydrometer, a sounding tape, a notebook, and a calculator are enough to get started. But the difference between a difficult, error-prone survey and a fast, accurate one is often the equipment.
Essential Equipment
- Certified hydrometer (glass, calibrated at 15 degrees Celsius): For measuring water density. Keep the calibration certificate with the hydrometer. Replace it if it gets chipped or if the paper scale inside has shifted.
- Ballast tank sounding tape with water-finding paste: The paste changes colour on contact with water, so you can read the exact ullage or sounding level even in dark tanks.
- Access to draft marks: Either a survey boat for the outboard side, or safe dock access. Reading all six marks from the quay is acceptable only if the ship is moored starboard side to and you can read both sides from the dock. Otherwise, you need a boat.
- Calculator or draft survey software: Manual calculation is fine for learning. For professional work, use approved draft survey software that includes the ship's hydrostatic data and automates the correction formulas.
- Notebook and waterproof pen: Write everything down. Do not trust your memory. Record the time of each reading.
Modern Equipment That Eliminates Common Errors
Several technologies have emerged in the last decade that remove the biggest sources of manual error:
- AI camera systems: Cameras mounted at each draft mark position, combined with machine vision algorithms, read all six draft marks simultaneously and to sub-centimetre accuracy. This eliminates parallax error, wave-induced reading scatter, and the simple mistake of reading the top of a digit instead of the bottom.
- Bluetooth digital hydrometers: These send density readings directly to calculation software via Bluetooth. No transcription errors, no manual temperature correction arithmetic.
- Integrated survey software: Combines draft readings, density, ballast soundings, and fuel figures into a single calculation pipeline. The software applies all corrections automatically and produces a survey report with an audit trail.
GOTEC's digital draft survey system integrates all three: AI cameras that auto-read six draft marks simultaneously, a Bluetooth hydrometer that auto-sends density to the software, and an integrated calculation engine that eliminates manual arithmetic errors. For surveyors handling multiple vessels per day, or for terminals where survey accuracy has direct commercial consequences, the time savings and error reduction pay for the equipment quickly.
Need Reliable Draft Survey Equipment?
GOTEC's AI-powered measurement systems reduce calculation errors and save survey time. See how our integrated hardware and software platform improves draft survey accuracy.
View Products Contact Us9. Frequently Asked Questions
What is the formula for a draft survey calculation?
The core calculation has four main steps. First, calculate the Quarter Mean draft: QM = (Fwd Mean + Aft Mean + 6 x Mid Mean) / 8. This weighted average corrects for hull bending. Second, apply the 1st trim correction: D_corrected = QM + (Trim x LCF) / LBP, where LCF is the Longitudinal Center of Flotation from the hydrostatic tables and LBP is Length Between Perpendiculars. For large trims, apply the 2nd trim correction: TC2 = (50 x Trim squared x dM/dZ) / LBP squared. Third, find displacement at D_corrected from the hydrostatic tables. Fourth, apply the density correction: True Displacement = Table Displacement x (Measured Density / 1.025). The cargo weight is the difference between corrected displacements before and after loading, with all non-cargo weights subtracted.
When should I use the Quarter Mean formula instead of a simple mean draft?
Use the Quarter Mean formula whenever the ship has any significant trim or hull deflection. In practice, almost every cargo ship has some trim during surveys, so Quarter Mean is standard. A simple average of forward and aft mean drafts is only acceptable when the ship is on an even keel with zero trim and zero hull bending. If trim exceeds about 0.5 metres, using a simple mean instead of Quarter Mean can introduce an error of several hundred tonnes. The Quarter Mean formula weights the midship reading six times more than forward and aft because the midship section of the hull contributes the most to displacement volume.
How does water density affect draft survey calculations?
Water density has a significant effect because hydrostatic tables assume standard seawater at 1.025 tonnes per cubic metre. If the actual density differs, apply: True Displacement = Table Displacement x (Measured Density / 1.025). For a tabulated displacement of 28,450 MT with measured density 1.018, the true displacement is 28,255 MT, a difference of 195 tonnes. Density deviations occur frequently in river ports, after heavy rain (freshwater layer on top), or in brackish estuaries. For a Capesize vessel, a density error of 0.002 represents roughly 100 to 150 tonnes of cargo error. Always measure density with a calibrated hydrometer at multiple depths.
What is the acceptable error tolerance for a draft survey?
The UNECE standard for draft survey accuracy is plus or minus 0.5% of cargo weight. For a 50,000-tonne cargo, that is plus or minus 250 tonnes. For a 180,000-tonne Capesize shipment, the tolerance is plus or minus 900 tonnes. In good conditions with an experienced surveyor, manual surveys achieve about 0.3% accuracy. In rough water or poor light, errors of 1 to 2% are common. The biggest error sources: misreading draft marks in waves (each centimetre equals about 60 to 100 tonnes on large bulk carriers), incorrect density measurement, and missed ballast tank soundings.
What equipment do I need for a draft survey calculation?
The essential equipment includes: a certified glass hydrometer calibrated at 15 degrees Celsius for measuring water density, a ballast tank sounding tape with water-finding paste, access to the ship's hydrostatic tables or approved draft survey software containing them, a boat or safe dock access for reading outboard draft marks, and a calculator. Modern optional equipment includes Bluetooth digital hydrometers that auto-send density readings to calculation software, and AI camera systems from manufacturers like GOTEC that read all six draft marks simultaneously using machine vision, eliminating parallax errors and wave-induced reading errors. The GOTEC system integrates cameras, hydrometer, and calculation software into a single workflow.
10. References and Further Reading
The draft survey calculation methods described in this guide are based on the following authoritative sources:
International Standards
- UNECE Code of Uniform Standards and Procedures for the Performance of Draught Surveys of Coal Cargoes (document ECE/ENERGY/19, 1992). United Nations Economic Commission for Europe, Committee on Energy, Working Party on Coal. This is the foundational international standard for draft survey methodology. It defines the standard forms (A through E), the accuracy requirement of plus or minus 0.5%, and the procedures used by surveyors worldwide. Available at the UN Digital Library.
IMO and SOLAS Instruments
- SOLAS Chapter II-1, Part A-1 (Regulation 3-10): Requires every ship to carry a stability booklet containing hydrostatic tables, capacity plans, and all data required for draft surveys. IMO, London.
- IMSBC Code (International Maritime Solid Bulk Cargoes Code): Mandatory under SOLAS Chapter VI. Governs the safe carriage of solid bulk cargoes that are typically measured by draft survey. IMO, London. Available at the IMO website.
Classification Society Rules
- DNV Rules for Classification of Ships, Part 7: Fleet in Service. Covers survey arrangements including requirements for hydrostatic data availability. DNV rules and standards.
- Lloyd's Register Rules and Regulations for the Classification of Ships. Includes requirements for draught survey data manuals and stability documentation. Lloyd's Register rules.
- IACS Common Structural Rules for Bulk Carriers and Oil Tankers. Structural standards referenced by all major classification societies. International Association of Classification Societies.
Industry Guidance
- Draught Surveys: A Guide to Good Practice, 2nd Edition (2009). Jim Dibble and Peter Mitchell. North of England P&I Association. ISBN 978-0-9558257-5-0. The standard industry reference for practical draft survey procedures.
- Carefully to Carry, Chapter 16: Draught Surveys (2023). UK P&I Club. A practical guide covering draft reading, density sampling, ballast tank sounding, and calculation worksheets. Available at the UK P&I Club website.
- The Second Trim Correction in Draught Survey Procedure: Accuracy Analysis (2024). TransNav, the International Journal on Marine Navigation and Safety of Sea Transportation. Provides updated analysis of the Nemoto correction accuracy limits. Available at TransNav journal.
Maritime Training and Certification
- International Institute of Marine Surveying (IIMS): Offers professional qualifications and continuing education for marine surveyors. iims.org.uk.
- The Nautical Institute: Publishes training materials on cargo operations and ship stability. nautinst.org.
Related Guides
Ship Draft Guide
What ship draft means, how draft marks work, and typical drafts by vessel type.
How to Read Draft Marks
Metric and imperial marks, wave compensation, and common reading errors.
Draft Survey Glossary
Key terms: displacement, TPC, LCF, MTC, and more.