The main principle
If the common adventure consisting of the ship and the cargo is exposed to a peril at sea, the losses and expenses which are intentionally incurred to save the common adventure from the peril shall be shared by the saved interests in proportion to their values.
This principle serves to encourage masters and others to take the best possible action to save the common adventure from danger without regard to the interest sacrificed knowing that the losses will be compensated by all interests.
Many examples may be given.
• One is a ship which is leaking as a consequence of a collision. Salvors arrive, put pumps on board, and tow the ship into safety. The cost of this operation will be allowed in general average.
• Another example would be a fire in the cargo which is extinguished by pumping CO2 into the hold where the fire has occurred. The cost of renewing the ship’s supply of CO2 is allowed in general average.
• A third example is the refloating of a grounded ship by the temporary discharge of (a part) of its cargo to another vessel, the cost of which will be allowed in general average. Rule VIII of the York-Antwerp Rules (YAR) contains detailed rules about this situation.

The concept of general average has existed almost as long as seaborne traffic. Roman law contained rules about general average and provided inter alia that Rhodian law decrees that if goods are thrown overboard to lighten the ship all shall make good by contribution that which has been given for all’. It is assumed that this part of the Rhodian law dates back as early as 500 bc.
As this Manual is published by the IMO International Maritime Law Institute (IMLI) in Malta, it may be appropriate to mention that the Bible contains a dramatic account of the events leading up to the grounding in Malta of a ship on which St Paul was a passenger. To avoid this grounding, a number of (unsuccessful) general average acts were undertaken.
The principles of general average were upheld during the Middle Ages.

The York-Antwerp Rules
In the latter half of the nineteenth century, the rules on general average were unified
in the YAR which have been amended a number of times, most recently in
1994 and 2004. However, as the YAR 2004 are not much in use, this Chapter will
mainly be based on the YAR 1994.
The YAR are administered by the Comité Maritime International (CMI) and revisions
of the rules are made by the CMI. Thus, the YAR are a private set of rules, not
an international convention.
Almost all bills of lading and charterparties contain a clause making the
YAR applicable as a part of the contract, and they have therefore an almost
unified international application. Also, some maritime codes such as the
Scandinavian codes have enacted the YAR by a similar reference in the code
to the YAR.