I. Principles and Historical Evolution of Draft Survey Method
(I) Basic principle: The draft survey method operates on Archimedes' principle. It involves measuring a ship's draft (waterline readings) before and after loading or unloading, then calculating the variation in displacement using the ship's technical data (such as ship type, capacity chart, and constants). This change in displacement directly correlates to the cargo weight. In essence, the method relies on the relationship between the weight of the cargo and the variation in the ship's displacement, with the ship's draft depth serving as the basis for weight estimation.
(II) Historical evolution: The quest to accurately measure cargo weight dates back to the early days of maritime trade. Initially, rough estimates based on experience were the norm. Over time, as scientific knowledge and understanding of ship dynamics and buoyancy advanced, draft survey methods evolved into a systematic and standardized approach. What began as simple manual draft measurements and rough calculations has transformed into a highly accurate process leveraging advanced electronic measuring instruments and specialized software. Today, the draft survey method is a cornerstone of bulk cargo measurement in international trade, offering unparalleled precision and efficiency.
II. Laws and Regulations Related to Draft Survey
(I) The Law of the People's Republic of China on Import and Export Commodity Inspection and its implementing regulations stipulate the role of entry-exit inspection and quarantine agencies in verifying the weight of import and export goods, as well as overseeing institutions involved in such processes. As a key method for determining the weight of bulk commodities, the draft survey method must comply with this legal framework to ensure accuracy and fairness, protecting the legitimate rights and interests of all trading parties.
(II) Customs Law of the People's Republic of China: Under this law, customs authorities oversee import and export goods, including reviewing draft survey results for bulk cargo. These reviews ensure accurate weight declarations, prevent illegal practices such as smuggling, fraud, and tax evasion, and protect national revenue while maintaining trade order.
(III) Administrative Measures for the Quantity and Weight Inspection and Survey of Import and Export Commodities: These measures define the scope, requirements, and subsequent supervision and management of quantity and weight inspections conducted by customs authorities.
(IV) Rules for the Weight Survey of Import and Export Commodities: These rules outline the fundamental principles of draft survey, including methods for measuring ship drafts and onboard materials, as well as step-by-step calculation guidelines. They provide a standardized framework to ensure the accuracy and consistency of weight measurements.
(V) Announcement on Adjusting the Supervision Methods of the Weight Survey for Imported Bulk Commodities: This announcement replaces the mandatory weight certification for each batch of imported bulk commodities with an on-demand approach, where businesses can request certification as needed, and customs may perform inspections at their discretion. This provision streamlines customs clearance processes, allowing companies greater flexibility in selecting draft survey providers. The Customs will still conduct random inspections and validations based on regulatory requirements.
III. Importance of Draft Survey in Import and Export Trade
(I) Promoting trade fairness: Bulk cargo transactions often involve heavy weights and high monetary value. As a reliable, scientific, and efficient weighing method, the draft survey method provides accurate weight measurements, minimizing disputes over weight discrepancies and fostering fairness in trade.
(II) Stabilizing bulk commodity supply: The draft survey method is instrumental in bulk commodity settlements, enabling quick and precise weight assessments to support production planning and inventory management. This ensures uninterrupted supply chains, prevents shortages or overstocking, and maintains the smooth flow of bulk commodities in global and domestic markets.
(III) Ensuring safety and accurate cost calculation: Since freight charges are directly tied to cargo weight, draft survey accuracy is critical for cost calculations by shipping companies and trading parties. Furthermore, precise weight measurements are essential for maritime safety; miscalculations could result in overloading or uneven distribution, compromising vessel stability and navigation safety.
IV. Future Development Trends of Draft Survey
(I) Advancing intelligence and automation: With the adoption of IoT, big data, and AI technologies, draft survey weighing is poised to become fully automated. Sensors may collect draft readings, ballast water levels, and other critical data in real time, while intelligent systems analyze current and historical data to calculate cargo weight with precision. Automated reporting processes will minimize human intervention, significantly enhancing efficiency and accuracy.
(II) Precision analysis through big data: By harnessing big data capabilities, draft survey processes can achieve in-depth analysis of extensive weighing data and related information. This enables real-time monitoring, predictive risk assessment, and intelligent process control. Anomalies can be accurately detected, and trade fraud effectively mitigated.
(III) Driving global standardization: As global trade expands, countries are increasingly focused on creating and harmonizing international standards for draft survey weighing. Unified protocols and practices across the globe will facilitate smoother bulk commodity trade and ensure draft survey results are recognized and trusted worldwide. (Yang Yang, Li Huafeng, Cui Yue and Shao Dehua)
Disclaimer：The above content is translated from Chinese version of this website. The Chinese version shall prevail.