Are you saying that the water ballast inside a boat hull
does not affect it's stability? That the water ballast
"weighs nothing" until it is above the waterline?


Dave Doe wrote:
Nope, never did. I'm saying it's stability is indeed improved (more
mass to move)

That would be an issue of inertia... dynamic stability, if
you like the term.

... but question its righting ability vs lead keel - and
posed a question about that.


Well, I don't think that anybody has claimed that water
ballast provides equal righting moment to external lead
ballast. But it can provide significant righting moment,
especially if the boat is designed from the start to utilize
water ballast effectively.


The problem is that water in the ballast has the same density of the
water it is in

Well there you go again. The water ballast is not "in water"
it is in the boat. Will no amount of repetition get this
point across? 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?

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?

DSK