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Re: [PSUBS-MAILIST] Ballast Question
On Monday, Dec 30, 2002, at 16:22 US/Central, Carsten Standfuss wrote:
> Bigger tanks partlly filled with water, soft or hard, ambient or not,
> pressure compansate ambient or not.. will not work on a submarine..
>
> The reason is what we call the "free surface". In simple words:
> If the boat move under an angle for example to the bow - the water
> in the tanks follow this angle the and the longitudinal trim and
> stability get very quick out of control.
I think I'm following you here. You mean that if the tank is long (or
wide), everything might be fine, until from maneuvering or waves or
whatever the boat gets tipped one way -- and then all the water in that
tank "sloshes" to one end and you can't get upright again? Right? Or is
it something else?
Would it help if the tanks had some kind of baffles to minimize that
sloshing? I mean, assuming there was some compelling reason to make the
tanks that way in the first place. Which there probably isn't.
For both the reasons in this thread: the one you mention, and the one
about the air in partly full soft tanks compressing as you go down and
resulting in faster and faster sinking -- I'm so glad I didn't rush
right out and build a submersible out of that milk tank with two long,
open-on-the-bottom ballast tanks strapped to the sides like I was
thinking right about the time I first discovered the P-Subs list.
Looking back, these seem like totally obvious high-school-physics
factors -- but they never, ever occurred to me. Things that seemed so
simple and easy turned out to have a lot more going on.
David
buchner@wcta.net
Osage, MN, USA
http://customer.wcta.net/buchner