Stability Calculation of Ropax

[eng.naval]

I'm doing an intact stability calculations of a RO-PAX.
Now, my question is on what depth do I perform stability calculations.
because a ro-ro or a ro-pax has two decks:

1- The main deck, which Floodable length calculations are carried
2- The superior deck

Now. on which deck or depth do I perform my stability calculations for this ship.

I'll be very thankful if anyone would help.

[Ad Hoc]

If you are doing "Intact Stability", it doesn't matter.

"Depth" is not an input.

[Guillermo]

I think eg.naval is asking what are the 'closed volumes' he has to use to calculate the KN values and, of course that depends on what deck he is considering, thus influencing the available freeboard and so the ultimate stability. As I have not experience with RO-PAX, I cannot say much more.

Cheers.

[eng.naval]

Yes Guillermo, this is exactly what I'm talking about, Nevertheless the depth will also make a difference when I start to heel the ship and taking offsets to plot GZ Curve. Although i'm not doing that hand calculations.I'm using MAXSURF, so i've already done the model with the superior deck, and when I did floodable calculations I entered the offsets of the margin line(which is at the MAIN DECK) maually, but with stability I was confused to use the superior deck or redo the model to the main deck and calculate stability.
I wish somebody can help on that.

[Guillermo]

In my opinion, if you can consider the volume between the two decks as watertight, then you may use the superior deck for intact stability calculations, as it happens with twin decked stern trawlers.

Cheers.

[eng.naval]

Actually yes it's watertight.But, the problem is that the ramp starts from the main deck and of course it's watertight and secured during the voyage, but some professors disagree because this particular thing which got me confused,
Thank you Guillermo.

[Guillermo]

I think that concern is related with the development of the rules since the sinking of the Estonia. New flooded stability criteria have been released, but I think this doesn't affect to the static intact stability calculations up to the superior deck if ramps and bows are truly watertight.

I hope someone else with more knowledge on this kind of ships can pop up here and tell us.

Cheers.

[Ad Hoc]

eng.naval

You are beginning to mix two separate issues.

You refer to "..stability calculations.."
As i noted for Intact, it doesn't matter, since the watertight deck is the watertight envelope for the stability calculation.
You latter post you say "...and when I did floodable calculations .."
Which means you are doing Damage stability calculations.

The rules have nothing to do with what your prof's say. The rule is the rule.

"...the problem is that the ramp starts from the main deck and of course it's watertight .."

If it is watertight (as defined by SOLAS) there is no debate. You define the hull along the watertight envelope.

What you prof's are debating is an operational issue and has nothing to do with your analysis.

[eng.naval]

Thanks Ad Hoc and thank you Guillermo.
You were very helpful.
If it's possible I have only one more question to ask.
In what rule book can I find this part about Intact Stability calculations.I have LR, SOLAS and GL and I couldn't find any regulations which cover this part.I wonder if there's any book that contain this part.
Thanks again

[Guillermo]

IMO's Code on Intact Stability

https://www2.imo.org/b2c_imo/b2c/init.do

Cheers.

[eng.naval]

Thanks Guillermo