Dividers inside ballast tank?

[robse]

Hi guys.
If you were to build a ballast tank app. 7inch long, diameter 5½inch, would you then place dividers with small holes in them, inside the tank to prevent the water from moving freely inside a half-full tank?
(The tank will be placed in the buoyant center of the sub, in the middle)

I'm having slightly mixed feelings about it.. Slowing down the movement of the ballast water will also prevent the water from running back to the "right place" quicky..

[Guest]

That's quite a short tank,

That's quite a short tank, so you'll probably avoid having to fit baffles.

Try it and see.

Andy

[theo]

YES, YES!!

Robert,

It is my opinion that if you might want to put in dividers (baffles), put them in. If you put holes in the bottom of the ballast tank that lets water into each section of the ballast tank as well as holes at the top of each divider as you force air (propellant gas) into the center section of the ballast tank, you will be satisfied with the result. You can always take the dividers out if you don't want them. My thinking being, it will help the sub to not porpoise as much while you are running under water.

Jack

[Guest]

I agree with the above,I

I agree with the above,I have always installed baffles even in 5 inch long ones.
See my post about glue less baffle tank in the Type XXI modification in building threads.
When full or in transition the the stability of the sub is much better than not using baffles ,ben there and done it ,big difference!
Just be sure to make small holes and a flat area at the top and bottom of each baffle.
A simple 3 holes manifold at the top for blowing evenly out the water works great also.
In my tank post no holes are used just the lose fitting disks or baffles will alow water to flow but under control.
And the vent is a single line with slits cut in the center of each baffle area,that way no matter what attitude the tank is in the air will always escape or water and completly vent the tank,see diagram.

Dave Amur ship yard

[Guest]

pics
http://www.postimage.org/gx14FsJi.jpg

http://www.postimage.org/Pqqa_yi.jpg

http://www.postimage.org/aVWpUr9.jpg

pics

[robse]

Thanks, everybody http://www.subcommittee.com/forum/icon_smile.gif
I'll got build

Thanks, everybody
I'll got build the tank including dividers with a few small 1/4" holes here and there.

[raalst]

the best way is of

the best way is of course to always
have your tank either totally empty or totally full.

This avoids pesky shifting air bubbles.

btw, the size of your sub counts too, a short tank can still
mess up a short sub.

[robse]

Hi Raalst

My sub's app. 81" long, and now with one central MBT. In both the bow and stern a big block of foam gives the needed positive B, so I hope that any washing back and forth in the MBT will not give the sub a list..
The idea with a not either full or empty tank is to be able to control the depth while not sailing. (thus no dynamic diving active.)

Maybe it would be better with a MBT of the piston-type.. No movement of the water is possible there regardless the level.. hmm..

[Guest]

You will fing that a

You will fing that a Engel pump will move the CG forward or backwards depending on the direction of the instalation.
And they are costly,I just build my own tanks from PVC add some baffles that are also from pvc .When submerged the tank is almost full at nuetral B ,just pump more water in and she dives like an elivator,that way theres not enogh air in the tank to make the sub go out of ballance and preciese depth and hover is easy to achieve.My ballast system is a non tank presurrized type that way complete volume of the tank is used and the pump ect are not stressed at all.See diagram.
With an Engel pump it is deficult to adjust the depth without the CG moving.
Like in real subs the ballast tank or tanks are not like Engel pumps.You would need 2 pumps to achieve what one cheap tank can do with ease.
I found that out the hard way.

Dave Amur ship Yard

[robse]

That is nice!!

Really lookes and sounds cool! ... one thought though: It cannot resurface if you dive below the surface, cause you need the snorkel inside the sail to be in free air, right? Or do you compress enough air in the tank when diving..? Sorry if this sounds silly questions, but I'm close to understanding the system

[Guest]

No the tube to the

No the tube to the sail is only for the fill venting.
And it does not have to be located at the sail ,as long as it vents above the serface the air escaping will not get traped in the outer hull,like the U-32 the hull is closed from stem to stern so I had to run a vent line to the sail and bend it as shown like a snorkle to keep out any residual water.
As water is pumped out air from the WTC takes it place and a vacume is formed in the WTC the sub risses to the serface and when you like open the WTC relife solinoid to return the WTC to normall PSI.Then close it and your ready to dive again.Simple as that.
Be sure to instal the one way valves in the right direction! If not you will be flooding your WTC.

Secound modified Robbe XXI has been tested and works perfectly,hovers at nuetral and slowly dives when more water is pumped in.

Dave Amur Ship Yard

[Guest]

The baffles are realy only

The baffles are realy only used durring the transition of filling to empting the tank so that the sub will stay as level as possible durring the above action,just like the real ones do.
If your sub is well ballanced you wont have any truble diving a serfaceing with ease,including hoverring.

Dave

[robse]

Ok, now I see! http://www.subcommittee.com/forum/icon_smile.gif

Ok, now I see! Thanks!
That's pretty smart, and I will look into it while constructing the MBT it self.