Convention on tonnage measurement of ships, 1969
Although this might seem an obscure subject for an international convention, it is
one of great interest to shipowners because ports, canals and other organizations
fix their charges on the basis of the ship’s tonnage. This created an incentive to
manipulate the design of ships in such a way as to reduce the ship’s tonnage while
still allowing it to carry the same amount of cargo. Occasionally this was at the
expense of the vessel’s stability and safety.
In 1969 the first International Convention on Tonnage Measurement was adopted.
It proved to be so complex and so controversial that it required twenty-five states
with not less than 65 per cent of the world’s gross merchant tonnage to ratify it
before it became law. The required number of acceptances was not achieved until
1980 and the Convention came into force in 1982. The convention establishes new
procedures for computing the gross and net tonnages of a vessel. At the end of
1996 116 states had ratified it.