# Stability calc in excel.........

Discussion in 'Stability' started by athvas, Aug 21, 2013.

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### athvasSenior Member

Without any software I want to perform the hydro-static calculations, intact stability Calculations. Has anybody done it in Excel.? Does anyone have such excel spread sheet plz share

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### TANSLSenior Member

Perform intact stability calculations in Excel seems like a pretty huge task. Not only is creating a spreadsheet but you have to give it plenty of "macros" created in Visual Basic. Not to mention how to apply the various stability criteria, how to carry out passage to one band studies, wind study and some other studies.
If someone has done this, would do well not to share, for free, with others. Anyway, if you find something like that, please tell me how to get it.
The hydrostatic calculations would be easier to find but certainly will use very imperfect integration methods (compared to current methods of calculating) for some types of boats: boats with knuckles, transom, bow bulb.
Cheers

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### athvasSenior Member

Yes TANSL, You r right its a tedious process.... As iam not aware of macros and VB in excell i'm i just wondering if anyone have attempted to do this exercise......

Last edited: Aug 21, 2013
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### MikeJohnsSenior Member

Sure we did all intact stability with spreadsheets .

You need accurate tabulated "Curves of form" and "weights and moments" (from another spreadsheet) it's a numerical solution that's not terribly hard and the inputs are usually limited to normal operational parameters wrt trim and list.

I don't have a spreadsheet I can share but it shouldn't be hard to find one, try searching "ship stability spreadsheet".

I just searched, have a look here http://hawaii-marine.com/templates/ they want a few \$ but somebody should have a free one there were quite a few floating around before 3D and GHS took off.

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### TANSLSenior Member

I have developed applications for conducting naval architecture calculations and, frankly, I think it is impossible to achieve, with Excel, something which rigorously calculate stability in the various loading conditions.
Just by making a few silly questions:
- How to calculate the corrections to GM due to free surfaces in tanks?
- How to calculate the actual equilibrium waterline in each load condition?
- How to calculate cross curves of stability?
There are several other questions that do not know the solution that could be given with a spreadsheet.
normal operational parameters : trim = + or - 5% trim and heel from 0º to 80º (180º for sailing boats)

No doubt that you can make approximations but I have doubts that the accuracy achieved by these approaches could be accepted by the authorities of each country or Classification Societies.
Anyway, I will be very, very, happy if someone finds something in Excel, to calculate with the appropriate correction.

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### AlikSenior Member

There is a classification society so called Ukrainian Register of Shipping that REQUIRES manual calculations, or use stability software 'approved' by them (that does not exist on the market). Say, they will not accept HST, GHS, Orca or something like that. So for these guys, the calculations are actually made in Excel by taking offsets from lines plan, and by imitation manual calcs. The problem is that such calcs can never consider free trim, thus GZ can be 5-20% higher than actual, this means an error to dangerous side. We tried many times to explain this issue, but for them seems this great corruption idea...

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### TANSLSenior Member

I think it will be necessary to create a program that passes MaxSurf, HST, GHS, Orca, etc.. outputs into an Excel spreadsheet.
It will be very usefull for Ukrainian designers. Shall I start working on it?

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### AlikSenior Member

Forgot to say, the calc method should be from the book they have... So it will not help.

Don't worry, most of designers from Ukraine already told Register to **** off, and work with BV and others.

9. ### dskiraPrevious Member

I don't see the problem. I did my own spreadsheet system for stability and weight distribution, intimately associate as you know.
It's easy, but takes time to make it perfect for the way you work.
Before I did it on hand written booklet, one per project, I have several hundred of these on the basement. Fortunately Excel came over, and I linked my integrator to it.
Quite a straight forward set of calculation, and it is far from rocket science. It just need to be very accurate and disciplined and experienced.
I think you have to simplifies and not be overwhelm with repetitive calculations.
But that my experience, anyone has is own

P.S. The StIX (or CE) has seven way to ask the same question. When naval architecture is on the hands of technocrats.

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### TANSLSenior Member

dskira, First, I want to express my admiration because I think you had to do a huge job to get something valid with Excel.
I do not know what system you use to longitudinaly integrate the values ​​of the sections. If you could describe it, I could get an idea of what the real situation and discuss it with you.
Sticking to hydrostatic calculations, which are the simplest, how you calculate the wetted surface of the hull?.
This is an interesting topic (naval architecture versus Excel). It suggest me a lot of questions for you.
Cheers.

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### jehardimanSenior Member

Actually, I think there is a slight disconnect in what people are talking about here.

To develop a "hydro static intact stability booklet" for a ship in Excel (or Lotus 123 for that mater, but Quattro Pro was the best) is fairly easy but, as pointed out, is tedious. The '67 edition of PNA and HSD lay it out in "real" spreadsheet form (for those of you old enough to have used paper spreadsheets) so it is straightfroward.

To develop a "hydro-static intact stability calculation" for a vessel at any displacement or attitude in Excel is another matter.

Last edited: Aug 22, 2013
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### MikeJohnsSenior Member

It's not automatic but it's quicker than running through iterative solutions manually. As you point out there's still a lot of manual input.

When the earlier computers came along there was a natural shift to a spreadsheets which made life much easier in the small design office.

Free surface isn't automatic, it's a manual change in the weights and moments input.
And you have to use an iterative approach for equilibrium waterline, but the big problem was that these models were not free to trim.

I'd presumed this was a student exercise. The software we have now is so quick relative to the older methods but it's still a numerical method with an iterative solution.

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### MikeJohnsSenior Member

Supercalc was good with inbuilt circular ref iterative solver, we used that for a from 1982-1990, then shifted to Excel and Mathcad and then things really took off.

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### TANSLSenior Member

The operations of addition, subtraction, and multiplication (and some other) can be done with Excel. However, the shapes of existing ships make integration procedures we used 30 years ago (Simpson, trapezoids, ...) lead to errors which today are considered unacceptable. These procedures, used in other calculations, such as the wet surface, give rise to errors that can exceed 30%.
How can Excel calculate flotation area and its center of gravity in a case like that of Figure 1?.
How can calculate with Excel the equilibrium flotation of a boat that is in the situation in Figure 2?
How to take into account the appendages volume, some of them only partially submerged?
There are plenty of questions but, assuming that these calculations can be performed with acceptable accuracy, is it worth trying?. Never get accurate enough, nor fast, nor cheap

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### jehardimanSenior Member

Computers are not "accurate" for 1 and 2 either, they just have a false sense of percision. A lot of computer and calculation "accuracy" is just mental mastrabation. As I pointed out in some of the computer threads, computer water is not real water and computer shape is not real shape. Considering that you will never know the displacement of a 10,000 ton ship to 10 tons (if you are lucky) anyway, a good set of Bonjeans will be as good as any other output.... the difference will be immeasurable in the end (computer output has a greater chance of error IMHO because there are more numbers which mean more errors).

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