principal on stability calculation in delftship

[rery prabayana]

Dear All, i see on report of stability calculation and i found several defferences with my manual calculation. its about GG’ :
GZ = KN. sin(a) – (KG. sin(a) + GG’. sin(a) + TCG. sin(a))
GG’ = Free surface moment of inertia total / Displacement
why the value of GG’ in program smaller than my manual calculation each any heel angles ??
my friend used maximum FSM in tank load conditions.

please help me, because i still confused

Regard,
Rery Prabayana

[Marven]

Can you post the numbers or VCG, GG’, KM and also the results of the stability calcuation here?

[rery prabayana]

Dear Marven,
I have attacted my calculation

Thanks
Rery

Attachments:

• Stabilityreport.pdf

[rery prabayana]

I found that delftship calculation if setting tank in 100% filled, FSM default or maximum value the result report of GG’.sin(a) in same value……..
I think surface area of tank changed together with heeling and effected for FSM calculations…it’s that true???

[Marven]

The FSM of a tank is only used to correct GM or.
If the FSM setting is not set to “default” then it is also used to correct the righting levers. For the normal setting the software uses the actual COG of liquids in tanks which is more accurate. This is also why you see a varying GG’ as the free surface moments of tanks tend to increase or decrease with the heeling angle of a vessel.

For tanks with a filling percentage greater than 98% the IMO allows the FSM to be set to zero.

[rery prabayana]

Hi Marven, thanks to your help..
I found the mistake is my friend not fully modified in “project setting – loadcase“, he setting in “include shift of COG”,
If I change in “always use maximum FSM”, the program report same with my manual calculation..

regard,

[Marven]

That’s correct. The “Include shift of COG” setting indicates that the actual cog for liquids is used in the calculations which is the most accurate setting. In fact it reflects exactly what happens with the fluids in practice. By disabling the setting you downgrade to the conventional method which only approximates what happens. The calculated righting levers can be either too high or too low depending on the tank configuration that you are using.

[Author]

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