Re: [PSUBS-MAILIST] Center of gravity Vs. Center of Bouyancy

["Captain Nemo" <vulcania@interpac.net>]

Oh yeah, one more thing...

Anticipating that the question "What's Hydrostatic Center of Gravity?" will
arise:

Think of HSCG as the boats balance point when afloat, submerged at neutral
buoyance, and NOT MOVING.

HSCG does not take into consideration possible attitude changes induced by
hydrodynamic forces resultant of motion.

Hydrodynamic Center of Gravity (HDCG) is where the boat will balance when
underway.

As an example of where this comes into use:  When I want to dynamically dive
my NAUTILUS, I flood down almost negative, but retain a little positive
buoyancy.  She's sitting deep awash (all but submerged) with the tail low.
In this configuration, my HSCG is shifted forward from where it would be at
a normal attitude.  Now, when I get running to "crash dive", the
hydrodynamic forces on the hull and planes bring the boat up level again:
thus HSCG and HDCG converge.

Go download and watch the AVI clip of my sub during the proving tests back
in '91, and you will see this happen.  It's available on this website at:

http://www.psubs.org/psub_pic/nemo_pic/NAUTCLIP1A.avi

It might take a while to download, depending on your hookup and cable speed.
You'll need a media player, too.  Oh, and it's set to music, so adjust your
volume according to preference.

VBR,

Pat