Tonnage Survey (Measurement)

Montenegro Marine Surveys are authorized by the International Naval Surveys Bureau to perform Tonnage Surveys and stability calculation.
There are two basic tonnage measurement systems presently available. The primary system is the Convention or international system, which is derived from the provisions of the International Convention on Tonnage Measurement of Ships, 1969. The Regulatory or national system has three subset systems, namely Standard, Dual, and Simplified. The Standard is the oldest system, dating back to the 1860s, and is based on the British “Moorsom” system. Dual measurement was developed in the mid 20th century to benefit shelter deck vessels by providing alternatives to fitting them with tonnage openings. The Simplified system was initially authorized by Congress in 1966 for recreational vessels to reduce the measurement cost burden for owners and the measurement workload on the government. Later, the Simplified system was extended to certain commercial vessels. Convention tonnage is dimensionless and expressed as GT ITC (or simply GT) for the gross tonnage and NT ITC (or simply NT) for net tonnage. Regulatory tonnage is calculated in units of register tons of 100 cubic feet per ton and expressed as GRT for gross register tons and NRT for net register tons.
Tonnage has nothing whatever to do with the vessel’s mass, weight, or displacement but both gross and net figures are a measure of the vessel’s internal volume.
The vessel has to be measured for tonnage by our surveyor and the vessel’s registered Official Number and Registered Tonnage has to be ‘carved into the main beam.
The latter point is often circumvented by the material from which the vessel is built and the required data may be bead welded or chiseled onto a steel hull or stamped onto a brass or wooden plate firmly affixed to the hull in other vessels.

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