2
leading to inaccuracies in Draught Surveys
ERR RS O BY WEST OF ENGLAND P&I CLUB
The Club says it regularly receives claims arising from alleged shortages of cargo as a result of discrepancies between draught survey results.
Draught surveys by their very nature are not an exact science, and the accuracy of the calculated cargo figure may vary typically by between 0.5 and 1.0%. However, there are occasions when considerable differences in the cargo figures derived from the draught surveys are obtained. The purpose of this Loss Prevention Bulletin is to remind deck officers of the principal sources of errors which may affect the survey results, such that they can be taken into account when shortages in the cargo are found.
DRAUGHTS
It is imperative that the draught marks are read as accurately as possible. Ideally this should be done from a boat so that the marks can be approached closely and read. However, poorly painted, rusty, or draught marks covered with marine growth make reading the draught accurately problematic, therefore it must be ensured, so far as possible, that the draught marks are kept in a readable condition. The presence of wind waves on the water surface will necessitate an estimation of the average draught by observation of the peaks and troughs of the waves against the hull. Darkness and shadows also make accurate reading difficult; therefore good lighting will be required at night. The turn of the hull around the stern leading to elongation of draught marks being viewed from an oblique angle, especially when this has to be done from an adjacent wharf at a higher level, can lead to difficulty in accurately determining the draught.
12M 8 6 4 2
11m 8
In a recent Loss Prevention Bulletin, West of England P&I Club has gone to great lengths to explain how discrepancies in draught surveys can occur, which can lead to claims.
As an example, an error of two centimetres in the mean draught would lead to an error in the displacement of approximately:
• 68t – Handysize Bulk Carrier (10,000 – 35,000t deadweight)
• 90t – Handymax Bulk Carrier (35,000 – 59,000t deadweight)
• 112t – Panamax Bulk Carrier (60,000 – 80,000t deadweight)
• 300t – Capesize Bulk Carrier (> 80,000t deadweight)
It is therefore advised to ensure that the inspection and maintenance of the draught marks be included in the planned maintenance system on a vessel.
DENSITY
Although there are numerous possible causes of inaccurate dock water density, it must first
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