NSM surveyors utilize the vessel's immersion scales to calculate the exact weight of cargo. This is the industry-standard method for bulk commodities where shore scales may be unavailable or unreliable.
In the global bulk shipping sector, the Draft Survey is the recognized international standard for determining the quantity of cargo loaded or discharged. Since traditional weighing scales are often unavailable at remote terminals or impractical for massive volumes, the vessel itself becomes the scale. This method relies on Archimedes' Principle, measuring the ship's displacement in the water to calculate the weight of the cargo on board. At North Surveying & Management B.V., we understand that accuracy is paramount; a minor miscalculation of just a few centimeters in draft can lead to a financial discrepancy of hundreds of metric tons.
Our surveyors approach every draft survey with extreme technical rigor, performing "six-point" readings that include Forward, Midships, and Aft drafts on both the Port and Starboard sides. This comprehensive measurement allows us to account for hull deformations such as "hogging" or "sagging," where the vessel’s structure bends slightly due to weight distribution or sea conditions. We don't rely on guesswork; we use high-precision hydrometers to test the exact density of the water surrounding the hull at the time of the reading, as buoyancy changes significantly between seawater, brackish water, and fresh water. This attention to detail ensures that the displacement calculations are mathematically flawless.
Beyond the external draft marks, our survey involves a total audit of the vessel's internal consumables. We gauge all ballast tanks, fuel tanks, and fresh water tanks to determine the "deductible weights" that are not part of the cargo. We also establish the vessel’s "constant"—the weight of the ship's stores, spare parts, and crew effects—which is critical for identifying the net cargo weight. By reconciling the initial survey with the final survey, we provide a definitive figure that serves as the official weight record for commercial invoices, Customs declarations, and Bill of Lading documentation.
To ensure the highest level of maritime certainty, our surveyors follow a standardized calculation workflow. This methodology eliminates mathematical bias and provides a legally defensible weight certificate: