# Damage stability (Loss of buoyancy method)

Discussion in 'Stability' started by Umair, Jul 25, 2020.

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### UmairJunior Member

Hello Experts!
I hope you all are doing well. First of all I Appreciate the platform because through that I have been able to design a program to calculate intact stability using KN CURVES.
Now I am moving towards damage stability I have few queries

1. Which method is better loss of buoyancy or added mass method for damage stability like I want to draw the floodable length Curve.

2. Both the method have iterations like I have to trim the boat and recalculate or just it's in the case of added mass only?

3. Is there any supporting details, examples or book in which these calculations are done manually because after reading so many books I just found the example of simple box and it's non iterative calculations.
PLEASE DO SHARE YOUR KNOWLEDGE or ANY RELAVANT WORK. Looking for some positive feedback.

Thanks community!

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### jehardimanSenior Member

1) Added mass is more conservative, loss of buoyancy is much harder, but more accurate. Realistically, for cargo spaces, it is impossible to have any faith in the loss of buoyancy method.
2) Both will require iterations for a floating vessel, even if you have perfect knowledge of the ever-buoyant volume. See 1) for cargo spaces.
3) Get a copy of SNAME's Submersible Vehicle Systems Design. It works through an inside out (loss of buoyancy case) and an outside in (added mass) calculation for submerged vehicles which is similar to the damage control problem. Additional, I would recommend Rawson and Tupper's Basic Ship Theory for background of each method.

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### UmairJunior Member

Thanks sir!
Sir can you recommend me some book or reference paper or any calculation you have done that help me to understand the concept of iteraction. I am working on loss of buoyancy method.

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### UmairJunior Member

Sir these are the steps I followed, iterate it after triming the ship and doing the recalculation. But can you check the method

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### TANSLSenior Member

@Umair, the theory is very simple. Once the compartment or compartments have been flooded, the equilibrium floatation must be calculated to check that the margin line is not submerged at any of its points.
In practice the question is more complicated. An initial equilibrium floatation must be estimated by the weight addition method or by the loss of buoyancy method. Then the position of the buoyancy center of that floatation is calculated and, since its position will not coincide (it would be a miracle to guess the first time) with that of the center of gravity, the trim and the boat heel are changed and the CoB position. And this continues until CoG and CoB coincide in their longitudinal and transverse position. That is the equilibrium floatation after the failure and, as I said before, it is verified that no point on the margin line is submerged. It is, as previously stated, an iterative trial / error process.
I think that you should not consider doing it by hand because it would be a huge job and the accuracy of the results would not be guaranteed.

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