Question:

I have altered some compartments to improve the stability.  Suddenly the error: Model part bad: Negative waterplane area.

What can cause waterplane to become negative, and how can I fix it?



Answer:


The Negative Waterplane error message is usually the result of a deduction extending outside the boundaries of the shape it 
is deducting from.  If you can have a waterplane cutting the model in such a way that it passes through the deduction, and 
the net waterplane area is negative, you will get this error message.

When there is flooding, the flooded spaces deduct from the hull.

The first suggestion is to use Model Converter's Fixup program:
MC GEOMETRYFILE.GF FIXUP

If this doesn't help, try using Section Editor to look for geometry irregularities-- specifically in and around complex tank 
regions with lots of deducting points, or by studying different isometric views to see if there are any lines or points where 
they shouldn't be.
  
A preventative suggestion would be to keep as few deducting components as possible in your model.