Draught surveys are heavily relied upon as the best means of accurately determining whether or not there has been a loss of cargo during a ship's passage between the load port and discharge port - between surveys. However, it is not an exact science and allows plenty of room for error.
The draught survey involves the measuring of the ship in her pre-sailing condition / arrival condition, and consumables and other variables on board. It is possible for errors to be made when sounding tanks, reading draught marks, or during calculations. External factors that may affect the surveyor in his ability to conduct the survey will include weather/sea conditions, availability of draught marks, vessel trim/balance and particulars, etc.
The article 'Measurement of bulk cargoes - draught surveys' - a UK Club
Carefully to Carry Committee publication, explains draught survey theory and practice to make clear the limitations of draught surveying, and best practice methods. This publication will prove useful to those in the industry requiring an understanding of draught surveys, and will also help those aboard ship understand what exactly the draught surveyor should be doing.
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- Available in pdf format only (496kb)
- Available in Chinese (Mandarin)
- Available only to Club Members
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In this article:
Draught surveys - practice
- Reading the draught marks
- Density of the water in which the vessel is floating
- Ballast water tanks
- Density of the ballast water
- Establishing the correct weights of oils on board
- Calculations and associated corrections of vessel’s displacement from draught readings
- Documentation
- Expert opinion
- Cumulative errors
- Worked example
Draught surveys - theory
- Archimedes principle
- Density
- Reading the draughts
- Metric marks
- The stability book
- Calculating a ship's draught
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- Perpendicular correction
- 3/4 mean draught
- First time correction (layer correction)
- Position of Lcf
- Second trim correction (Nemoto's correction)
- Heel correction
- Density correction
- Alternative hydrostatic information
- Measuring the variable quantities
- Sounding of ballast and fresh water tanks
- Fresh water
- Fuel and oil
- Calculating volumes
- Small trimmed ballast volumes
- Weight of the ballast
- Sounding problems
- Condition of the vessel at time of survey
- Ballast tank condition
- The manometer
- Marine hydrometers
- The draught survey certificate
- Salinity refractometers
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