Re: Ballast tanks

["Alan D. Secor" <secor@btv.ibm.com>]

The post below is exactly what I was tryin to say in my last post but I 
included a way to get around the air compression problem.  My ballast
tanks have a vent valve at the highest point and a valve for injecting
air.  The air valve is just a ball valve.  Fine control is not really 
needed since the only time you add air is at or near the surface.

Again, the Kitterege sub has a simular ballast system with open ballast
tanks fore and aft.  It does have what he calls a VBT or Variable Ballast 
Tank which is closed with the exception of 2 valve openings.

Al

> Hi all;
> 
> Again, for my two cents...
> 
> A ballast tank open to the environment is possible, and easiest if the normal
> dive condition is a fully flooded tank.  In the absence of external controls
> for a tank open to ambient water pressure, any air inside the tank will
> compress with depth ( i.e. pressure), and so you lose bouyancy as you dive.
> Conversely, you gain bouyancy as you ascend if there is air in the tank.  This
> is not a good idea.
> 
> Military subs (at least WWII vintage diesel boats) have ballast tanks which
> are valved at top and bottom.  In dangerous situations, they will open the
> bottom vents while running on the surface to charge batteries.  This was
> called 'Riding the Vents" and allowed quick submergence because the tanks
> would flood as soon as the upper vents were opened.
> 
> A ballast tank can be open to ambient if you control the water level in the
> tank, and simultaneously therefore, the air pressure in the tank.
> 
> Is anyone in this group familiar with designs which actually do this?  Has
> anybody actually studied the ballast system on the Sport Sub, for example?
> 
> I have an idea that the water level and air pressure in an open ballast tank
> could be accomplished very easily with a scuba regulator, but the flow rate
> may be a limiting factor.
> 
> Comments?
> 
> Stan
> 
> 
> 
> 
> 
> 
> 
> In a message dated 98-03-13 21:53:06 EST, you write:
> 
> <<    My second question is "Is it OK to have the hard ballast tanks (for
>  nuetral bouyancy) open to the environment or must they be a pressure tank?"
>  All the reading I've done indicates that they should be a pressure tank but
>  I wonder about having them open to the atmosphere. Has anyone made their
>  nuetral bouyancy tanks soft (or open to the atmosphere)?
>   >>
> 

--
Alan D. Secor
e-mail: secor@btv.ibm.com