Normally, the party who has made an extraordinary sacrifice or expenditure to avoid a peril (and who needs to recoup his loss), which in most cases is the shipowner. If ship and cargo have both been saved by a jettison of cargo, however, it may be the owner of the jettisoned cargo who appoints an average adjuster and declares general average. Generally, the party to the adventure who requires contributions from the other parties will be the one who appoints the adjuster, and the adjuster will give guidance on making a declaration.
