damage stability calculation

The D&Os contain moment to trim and moment to heel. For most wall sided "ship shaped" hulls, there is not a significant error of the curves at most trims because of the geometry being limited by the margin line (remember I said computers caused more rigious stability rules, like water on deck). If you decide there is enough flare or tumblehome to make it significant, just lift the correction off the body plan with flimsys and a quick double cross SM.

 

Sorry but do not quite understand the indicated phrase.
Anyway, I think a damage usually produces a significant trim and heel so the position of the center of buoyancy and the center of gravity of the waterplane can vary greatly. The area of ​​the waterplane is complicated to calculate and the value of its moment of inertia, around an axis passing through, don´t forget, the new center of gravity, changes a lot. Therefore, an estimate of the metacentre seems very inaccurate and, therefore, the calculation of GZ values can be not aceptable = equilibrium floatation difficult to determine.

 

GZ Curve

I am wondering when the GZ value will be negative,

following the example attached, if angle = 85 then GZ = 135 (!!) ?

when the GZ value will be negative ?

Can get my mistake of understanding ?

 

If you have much experience pulling data from a set of lines and know parallel axis concepts it is neither time consuming nor difficult and as I said, the forms are standardized. Again, you seem to think computational difficulty = better accuracy, which is not the case.

You are trying to use wall sided small angle theory for damaged stability, which will not work. GZ is a function of GM for only small angles of heel, for large angles, especially in the damaged condition, you need to calculate GZ from CG and CB. Make sure you understand this difference. Go see these old threads (and ignore the scarcasm in the second one.)

http://www.boatdesign.net/forums/stability/metacentric-height-27171.html

http://www.boatdesign.net/forums/boat-building/calculation-gm-8852.html#post60405

 

Thanks jehardiman !

It seems like nearly huge work for by hand calculation to get the GZ in damaged condition ? I have found some reference in Attowd's book but complicated.

Is there any other reference available to understand by sample calculation for GZ (damage condition ) ?

 

Jehardiman, probably I'm not getting anything but I do not know where are these so standardized forms such as when a damage as in attached picture occurs.
And of course, take easurements with a computer is much more accurate than extracting data from a drawing on paper. Don´t know if you mean it or not.
I know Steiner's theorem but the difficulty is not to draw an axis parallel to the centerline but find the point at which we must draw this parallel axis.
But the important thing now is to explain CB Dr34m3r how to calculate BM using Bonjean values.

 

yah. still not clear about getting GZ in damaged condition. No single formula for it , i was following added weight method ?

 

Hmmm

Ok, so the whole methodology and procedure has been outlined already on this thread by several posters, notably JEH; all telling you it is not a single formula procedure.

So, looking at the steps one must take, from JEH, looking at the first iteration:

Can you post your calculated volume for the damage void 7P?

 

volume

Calculated damage volume is like the picture attached . ( as i only have the images of the plan not actual cad files, so i am not worried about the value but emphasizing the procedure of calculation )

 

Do you have to study the simultaneous flooding of two compartments?

 

yes, assuming, both flooded at the same time.

 

That is a very restrictive condition that, even for passenger ships, is not normal to have to study. Is your boat a type that force you to study two compartments?

 

This is not a passenger ship , if you look at the plan. I have to test the case to damage in two compartments.

 

Your Resultant Displ would be 20532.56 Tons. Correspondingly your lcg , tcg , vcg values to change.

Lcb, lcg values from which reference ? from aft ? . You have mention vcg of Hull as 18.349 ... How it could be ?... It seems too large

 

I know that some people will say that is nonsense what I say but my advice is to get a good naval architecture software and to use it for your boat. Later, or at the same time, make assumption of what and how you would have to do to calculate it by hand. In my opinion it is not a case that can be learned from this forum. You need some expert close to you, advising you, checking your progress, and explaining the concepts and procedures that must be employed.
Sorry, me at least, I feel myself unable to guide you along this path.
Cheers