# Bonjean curve formula

Discussion in 'Software' started by Dr34m3r, Jun 15, 2016.

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### Dr34m3rSenior Member

any one can tell the formula for calculating the moment of area above BL , which is also included in bonjean curve table beside the area of each section ?

basically want to know the formula being used to calculate the MOM BL coloumn,

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### NavalSArtichokeSenior Member

Any standard text on naval architecture should show you the procedure. Some of these texts can even be found online.

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### Dr34m3rSenior Member

i did not find the formula exactly , so i ask here.

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### TANSLSenior Member

I'm not sure what "MOM BL" means but in general, hydrostatic values are not calculated by a formula. Overall it is a calculation procedure in which they are involved several formulas. With certain values obtained by this method, we then calculate some coefficients for which, indeed, one can talk of a formula.

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### NavalSArtichokeSenior Member

I think "MOM BL" indicates that the moment of area is referred to the baseline.

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### NavalSArtichokeSenior Member

Well, there are a couple of ways it can be done. If you have a table of offsets for each station, you can set up a Simpson's integration to obtain the area and first moment of area about the BL. If you have only a table of Bonjean areas, you can still set up a Simpson's integration using that data. In both cases, it's best if the offsets or the areas are tabulated at regular intervals; this makes the Simpson's integration much easier.

That's also why I recommended that you find a suitable textbook for naval architecture. These calculation procedures are often well-illustrated in such texts to show you how to set up your own calculation.

Like TANSL said, it's not a formula, it's a procedure which uses a tabular form.

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### b1ck0Senior Member

Things become much easier once you know what you want to calculate ...

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### jehardimanSenior Member

Formula = Summation from 0 to x of (B|x+B|x+dx)/2*dx*(x+dx/2)

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### Dr34m3rSenior Member

@Jehardiman:

for the third value , T =1
so you mean,
B = 1 m , x = 2.9 , dx = 0.5 ?

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### jehardimanSenior Member

If you want it in terms of that table you posted

T is the vertical distance from the baseline
B would be the beam of the body at T.

B is not necessarily continuous over T

Area X at T would be
Summation from 0 to T of (B|T + B|T+dT)/2 * dT

MOM BL at T would be
Summation from 0 to T of (B|T + B|T+dT)/2 * dT * (T + dT/2)

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