How do you move from a multi organisation structure to a single organisation structure in oracle inv

We would like to move from multiple organisations to single organisations in order to better manage the flow or materials in our warehouses.

We have 17 organisations setup in oracle inventory management system.  the main org receives stock on behalf of the other 16 warehouses and then distributes once requested via a requisition.  We can only manage the min max level and average cost at the org level but we would like to be able to plan across all the organisations.  Maintaining standards at the enterprise level according to our corporate goals. Has anyone done this before? Our questions are :-

 What are the steps to make the move from mulit to single org?