Harbor

The resolution defines how a ship’s internal volume should be measured in accordance with standard international rules, resulting in ‘gross tonnage'(GT) and ‘nett tonnage'(NT). GT is roughly the volume of all enclosed spaces, and NT is calculated after certain deductions for non-revenue earning spaces (e.g. allowances for the bridge, engine room, crew accommodation, etc) have been taken from the gross figure. As a result, GT is a measure of how large in volume a ship really is, and most safety regulations are therefore based on this figure. NT is more a measure of a ship’s cargo spaces, and hence her earning capacity. Harbour and canal dues and similar expenses are usually assessed against one or other of the tonnage figures. Registered Tonnage: These (also known as ‘national tonnages’) applied to vessels built before 1982 and remained in use until 1994 when replaced by the new ITC system. This system also referred to gross and nett tonnages commonly abbreviated to GRT and NRT. Do be aware that many people who should know better still confuse these two measurements with GT and NT and it is important to clarify exactly which figure is being referred to. Canal Tonnage: Both the Suez and Panama Canal Authorities have their own rules for the measurement of gross and nett tonnage, upon which their fees for canal transits are based. There has been talk of these authorities adopting the IMO tonnage but so far no definite decision has been taken. Cubic Capacity: As we have already considered in Lesson One, when calculating cargo intake, not only does a voyage estimator or ship’s officer have to consider deadweight and load line zones, as well as requirements for bunkers, etc. it is necessary to calculate how much cargo the hold spaces will accommodate.