What is net tonnage, how is it calculated, does it have a unit, and do containers on deck count?
Short answer
| Gross tonnage | Net tonnage | |
|---|---|---|
| Volume used | V, all enclosed spaces | Vc, the cargo spaces |
| Formula | K1 × V, K1 = 0.2 + 0.02 × log10(V) (regulation 3) | K2 × Vc × (4d/3D)² + K3 × (N1 + N2/10) (regulation 4) |
| Floors | — | first term not less than 0.25 GT; NT not less than 0.30 GT |
| Unit | none, dimensionless | none, dimensionless |
| Containers on deck | not enclosed, not counted | not enclosed, not counted |
- Net tonnage: derived from the cargo-space volume (Tonnage Convention 1969); gross tonnage from all enclosed spaces; capacity indices, not weight, not a box count.
- Unit: none; GT and NT are dimensionless, computed from volumes in cubic metres.
- Formulae: GT = K1 × V (regulation 3), K1 = 0.2 + 0.02 × log10(V); NT = K2 × Vc × (4d/3D)² + K3 × (N1 + N2/10) (regulation 4); the factor not over 1, NT not less than 0.30 GT.
- Not from containers: TEU is a commercial count; a container ship’s NT comes from the measured volume of its holds (Vc).
- On deck: regulation 2 counts enclosed spaces only (to the uppermost complete weathertight deck); open-deck containers never enter V or Vc, so the deck stow does not change tonnage.
- Certificate: International Tonnage Certificate (1969) from the Administration or its RO; quoted as GT and NT, never confused with deadweight or TEU.
Full answer
The full answer explains each point step by step, with the regulations and figures behind it and the discussion from other candidates. It is in the MEO Class I section of the Marine One forum, open to members enrolled for the MEO Class I exam.