What is the Cube box concept

I have heard the term “cube rule” or something like it, connected with multi-hulled Footies, but have not been able to picture the idea fully. It sounds like instead of a box 12x6x12 inches (LxWxH) the cube rule boat would fit into a box 12x12x12? Originally, I assumed a multi-hulled Footy could fit the Footy box, but on its side, without the rig of course.

Could someone please detail the Cube rule?

thx

Go Oracle 4.