Challenges to Accident Prevention for High-Speed Vessels Used in the Brazilian Amazon

Abstract

The Brazilian Amazon has one of the largest river networks in the world, connecting riverine communities, many of which have no roadways. The use of high-speed vessels, including those that are locally made, is necessary for the transportation of people to perform their day-to-day activities. However, regional news and social media data have shown that these vessels are involved in accidents. This work describes some of the key challenges to improving the sustainability and safety of regional high-speed vessels. Field research was performed in the state of Amazonas to document regional vessels and provide graphic evidence of the possible risk factors that could cause accidents as the path to prevent them. Some risk mitigation alternatives were discussed. Cameras and a drone were used to capture information either from the shore or from small boats. The main challenges are related to the adequate management of seasonal changes in river depths; wave and wind behavior; wave wash effects; the interaction of vessels with rocks, sand banks, mud, and vegetation; embarkation and disembarkation activities; the monitoring and regulation of safety requirements and dangerous operations; and the slowness in implementing technological advances that would improve vessels’ safety. It is hoped that the work in this paper will contribute to improving the sustainability of marine activities in the Amazon and similar regions worldwide.

1. Introduction

The Amazon region has one of the largest hydrological systems in the world, the Amazon River basin, of approximately 6 million km². This system has diverse floodplains, wetlands, and some of the largest rivers in the world, such as the Solimões–Amazonas, Madeira, and Negro Rivers [1]. The former flows into the Atlantic Ocean with an average annual discharge of 206 × 10³ m²s⁻¹ [1,2]. Most of the Amazon hydrological system is in Brazil, in which many types of vessels carry out the day-to-day activities of vital social and economic importance. Among them, it is common to find medium- and small-size vessels that can operate at high speeds. Due to the vast size of the region and the complexity of its waterways to access remote communities, the use of these vehicles is of significant relevance in transporting people in a shorter time than the larger passenger vessels. This effectiveness is crucial for performing daily activities such as getting to places of education, health, and emergency; for security; and policing, fishing, and the commerce of refrigerated products, as well as environmental research. However, although regulation activities are frequently performed by regional authorities [3,4], these vessels are often involved in accidents (Appendix A). It is, therefore, important to increase the research into the possible causes of these accidents and suggest changes that can be made to prevent them.

Many types of vessels that operate in the Brazilian Amazon have been designed and built in the region using empirical knowledge from previous experience, rather than recent, applied scientific approaches (these vessels are described as regional vessels in this study).

The vessels in the Amazon can operate at different velocities according to their size. For example, large ships such as gaiolas and ferryboats have been developed to transport significant amounts of cargo and passengers between major cities of the region, as described by [5]. That work described the main characteristics of these vessels and made recommendations to improve their safety and efficiency. On the other hand, there are also many smaller vessels that can transport fewer passengers at higher speeds. Among them, high-speed regional vessels, known as expressos (or ajatos), rabetas, voadeiras, and cabin boats (like ambulanchas and lanchas escolares) as described by [6], can also be found. Moreover, other types of high-speed vessels, including small yachts, military ships, boats equipped with control stabilizers, and waterjet-driven vessels, are also used. Regarding regional high-speed vessels in the Brazilian Amazon, Neto et al. [6] presented a preliminary classification of the most common types considering the maritime regulations applicable [7].

Normally, small regional vessels have lower costs than modern or imported vessels. This advantage, combined with the ease of construction and the scarcity of roadways between Amazonian cities, means that even in remote locations, there is an abundance of such high-speed boats. They are often the only means of transportation, allowing basic activities to take place. Unfortunately, it is difficult to monitor all the vessels to ensure they meet safety requirements and perform operations safely.

The safe and efficient use of high-speed vessels can present several challenges. Faltinsen [8] explains many of these, highlighting the importance of research into the design of these crafts and their uses. The author stresses the importance of improving steering control and maneuverability so that they perform well despite dynamic instabilities. The structural integrity and the safety of crew and passengers in high-speed vessels can also be affected by dynamic instabilities and other operational problems such as the impact of the hull with water (slamming [9,10]), the shipping of water on the deck [11,12], surf-riding and broaching [13], and rapid accelerations [14].

Due to the challenges found in guaranteeing safer operations of high-speed vessels, the IMO, which regulates marine activities worldwide, has developed conventions on technical requirements to be met by high-speed vessels, such as the International Code of Safety of High-Speed Crafts, 2000 HSC Code [15]. However, it is not mandatory that signatory countries implement these codes completely in their national regulations.

Regarding the international scenario, Antão and Guedes Soares [16] studied the causes of accidents involving high-speed crafts compared to ocean-going vessels. They pointed out the need for improvements in navigational equipment and procedures for high-speed vessels such as catamarans, hydrofoils, hovercraft, monohulls, surface effect ships (SES), and SWATH (small-waterplane-area twin hull) ships. The results of this research suggest that fatal accidents can occur due to capsizing or listing, collision, fire or explosion, flooding, grounding, damage in heavy weather, mechanical failure, and other factors.

A comparison of risk factors for conventional and high-speed ferry boats in Spain was performed by Louro et al. [17]. They found that risk factors in accidents were often associated with a lack of time for journeys; the poor maintenance of ships and equipment; and crew routines that can lead to overconfidence, fatigue, and the performance of multiple functions. Crew routines can be affected as the size of crews could be reduced and supervision of onboard activities could be scarce.

The consequences of high-speed accidents have been studied by Lam et al. [18] in terms of injury patterns following ferry accidents in Hong Kong waters. They showed that the high-speed vessels may have a greater impact compared to the conventional ones because of the potential for more severe human injuries. It was reported that the most common injuries were neck sprains, dental injuries, lumbar and back sprains, femoral and neck fractures, lower limb lesions, and head and neck injuries. As a general recommendation of the authors, to reduce the number of injuries and deaths, the availability of life jackets and the mandatory use of seatbelts were encouraged.

In terms of accident prevention for inland navigation in the Amazon region, Padovezi [19] highlighted human factors and environmental challenges as a cause of accidents in the region. More recently, Fontes et al. [5] discussed the main factors contributing to accidents involving long-distance vessels on Amazon waterways. This work presented accident statistics as well as a list of possible social, technical, and environmental factors that should be considered in accident prevention initiatives focused on these vessels. Subsequently, Fontes et al. [20] discussed the possible environmental impacts of shipping accidents in the Amazon region. Also considering large vessels, de Souza et al. [21] discussed the main challenges for freight transport on the Madeira River, an important route for the transport of agricultural products from central Brazil. More recently, Marinho et al. [22] discussed the importance of considering human factors in accident prevention alternatives in the Amazon region. Regarding regional high-speed vessels, Soares [23] described problems related to ship-generated waves caused by medium-sized, high-speed vessels, which can affect the stability of small boats or swimmers, as well as contribute to the erosion of riverbanks. Hydrodynamic analyses of long-distance expresso-type vessels were presented by [24,25,26]. Furthermore, the dynamics of rabeta and voadeira boats were investigated by [27,28], respectively. From information found in these works and in the regional media, such as [29,30,31], it is evident that further research into high-speed vessels in the Amazon region is still necessary to mitigate the risks and increase the safety of these vessels. This is also necessary if Brazil is to meet the United Nations sustainable development goals (SGSs, [32]) related to ensuring healthy lives and promoting well-being for all at all ages (third SDG target).

This work aims to identify and document some of the main challenges to be considered in initiatives aimed at preventing accidents involving high-speed regional vessels in the Brazilian Amazon. Field surveys, graphic evidence, and literature reviews were carried out to identify and discuss the key risk factors and some alternatives to mitigation in terms of accident prevention. The research includes descriptions of the main types of high-speed vessels found in the Brazilian Amazon; however, the challenges discussed can be applied to a wide range of vessel types. The surveys were carried out in some cities of the State of Amazonas, considered as representative of the Brazilian Amazon, using cameras and drones to document risk situations. This paper complements the knowledge of previous works related to marine accidents in the Amazon, such as [5,20], highlighting the challenges to be overcome in the prevention of accidents involving high-speed vessels operating in the Amazon waterways.

The paper is structured as follows: Section 2 presents the methodology followed, including a description of the regional study case and the methods employed for the surveys. Section 3 gives a description of the main types of high-speed vessels currently found in the region. Section 4 presents the results and a discussion of the challenges identified, which are grouped in subsections. At the end of each subsection, the key risk factors and alternatives to mitigate them are discussed. Finally, Section 5 presents the main conclusions of the research.

2. Methodology

This research was performed through some fieldwork campaigns to identify the main challenges in accident prevention for regional high-speed vessels in the Brazilian Amazon. From these campaigns, the documented evidence is presented and discussed in the results section. Literature reviews were also performed. The following paragraphs describe the methods employed in these phases of the research.

Regarding the study area, the State of Amazonas, in the central Amazon forest, was considered for a case study, representative of the Brazilian Amazon (Figure 1). It has a network of rivers that are essential for the economic development of northern Brazil, with the main being used for navigation, such as the Negro, Solimões, and Amazonas. The latter is considered the largest river in the world in terms of drained area [33,34]. It has an estimated length of 6900 km, discharging a mean of 31 ton/s of sediments into the Atlantic Ocean [35].

According to the demographic census of 2022, the State of Amazonas has an area of 1.559 × 10⁶ km², a resident population of 3,941,000 inhabitants, and a demographic density of 2.53 inhabitants per km² [36]. Its capital and economic center is Manaus, with an area of 11.401 × 10³ km² and a population of 2,063,000 inhabitants [37]. The main activities are related to services and agricultural and manufacturing industries. In 2021, it was ranked fifth of the cities with the most GDP (gross domestic product) in Brazil [38]. Manaus serves as a hub for several transportation routes in the central Amazon forest, supporting vessels that navigate the rivers to other cities and to tiny communities in the region.

Figure 1. The State of Amazonas in northern Brazil. Source: Instituto Brasileiro de Geografia e Estatistica—IBGE [39]. The figure was used with the authorization of IGBE (protocol number 20240905004).

Figure 1. The State of Amazonas in northern Brazil. Source: Instituto Brasileiro de Geografia e Estatistica—IBGE [39]. The figure was used with the authorization of IGBE (protocol number 20240905004).

With respect to the field research, it was performed between April 2023 and August 2024. Pictures and videos were taken around the cities of Careiro, Iranduba, Itacoatiara, Manacapuru, Manaus, Novo Airão, and Parintins using cell phone cameras, a professional camera (Canon EOS R50), and a drone (DJI Mini 4 Pro). These specific areas were chosen to obtain information on representative rivers around Manaus (Negro, Solimões, and Amazonas Rivers). Information from the survey included some examples of high-speed vessels being used in different cities, as well as evidence of the main challenges that need to be considered for accident prevention. Some of the images were captured from the riverbank, whereas others were from the vantage point of small vessels, including rabeta and voadeira boats. The most representative images were selected for discussion purposes.

To support the findings and discuss the challenges identified, information from the literature was consulted, including local news, academic works, journal, and congress papers, as well as social media. In addition, databases and editorials, such as Elsevier, Springer, Wiley, MDPI, Google Scholar, and Web of Science, were consulted to find more scientific literature on the topics identified as challenges. The search words included the name of the challenge identified, and marine accident-related terms. Maritime regulations applicable in the Brazilian Amazon were also consulted. These Brazilian Navy Maritime Authority Norms (NORMAM) are available in [40], and include the main procedures established by the conventions of the IMO, of which Brazil is a signatory. Information regarding the geographical and statistical aspects of the Amazon region from the Brazilian Institute of Geography and Statistics [41] was also consulted.

3. Regional High-Speed Vessels

The field surveys enabled the documentation of the main high-speed regional vessels commonly navigating in the Brazilian Amazon. Regional vessels are medium-size and relatively small passenger boats that have been built in the region, predominantly by local artisans who rely on previous knowledge for the boat’s design and construction [6]. Common crafts of this kind are locally known as expresso, ambulancha, lancha escolar, voadeira, and rabeta according to the preliminary classification made by [6]. Appendix B summarizes a technical explanation of these vessels. Figure 2 shows some illustrative examples of the vessels found in the cities of Manaus and Iranduba (Figure 2a–e), Itacoatiara (Figure 2f–j), and Parintins (Figure 2k–o) during the surveys.

Expressos are long vessels, typically constructed from aluminum or a combination of aluminum and lightweight materials, such as wood and fiberglass. They are used for the transportation of passengers over long distances between major cities in the Brazilian Amazon. Expressos can carry dozens of passengers in a shorter time than other types of vessels, such as recreios or regional ferryboats. Further information on expressos can be found in [5]. Sometimes, these vessels are also modified, opening the rear part of the superstructure to allow cargo transport. Shorter versions of expressos are regionally known as miniexpressos.

The ambulancha and lancha escolar are cabin boats, frequently utilized for the purposes of healthcare and emergency transport, as well as for conveying students to and from educational institutions, respectively. These boats feature a covered section or superstructure, which provides protection from environmental conditions. These vessels are constructed from aluminum or fiberglass and are equipped with outboard engines. These boats offer essential services to the population and are generally operated by regional governments. Other applications include policing and environmental monitoring. Cabin boats are also used by private companies for providing commercial services, or for recreational purposes. Some research regarding the activities and hydrodynamic performance of this type of vessel can be found in [42,43].

The voadeira is a small, simple vessel featuring a hull made of lightweight materials and a sunroof. They have an outboard engine, which enables them to navigate to isolated locations quickly and commonly to accommodate up to ten passengers. These vessels are common in the Amazon region and are frequently used for transporting between riverine communities, performing recreational activities, or being employed by local governments and the service industry. In some cases, larger regional boats are equipped with voadeira as auxiliary vessels. Some versions of voadeira in the region are known as bote, canoa, and lancha.

The vessels known as rabeta can be defined as the most economical and, probably, the most widely used motorized boat in riverine communities in the Brazilian Amazon. These are generally constructed by local artisans or small shipyards, relying on their practical experience and expertise, mainly by following previous models. Rabeta hulls are typically built of aluminum or wood and have propulsion systems that comprise a conventional gasoline motor at the stern that drives a protruding shaft with a simplified propeller. The propellers of these vessels are also manufactured in the region and are readily available for purchase in city markets and tool stores.

It is important to mention that besides the vessels described above, other types of high-speed vessels are also present in the Amazon region, including small yachts, military ships, and waterjet-driven vessels, as described by [28]. In this framework, the risk factors discussed below are applicable to all kinds of high-speed vessels existing in the Brazilian Amazon.

4. The Main Challenges to Prevent Accidents with Regional High-Speed Vessels

The field survey performed in the state of Amazonas highlighted several risk factors that should be addressed when planning accident prevention initiatives related to regional high-speed vessels in the Brazilian Amazon waterways. The following subsections present these challenges and discuss some alternatives for risk mitigation.

4.1. Seasonal Variations in the River Basin

The hydrography of the Amazon basin is subject to significant seasonal variations throughout the year. One of the main risks encountered by vessels navigating in these waters is the variability in river depth that occurs between the wet and dry seasons [44,45]. Maciel et al. [46] emphasized the urgent need to plan proactive conservation measures to safeguard the ecological integrity of the Amazon following recent environmental crises, such as the severe 2023/2024 drought that affected Amazonian rivers and floodplains. According to these authors, significant variations in the open water extent were observed due to the two worst droughts recorded in the Amazon region, which occurred lately in 2020 and 2023, as well as the extreme flood that occurred in 2021. In the current year, international news also have alerted that extreme flooding and droughts are becoming relevant challenges for Amazon people and ecosystems [47].

In the Brazilian Amazon, the recent decrease in river levels during the dry season has affected the transportation of people and cargo on many rivers, causing socioeconomic impacts in the main cities and remote communities. This has resulted in delays in deliveries and contributed to the occurrence of accidents such as grounding, which have led to the loss of cargo [48].

The images in Figure 3 show an example of the seasonal variations affecting river levels. The pictures were captured at different points in time during the dry and wet seasons of the Negro River. Figure 3a was taken in November 2023, an extremely dry period. In certain locations, the riverbed is visible, comprising a mixture of sand, mud, and vegetation, making navigation difficult even at low speeds. Figure 3b, taken 40 days later, at the same location, shows how much the level of the water level has risen. By May 2024, Figure 3c, the Negro River had reached a surface elevation that inundated the vegetation.

The images seen in Figure 3 are only some examples of the drastic changes in water levels that have occurred in the Amazon rivers in recent years. Other reports on the same problem have been published recently in international media, including [49]. During the 2023 dry season (Figure 3a), extensive wildfires resulted in a haze that impaired visibility across multiple regions, causing some parts of the Amazon basin to be filled with smoke, inducing a loss of visibility that affected navigation. In 2024, wildfires in the dry season have caused comparable effects [50]. The increased difficulties brought about by the recent alarming variations in river depths have led local governments to establish committees to develop risk prevention strategies [51] in an effort to minimize the consequences of these changes.

The key risk factors due to seasonal variations for the operation of high-speed vessels relate to the reduction in visibility due to wildfires and the reduction in river depths during dry seasons, both of which may cause grounding or collisions (see Section 4.4).

Sustainable development initiatives regarding climate variability and change in the Amazon basin are being considered by the Brazilian government through the funding of research applied to the Amazon, as in [52]. Internationally, this is also being undertaken through a project called Amazon Basin, supported by the Amazon Cooperation Treaty Organization (ACTO, [53]), an intergovernmental organization formed by the eight Amazon countries: Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname, and Venezuela. It is hoped that similar initiatives, supported by government or independent organizations, will promote research and development activities that increase the safety and sustainability of marine operations in Amazon waterways, including the effects caused by seasonal variability.

4.2. Wave and Wind Behavior

Waves and winds may induce forces and moments that affect the stability and dynamics of marine vehicles. At high speeds, these interactions can be even more dangerous, resulting in dynamic instabilities [8]. Although scarcely documented, extreme meteorological events in the Amazon are numerous and recurrent on a short-term scale, including convective storms with electrical discharges, intense gusts of wind, hail, and torrential precipitation [54]. These events have the potential to cause substantial surface waves that can affect the dynamics and stability of small vessels.

Wave steepness is one of the factors that could most affect the stability of a vessel. Obviously, the operation of high-speed vessels in the open sea is more affected by steep waves than such craft in the Brazilian Amazon, where constant amplified waves do not occur. In normal circumstances, the free surface of the rivers exhibits minimal wave activity, as seen in Figure 4a. However, strong winds and waves with considerable elevations are indeed possible, as illustrated in Figure 4b.

In the Brazilian Amazon, operations of vessels in inland navigation are mainly regulated by the Maritime Authority Norms (NORMAM 202, [3]), which classifies the inland navigation areas. In sheltered areas (Area 1), such as rivers, channels, lakes, lagoons, and bays, significant wave heights are not usually found, so it is assumed that waves do not present a challenge for vessels. However, in areas with reduced shelter (Area 2), wind, currents, waves, or tides can impact navigation. This is mainly the eastern Amazon, close to the Atlantic Ocean, where it is recommended that small vessels refrain from operation during harsh environmental conditions. Notwithstanding, the sheer size of the region and the complexity of the river network make it difficult to monitor the operation of high-speed vessels in such conditions.

The Amazon basin is characterized by a tropical climate, with a prevalence of sunny days. However, during extreme environmental conditions, irregular wave states can be formed, as seen in Figure 4b, affecting the operation of high-speed vessels that operate on long-distance routes for several uninterrupted hours, such as expressos.

It has recently been reported [56] that during convective storms, there are downdrafts with enough force to snap or completely uproot trees in a phenomenon known as windthrow. Similar phenomena have also been reported, such as downbursts by [57], which are defined as intense winds that can reach speeds of up to 100 mph and can damage forests, structures, and buildings, including those in the Amazon. These events could contribute to hazardous conditions on waterways; however, detailed research on the effects of these winds on the behavior of marine vessels and resulting accidents has not been reported in the literature. Furthermore, to the best of the authors’ knowledge, there is no detailed monitoring of wave height variations in Amazonian rivers at specific locations and in severe environmental conditions. However, local news and social media have documented instances of regional vessels experiencing distress during such events, as seen in Figure 4b. Moreover, some reports of shipping accidents in the region in which the presence of adverse environmental conditions has been suggested prior to the accidents have been reported (e.g., [58]).

The key risk factors associated with the interaction of high-speed vessels with waves and wind relate to dynamic events, as explained by [59]. These can include slamming [60], wave overtopping [61], unpredicted bending moments and shearing forces that can cause structural damage [62], and high acceleration. The latter should be within acceptable limits to ensure crew and passenger safety [14,63]. Other problems, defined by [8], include the reduction in steering control and the occurrence of dynamic instabilities.

Risk mitigation strategies could include more scientific research, led by academic institutions, to gain a deeper understanding of the stability and dynamics of regional high-speed vessels. It is important to better understand the resonant conditions of their motions, as well as their response to different types of wave and wind environments. This can be achieved by numerical or experimental approaches to analyze their behavior in regular and irregular waves of varying periods and amplitudes. However, it will be difficult to monitor in more detail the variation in wave heights and wind velocities in the various navigation areas, as well as, perhaps, a characterization of wave and wind energy in the main navigation zones.

It is worth mentioning some of the initiatives to increase the monitoring of meteorological activity in the Amazon region. These include the SELVA (Electronic Environmental Surveillance System, [64]) and SIPAMHIDRO (Integrated Hydrometeorological Monitoring and Alert System, [65]) projects. The former is mainly focused on monitoring air quality, whereas the latter integrates data from different monitoring sources, providing information about meteorological events, river depth variations, probability of rain, and flooding risks, among other variables. However, no local measurements of waves by buoys or similar devices are provided. Although monitoring waves by a pilot buoy in Negro River has been tried in [66], more initiatives are required to measure this type of data over long periods for several points in the Amazon region.

4.3. Ship-Generated Waves

When a ship moves through a body of water, it disturbs its free surface, generating wave trains that propagate away from the ship [67]. As the velocity of the vessel increases, the amplitude of these waves tends to increase, becoming more energetic [8]. These waves can yield some issues, particularly in enclosed water bodies, as they can interact with other vessels, small floating objects, and people swimming nearby. Ship-generated waves also can interact with riverbanks, contributing to sediment resuspension and shoreline erosion, as well as impacting aquatic ecosystems [68]. This phenomenon, known as wave wash or wake wash, is important in investigating safety risks in ship operations and environmental conservation approaches [69,70,71].

In Figure 5, the waves generated by a variety of high-speed vessels in the Amazon region are shown. Figure 5a shows the wave trains created by three vessels in a wide river. Figure 5b,c show the wakes formed by rabetas in the calm waters of different rivers. In Figure 5c a bare riverbank, without vegetation, is seen. Perhaps the repeated, energetic interaction of waves can affect this type of riverbank, contributing to erosion. This is more clearly demonstrated in Figure 5d, where an expresso-type vessel can be seen leaving a substantial wake in a narrow river. Figure 5e–h illustrate how different types of floating bodies are exposed to the interaction with ship-generated waves.

Risk factors related to ship-generated waves are the effect that the incident waves can cause on the dynamics of other ships and floating structures, particularly small ones; interaction with the riverbank, which can contribute to erosion processes; and the safety of the people who are involved in aquatic activities nearby without lifesaving gear.

Risk mitigation initiatives must include the evaluation and monitoring of the heights and energy of ship-generated waves to establish adequate speed limits, as proposed by [72]. In some works (e.g., [69,73]), regulating the speed of ships has been proposed to reduce wave heights, and thereby reduce the energetic process caused by the waves (i.e., the wave wash criterion). More research into establishing adequate operating speed limits and characterizing the waves generated by high-speed vessels through analytical, numerical, and experimental work could help to create safer operating practices in the Amazon region. The role of academia is fundamental in furthering research into these topics, as is the support of government and the private sector in funding these initiatives.

4.4. Risks from Rocks, Sand Banks, Mud and Vegetation

The navigation of all types of vessels in the Amazon river system presents operational risks related to their interaction with different bodies, including the possibility of collision with rocks, impact or grounding on sand banks, or interaction with mud and vegetation. High-speed vessels are usually made of light materials and are susceptible to severe damage in these interactions because of the speed at which they operate. These interactions also may cause injuries and risks to the crew and passengers. Possible damage to the vessels includes perforation of the hull, which can induce capsizing or flooding, or affect stability and contribute to their wrecking. In addition, the efficiency of the propulsion system can be reduced during the interactions, affecting the maneuverability of the vessels.

In the dry season, when water levels are lower, increased exposure to rocks and sand banks can increase the risk of accidents for high-speed vessels. The presence of rocks is not always apparent, as illustrated in Figure 6a, but rocks close to the shore, which are submerged during the wet season, and thus invisible, can pose a significant hazard and cause severe collisions. Figure 6b illustrates an example of large rocks, invisible during the wet season. Impacts and groundings also may occur in the dry season when sand banks become more exposed, forming large beaches or unexpected underwater dunes, as seen in Figure 6c.

Navigation in mud (Figure 6d), which is common in the dry season, is also a risk since it can reduce the efficiency of the propulsion system or cause damage to the propeller.

During the wet season, other risks arise in restricted waterways limited by vegetation, where forests are partially flooded and only small vessels can operate, as seen in Figure 6e. In such instances, vessels moving fast can easily collide with submerged vegetation. It is also common to observe isolated tree branches adrift in the water (Figure 6f), which can pose a collision hazard and cause damage to the vessels. Also, vegetation is often seen floating on the river surface in the wet season, including trunks of considerable size (Figure 6g) and plants (Figure 6h).

The vegetation that can be found in these environments can become caught in the propeller (Figure 6i), which can result in a reduction in propulsive efficiency. Collisions with tree trunks, branches, or rocks can cause damage to the propulsion system (Figure 6j) and damage the main body of high-speed vessels, which are usually constructed from lightweight materials, such as aluminum, wood, or fiberglass.

Risk mitigation strategies should consider that Amazon rivers have variable geomorphology, which also depends on physical, topographic, and climatic variables, as presented by [74]. Sediment transport is also relevant in many rivers, such as the Solimões and Madeira [21], as it can contribute to the formation of sand banks and fluid muds of variable concentration, thickness, and distribution [75,76]. Changes in sediment concentration in the rivers of the Amazon region have also been attributed to deforestation [77].

It should also be taken into consideration that the recent extreme droughts have contributed to the appearance of new rocky areas [78], and that the presence of vegetation, during the wet and dry seasons, is a frequent challenge to navigation. To lessen the risk of accidents, it is suggested that vessel operators must have zones of risk clearly identified for them. However, this will need collaboration between the government and maritime authorities. Another option would be to improve bathymetric knowledge of the Amazon rivers; however, it may be complex given the high sediment concentration and transport in many Amazon rivers, as well as the vast distances to be mapped. Dredging is being considered by Brazilian government agencies to improve the main navigation routes due to the recent historic droughts [79,80]; however, this type of activity would be expensive and, in many areas, would require environmental impact analysis.

Improved signposting would help to identify danger areas, as well as to reduce operational speeds. Alternative modes of propulsion could be a longer-term aim for research, offering other means of navigating muddy waters or areas with floating vegetation.

Academic research into innovations in regional high-speed vessels is called for. Topics related to this challenge could include structural design through simulation tools evaluating impact conditions [81]; research into the use of more resistant and sustainable materials in the fabrication of vessels; and the use of alternative navigation technologies to detect risk situations [82].

4.5. Accessibility

In the Amazon waterways, the availability of infrastructure for accessing ships is a significant challenge, given the scarcity of suitable facilities, as described by [83], who classified the accessibility in some regions in the Amazon. The seasonal variations in the water levels, as well as difficulties in reaching remote locations, can reduce operational efficiency and pose a serious risk to the safety of passengers and crews when embarking and disembarking high-speed and other types of vessels.

In the dry season, access to vessels may mean walking downhill, sometimes for extended distances and with considerable personal baggage, as the rivers represent the main mode of transportation for most Amazon communities (Figure 7a–c). This may be impossible for some passengers, having significant social implications.

In the large urban centers, such as Manaus, private marinas with appropriate means of access facilities can be found, offering shelter for small high-speed vessels. However, it is necessary to pay monthly sheltering fees.

In many cases, high-speed vessels are moored at very simple fixed, or floating, installations, as shown in Figure 7d and Figure 7e, respectively. Boarding infrastructure that accommodates changes in the water level of the river may be available in the main ports of some cities, such as the articulated floating structures used for large cargo and passenger ships shown in Figure 7f. In the absence of docking infrastructure, vessels are moored next to the riverbank, as seen in Figure 7g.

Risk factors include the lack of adequate access jetties, which can be dangerous for passengers as well as lead to the erosion of the riverbank. Floating jetties, formed of a series of wooden boards, are common, especially in the wet season (Figure 7h); however, access to all people by these means can be challenging, since they could keep underwater during eventual motions of the free surface of the water, as in wave interactions.

Improving the accessibility to high-speed vessels in the Amazon region is a serious challenge, as the Amazon waterways are very extensive, with variations in the river levels through the year, and boarding infrastructure that is suitable for different passenger needs is still necessary. Government and industry participation in improving accessibility should be continued at the existing facilities to make access safe for all people, and the monitoring of embarking and disembarking procedures should be increased to prevent accidents. Academia can contribute to studying the alternatives available, as well as researching the development of innovative embarking structures, including portable boarding jetties that can be installed in remote locations or carried inside high-speed vessels.

4.6. Supervision and Regulation

The main conventions and procedures for regulating the safety and sustainability of marine activities in Brazil, including the operation of vessels, come from the IMO, which also aims to meet the United Nations Sustainability Goals [84]. These regulations are mainly implemented by the Brazilian Navy through Maritime Authority norms (NORMAM, [40]), which also apply to high-speed vessels operating in the Amazon region. However, there are other authorities concerned with inland navigation in the Amazon, such as the National Water Transport Agency (ANTAQ), linked to the Ministry of Infrastructure, which is responsible for the regulation, tariff control, study, and development of water transport in Brazil. Regarding environmental aspects, the Institute of Environmental Protection of the Amazon (IPAAM) is a state authority in charge of implementing national and state environmental policies. Statistics on marine accidents in Brazil are also recorded by the Brazilian Navy, as explained in Appendix A. The operation of high-speed vessels in the Brazilian Amazon may require more attention to identify risks to the safety of people. Unlike large cargo and passenger vessels operating in the Amazon waterways, the supervision and regulation of the activities of smaller and faster vessels can be more complicated because of the ease with which they can be built, operated, and hidden, as well as the fact that they can access remote locations, often at high speeds.

Several riverine communities depend almost entirely on small high-speed vessels, such as rabetas or voadeiras, as these are often the sole means of transporting goods and people. However, activities posing a risk to safety can be seen in Figure 8a–d. Often, small boats hitch onto larger, slower vessels to sell or exchange local products, such as fish or fruits, as shown in Figure 8a,b. Risk situations can occur when people of all ages use motorized small boats to perform these activities without safety equipment.

The overloading of high-speed vessels is also common, as seen in Figure 8c,d. This may considerably reduce the freeboard of the vessels, affecting their stability and making them more likely to take in water from the waves generated by other craft. Apart from this, poor waterproofing of the submerged hull of the vessel may also contribute to flooding, resulting in the loss of stability and sinking. Many high-speed vessels have light hulls made of aluminum or wood, very susceptible to damage when involved in collisions. The vulnerability of many riverine communities to hazards related to the lack of suitable materials and construction methods for vessels cannot be disregarded.

Situations involving the use of volatile products, or fire, can be especially dangerous if the vessels are made of wood. High-speed vessels in the Amazon often go to floating gas stations for fuel; these are also susceptible to accidents, such as explosion or fire, as recently reported in [85].

Risk mitigation strategies should consider the dissemination of safety recommendations and regulations for high-speed vessel operations. The role of government is crucial to continue initiatives to prevent accidents and the application of regulations. For example, considerable efforts have been made by regional authorities to provide basic safety items for riverine communities [86]. Nevertheless, the size and topography of the Amazon basin, combined with the abundance of small high-speed boats, make it difficult to check on all the existing vessels in the region. It is suggested that the provision of basic training to operators, the dissemination of technical information to shipbuilders, and the donation of basic safety items to riverine communities be supported and continued.

4.7. Technical and Scientific Knowledge Implementation

The design and building of many regional high-speed vessels in the Brazilian Amazon are typically based on previous experience, with no or little application of recent technical and scientific knowledge. Modifications are frequently made to the existing designs according to the shipowner’s requirements, with little consideration for experimental or numerical analysis to improve hydrodynamic and structural performance.

Figure 9a,b show examples of repair work to expresso vessels in dry and floating docks, respectively. There are many shipyards on the banks of the Amazon rivers, including those that are well established and certified and those that perform empirical repairs with limited inspection [87,88]. There is little documented research into innovations regarding the design, construction, and performance of regional high-speed boats based on technological and scientific advances. In recent years, some academic works on these topics have been published by the two universities in the Brazilian Amazon that offer undergraduate courses in Naval Architecture and Marine Engineering: the Federal University of Pará (UFPA) and the State University of Amazonas (UEA), e.g., [25,26,27,89]. However, there are still gaps that have not been analyzed and documented technically, which would improve the safety and sustainability of regional high-speed vessels, as pointed out by [43]. For example, the use of recent technologies to improve navigation safety (e.g., 4.0 industry-related technologies [82,90]) or to improve steering and maneuverability [8] could be evaluated.

The area of hydrodynamics, including ship resistance, dynamic behavior, and instabilities, in high-speed marine vessels is worthy of investigation, as highlighted by Faltinsen [8]. Further attention is also required on propulsion systems, structural behavior, steering control, and safety requirements to reduce risks to high-speed vessels. Finally, more specific regulations released from IMO conventions, such as the HSC 2000 Code [15], could provide guidelines for more rigorous requirements for the safety and operability of regional high-speed vessels. Academia, government, and industry should support technological development and research projects to improve the safety, efficiency, and sustainability of regional vessels. These initiatives could be based on achieving the United Nations sustainable development goals [84] and encouraging cleaner and more sustainable technologies for the operation of vessels, as in [91].

5. Conclusions

The objective of this research was to identify the principal challenges to the prevention of accidents involving high-speed vessels in the Amazonian waterways. Evidence of potential challenges was collated with a view to facilitating a discussion of the existing gaps and possible solutions, aiming to contribute to the generation of scientific literature that can support decision making.

The challenges were classified as follows: seasonal variations; behavior in waves and wind; ship-generated waves; interaction with rocks, sand banks, mud, and vegetation; accessibility; supervision and regulation of dangerous activities and safety requirements; and the reluctance to apply recent technical and scientific knowledge.

The seasonal variations in conditions for marine activities in the Amazon are currently a cause of concern. In particular, the navigation depths which contribute to the risk of collisions with rocks, sand dunes, and vegetation are of increasing importance. Improved bathymetry, the erection of warning signs, and dredging are potential solutions to reduce the incidence of accidents; however, the viability of such projects would be needed.

The study of vessel behavior in waves and wind, as well as with ship-generated waves, would provide evidence on dynamic instabilities that could potentially lead to serious accidents in severe weather conditions. It is imperative that the application of specialized technical and scientific knowledge in these areas be supported.

The accessibility to vessels requires attention; sometimes no viable alternative exists for all people. Improving boarding zones, including those in remote areas, would have a positive social impact.

Increasing the monitoring of dangerous activities and safety requirements for the existing fleet of high-speed vessels in the Brazilian Amazon is a challenging task, mainly due to the size and topography of the region and the sheer number of such vessels. Donating safety items, instruction, and divulgation of information amongst riverine communities should be continued and encouraged.

Specific areas for future research may include the effects of seasonal variations on vessel behavior, the characterization of the mechanical behavior of vessels (hydrodynamic and structural) under different load and operation conditions, and planning strategies to implement maritime legislation.

Prioritization could relate to reducing social and environmental impacts caused by vessel accidents, and increasing the efficiency, safety, and sustainability of high-speed, and other, vessels operating in the Amazon.

Finally, the possible means of reducing the number of accidents involving regional high-speed vessels may include greater involvement from governmental, industrial, and academic sources to establish risk mitigation initiatives. Joint projects into the increase in the safety of marine activities in the Amazon waterways, as well as promoting the divulgation of safety procedures and good practices for vessel operations, should be considered. Increasing investment in scientific and technological development, particularly in the design, innovation, and construction of regional vessels, is imperative if we are to improve efficiency, safety, and sustainability. This would require further support from funding agencies, especially for the implementation of recent technologies.

It is hoped that this research will be useful to decision makers, providing a foundation for new lines of research that prioritize sustainability in the riverine activities of the Amazon region.