.
Here we have an example of...

... floatation equivalency in action. There are two boats, yes?
And each of the boats is on the surface of the water, inasmuch
as at least a portion of each is above the water surface, yes?
And any boat that is "afloat" or "floating," has at least some
portion above the water's surface, yes? Therefore, we can say
that a boat that is in the water with a portion of its hull above
the water surface is a 'floating boat,' yes? And the state of
floatation is directly tied to the question of floating as opposed
to not floating, and floating is equivalent to floating, yes? And
so, the two boats pictured are equivalent in their respective
states of floatation, and they exhibit floatation equivalency.
If Bishop Fellay were to explain it, I'm sure he could take another
15 or 20 minutes.