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Permit center of gravity - WHere is the center of gravity....

R/C Submarine modelers

Postby THH » Sat Apr 05, 2003 3:42 pm


i just bought a Permit Sub Hull from Scale Shipyard. I plan to use a homemade WTC.
Where is the center of gravity for this hull where i can place the center of the ballast tank.

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Postby raalst » Sun Apr 06, 2003 3:50 pm

The center of gravity is the imaginary place where the
gravity pulls the boat down.
This is actually a sort of "average" of all that has a weight
in your boat (like prop, motor, wtc, hull, etc.)

So, in short, the CG of your boat can only be determined
when you have put in all the stuff. you vary the CG with
pieces of lead and maybe with shifting the WTC forward
or aft.

what you want is that the center of buoyancy is in the
same place (actually right above) as your CG.

buoyancy is only determined by water displacement, so
it can be determined without having the WTC filled with
electronics (hopefully the electronics do not displace water,
but the WTC does ;-)

so, determine CB first, then tweak CG by shifting weights

good luck !


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Postby JWLaRue » Mon Apr 07, 2003 7:17 pm


It will somewhat depend on which boat in the class you are looking to build. There were three different lengths within this class......!

But in general, for a 1/96th scale Permit the c.g. would be somewhere aft of the sail. I *think* it would be about an inch behind it...but I cannot find my drawings to confirm.

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Postby Captain Bergevoet » Fri Apr 11, 2003 1:52 am


Ronald is right. As a naval architect I know a lot about this subject. The centre of gravity can almost be anywhere you want it to be.
Like Ronald said, you want to make sure that your CoG ends up exactly below the CoB (Centre of Buoyancy).

It`s always a good thing to make some calculations of the CoB and CoG before you place everything in, so that you`re sure it is pretty close when you start trimming.

If you need any advice how to do this, please send me an E-mail, and I`ll explain it to you.

Greetings from the Deep,


Edited By Captain Bergevoet on 1050040403
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Postby THH » Sat Apr 12, 2003 11:22 am


thank you all for this excellent answers.


it would be nice to have your explanation by mail. Please go to my Homepage and use the email button.

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