In article ,
John Kimmel wrote:
Roy Smith wrote:

One of the fundamental truths of boat design is that the center of gravity
has to be lower than the center of bouyancy. If it's not, then eventually
the boat (helicopter, whatever) will figure out how to turn itself over so
that it is.

Absolutly wrong.

Beg to differ. The only _truly_stable_ geometry is 'heavy side down, light
side up'.

One _can_ design craft with a secondary, 'meta-stable', mode that is
'heavy side up'. one of the simplest examples of which is a catamaran.

The center of bouyancy of most large boats and ships
is well below the center of gravity.

Which is why most large boats and ships, *when*sufficiently*provoked*,
_will_ turn turtle.

The proof that the 'normal' mode of such craft is _not_ stable is shown
by the fact that there is a far larger range of 'roll attitude' from which
the ship will go 'bottom up', than there is where it will return upright.
And, once a ship _does_ go over, it is very, *VERY* difficult to get it
back upright. Anybody who has sailed a small sailboat is well aware of this;
it is all too easy to tip it over, and *way* more difficult to get it back
upright.