Re: [PSUBS-MAILIST] Ballast

[Ray Keefer <psubs2001@yahoo.com>]

Hi Cliff,

--- Carsten Standfuss <Merlinsub@t-online.de> wrote:
> What is the difference between soft and hard
> ballast?
> 
> I?m planning to use only sealed ballast tanks
> (valves at top and bottom)
> to help maintain neutral buoyancy at varying depths.
>  I have assumed
> that soft ballast
> would be an open bottom ballast tank that would
> allow buoyancy to change
> with depth,

It would except for the typical use of soft ballast
tanks is to either be full of air on the surface or
full of water submerged. When full of air you want all
the bouyancy you can get to keep it on the surface.
When full of water there is no compressable air to
change you bouyancy as you change depth.

A hybrid would be a soft tank with floats, sensors,
valves that adjust air volume as depth is changed.
Think of the main cabin of a SportSub as an example.
As the sub decends, air is compressed in the cabin and
more air is automatically added. As the sub ascends
the air expands and excess cabin air is automatically
vented. The disadvantage is more complication and more
air usage. Both of which can be solved.



> but have talked myself into the
> possiblity that hard ballast
> might
> actually refer to hard weight (trim, drop).  

A hard tank is called hard because it has to withstand
pressure differentials at depth just like a 1 ATM
hull.

> Also,
> the term variable
> ballast would mean any ballast tank that air could
> be added to or
> subtracted from, right?

Yes. Either a hybrid soft ballast tank you can adjust
the air volume in to set, like the SportSub main
cabin, or a hard ballast tank with piping for
compressed air.

> 
> Thaks,
> 
> Cliff
> 


Regards,
Ray

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