- Tonnage

 

    Is a measurement of a ship, so it can be expressed by its weight in tons or its volume in cubic meters (feet).

 

- Gross tonnage

 

    (gross tonnage) or GT for short reflects the volume of enclosed ship spaces, determined in cubic feet, divided by 100.

 

    The gross tonnage parameter is considered in relation to the ship, not its cargo, and is a measure of volume. It is calculated on the total volume of the ship in cubic meters using an additional multiplier (coefficient).

 

- Net tonnage

 

    (net tonnage) or NT for short does not take into account the volume of the engine room, crew quarters, and takes into account only the volume of cargo spaces and spaces intended for passenger accommodation.

 

 

It should be noted that physical units of measurement cannot be used to determine tonnage, despite the fact that in documents it is reflected in tons, for example, GT = 0000 tons.

 

Another weight/volume characteristic of a sea or river vessel

 

- Deadweight or DWT. 

 

    This is one of the main characteristics of any sea or river vessel, indicated in their brief description, having an exact physical calculation in metric tons. 

 

    This parameter reflects the vessel's carrying capacity, not only cargo, but also all supplies, including fuel and water, the weight of the crew and passengers, if any. This is the difference between the cargo lines of a fully loaded vessel and an empty vessel. 

 

    Recall that these lines indicate the maximum permissible draft that ensures the safety of navigation.

 

 

If we characterize the meaning of the main quantities, they reflect the following:

 

- Gross tonnage

 

    Is a reflection of the actual geometric dimensions of the vessel, the larger it is, the larger the dimensions of the hull, the ship's superstructure.

 

- Net tonnage

 

    An indicator reflecting the actual useful capacity of the vessel, i.e. a reflection of its transport capabilities.

 

- Deadweight

 

    An indicator that also reflects the ability to carry cargo, only not in cubic meters of available space, but in tons of payload.

 

- Displacement

 

Displacement is the volume of water displaced by a vessel measured in cubic meters. 

 

 

    In turn, displacement tonnage is defined in metric tons and indicates the mass of water displaced by a sea vessel, while at the time of measurement it has a full supply of fuel and other supplies on board. 

 

    There is also the concept of “light” displacement, which provides for the weight of water displaced by an empty vessel, without cargo, fuel on board and other categories of supplies. 

 

    The concept of displacement tonnage may be used in the process of describing the weight parameters of a vessel. In this case, it is defined in tons or pounds (1 ton = 2240 pounds). 

 

    These terms were introduced into circulation by the IMO International Convention on the Measurement of Tonnage of Ships. It was adopted in 1969, but came into force only in 1982. Before this, there was no unified system for determining the tonnage of ships, so the actual parameters could differ for the same object. 

 

 

    The application of the convention is provided for all ships whose date of construction is later than 18.07.1982, when this international IMO document came into force. 

 

    With the transition to it, the shipbuilding industry moved away from the practice of using register tons. From that moment on, gross and net tonnage became the main parameters for determining the characteristics of ships. 

 

    For comparison, gross register tonnage was previously defined only as a set of closed spaces located above the deck and used to accommodate cargo, dry stores, fuel, water, crew and their belongings. 

 

    When determining net registration tonnage, only cargo spaces were taken into account.

 

    It should be recognized that the “gross tonnage” parameter is not used in practice, but it is an important value when conducting registration activities in the countries of the home port and for international classification societies that establish requirements for the safety of navigation, the assembly of ships, determining the amount of registration fees for each ship, etc.

 

    These parameters also act as the main units of account in the process of determining the amount of port dues from ships.

 

 

    According to the Steamship Mutual P&L Club, the measurement of ship tonnage is used in several situations:

 

- Port dues

 

    can use both gross and net tonnage data to calculate the final value. The choice of parameter is the prerogative of port authorities.

 

- Pilotage dues

 

    for the provision of pilotage services can also be calculated based on the gross or net tonnage of the vessel in accordance with the practice of local port authorities.

 

- Canal dues,

 

    charged for the passage of ships through canals, such as the Suez or Panama Canals, are in most cases calculated based on the parameters of the net tonnage of the vessel.

 

- Other,

 

    small charges are also determined in accordance with the value of the net tonnage, but it is possible to use the gross value (used extremely rarely).

 

    In some cases, tonnage is used to compare ship sizes, and having larger geometric dimensions does not necessarily indicate that it has a larger capacity. 

 

    If we talk about the most capacious ships today, then these are ocean container ships with indicators of slightly more than 230 thousand tons, and the largest passenger liners are slightly inferior to them - about 228 thousand.