M/S Cruiser Sea Diamond (former Bikra Princess) sank on April 6^th, 2007 a few hundred meters away from the commercial harbour of “Athenio” in Santorini “Thera” island alias “Thira”, in “caldera” location, in “Athenio” bay. The day before the incident the vessel ran aground on reefs which resulted in a 20 m long crack to be formed at the ship’s hull stabilizer level. That caused seawater inflow to the lower decks in huge amounts. The wreckage was fatal, given that two of the passengers aboard are declared missing ever since.

The vessel incurred severe environmental pollution at least the first months after the occurrence of the naval accident. Oil spillage polluted the nearby coastline whilst antipollution experts attempted for a long time to constrain the pollutants’ fate with controversially results. Despite the strenuous efforts in 2009 to pump out marine fuel oil and lubricants contained in numerous ship’s tanks, the results were poor and significant quantities of oil sludge, lubricants, hydraulic fluids, marine fuel oil not to mention significant heavy metal quantities as structural part of electrical and electronic devices mounted on the ship, still remain to be removed in an indeterminate future period [1]. Ever since, in the vicinity of the wreckage, sea body column and sea basin sediment are being environmentally monitored by the Technical University of Crete [2] [3] and the National Centre of Marine Research (NCMR) [4] [5].

The present study was financed by the Greek Public Authorities and accomplished for the purposes of the Appeal Court decision of the city of Piraeus. The Court assigned a judicial technical report to be conducted so that a clear assessment to be made for the condition of the wreckage in environmental terms and the formulation of a prognosis of the corrosion evolution process along with the endurance of the hull before wiping out in the sea bottom. Two judicial environmental experts enlisted in First Instance Court Catalogues of Piraeus, coordinated a multi-disciplinary scientific team to visit the island of Thira. Prior to sampling and hull survey, an autopsy took place to evaluate the surrounding in the vicinity of the spot of the fatal sea accident.

Based on videos and high-quality photos taken from ROV inspection, iron plates’ analysis was made along with the use of corrosion prediction computer modeling¹⁴. The scope was to be estimated the wreck condition at that time, expressed as the following introduced outcome i.e. as the plates’ total thickness loss or the “time-to-perforation” or even the remaining thickness of the main structural plates and thereof remaining vessel’s life before wiping out. “Remaining life” in our case is the time required for seawater corrosion to “consume” or corrode away the remaining thickness of the superstructure, the deck and the hull plate. In the absence of SRB¹⁵/IOB¹⁶, the remaining life is equivalent to the time-to-perforation. The time-to-perforation is the time required for localized corrosion i.e. pitting to perforate the remaining thickness under the worst-case scenario when SRB and/or IOB are present on the wreck.

CO₂Compass-SE (Shipwreck Edition, Version 9.18©), a commercially available computer modeling and prediction software is used to model the effects of seawater physicochemical parameters [62]. The scope of corrosion model implementation was the assessment of the structural plates situation at the inspection time given as follows:

1) Corrosion rate estimation of the hull plate thickness loss in (mm·y⁻¹).

2) Corrosion rate estimation of the superstructural thickness loss in (mm·y⁻¹).

3) Assessment of the effect of Zn sacrificial anode/(ICCP)¹⁷, coatings, (Figure 12, Figure 13) and the developed microorganism’s film on the deterioration of the superstructure, deck and hull’s plates.

4) Estimation of the remaining time life—in years—due to seawater corrosion phenomena, and perforation advance (consumption), to the detriment of super-structural, deck and hull’s plates initial thickness.

The parameter values, assumptions and their respective values are used as inputs in CO2Compass-SE corrosion prediction software (Table 19, Table 20). Corrosion of iron and steel in seawater is influenced by the seawater chemistry which varies with water depth [63] [64]. The shipwreck is at a water depth ranging from 86 m to 147 m, with an average depth of about 117 m. It is well established that both (DO) and temperature decrease with water depth increase in deep seas (Figure 14). Salinity and chlorinity are considered convertible and either parameter was required as corrosion modeling input. Hull coating is co-estimated in model prediction, since it plays a vital inhibition role to the sea corrosion advance (Figure 15 & Table 21) [65].

The original design thickness of steel plate used for the superstructure (deck 9 and above) is 6.0 mm (Figure 15). The remaining thickness as on July the 5th (of the inspection year) was 4.86 mm. With the assumption that the seawater physicochemical parameters will not undergo significant changes in the future, the remaining superstructure (deck 9 and above) would disappear in 108 years period running from the inspection time reference and beyond. Superstructure between decks 9 to 6 (Figure 15), would disappear in 120 years and superstructure between decks 6 to 5 would disappear in 145 years.

Most of the hull plate would disappear in about 300 years period. One zone of the hull plate located at (BWL)¹⁸ between decks 2 and 1 would take from 345 up to 608 years to be consumed (wiped out) due to the fact that its initial design thickness at certain parts is at least 4 times higher than that of the superstructure.

In the presence of SRB and/or IOB microorganisms, under the worst-case scenario, localized deep pitting would have already perforated the shell plate in the superstructure from deck 9 and above. The time-to-perforation for the hull plate varies from 8 to 38 years depending on the initial design & structural thickness of the plates. There is no evidence whatsoever to indicate SRB/IOB presence on the hull at the inspection time. However, the predicted time-to-perforation under worst case scenario i.e. when SRB/IOB are present should be adopted when assessing the risk of the fate of toxic agents in the waterbody.

The predicted corrosion rate is estimated to be 0.07 (mm·y⁻¹) which implies that carbon steel structures such as hull plates, deck plates and superstructural plates have undergone 1.158 mm thickness overall loss, over the past 12.25 years due to seawater corrosion. The remaining life (from 5th of July 2019 onwards) for the 10 mm thickness plate is 208 years, meaning that the superstructure, deck and hull plates given the original design thickness of 10 mm will be consumed by seawater corrosion in 208 years (Figure 16, Figure 17). The above under the assumption of a prevailing water current velocity of 33 (cm·s⁻¹).

Corrosion prediction at water current velocity of 13 (cm·s⁻¹) in 2009 with SRB/IOB presence, indicates that the predicted remaining life of the structures due to sea corrosion is 223 year from 2009 onwards (Figure 18). Corrosion model results can be summarized below:

According to the Appeal Court’s Decision, an environmental assessment of the water body and a judicial technical report should be conducted by a team comprised of two judicial environmentalists. They were assigned to conduct the survey, the sampling and supervise chemical analyses. Finally, they took over the obligation to compile within a time limit and file the final report.

The results of chemical analyses indicate that in a perimeter within 150 - 300 m pointing the center of an imaginary circle on the surface spot above the vessel’s hull stigma, heavy metals concentration detected in many predetermined sampling spots. The results were significantly higher compared to the ones of a certain sample, taken purposely from a remote spot considered it as the “reference” sample.

PAHs, TPHs are, in general, low or below detectable level in the sea column. The only exception appeared to be a couple of samples taken from a scuba diver, member of the scientific group, during the 2nd sampling attempt when considerable quantities of TPHs and a PAH (naphthalene) were measured. Given that PAHs were detected merely in one sampling station, it considered not to be of local ambient biogenic origin. The vicinity to the wreck support strongly the approach that TPHs results could be attributed to the presence of the wreckage in the area as random entrapped oil-based releases from the vessels’ hull. PCBs were not detected in the sampling area.

As regards heavy metals concentration level in aquatic sea column, the results indicate that, apart from (Fe) conc. which was expected given the volcanic seabed sedimentation background, only in certain locations heavy metals i.e. (Pb) and (Ni) were measured above the detection limit.

Sea bed sediment sampling presents a high fluctuation of heavy metals not correlated in between which is an obstacle to draw solid conclusions. High fluctuation is rather explainable since the region of our interest was susceptible to side effected parameters such as the high local sea traffic (highly touristic sea channel), the environmental interaction with the relatively close distanced commercial port of “Athinio”, subsurface sea currents and former mining activities in the near coastline.

Sampling analyses in seabed sediments indicate that the Contamination Factor (CF) regarding the mid Earth (Crust), referring to (Cd) and (Pb) pollutant agents correspond to a moderate up to a very high contamination level state (CF > 6) which is more or less in accordance with (I_geo) index as regards the preindustrial period shale concentration. The modified contamination degree (mC_d) solidifies a moderate to high level contamination state. (PLI) consolidate an overall very low contamination state.

(Pb) and (Ni) conc. were detected inbound offshore booms along with rare sampling stations. (Cd) can be justified by the dispersion and fate of marine fuel oil remnants. Steel hull plates consisting mostly of alloys Fe-Cu-Cr-Ni-Mo, according to ASTM standards, are in an advanced state to provide oxides and provoke extended ion mobilization in the seawater body. Ongoing physico-biochemical interaction of electrical and electronic devices of the M/S cruise might give rise to pollutant elements and justify considerable detected conc. Engaged heavy metal compounds, transformed into mobile complex ions incur gradually degradation of the aquatic ecosystem quality.

Organotin compounds as a part of the biocidal hull protecting layer are not our case since Sea Diamond’s hull was layered, already, by ecofriendly antifouling coating on an early stage. Marine HFO contains sufficient traces of V and Ni which are not measured in the seawater column. According to EU Regulation No 1881/2006, (Hg), (Cd) and (Pb) in fish stock samples were below the detected limits.

CO2Compass®-SE Version 9.18 software implementation for sea corrosion, predicts perforation of hull plate at localized spots providing SRB/IOB presence within (8 - 38 years) whereas the exposure of the double bottom hull is expected to occur in ~295 years period.

We gratefully thank the public local authorities of the municipality of Thira “Santorini” that supported substantially the project in accordance with the Piraeus tri-member Appeal Court board. We are also grateful to the “Topical Steering Committee for the Sea Diamond Removal” who were steadily supportive and encouraging in every way for the completion of our assignment.

The authors declare no conflicts of interest regarding the publication of this paper.

Giakoumatos, S.D.V. and Kalogirou, E.N. (2020) “Sea Diamond” Wreckage—12 Years after the Fatal Maritime Accident, the Vessel Remains an Environmental Concern. Open Journal of Ecology, 10, 537-570. https://doi.org/10.4236/oje.2020.108034