Simulating Costa Concordia

Great work! Thank you Mr Winkle and Mr Smartbright!

So for the capsize, for me, question (1) is whether or not there is longitudinal stability/aft buoyancy sufficient to keep the bulkhead deck/line handling deck openings or starboard side internal openings at the 01 level from being submerged.
Question (2), is whether there is effectively a longitudinal bulkhead restricting flooding to the low side or delaying cross flooding that would support equilibrium. For example, if the service alley, or back/central partitions of the inner cabins were relatively impervious, whichever side started flooding first would tend to fill up, while the opposite side would remain relatively buoyant, creating a serious imbalance.
Question (3) would be whether or not there is longitudinal flow of water up the passageways on the Orlando deck on the starboard side only. Your sketches suggest there would be if horizontal or vertical openings were there off of the mooring deck. Alternatively, if there were central openings from the flooded compartments aft to the starboard side cabins, the one sided flooding could also occur internally.
Q4: What vertical penetrations are allowed in the bulkhead deck?

Photos and your drawings at the start of abandonment show the mooring/bulkhead deck well underwater on the starboard side aft and the list growing shortly after the final grounding, with the boats still in the davits.

 

To try to answer your questions:

1. The final equilibrium condition (assuming no flooding of Deck 1 or other spaces outside the original 5 flooded compartments) clearly has the external starboard aft corner of Deck 1 fully immersed (to Deck 2 level) but with the centreline still above water. There is no information available so far as to opennings which may have been compromised by this situation, although there will undoubtedly be breather/sounding pipes to the lower tank spaces aft around the mooring deck. Crew access to this deck is not clearly identified either.

2. Given the time taken, it must be assumed that all longitudinal compartmentation of 0 and A decks had been well and truly compromised by the slowly forming free surface within them with flooding up through what would be non-watertight decks and stairwells. However this will have provided much of the earlier resistance to acheiving the 13.2 degree heel observed over about 75 minutes.

3. The big question is whether water had reached the internal area of Deck 1 aft where it would be free to flow forward along the starboard passageway which was only subdivided by fire doors. It is clear that this deck was completely submerged at the after starboard end but the mechanisms available to flood it are far from clear. I have hypothesised that the ventilation and grey water drainage systems originating below this deck may well have flooded up from below being driven by innundation of the same systems on decks A and 0. There should have been isolation mechanisms, but in the general confusion of the disaster it is unlikely they would have been fully implemented and any automatic electrical control would probably have been lost. By such means it is probable that flooding finally spread beyond the confines of the 5 originally flooded watertight compartments.

4. This follows directly from my discussion in 3. above and also includes the three main lift-shafts/stairwells on the centreline which penetrate down to at least Deck 0 and probably Deck A, the after one being directly above flooded compartment 4.

Finally, once the after draft on the centreline reached about 14.0 m then water in the main stairwell aft on Deck 0 will have overtopped Deck 1 and spread along the starboard side of Decks 1 and eventually 2 which effectively was the point at which the vessel foundered/capsized. Given this scenario, the need for further damaged compartments from the grounding is probably superfluous.

 

Preliminary Italian Report given to MSC90, May 18th, London

No-one seems to have found this so far - I got a link from another web forum. Although it confirms many of the basic facts there is also an analysis of the flooding using a NAPA model of Costa Serena (pp 46-53). The most important information comes from page 47 - a part profile of the vessel with the WT hull and compartments outlined. The key data is that Deck 0 is not part of the WT hull, but part of the SS. However, their time line does not match up with the heeled photo we have been using for reference as they can neither match my estimated trim or heel (see Post 133) at the 70-75 minute stage, claiming 7.12 degrees to port at 70 mins and 5.15 to port at 90 mins and a final condition of 2.06 degrees to port with 17,641t of water on board in only 4 compartments, with only a minor amount of water in comp 8! No attempt seems to have been taken to account for the effect of free surfaces, wind heel or the damaged waterplane - a case of garbage in, garbage out it seems!

 

Revision of Post 133 in the light of MIT Report

A number of issues are clarified in this report, but their analysis of flooding is entirely inconsistent with the observations. The first reason seems to be that no account has been taken of wind heel effects even though the report estimates the wind speed to be 19 knots at the time of grounding. Only 4 compartments (4-7) are considered as flooded even though their estimated damage length runs into compartment 8 (albeit as a small scale scrape) and Deck 0 is identified as the bulkhead deck. Engineer testimony is given in support of 4 compartment flooding, although it seems clear that a small amount of floodwater is considered in the final stages in comp 8. Finally it is clear that the initial displacement of the vessel has been underestimated in my earlier analysis. If we return to the data collected on Costa Favolosa then the quoted displacement at the design draft of 8.2 m is 55,828t with a corresponding Cb of 0.753. Whilst this is clearly a maximum, I have assumed this as a starting point in the following re-analysis.

From the final drafts of 12.05m (AP) and 7.10m (AP) giving a trim of 4.95m by the stern (deduced from the photograph prior to grounding together with a list of 13.2 degrees) it has been possible to estimate a mean draft of 9.89m at an LCF of 15.75m aft amidships to give an estimated increase in displacement of 14,632t over an average complete waterplane area of 8447m2. This must correspond to the inflow of water within the 4 compartments plus the added weight of the rock (estimated at about 70t). Up to this trimmed waterline, the internal volume of compartments 4-8 above the TT are estimated at 2958, 2836, 5092, 4098 and 3173 m3 which translate to weights of 3032, 2907, 5219, 4200 and 3252t if filled to an equilibrium condition. Taking only the first 4 of these compartments, containing an added weight of 14,562t of water compared with a potential added weight of 15,358t, suggests about 796t is still available for flooding, giving an average waterline 0.46m short of equilibrium. Given the heeled condition and the many compartments within A deck that might impede the flow of water (particularly at relatively low heads) this does not seem unreasonable as a first estimate. However, this discrepancy can also be explained if the vessel was not floating at the full design draft of 8.2m initially, but at some slightly lower draft. Any reduction in deadweight would compensate with the same increase in floodwater at the rate of about 887t for every 0.1m reduction in initial draft.

Assuming an added mass of flood water of 14,562t with a VCG of about 6.17m and initial and final WPA’s of 8420 and 8474m2 respectively and extreme dimensions (with assumed shell thickness of 15mm). Using Morrish’s Formula for KB = 5T/6 - V/(3Aw):
KB1 = 4.688m
KB2 = 5.550m (Added Weight)
Deducting the moment effects of Floodwater:
KB2 = 5.395m (Lost Buoyancy)
Considering the waterplane in both cases to be a rectangle with a triangular forward end:
BMt1 = 15.971
KMt1 = 4.688 + 15.971 = 20.659m
Using a Lost Buoyancy approach and assuming a permeability of 85%:
BMt2 = 16.040 – Damaged FSE
Damaged FSE = 0.85 x 53.65 x 35.533 x1.025 / (12 x 55828) = 3.129m
BMt2 = 12.911 m
KMt2 = 5.395 + 12.911 = 18.306m
Finally, by assuming that the Wall Sided Formula gives a good approximation for such a ship (especially in a damaged state) we can solve for GZ = 0 in the final condition at 13.2 degrees:
GMt2 = - (12.911 x tan2 13.2)/2 = -0.355m
At 13.2 degrees: GMt2 = 2 (.355)[1 + 2 (.355)/12.911]0.5 = 0.729mThus KG = 18.306 + 0.355 = 18.661m
and GM1 = 20.659 – 18.661 = 1.998m

These results all seem to fit with the generally accepted characteristics of such vessels with a reasonable initial GM. It can clearly be seen that as the vessel sinks under the effect of further flooding the KMt very slowly increases (under the effect of rising KB, BM and FSE being effectively constant using a lost buoyancy approach) which would gradually reduce the angle of loll and that in this condition the residual stability beyond 13.2 degrees was considerable with a GM of 0.729m at that angle.

So far we have taken no account of wind heel. At 19kt, the wind pressure is about 60N/m2 on an exposed area of about 11275m2 with a lever from the centre of lateral resistance of about 26.65m. This produces a wind force of about 69t and a wind heeling moment of 1838t-m to starboard (after the turn). This counteracts the effect of the rock which can be assumed to be about 70t net offset about 16m from the centreline providing a moment to port of 1120t-m. The net heeling moment to starboard is therefore about 718t-m. With a GM of 0.729m at 13.2 degrees the contribution to the heel is sin-1[718/(0.729 x 55828)] = 1 degree to starboard. If we assume the angle of heel due to the free surface alone is about 12 degrees then:
GM2 = -0.292m
KG = 18.598m and
GM1 = 2.061m
At 12 degrees: GMt2 = 2 (.292)[1 + 2 (.292)/12.911]0.5 = 0.597m and wind heel is sin-1[718/(0.597 x 55828)] = 1.2 degrees to starboard giving the 13.2 observed. It is important to note that even at low positive GM values that wind heel would have been significant, explaining the slow transition from low port to low starboard heel angles on either side of the turn.

It is clear from this analysis that with only 4 compartments flooded, the free surface effect is sufficient to maintain a negative GM in the flooded state, although it took some time to become fully effective as the flow of water around the upper part of the flooded volumes is restricted by the presence of A Deck and its non-watertight compartmentation – hence the time taken to develop the final loll. Once lolled, the vessel is relatively stable, having a significant GM and positive reserve of stability. This seems to have been potentially survivable damage if there was no progressive flooding of the spaces above Deck A or the surrounding compartments below either internally or externally. Stability would only be further destroyed if the free surface increased though flooding of compartment 8 and/or flood water spread to peripheral areas above Deck A. Flooding through ventilation and plumbing systems to starboard may well have started on Decks 0 and 1 as this is clearly underwater at the after end due to trim and heel. It is interesting to note that once the angle of heel reached around 25 degrees, the open part of deck 3 floods and there is a significant loss of GZ from that point onwards (even assuming that the superstructure remained watertight). This could have been achieved by the additional flooding of compartment 8 through its contribution to a fully effective free surface over 69.9 m.

The final capsize therefore requires the spread of flood water to other compartments or spaces above the bulkhead deck. Grounding damage would have ensured the former.

 

I'm not sure if this thread is still alive or even read at all?
Nor do I know how serious the above appeal could be taken.

Anyway, I recently have reconstructed the hull lines from the two page data sheet about the COSTA FAVOLOSA within the "Significant Ships of 2011" publication that someone was so kind to attach to his post in this thread here.

I hadn't used any other source than that.
But I omitted what seems to me to be a small trim wedge at the transom.
And I didn't blow my lines up to the claimed block coefficient of 0.753 in the above mentioned data sheet
because I felt that this would have driven the hull lines more into the bulker realm and would have been too fat for a cruise ship.
However, I reached quite hefty 0.69, where I adhere more to the stated 50000 t of displacement in the German Wikipedia article about the CONCORDIA Class.
Anyway, it should be fairly easy to make the lines fuller if needed.

I posted the lines in my thread in a German model boaters' forum here:

http://www.rc-modellbau-schiffe.de/wbb2/thread.php?postid=306782#post306782

while the hydrostats for the DWL of my lines can be viewed here.

Of course, I am fully aware that this might rather meet the hobbyist's standards of a scratch model boat builder than be fit for scientific work as outlined in this thread.


Regards
Ralph

 

Concordia Model & Hydrostatics

Ralph, you have made an excellent effort here and my only comment would be that the Sectional Area Curve needs to be flattened out a little just aft of amidships to reflect a considerable length of parallel mid body visible in the capsize and various build photographs of the vessel. This would allow your block to rise a little to around 0.71 reflecting the somewhat higher displacement figures generally quoted for these ships.

Do you then propose to model the decks and bulkheads to see if you can recreate my flooding scenario above? I would be interested to see the results.

Keep up the good work!

 

A Useful Technical Report - if you speak Italian!

Just noted the following extensive technical report (in Italian) on the CC added in the 'Costa Concordia, 80 deg list, really scary !!' forum by Italian student 'bit'.

http://www.scribd.com/doc/105718306/Relazione-Tecnica

Can anyone make any use of it in this forum to advance our understanding of the sequence of events? It certainly confirms the Freeboard Deck at 11.2 m and the bulkhead arrangements. At different points it seems to discuss 3, 4 and 5 compartment flooded scenarios - not yet detected any influence of wind or free surfaces - can anyone help here?

 

Hello IEWinkle,

thank you for your appreciation of my lines reconstruction attempt of COSTA CONCORDIA class.

I agree that the lines still need a little increase of fullness/parallel midship body.
I am really a little baffled to read on page 183 of the Italian report (is this a draft or an excerpt of the official investigation of the CONCORDIA disaster?) that she had a block coefficient
(i.e. coefficiciente di finezza totale - they don't mean the prismatic coefficient which always is a bit higher due to division of CB/CM though, and which in German is called "Schärfegrad (degree of sharp/fineness?)
of even 0.775 for the draught during this part of the voyage,
and a displacement (dislocamento) of 56650 t (is this with an assumed specific density of 1.025 t/m**3 of the seawater, and does it include a factor for shell and appendages?) is given in the report.
With regard to the ship's hydrodynamics I wonder how the naval architects that constructed CONCORDIA's lines did cope to get a soft aft shoulder of the SAC to avoid excessive flow separation and a achieve a homogenous wake field in the propellers' plane?

As for your appeal to me to further refine my hull lines model to take (watertight bulkhead?) decks and bulkhead positions into account and submit it to further flooding and heeling as well as damage stability simulations,
I have to tell you that this would be far beyond my capabilities for I am not a naval architect with a decades long record of practical experience in shipbuilding like you,
but only do some hull fairing as a pastime in the humble confines of scratch scale model boating.
But I would be happy to supply my CONCORDIA hull model in form of the DELFTship fbm file to whoever was willing and apt to carry out the tasks that you suggested.


Regards,
Ralph

 

I would not be surprised that the Cb is at least 0.75 for this type of ship and the quoted displacements are up to 55,000 tonne. The flow into the propellers is gained by the relatively shallow draft and relatively flat bottom rising around the substantial skeg. Power is also relatively low with service speeds little more than 16 knots although more is installed on relatively small diameter props set fairly well away from the bottom shell to avoid boundary layer. All final quoted displacements will be extreme with shell and appendages included in sea water.

I hope some of the others in this forum might take you up on your offer to supply your hull model for further development.

Currently away from base at present with relatively little data at my disposal so cannot comment further at present.

 

CC flooding process

Hello All,

I have got the communication (MSC 91/7/7) of Italia to IMO for the coming MSC meeting (26 of november)... unfortunately only in french.

I have tried to extract below the most interesting info for this thread, without any personnal interpretation.
Hope it will be of interest (I am sure Prof. Winkle will find some confirmation of his views...).

Compartments involved :
Length of damage = approx. 53 m
Variable damage height = up to 7,30 m
(between frame 52 and frame 125)


N°4 = propulsion thrust bearings, ventilation systems, various hydraulic systems
N°5 = electrical propulsion motors, fire and bilge pumps, propulsion transformers, ventilation tranformers
N°6 = three diesel genarators (aft)
N°7 = three diesel generators (fwd)
N°8 = ballast & bilge pumps

Flooding evolution :
Compartments N°5 has been flooded in few minutes after initial impact
Both compartments N°5 & 6 have been flooded very rapidly
Compartments N°4,7 & 8 have been flooded simultaneously later on

Deck 0 is the bulkhead deck

Aft draught has been considerably increased in the process of flooding which has lead to immersion of deck 0 (bulkhead deck)

Free surface effect in above flooded compartments before final stage (40 minutes) has been very important and is the explanation for the starboard list

This list has had adverse effect such as flooding of compartment N°3

Water has penetrated compartment N°3 through deck 0 (bulkhead deck) and staircases connecting the deck to deck C

45 minutes after initial impact, starboard list was approx. 10°
69 after initial impact, vessel grounds on Giglio Island ; starboard list is nearly 20°
84 minutes after initial impact (15 minutes after grounding) starboard list is approx. 30°

François-Xavier Nettersheim

 

@Totholz: is the official investigation of the Concordia disaster
Ciao

 

Thanks for this useful input. The progressive flooding of comp 3 through the aft stairwell seems to be very important as the final initiator of the capsize.

 

MSC 91/7/7 - English Version

For those who prefer it in English try:

http://www.mastermariners.org.au/co...--investigation-into-costa-concordia-accident

 

Lines of sister Costa Serena

Ralph, Have you seen the Lines Plan and other drawings of C Concordia's twin C Serena by Duffy 53 in Post 1122 and following on the adjacent web forum:http://www.boatdesign.net/forums/al...age-costa-concordia-cruise-ship-41313-75.html?

To all intents and purposes they should have been identical although I note an increased draft of 8.3 m for Serena quoted in its Wikipedia site. You can also see his model!

 

Hello Prof. Winkle,

many thanks for pointing me to Duffy's generous post.

I am impressed. These drawings look to me as if they were original shipyard drawings from Fincantieri.
So I downloaded them immediately before this forum's moderators are urged to discard the links because of legal issues.
And I hope that Duffy isn't getting into trouble over them.
There are quite a few pettifoggers and shysters scouring forums and the like under the pretence of defending copyrights while they only found a lucrative business model in admonishing and "bringing to justice" alleged copyright infringers.

So it looks that my hull line guesswork was a little in vain when the original lines are now available.
But you have to admit that I was quite close with the foreship.
While my aft ship was maybe a little too conservative.
Actually, I wouldn't have expected in the aft ship hull lines of the CONCORDIA Class to be such an extend of "tunnel" or concave (from the basis) sections in the roach region.
Although I shouldn't be too surprised, as this kind of aft ship seems to be kind of state of art in today's (fast) Ro-Pax vessels,
especially when they are also fitted with a pronounced duck tail and trim wedge.
But unfortunately I couldn't find any photo shots of CONCRODIA's in dry dock that showed her underwater body from stern.

Unfortunately, the PDF of SERENA's lines plan doesn't state the form parameters nor at least the (volumetric) displacement.
And there seems to be a wrong numbering and spacing of the construction frames along the base line.
From looking at the body plan it is evident that these are construction and not building frames which are evenly/equidistantly spaced by LPP/20, viz. the conventional Simpson's spacing.
Thus frame 20 should coincide with the FP (or building frame abt. 344) while in the sheer plan it is drawn at building frame 317.
But this is really negligible if one has the pleasure of getting hold of her original lines.


Regards,
Ralph