1. Introduction
Ship accidents often result in significant property damage and environmental harm, including severe marine pollution from oil spills and long-lasting ecosystem damage. In cases of explosions or fires, rescue operations are often delayed compared to land-based incidents, leading to increased casualties (Weng and Yang, 2015;Zhang and Thai, 2016;Wu et al., 2017). Advancements in technology have made it possible to investigate collisions using data from Voyage Data Recorders (VDR) and the Automatic Identification System (AIS). However, smaller vessels, such as recreational fishing boats and commercial fishing vessels, often lack these technologies or disable their AIS during operations, complicating accident investigations. Moreover, some vessels involved in accidents may flee the scene to evade liability for the damages caused, including those related to environmental conservation and property restitution. In such instances, forensic analysis of ship paint can provide critical evidence to help identify the responsible vessel and support the investigation into the collision.
The analysis of paint samples collected from collision sites is a critical method for determining ship collisions. Paint composition uniformity and friction traces on the ship's exterior provide vital evidence. However, the analysis is challenging due to the limited sample size, the complexity of chemical components, and the harsh marine environment. Techniques such as Fourier Transform Infrared Spectroscopy (FT-IR) to identify resin components, Raman Microscopy to analyze pigments and additives, Pyrolysis-GC/MS for distinguishing polymer binders, and SEM-EDS for elemental composition comparisons are commonly employed (Burgio et al., 2000;Caddy, 2001;Buzzini et al., 2006;Wampler, 2006;Zięba-Palus et al., 2008). These methods enable a detailed examination of ship paints, despite the difficulties posed by factors such as seawater corrosion, multi-layered paint systems, and physicochemical characteristics of anticorrosive (AC) and antifouling (AF) paints.
Ship paints are uniquely designed to endure highly corrosive marine environments, unlike paints used for buildings or vehicles. They must protect against seawater exposure, UV radiation, and mechanical damage while allowing easy repair of partial damage (Berendsen, 1998;Konstantinou and Albanis, 2004;Almeida et al., 2007;Thomas and Brooks, 2010). AC paints are typically applied to the lower layers of a ship to prevent rust formation on iron plates, which is critical in corrosive conditions (Kalendová et al., 2006;Amara et al., 2018). Meanwhile, AF paints prevent the attachment of marine organisms, such as barnacles and weeds, to submerged ship surfaces, reducing drag and improving fuel efficiency. Without AF paints, increased friction can lead to up to a 40% rise in fuel consumption, which in turn amplifies harmful gas emissions (Berendsen, 1998;Amara et al., 2018).
Understanding the characteristics and environmental peculiarities of ship paint, and conducting an analysis based on this understanding, plays a crucial role in determining the cause of ship accidents, particularly in collision incidents where identification through VDR or AIS data may be challenging. This study also aims to provide an educational guideline addressing the complexities and specificities of paint analysis in ship collision incidents, especially ship paint sampling including paint characteristics. This study discusses the considerations for sample collection and analysis due to factors such as the composition and characteristics of ship paints, ship painting features, environmental conditions (temperature, salinity, etc.), and paint leaching phenomena. Additionally, collision scenario was experimentally simulated using commercially available ship paints to evaluate the complexities encountered in post-collision paint analysis. The findings highlight the importance of professional training in the understanding, sampling, and analysis of ship paints, as well as the need for clear guidelines to ensure accurate results in ship paint analysis.
2. Materials and Methods
2.1 Sample preparation for collision scenario
To evaluate the complexities encountered in post-collision paint analysis, collision scenario was experimentally simulated using commercially available ship paints. Comprehensive analyses, including IR spectroscopy and SEM-EDS, were performed to determine the composition and characteristics of the collected samples.
To conduct a collision simulation experiment, two commercially available ship paints were purchased. The two paints were applied on an iron plate of dimensions 14 × 10 cm according to the ship painting criteria, and the plates were dried completely (Fig. 1). Next, friction was caused between the plates to produce a friction trace like that in a ship-to-ship collision, and paint samples were collected from the area of friction according to the analytical procedures. Although the collision intensity and mechanism in actual ship collision accidents may vary, both vessels in the experiment exhibited visible scratch marks and paint detachment, indicating a level of impact sufficient to cause mutual abrasion. For the purpose of analysis, the two test samples used in the collision experiment were designated as the damaged ship (SA) and the offending ship (SB).
The ship paint morphology and friction traces were observed using a Leica microscope (Leica, M205C), obtaining images with the following camera settings: exposure time 30 ms, gain value 1.0, saturation 1.50, and gamma 0.58.
2.2 Paint analysis
The fourier transform infrared spectroscopy (FT-IR) was performed to analyse the paint resin. The FT-IR spectra were obtained at 32 scans, resolution 16 in wave number range of 4000 ~ 650 cm-1 , using the attenuated total reflectance (ATR, ZnSe crystal, Thermo iN10). Further, the scanning electron microscope - energy dispersive X-ray spectrometer (SEM-EDS) was performed to analyze solid materials. The samples were scanned and the elemental compositions were determined using the scanning electron microscope HITACHI S-3400N equipped with an energy dispersive X-ray spectrometer SK09WOXN. Samples were collected from all 10 parts and used for analysis, and representative values are presented in the paper. Representative values were selected based on recurring outcomes, with both singular and mixed cases reported. Mixed values, which are a key focus of the main text (Figure 7), were represented by samples exhibiting clearly distinguishable mixing characteristics
3. Results and discussion
3.1 Appropriate Sample Collection Considerations
3.1.1 Accident and sampling of ship paint
Ship paints are crucial for analytical investigations involving collisions, as they help identify the potential contact between the offending and damaged materials. Chemical analyses of ship paint are conducted in three primary scenarios: ship-to-ship collisions (Fig. 2(a)), ship-to-structure collisions (e.g., buoys, Fig. 2(b)), and damage caused by fishing gear from suspect ships (Fig. 2(c)).
Sampling Methodology: In ship-to-ship collisions, the paint samples must be carefully collected from the collision area. It is crucial to use non-reactive tools, such as stainless-steel scrapers or tweezers, to prevent contamination from external sources. Paint samples should be collected from multiple locations along the collision site to ensure representative data, especially in areas with varying degrees of paint damage. To minimize cross-contamination, it is recommended to use clean gloves and to store each sample in separate, labeled containers. When collecting paint from a ship's hull, care should be taken to avoid disturbing areas that may have been exposed to environmental elements, such as seawater or marine organisms, which could alter the chemical composition of the paint.
In ship-to-ship collisions, the collision area can be identified when the paint colors between the suspect and the damaged ship differ, facilitating evidence collection. However, most antifouling paints contain copper, which imparts a reddish-brown color, making it challenging to visually detect collision areas between ships using similar copper-containing paints. Historically, paints containing zinc oxide, copper, or organotin were preferred due to their excellent antifouling properties. However, the biological toxicity of organotin has led to restrictions and an increase in the use of cuprous oxide (Cu2O) as a key component in modern antifouling paints, which has resulted in a higher prevalence of reddish-brown ship hulls (Peres et al., 2015;Zhao et al., 2016;Faÿ et al., 2019;Pérez et al., 2019).
In cases of fishing gear damage, paint fragments from the ship often conglomerate with fishing gear or ropes during friction events, complicating the isolation of ship paint samples (Fig. 3). Sample collection from fishing gear requires extra care to avoid contamination from surrounding debris or marine life. Fishing gear should be gently cleaned to remove surface contaminants before collecting paint samples, ensuring that the paint is the only material being analyzed. Special attention should be given to the fact that paint fragments may adhere to fibers such as polypropylene(PP) or polyethylene(PE), complicating isolation. In these cases, a fine powder of paint may adhere to the fibers, and separation techniques such as centrifugation or washing with a non-polar solvent could be applied to help isolate the paint particles.
Additives such as solid powders (e.g., talc, clay, glass, Al(OH)3), SiO2, CaCO3, BaSO4, TiO2, and Ca3(PO4)2 are commonly used to enhance paint flow, antifouling properties, and surface aesthetics. Additional antifouling additives include compounds of Zn, Cu, and Si (Peres et al., 2015;Zhao et al., 2016;Faÿ et al., 2019;Pérez et al., 2019). Ship paints are generally soft and low in hardness due to their solid material content, while increased solid content results in powder-like properties.
Fishing gear typically consists of fibers like polypropylene (PP) and polyethylene (PE). These fibers exhibit negligible absorptivity and hygroscopicity, with strong water repellency, durability, and quick-drying properties. Ropes used in fishing gear are composed of PP-based fibers, which form intertwined microfibers to enhance connection strength. When paint fragments in fine powder form adhere to these microfilaments, isolating the suspect ship’s paint traces becomes difficult. Moreover, a minimal sample size may produce insufficient signals for meaningful interpretation, while larger sample quantities risk contamination with other materials. To address this, sample handling protocols should include measures to avoid excessive manipulation and contamination. Handling should be done in a clean, controlled environment, and samples should be kept sealed in inert containers until analysis. Analytical evidence containing mixed ship paints and other substances often results in overlapping Fourier-transform infrared (FT-IR) spectroscopy. This necessitates careful exclusion of the damaged material’s composition data, especially when analyzing trace microparticles. The expertise and experience of investigators significantly influence results, as the sampling process greatly impacts the final outcome.
3.1.2 Ship Painting and Paint Characteristics
Ships are regularly repainted due to the highly corrosive marine environment caused by high-salinity seawater. Without anticorrosion and antifouling paints, iron plates on ships corrode, increasing friction between the ship and seawater, reducing speed, and causing economic losses. To mitigate these effects, ships undergo periodic maintenance at repair dockyards, where new paint is often applied over existing layers. The repainting intervals vary from months to years depending on the paint type and application method.
Advanced antifouling technologies, such as self-polishing copolymer (SPC) paints, are widely used. These paints help sequentially shed outer layers during sailing, preventing marine organism adhesion but creating non-uniform surfaces (Lee, 2010;Yang et al., 2014;IMO, 2001). Consequently, ships that undergo periodic repainting, experience partial paint loss, and are exposed to extreme salinity often develop heterogeneous paint surfaces. Fig. 4 illustrates ship paint samples collected from the same ship and location, revealing 2–4 distinct paint layers. FT-IR analysis of the topmost layer (Fig. 5) demonstrates heterogeneity in resin components, even within samples from identical locations. Differences were observed in areas with and without top-layer paint loss (Fig. 5(a)–(c)), attributed to extreme salinity and marine organism adhesion.
While controlled analysis of the topmost layer’s recently applied paint may suggest uniformity, older paint layers may persist due to low hardness and brittleness, leading to partial losses. Post-collision, paint transfer from damaged to offending ships is less likely when the topmost paint layer is partially lost. Thus, paint analysis must account for diverse scenarios and complex conditions during ship accidents. During sample collection, experts should carefully document the layers present on the ship’s hull for layer identification. Paint layers should be categorized based on their relative age and condition (recently applied, partially eroded, or degraded).
3.1.3 Ship Paint Leaching
Impact of Environmental Conditions on Leaching Rate: Salinity is one of the most significant factors influencing the leaching rate of copper and zinc from antifouling paints. In high-salinity conditions, the solubility of copper increases, leading to its faster dissolution into the surrounding seawater. It has been observed that in regions with a salinity of 27 PSU, the leaching rate of copper is almost three times higher compared to areas with salinity levels of 6 PSU (ranging from 6.4 to 7.5 PSU) (Laidlaw and Woods Hole Marine Oceano Inst., 1952;De la Court, 1988;Lagerström et al., 2020). In regions with even higher salinity, such as the South Korean Sea, where salinity levels average between 32.1 and 33.7 PSU, the rate of copper leaching from ship hull paints is significantly accelerated (Korea Meteorological Administration). Similarly, water temperature also plays a crucial role, as warmer seawater enhances the solubility of metals, thereby increasing the leaching rate (De la Court, 1988;Lagerström et al., 2020). Therefore, when interpreting ship paint samples, both salinity and temperature conditions must be carefully considered, as these factors can have a substantial impact on the residual copper content.
Furthermore, different types of antifouling paints exhibit varying leaching rates based on their chemical composition. Paints containing cuprous oxide (Cu₂O) release copper ions more readily compared to those containing other antifouling compounds such as zinc pyrithione or organotin derivatives (Kwon et al., 2015). As a result, ships using high-Cu₂O-based antifouling paints are more likely to exhibit higher copper concentrations in the surrounding seawater, which may be useful for analyst in identifying paint traces left at collision sites.
Temporal Discrepancies and Environmental Factors: Delayed identification of suspect ships increases the likelihood of discrepancies between the paint samples collected from friction traces on the damaged ship and those obtained from the suspect ship. Over time, especially if the ship has been exposed to high-salinity waters for extended periods, copper leaching may reduce the copper content in the paint of the offending ship.
Consequently, analyst must consider the temporal characteristics of paint leaching as well as environmental factors such as salinity, temperature, and the type of antifouling paint used. Data on copper leaching rates in various environmental conditions, including those reported in regions with different salinity and temperature levels, can provide valuable insights for forensic investigators. Such data can help to interpret the residual copper content accurately and mitigate potential deviations in the analysis.
3.2 Paint analysis according to collision scenario
To demonstrate the complexities that may arise in paint analysis following a ship accident, a virtual collision experiment was conducted using commercially available ship paints. In this chapter, we compare two essential and widely employed analytical techniques, FT-IR and SEM-EDS, to highlight their effectiveness in such analyses.
3.2.1 Composition of each ship paint
An experiment to simulate an actual ship-to-ship collision accident was conducted with a subsequent post-collision paint analysis, and the possibility of uniformity determination was discussed. The goal of the experiment is to highlight the complexity in analyzing the paint composition uniformity in an actual ship collision accident. The cases where the area of collision could be identified based on colour variation were excluded, and two types of ship paints of a uniform colour were used in the experiment.
An FT-IR analysis was performed for the composition analysis of the paints used in the experiment, and the results are presented in Fig. 6. The SA ship paint produced the characteristic peaks of epoxy resins at 1607 cm-1(C=C stretching aromatic ring), 1510 cm-1(C–C stretching of aromatic ring), 1248 cm-1(n aromatic C-O), 1183 cm-1(C–O aromatic ring stretching), 1035 cm-1(n aromatic C-O), 915 cm-1(C–O oxirane stretching), 831 cm-1(Aromatic absorbance)(Kiil et al., 2002;Cholake et al., 2014;Lagerström et al., 2020). The SB ship paint produced the characteristic peaks at 1728 cm-1(C=O stretching), 1182, 1116, 1072 cm-1(C-O stretching), 880 cm-1(C-H bending), while it contained copper, barium, and inorganic materials. An SEM-EDS analysis was performed for these paints(not shown). Here, C, O, Al, Si, and Fe were observed in the SA, while C, O, Mg, S, Cu, and Ba were detected as the main elements in the SB. The additives to enhance the flow of the ship paint mixture as well as the antifouling function, and for a cosmetic purpose, were also observed. Except for the elements C and O, the components of SA and SB varied.
3.2.2 Paint analysis for determination of collision
Because of the characteristics of ship paints with a high content of solid materials, low level of hardness, and a high level of brittleness, even a little force could generate a collision trace (SA: damaged ship; SB: offending ship) (Fig. 7). However, as the colour was uniformly reddish brown, the discrimination between SA and SB paints were not as easy as the detection of the collision trace. In an actual ship collision accident, even in the case wherein the colours of paints of the damaged and offending ships are identical, the layered painting in each ship is frequently observed (Fig. 4). This further increases the complexity of a collision accident between two ships with an identical colour.
An FT-IR analysis was performed on the samples collected from the areas displaying severe collision traces, (Fig. 7). Fig. 7(a)-(b) shows the IR spectra for the ship paints that detached from the area of friction in SA and the ship that is set as the damaged ship. Fig. 7(c)-(d) shows the IR spectra for the ship paints detached from the area of friction in SB, and the ship that is set as the offending ship. The patterns of IR spectra between the paint traces collected from the area of friction in the damaged and offending ships were similar (Fig. 7(a),(d)). This is an ideal result in a forensic chemical analysis, and it may imply the potential intercollision if the control paint is detected in the test paint.
However, the microparticles collected from the area of friction displayed a mixed state of IR peaks specific for SA-SB paints (Fig.7(b),(c)). For an easy comparison of IR peaks, the peaks were marked with arrows. The red and purple arrows indicate the SB-and SA-specific peaks, respectively. The peaks exhibited by both paints were excluded from the comparison. In detail, in contrast to the near-perfect agreement in the resin components of SB (Fig. 7(a)), the microparticles that were detached from the area of friction in SA showed the paint components of SA (purple arrow; Fig. 7(b)), and vice versa (Fig. 7(c)). This problem is caused by the collection of a mixed state of the two paints that shared highly similar colours, which is a common phenomenon in the analysis related to ship accidents that involve high levels of reddish-brown paints. In such cases, the paint resin components between the damaged and offending ships may be identified only if there is a variation in paint resin. Even in the case of different paint resin components, the content ratio between SA and SB cannot be obtained from the IR spectra, and only the level of the proportion each paint can be checked; the mixing ratio cannot be obtained from the IR spectra.
The discrimination of paints may be easy because the simulated collision scenarios imply that the characteristics of the paints used in the experiment are known. If the paint analysis was performed on a blind sample from the ship paints with a diverse history consisting of multiple layers, the analysis would not have been as easy. In the case of identical paint colours and resin components between the damaged and offending ships, trace amounts of paints may be analyzed and compared for the purpose of discrimination. To identify various trace components contained within the paint matrix, pyrolysis-GC/MS analysis can be conducted. Additionally, SEM-EDS analysis may be employed to characterize the types of solid components present in the paint and to estimate their relative distribution, thereby enabling a more detailed and precise analysis.
4. Conclusion
To provide an educational guideline for ship paint analysis, this study examined various factors influencing the analytical process, including the composition and characteristics of ship paints, painting methods, environmental conditions (e.g., temperature, salinity), and paint leaching phenomena. Considering these variables, collected ship paint samples were analyzed using multiple techniques, and the results are expected to play a critical role in determining whether a ship collision occurred.
Furthermore, an experimental collision scenario was simulated using commercially available marine coatings to evaluate the complexities encountered in post-collision paint analysis. The findings indicated that, although differentiation between visually similar paints is possible based on resin composition, accurate sampling—particularly from areas of frictional contact—and careful consideration of external variables are essential to ensure reliable results. In many instances, the frequent mixing of similarly colored paints in collected samples posed substantial challenges. In real-world scenarios, the presence of multiple paint layers with similar chemical compositions further complicates the analysis.
Given these challenges, future research should focus on refining sampling methodologies and developing advanced analytical techniques tailored to the unique characteristics of marine coatings. Immediate sample collection following incidents, along with comprehensive background investigations, is crucial to minimizing the influence of external factors. Moreover, an interdisciplinary approach that integrates forensic chemistry with maritime engineering holds significant potential for enhancing the reliability and efficiency of ship paint analysis. Addressing these areas will contribute to more definitive and timely conclusions in ship collision investigations.
