Numerical Investigations of the Capsizing Sequence of SS HERAKLION

Transcription

1 Ships and Ocean Vehicles, 2328 September 2012, Athens, Greece, 1 Numerical Investigations of the Capsizing Sequence of SS HERAKLION Stefan Krüger, TU Hamburg Harburg, krueger@tu-harburg.de Hendrik Dankowski, TU Hamburg-Harburg, Dankowski@tu-harburg.de Caroline Teuscher, TU Hamburg-Harburg, te@tu-harburg.de ABSTRACT The sinking of the RoRo- Passenger Ferry SS HEARKLION in 1966 was one of the most disastrous ferry accidents in modern Greek shipping. SS HERAKLION was originally built as combined freight and passenger vessel and was later converted into a RoRo- Passenger ship. Some technical aspects of the conversion were at least doubtful, however the ship started her final voyage on December 7 from Crete to Piraeus. The weather was rough, and the ship was travelling in a stern quartering sea condition with heavy beam winds. The rolling was strong, and after a course alteration into following seas the rolling increased. This caused cargo to shift and a side door was pushed open by a heavy truck which was not secured. Water entered into the car deck which resulted in a heavy list of the ship. When further water ingress took place, the ship the finally sank. After the accident, investigations were carried out at NTUA (on behalf of the Hellenic authorities) and at the Institute für Schiffbau (on behalf of the insurance company). There are some interesting aspects of the accident which are worth to be studied again by more advanced methods compared to the late 60s. Numerical evaluations of the accident (parts of this research were in close collaboration with NTUA, Ship Design Laboratory) have shown some interesting aspects of the earlier accident phase before and during the flooding of the main garage deck. The investigation has also shown options how the accident could have been avoided. The paper presents the treatment of complex full scale safety issues by numerical simulation methods. It shows that it is useful to apply different calculation methods for different phases of such accidents. The intact phase of the accident is treated by our seakeeping code E4ROLLS until water enters the car deck. The initial water ingress into the car deck is computed with Glim s method until a certain list is reached, and some conclusions are drawn. The paper will also show that scientific advances in ship theory can help to better understand the accident roots of such complex accidents, and these methods can help to find new answers to old problems. Keywords: SS HERAKLION, capsizing, passenger ferry, flooding of the vehicle deck 1. INTRODUCTION Marine casualties are typically complex event chains, especially when the casualty leads to the total loss of a ship due to capsizing or sinking. Whenever such a casualty needs to be investigated, lots of computations need to be made to figure out the event chain which has lead to the final loss. During these investigations, a variety of different computational methods is applied, which extends from simple hydrostatic calculations to complex dynamic simulations. The problem exists that all these methods require more or less sophisticated computational models, and both need to be validated. The validation of

2 Ships and Ocean Vehicles, 2328 September 2012, Athens, Greece, 2 Figure 1 SS LEICESTERSHIRE (top) and SS HERAKLION (bottom) after the conversion such methods can be performed by computing theoretical test cases, by the comparison with experiments or by full scale accidents. The validation by experiments has the advantage that all data and test conditions are well defined, which makes it quite easy to re compute these accidents. Further, any deviations between experiment and computation can in most cases be reasonably explained, and such deviations often result in the refinement of the computational procedure or in the model, or both. Therefore it is a conditio sine qua non to validate numerical methods by experiments. However, with respect to marine casualties, experiments never reflect the full event chain as they can only focus on a small part of the problem, and they are always performed under ideal conditions. Therefore it seems plausible to also use full scale accidents of ships for validation purposes. But the problem exists that these accidents never happen under ideal conditions where all data is exactly known. Mostly the ship has sunk and it cannot be accessed, important data are not known with sufficient accuracy and the surviving witnesses often do not clearly remember important facts. This makes the analysis of full scale accidents always challenging, and often it is not clear whether a numerical model or a computational procedure is actually suitable for the analysis. Therefore, TUHH is actually running a research project where we systematically collect data of full scale capsizing or sinking events, prepare the calculation models and figure out the relevant event chains. These data are collected in a database which will be used for the validation of other methods in the future. In the framework of these investigations, we came across the capsizing and sinking accident of SS HERAKLION, which took place in Although the accident was quite long ago and the ship has nothing in common with modern designs, the accident was characterized by a lot of interesting technical details which made the analysis quite challenging. Although no safety recommendations can be drawn from this accident, the technical analysis shows a variety of interesting details which allow the validation of a couple of computational methods. Our analysis of the accident, which was done in close collaboration with the National Technical University of Athens (NTUA) is presented in the following sections. 2. SHIP AND LOADING CONDITION SS HERAKLION was originally built as SS LEICESTERSHIRE by Fairfield Shipbuilding and Engineering in 1949 as Hull No. 2562, call sign SZNO. The ship was a typical design of a combined freight and passenger vessel the ship was bought by the Hellenic shipping company Typaldos Lines, and she was converted into a combined passenger and vehicle ferry, see Fig. 1. This major conversion showed already all later problems with RoRo- Passenger- ferries, which was a new ship type in those days and it was unclear for the authorities how to deal with this type of ship. Since 1949, additional safety requirements were put in place, and additional transversal bulkheads were retrofitted to meet a one compartment status. This was not consequently done, as Fig. 2 shows, because the additional transversal bulkheads did not extent down to the double bottom. An additional deck was fitted to serve as vehicle deck, which was accessed by side doors and ramps. As the watertight transversal bulkheads did for

3 Ships and Ocean Vehicles, 2328 September 2012, Athens, Greece, 3 obvious reasons not extent above the vehicle decks, the vehicle deck now was the freeboard deck, which made a complete set of safety relevant calculations necessary. An additional passenger deck was also retrofitted which resulted in a significant increase of the vertical centre of gravity. Figure 2 Sketch of SS HERAKLION after the conversion. The side door of the forward vehicle deck can also be seen. However, during the conversion some existing regulations could not or only hardly be fulfilled, a fact which was later proven during the accident investigations. Therefore, the issuing of some certificates was doubtful, and was also later withdrawn by the Hellenic authorities. The main dimensions of the ship after the conversion were the following: Length over all m, moulded breadth m, draft design 4.58m, depth to freeboard deck 5.35 m, depth to upper deck m, speed 17 knots. During the accident investigations by the Hellenic authorities it was found quite challenging to figure out the stability condition of the vessel during her final voyage. An inclining experiment with SS HERAKLION was never performed, and the stability information on the vessel was extremely poor. During the accident investigations, the light ship weight of SS HEARKLION was determined by Fragoulis (Fragoulis 1967) and Georgiadis (Georgiadis 1967). They used the available data of the inclining experiment of sister vessel SS XANIA instead and considered some additional weights and also some that were not on board of SS HERAKLION. The loading condition of the final voyage was based on the available loading list and contained cars, trucks, passengers, ballast and bunker and stores. However, some information was doubtful, also the inclining experiment performed with SS XANIA, which was based on level trim hydrostatics and small inclinations. Further, SS XANIA had a large amount of ballast water on board during the inclining experiment which also made the results doubtful. Some tank volumes were incorrect, too, and also the hydrostatic particulars were not fully available in the AEENA- accident reports. Therefore we had decided to recalculate all weight information, including a new evaluation of the inclining experiment (Teuscher 2011). This step was also necessary to generate the weight information for the mass moments of inertia computation for the dznamic analysis. It was found that due to the conversion, the centre of gravity was that high that the ship could only be operated when the complete double bottom fuel oil tanks were filled with ballast water. The loading condition during the final voyage resulted then in a total displacement of 7740 tons, draft at A.P m, Draft at F.P m, GM c 0.94m, freeboard to vehicle deck of abt m. The tank fillings of the loading condition according to our investigation is plotted in Fig. 3 (Teuscher 2011) Figure 3 Loading Condition of the final voyage. 3. THE FINAL VOYAGE On December 7 th, 1966 SS HERAKLION departed from the port of Souda Bay, Crete to make her voyage to the port of Piraeus. The departure of the vessel was delayed due to the late arrival of a reefer truck, which was then

4 Ships and Ocean Vehicles, 2328 September 2012, Athens, Greece, 4 stowed unlashed in the forward garage deck rectangular to the ship s centre line. At about hrs, the ship reached the open sea close to the island of Milos (see Fig. 4), steering a course of 352 degree. The wind was rough with 8 Bft (11 in gales). As the wind direction had changed overnight from about 180 degree to now 270 degree, the direction of the waves was still about 200 degree, bringing SS HERAKLION into the interesting situation of beam wind and stern quartering seas (see Fig. 4). The sea was rough with significant wave heights about 5-6 m, (significant) wave length between 80 and 120 m. The weather data were not recorded during the accident, but were later obtained from the German DWD (Wendel 1970). some cars tippled over. This cargo shift increased the steady list of SS HERAKLION to about 11 degrees. The crew decided to alter the course to 20 Degree to bring SS HERAKLION directly before the seas. She was now travelling in following seas and beam wind. Despite the course alteration, the rolling motion increased, and due to the severe rolling, the unlashed reefer truck pushed against the starboard side door and forced the door open. Due to the steady list of about 11 Degree and the roll motion, water immediately entered the vehicle deck which caused a list of about 60 degree. Due to unsecured openings, further compartments were flooded, the vessel finally capsized and sank. Only 46 persons of 264 could be saved, this made the SS HERAKLION accident the most disastrous marine casualty in Modern Greek shipping. 4. ANALYSIS OF THE ROLL MOTION IN INTACT CONDITION 4.1 General Considerations Figure 4 Accident scenario of SS HEARKLION. Source: AEENA. Due to the beam wind, SS HERAKLION had a steady heel to starboard side of about 8 Degree. Due to the seastate, the ship was permanently rolling with amplitudes about 20 degree, as the surviving persons reported. This rolling motion caused the cargo to shift, and The accident of SS HEARKLION can be split into four different phases, which do all have some interesting technical challenges: The first phase is the intact rolling in a beam wind following sea scenario. The second phase took place after the alteration of the course, which made the rolling even worse and lead to the opening of the side door. The third phase is characterized by the flooding of the vehicle deck until the ship reaches a large list, and the fourth phase is the subsequent flooding of further compartments including the superstructure until the ship finally sinks. This paper deals with the first three phases of the accident: Because it is obvious that these phases are strongly influenced by dynamic effects, they can only be analyzed with methods which compute the roll motion in following seas with sufficient accuracy. Although many tanks were filled, free surface effects can be disregarded, as most tanks were completely filled. The flooding of the vehicle

5 Ships and Ocean Vehicles, 2328 September 2012, Athens, Greece, 5 deck can also be computed taking into account the relevant dynamics, as the fluid motion influences the ship motion and vice versa. The relative motion between the ship and the wavy surface triggers the in- and outflow of the water on deck and needs to computed with sufficient accuracy. For these computations, we use the seakeeping code E4ROLLS which was originally developed by Söding and Kröger for the investigation of the ELMA- T.R.E.S. capsizing accident in E4ROLLS simulates all six degrees of freedom in time domain. The concept is that those degrees of freedom which are governed by hydrodynamic effects are computed linearly using RAOs (e.g. from a strip theory or panel code), whereas a non linear simulation is performed for those degree of freedom where the nonlinearities are the governing effects. The equation used for the roll motion reads: M && ϕ = wind + M sy + M wave + M Tank M xx d m I I xz 2 2 ( g && ζ ) hs I [(&& ϑ + ϑϕ& ) sinϕ (&& ψ + ψϕ& xz ) cosϕ] ( ψ sin ϕ + ϑ cosϕ) Here, M wave denotes the direct roll moment obtained from the roll RAO, and h is the righting lever in waves computed by the concept of Grim s equivalent wave (Grim 1960). The latter makes the computation extremely fast and at the same time reliable. E4ROLLS was intensively validated by model tests during German BMBF- funded research programs from Figure 5 Principle of Grim s equivalent wave (Grim 1960). 4.2 Stability, roll motion and critical resonances Figure 6 Polar Plot of significant wave heights required for a 25 Degree roll angle of SS HERAKLION in intact condition, 8s period Figure 6 shows the results of an E4ROLLScomputation for the final voyage of SS HERAKLION, intact condition. The polar plot was computed for a significant period of 8 s, corresponding to a wave length of 100 m. The seastate is represented by a JONSWAPspectrum, the radial energy distribution follows a cos 2 - function. This leads to a short crested, natural seaway. The polar plot shows the required significant wave height which lead to a roll angle of 25 Degree (abt. 8 Degree STB static heel due to wind plus the roll amplitude). For each node of the polar, 10 simulations of s each have been performed for each significant wave height, and the wave height was varied in steps until 25 degree roll angle were reached. The radial rings show the ship speed, the circumferential axis shows the encounter angle. Beam wind was assumed from 270 Degree (90 degree PS), this is the reason why the polar plot is not symmetric. From these results, some interesting conclusions can be drawn. The computations show that in the accident situation of SS HEARKLION, roll amplitudes of about 20 degree - as reported - were likely to occur, as the required significant wave heights are about 5-6m. This value is typical for wave lengths of 100 m- 120 m, as reported by the German DWD for the day of the accident (Wendel 70 and AEENA-

6 Ships and Ocean Vehicles, 2328 September 2012, Athens, Greece, 6 Reports). Most interesting is the fact that SS HEARKLION was travelling close to the 1:1 roll resonance situation in following seas. Based on the Stillwater GM of 0.94 m and valid for small angles only, the natural roll period of SS HERAKLION amounts to 14.6 s. This results in a theoretical speed of 12.5 kn in following seas at an encounter angle of 30 degree, which is approximately the encounter angle of SS HERAKLION before her first change in course. The polar shows the well known fact that resonance situations in following seas are not distinct points - as a linear theory might suggest - but more or less broad banded resonance areas which extent over a range of speeds and encounter angles. This behaviour is a consequence of the fact that the natural roll period of a ship in following seas is not a fixed value, but is varies due to several nonlinearities. For the accident situation of SS HERAKLION, the following nonlinearities occur (see also Fig. 7): As the righting lever curve of SS HEARKLION is of progressive type (positive form stability),, the natural roll period decreases with increasing roll angle or list. For the SS HERAKLION, the steady list due to wind and cargo shift plays a major role, and the larger the steady list becomes, the smaller becomes the roll period. For the roll period in waves, the stillwater righting lever curve is not relevant, but (as the two extremes) he crest and through leverarm curve. The stability varies between these two situations, and the resulting roll period depends on how long these extreme phases occur during one cycle. The resulting roll period is longer compared to the computed Stillwater period. The roll angle itself has an influence on the roll period, especially when the crest and through curves are analyzed. For smaller roll angles up to approx. 15 degree, the roll period decreases, for larger roll angles larger than 15 degree, the roll period increases. Figure 7 Righting levers of SS HERAKLION for Stillwater, crest and trough conditions. Computations by Wendel (Wendel 1970), coloured curves our computations. This is underlined by Figure 7, where the righting lever curves in waves of SS HERAKLION have been computed by Wendel (Wendel 1970) for a 100 m wave, wave height 7 m. The mean value between crest and trough (used by Wendel for his analyses) differs significantly from the Stillwater curve (blue line), an indication for the fact that any conclusion from the Stillwater natural roll period (for small angles) is not valid for the SS HERAKLION accident. Figure 8 Polar Plot of significant wave heights required for a 25 Degree roll angle of SS HERAKLION in intact condition, 8.5s period.

7 Ships and Ocean Vehicles, 2328 September 2012, Athens, Greece, 7 All these findings are confirmed if the computation is repeated for another possible accident scenario. Fig, 8 shows the limiting significant wave height now for a significant period of 8.5s (113 m corresponding wave length). It can now even better be observed how close SS HERAKLION sails at the 1:1 resonance and that the alteration of the course did not improve the situation. 4.3 Conclusions for the first two phases As shown, SS HERAKLION was travelling sufficiently close to the 1:1 following sea resonance situation, so that large rolling angles occurred. The polar also shows that changing the course was not a good choice, as the rolling motion was not reduced. The reason is that the ship was brought closer to the resonance at following seas, but the direct excitation (M Wave in the roll angle equation) due to the waves was reduced slightly when SS HERAKLION took the waves exactly from abaft. Even sailing at a higher speed than 15 knots would have improved the situation, but slightly. May be it was due the fact that SS HEARKLION was already delayed that the crew did not want to increase the delay by reducing speed or changing course. But had the crew done so, the accident could have been most probably avoided. In this respect, the SS HEARKLION accident is comparable to the loss of MV FINNBIRCH in 2005 and SS FIDAMUS in 1949, both ships capsized in following seas close to a 1:1 resonance (Kluwe and Krüger 2008). But there can be no doubt that SS HERAKLION was quite safe from the intact stability point of view, as our computations show. Fig 9 shows the horizontal acceleration computed for SS HERAKLION during the accident situation. It can be seen that accelerations of about 0.5 g occur to starboard side, this is sufficient to let the cargo tip over. 5. ANALYSIS OF THE WATER INGRESS INTO THE VEHICLE DECK 5.1 General considerations Figure 9 Horizontal accelerations computed for SS HERAKLION in the accident situation prior to the course alteration From Fig. 6 and Fig. 8 the fact can be derived that the whole accident could have been avoided if the crew had decided to select another course or speed combination. At that course, SS HERAKLION was clearly safe below a speed of 10 knots, and if she had opted for a course with bow quartering wind (e.g. 60 or 75 Degree STB) she could have sailed nearly any speed without being endangered. The sinking of SS HERAKLION took place when the reefer truck struck against the STBside door, pushed it open, which allowed water to enter the vehicle deck. It was shown in the accident investigations by Fragoulis, Georgiadis and Antoniou (Fragoulis 1967, Georgiadis and Antoniou1967) and by Wendel (Wendel 1970) that the flooding of the vehicle deck resulted in such a loss of buoyancy that the ship irreversibly must have capsized. But a more precise stability computation (loss of buoyancy method, free trimming righting levers) gives a more complex picture, as Fig. 10 shows:

8 Ships and Ocean Vehicles, 2328 September 2012, Athens, Greece, 8 Figure 10 Righting levers computed for SS HERAKLION after the flooding of the forward car deck. Figure 10 shows the computation of the righting levers of SS HERAKLION after the forward car deck is flooded. The computation assumes the complete superstructure to be watertight, as water will gradually enter these compartments. The heeling moment of the tippled cars has been taken into account, and also the heeling moment due to wind of 8 Bft, which must be added for the situation when the reefer truck struck the car deck open. From these calculations, it becomes obvious that after the flooding of the car deck, two equilibria exist, where the first equilibrium is about 10 degree STB. This first equilibrium is only theoretically stable, because a larger wind heeling moment (gales were reported to be about 11 Bft) is sufficient to let the ship heel to about 45 degree STB. It is also possible that the wave moments from the seastate force sufficient water into the vehicle deck to overcome this first stability plateau. But this computation shows that SS HEARKLION was not necessarily lost when the STB side door was pushed open: If the crew had managed to turn her in such a way that the wind heeling moment would have acted from STB side on the vessel, she would have had chances to survive even the water ingress. This possible scenario will also be analyzed in the following sections. Further, even the equilibrium at about 45 degree is stable. Figure 11 shows the floating position of SS HERAKLION after the complete flooding of the car deck including the wind heeling moment from PS. Figure 11 Floating position of SS HERAKLION after the flooding of the vehicle deck Figure 11 shows that SS HERAKLION must not necessarily sink or capsize even after the most unfavourable combination of heeling moments (tippled cars at STB, wind from PS). If the crew had followed the relevant guidelines and kept all weather tight doors and openings closed, the ship could have stayed in that position. It was however unclear during the accident investigations if and how internal progressive flooding has taken place. Of course these computations depend on the assumptions made, where the largest uncertainty lies in the masses and centroids. If the stability of SS HERAKLION had been smaller than computed, the first stability plateau might become completely unstable, which forces the vessel to heel to about 50 Degree STB even without additional external moments. However, these computations indicate that based on our assumptions the ship had had a good chance to survive the accident if the crew had taken other operational decisions. 5.2 Numerical simulations of the water ingress with E4ROLLS At present, we have two different methods to compute water ingress into vehicle decks: The first is E4ROLLS, which has been extended for water on deck problems by Petey (Petey 1988). The floodwater is modelled by Glim s method using shallow water equations. The inflow into the vehicle deck is computed by the net flux through the opening including the dynamics of the roll motion. This method gives good results

9 Ships and Ocean Vehicles, 2328 September 2012, Athens, Greece, 9 (BSU 2010) when the amount of water accumulated in the vehicle deck is small compared to the total mass of the ship and when the water inflow does not strongly influence the trim. Because in E4ROLLS only the additional roll moment (see M Tank in Eqn. 1) is modelled, the mass increase and trim moment are neglected at present (we are currently improving this). Further, as the direct wave moment (see M Wave in Eqn. 1) is obtained from the linear RAO, the results become less reliable when a certain static heel (typically 30 to 40 degree) is reached. From practical considerations, this is not a problem because the ship can be assumed as lost in case such large static heeling angles are reached. Further, we have developed a method for sinking computations E4SINKING (Dankowski 2011), which computes the static flux through the relevant openings and determines a hydrostatic equilibrium according to the added mass method. Dynamic effects can roughly be taken into account if the relative motion between ship and opening is computed (e.g. by E4ROLLS) and used for the flux computations. This method is of course more robust and for the desired purpose less precise, as the dynamics are underestimated. When analyzing the SS HERAKLION accident, Teuscher (Teuscher 2011) has checked both methods and found that they converged with respect to the most important results (flooding times and floodwater amount). We will in the following present the results obtained from E4ROLLS for the flooding of the vehicle deck. Figure 12: Time plot of the roll angle (top) and the volume in the vehicle compartment (sum of the curves in the bottom plot), accident scenario Figure 12 shows the computed time series for SS HERAKLION after the STB side door was pushed open. The computation was made for a speed of 15 knots, encounter angle 0, wind 8Bft, significant period 8.5 s, significant wave height 5 m. The vehicle deck was modelled by two compartments to take into account the sheer, therefore the total volume is the sum of these two (see Fig. 12, bottom time series). The hydrostatic computation resulted in about 1800t water accumulated in the vehicle deck at the equilibrium of about 45 degree. This coincides with the dynamic results obtained from E4ROLLS, where the static equilibrium is computed somewhat larger at slightly larger volumes in the vehicle deck. The first phase of the flooding shows that it takes approximately 500 s to flood the vehicle deck and to pass the first stability plateau, because the water inflow is forced into the ship by the motion. After this situation is reached, the vessel oscillates around this condition, but we have assumed that course and speed are kept during the simulation. It is now interesting to analyze alternative scenarios to check whether there had been additional possibilities to prevent the accident. In his investigations, Wendel (Wendel 1970) has suggested that the ship should take the wind from abaft and the waves from STB stern quartering. The idea was to get rid of the wind heeling moment by a starboard turn. Unfortunately, numerical simulations by

10 Ships and Ocean Vehicles, 2328 September 2012, Athens, Greece, 10 Teuscher (Teuscher 2011) have shown that SS HERAKLION would also have capsized during this manoeuvre. We have thought about another alternative which we present here for the first time, see Fig. 13. There, a turn to PS is computed. The open side door is now exposed to the sea, but the vessel has turned into a head wind condition. The ship is - like in the scenario suggested by Wendel - not exposed to the beam wind anymore, and the heeling moment becomes smaller. The main difference between the two scenarios is that now, the water is entrapped in the vehicle deck, as the ship heels to PS. This heeling increases the freeboard further, and the situation converges into a condition where the amount of water on deck does not increase further. The ship remains stable at about 25 Degree heel to port side, where about 500 t of floodwater have now accumulated on the deck. It is quite probable that this manoeuvre - a turn to PS - would have saved the vehicle deck from being completely flooded. 5.3 Conclusions for the water ingress The numerical simulations of the water ingress into the vehicle deck have shown reasonable results. The re computation of the accident scenario have shown that based on our assumptions, the vehicle deck is flooded and the ship takes a large heel. But the simulations have also shown that the ship was not necessarily lost when the refer truck opened the side door: The ship had some residual stability left even with the flooded vehicle deck, and if the heeling moment could have been reduced, the capsizing might have been prevented. The dynamics of the roll motion plus the wind heeling moment plus the moment of the tippled cars was too severe, and the residual stability was then lost. But the calculations have also shown that the ship could have been saved if the crew had turned her immediately to port side. In this situation, the open side door would have been directly exposed to the sea, which would have resulted in a PS heel. This PS heel would have led to a stable equilibrium floating condition with about 500 t of water entrapped in the vehicle deck, and the ship would have - according to our computations - survived. 6. CONCLUSIONS Figure 13: Time plot of the roll angle (top) and the volume in the vehicle compartment (sum of the curves in the bottom plot), alternative scenario The capsizing accident of SS HERAKLION was analyzed with numerical methods. It could be shown that the application of such methods to marine casualties - even if they are some time ago - can show new facets of such accidents that are worth a scientific investigation. In the present case, the accident

11 Ships and Ocean Vehicles, 2328 September 2012, Athens, Greece, 11 analysis came to a plausible event chain which is in line with the known facts and the observations of surviving witnesses. This is most important with respect to actual marine casualties, as it is important to use only validated methods and procedures for the evaluation of such accidents. The evaluation of the capsizing event of SS HERAKLION could plausibly show that it might have been possible to avoid the accident by operational measures, and this finding might be of some use with respect to the education of seafarers. However, the accident of SS HERAKLION has also shown that several safety rules were not followed, and it is most important that we obey all the existing rules strictly: All maritime casualties which we have investigated at our institute always showed a massive violation of existing safety regulations. 7. ACKNOWLEDMENTS The authors wish to thank Prof. Dr. Ing. S. Kastner, Univ. Bremen, for having initiated this work. We further thank Prof. Dr.- Ing. A. Papanikolau, Ship Design Laboraratory, NTUA for the excellent cooperation. 8. REFERENCES Addendum No 5 (Original in Greece) Grim, O "Beitrag zum Problem des Schiffes im Seegang". Schiffstechnik 1960 Fragoulis, 1967, " Expertise on the Sinking of SS HERAKLION". AEENA, Official Investigation Report, Athens 1967, Addendum No. 2, (Original in Greece) Kluwe, F. Krüger, S. 2008, "Evaluation of Minimum Stability Requirements for Ships in Following Seas taking into account Dynamic Effects. PROC. JSTG 2008 Petey, F 1988, "Ermittlung der Kentersicherheit lecker Schiffe im Seegang aus Bewegungssimulationen." Rep Inst. F. Schiffbau, Univ. Teuscher, C 2011, "Technische Untersuchung des Seeunfalles von MS HERAKLION unter besonderer Berücksichtigung des dynamischen Verhaltens im Seegang", BSc Thesis, TU Hamburg Harburg, 2011 Wendel K. 1970, Gutachten über den Untergang des Fährschiffes HERAKLION (Expertise on the Foundering of the Ferry HERAKLION., Inst. F. Schiffbau. TU Hamburg- Harburg, 1970 AEENA (Hellenic Maritime Accident Investigation Board) 1967 Official Report HERAKLION, Original in Greece, 1967, Athens BSU Bundesstelle für Seeunfalluntersuchung (Federal Bureau of Maritime Casualty Investigation) 2010,"Untergang des FK ORTGAL UNO am 13. Januar 2010 westlich von Irland (Foundering of FK ORTEGAL UNO 13th of January, 2010, west of Ireland). BSU Report 07/10, Hamburg, Germany Georgiadis, S. Antoniou A 1967, " Expertise on the Sinking of SS HERAKLION". AEENA, Official Investigation Report, Athens 1967,