Center of G and B vs. MBT

[robse]

Hi Guys.
Just to refresh my memory: Am I correct that the center of gravity and the center of buoyancy *must* by in line with the center of the Main Ballast Tank, if a sub has got one central MBT?

Reason for me asking is that my tank can not sit right in the middle, so if the above is true, then I must add lead to my sub, and trim in after that. It the above is false, then I can avoid making it heavier..

[Rogue Sub]

I dont know man. Ive

I dont know man. Ive never reallly worried about it to be honest. I usually try to get the ballast tank in the middle but as you are finding it is not always possible. I usually have to add more foam and weight to get it to sit submerged level right. Id just get it in the water and do some theory to practice for yourself.

Kevin

[don prince]

Gentlemen,

I'm just a blundering old

Gentlemen,

I'm just a blundering old guy who hasn't completed his 1st OTW Type VIIc (U-96); some day it will be finished. However, I do have a several books on U-Boats and model building.

"Model Submarine Technology" by Norbert Brüggen... Chapter 2 - Design - This chapter covers the center of gravity and the center of upward thrust (bouyancy) in great detail. Perhaps this information will help...

" It is also possible to install the diving tank offset slightly towards the bow. The boat can be trimmed out to a horrizontal attitude when submerged, but the boat is slightly stern-heavy when in the sutface. This helps to insure good hydroplane response during the surface manoeuver and produces more stable surface running.

Of course, it is possible to control the sub by deliberately shifting the center of gravity. A suitable weight trimming system can be produced by placing the heaviest components - the dive battery - on a slide, operated by a powerful servo.

This solution avoids the necessity of balancing the boat exactly, and also gives some extra control when the boat is static and at low speed, when the hydroplanes have no effect."

Regards,
Don_

[JWLaRue]

Robert,

While it's best to have

Robert,

While it's best to have the ballast tank as close to the center of the boat as possible, in practice for our models where we are basically looking to get a good surface and submerged trim, having the tank offset a bit doesn't hurt us that much. (Especially if you are planning on using an APC.) The placement of buoyancy foam can offset the differences.

The advice to place the tank slightly forward of the desired center would actually enhance the way the sub dives and surfaces....meaning that it would dive with a slight bow down angle and surface with a slight bow up angle.

....hopefully this makes sense,

Jeff

[robse]

Thanks, all http://www.subcommittee.com/forum/icon_smile.gif Being the

Thanks, all Being the second time around for placing the inside stuff, and trimming (Had a dual MBT system before) I really appriciate this help.
Now's the time to complete, and send on her first mission.

[Rogue Sub]

Yes get her to sea.

Yes get her to sea. I want to see video of all her little toys working.

Did you find dual ballast tanks to be to much to compensate for?

Kevin

[robse]

Nuke: Yep, now she MUST

Nuke: Yep, now she MUST go to sea.
When it comes to the dual MBT system, there were several problems. The system that should ballance the sub using the tanks was as such ok, but the sensors in the water corroded while I looked at them, which again confused the sub. Also, auto-ballancing is not needed, as the center of gravity will not move once the sub is done, so I scrapped it. Oh, and the combined volume of the tanks was too small to fully surface the deck and sail as I wanted to. *ups* hehe