.... You used the example of an empty jug vs one
1/2 full of water... is the water in the jug "in water" or
is it in the jug?



Well?
How about an answer on this one?


Let me propose this example- a cooler full of ice & beer is
lighter than water (hence lighter than water ballast) yet
can be pretty heavy when you're carrying it down the dock.
If you put it in the lowest possible location in the boat,
right down against the hull, and tie it in securely (to the
handles, so you can still open the lid of course), will this
improve the boat's stability?


Dave Doe wrote:
Not a lot no.

Which means yes.

Ah good, so now we've gone from "Water cannot be ballast
because it doesn't weigh anything when below the waterline"
to admitting that something that is in fact lighter than
water *can* function as ballast below the water line,
although not as efficently as denser material.

Think it over some more. I compliment you on your ability to
gradually recognize facts contrary to your prejudices. Most
people can't ever take this first small step.

DSK