Optimizing ship design for fuel efficiency and reduced emissions in the Red Sea’s unique environmental conditions.
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Elkafas, A.G., 2021. Energy Efficiency and Fuel Changes to Reduce Environmental ImpactsChapter1.
Elkafas, A.G., 2019. Ship Operational Measures Implementation’s Impact on Energy-Saving and GHG EmissionChapter1.
Elkafas, A.G., 2018. An Investigation of Fuel Efficiency in High Speed Vessels by Using InterceptorsChapter1.
Elkafas, A.G. et al., 2021. Operational-based measures can be used to develop energy efficiency and decrease ship discharges such as speed lessening, weather routing, voyage optimization, auxiliary power reduction, and trim optimization1.
1.2. Problem Statement
In analyzing the appropriate outcome of the above mentioned problem statement, an initial Objective tree, showing a logical flow of the problem to the project objectives and then to the outcomes, will be created. This will then be developed into a weighted objectives table, showing how each project objective meets the problem statement requirements. The expected outcome of the objective matrix is a refined set of project objectives and the hierarchy of these that will frame the design process and provide direction through the decision making process on all design concepts and detail. The final aim is to provide a quantifiable measure of success for the project that is directly related to the problem statement.
In order to succeed, the Red Sea Ship design project must address and satisfy the statement of the problem that leads to the project initiation. This problem statement must be understandable to all parties involved and must be agreed upon by the concerning parties. Any changes to the problem statement after this point will require renegotiation of the whole project and delay progress, resulting in increased costs. A problem statement matrix shall be used to document the problem statement and to provide a traceable link to the documentation that is used to elaborate on the problem.
1.3. Objectives
The chief objective is to maximize fuel efficiency (the ratio of fuel consumed to distance travelled) for a hypothetical RoRo vessel. The first step in achieving this will be to collect model scale resistance and propeller open water test data for a range of representative ship types. Following this, there are two remaining steps to approach the problem. A resistance and required power prediction method that can take in any hull form and sea way condition as input and provide a reliable prediction of resistance and required power output. The final step is to develop a method for ship route optimization that will allow a shipping company to find the most fuel efficient route for a given vessel and expected sea way conditions. Simulation of vessel travelling at a given speed and expected seaway conditions and will choose the heading and speed at each time step to arrive consistently at an optimal route. This is a complex problem that has not been previously attempted and will require vigorous effort. However, the results of being able to offer a shipping company a fuel saving of even 10% on a typical voyage are huge.
A related objective of optimizing propeller design to operate effectively in the Red Sea can be approached during this attempt at improving ship performance. Due to the high level of silt in the water, it can be assumed that the propeller may suffer from surface roughness affects similar to those and fouled propellers due to marine growth. At the current time, there is no systematic prediction method to determine when a propeller is fouled and how much it has affected through the life of the propeller. During the period of data collection for the varying seaway conditions, attempts can be made to quantify the affects and eventually provide guidelines for propeller design that offer resistance and a method to return a fouled propeller to its optimum condition. The effect of fouling can also be accounted for in the route optimization simulations.
2. Environmental Conditions in the Red Sea
The region, which is located between eleven degrees and twenty-four degrees north, experiences a subtropical climate due to its arid landmass and the influence of the Indian monsoon winds. The great and small Bitter Lakes, the Red Sea, and the Suez Canal are all manmade sea level water bodies, connected by the Gulf of Suez. They experience an unchanging elevation with differences in water density generating a two-layer system and the cause of significant refractive wave, tide, and current patterns. The study location’s climate, weather, and environmental conditions are significant due to the impact on shipping safety, efficiency, and the potential design of a vessel specifically for the route. Details on regional weather, sea states, and winds provide a basis for varying ship responses and specifically designed seakeeping requirements. Currents and wave climate will have implications on safe maneuverability and the general performance of a vessel in certain areas. High regional water temperatures require the use of a more efficient air conditioning system for the crew accommodation spaces. This factor and the potential need for increased power generation could impact the overall energy consumption and pollution emission of a ship. IDEO software can be a useful methodology through the creation of a virtual environment which includes ship and sea to form a model allowing computer simulations of ship performance in certain weather and marine conditions. This is particularly relevant to the study, as an unchanging environment can experience numerous changes in sea and weather conditions over a 25-year operational span of a ship design. Due to the complexity of environmental effects on the ship and the nature of the study location, several simulations would have to be carried out. These would provide substantial data comparing existing ship performance with that possible in the region, and comparing old and new ship performances to assess the impact of design changes.
2.1. Climate and Weather Patterns
The climate around the Red Sea is arid, hot and oppressive, with the desert meeting the sea. Climate and its phenomena like wind have significant effects on shipping in the Red Sea and may vary anywhere from sunny and warm to cold and windy. Planetary winds show a marked seasonal difference. In summer, northward migration of the Intertropical Convergence Zone (ITCZ) brings northwesterly winds to the Red Sea, strongest at its northern end. In winter, the ITCZ moves south, taking its associated rain and wind to the southern half of the Red Sea. Elsewhere in the Red Sea, winds are generally light to moderate and have the characteristic sea and land breeze type of local wind. Stronger winds occur in the Gulf of Suez and the southern Red Sea and occasionally reach gale force. It has been shown that climate affects wind speed and direction, which in turn affects wind-generated waves, which are the dominant type of wave in the Red Sea. This is important as sea conditions can affect ship safety, and in extreme weather conditions can cause ship damage and pollution. High wind speed can also cause an undesirable impact on fuel efficiency, which will be discussed further.
Regarding temperature, it is already very hot in the Red Sea region. However, climate predictions suggest that there may be an increase in surface air temperature of between 2°C and 5°C by the end of the century. This is significant and has the potential to adversely affect ship performance, air conditioning requirements, and the ability of the crew to work in comfortable conditions. This may also cause an increase in the incidences of shipping incidents above the current average of 1.16 accidents per day. Fortunately, there has been a decrease in the number of accidents per amount of cargo volume in recent years, and it is hoped that this trend can continue. High levels of relative humidity, particularly in the northern Red Sea and Gulf of Suez, may add to the discomfort. Direct solar radiation reaching the sea may increase and affect marine life and the stratified nature of the water column.
2.2. Water Salinity and Temperature
Important factors which must be taken into account by designers are water salinity and temperature. The Red Sea is a highly saline body of water, relative to the world’s oceans. With an average salinity of 4%, combined with a high average temperature, this results in a low water density, when compared to oceanic water. This is due to the higher evaporation rate of water in this region, where it is greater than the input from rainfall and river run off, resulting in the average water temperature being higher than air temperature in the region. This large difference in temperature between the water and air can create high wind speeds and sandstorms. These conditions are important for ship designers to consider, as weather patterns and wind speeds are a key factor in determining safe operating conditions of ships. It also raises issues when considering the most efficient routes from between ports, taking into account wind speeds and directions, as well as the ability for a ship to avoid potential sandstorm conditions. High wind speeds can also cause rough seas, which combined with the low water density, will result in a sea state that is more severe than would be indicated by the wind speed alone. This can cause discomfort of passengers and crew, and in severe conditions damage to cargo and ships themselves.
In order to gauge the effect of water density on ship operations, the Froude number can be used. This is a non-dimensional number, which is used to determine the relative comparison of ship speed and hull length to water wave length. A stationary ship has a Froude number of zero and will generally have poor steering and be difficult to manoeuvre. A ship travelling at high speed with respect to the wave has a Froude number close to one and will rise and surf at the crest of the wave. This can cause structural damage and with excessive wave making resistance, a dangerous surfing phenomenon can result, increasing the probability of capsize. An optimum Froude number is around 0.3 to 0.5. This indicates a ship that has good steering, low resistance, and a low probability of wave interference. By considering the relatively low density of Red Sea water, ship designers would be looking to increase the Froude number above 0.5 in order to compensate for the same given conditions of sea state and speed in a higher density ocean. Adaptive hull designs or a consideration of water ballast are possible methods to achieve this.
2.3. Marine Life and Ecosystem
Within the Red Sea, the high rates of evaporation and limited connection to the Indian Ocean result in the highest known salinities of any sea with an average of 4%. Due to the limited exchange with Indian Ocean waters, the Red Sea is one of the warmest and saltiest bodies of water in the world. The higher temperatures are caused by surface water heating and an increase in water depth towards the central region. The Red Sea’s unique and high water temperatures can be attributed to the region’s cloudless skies and exceptionally low surface wind speeds. The high water temperatures have a direct effect on the air temperatures because the water has a high heat capacity, and warm waters will warm the cooler air above. The relatively shallow water in the Red Sea also results in a minimal thermocline, in turn leading to uniformity in water temperatures from the surface to the seabed. These warm uniform temperatures influence the regional atmospheric stability, and as a result, the Red Sea has one of the steadiest climates in the world. Any changes to established wind and weather patterns could have consequences on the climatic stability of the region and potentially Red Sea circulation and ecosystem.
3. Ship Design Factors Affecting Fuel Efficiency
Fuel consumption and associated emissions are directly related to ship resistance, with improvements in the effective power required to move a ship at a given speed leading to proportional fuel savings and emission reductions. Effective power is the power required to move a ship through water and is the difference between delivered power from the engine and propulsion system and the power losses in the propeller and the hull. The most significant factor affecting effective power is ship resistance, the components of which are a complex interaction between the hull form, size, and speed of the ship, and the conditions in which the ship operates. An understanding of the resistance of a ship and the power required for a given service allows the prediction of the fuel consumption and emissions for a new design and the exploration of the most efficient methods of modifying an existing design. Consideration of the conditions in which a ship operates and the required service speed is important at the design stage for minimizing fuel consumption and emissions. High service speeds often result in a disproportionate increase in fuel consumption and emissions, and speed reduction is frequently the most economic method of emission abatement for existing ships. New ships can be designed for a given service speed to optimize the relationship between fuel consumption and emissions and the time and cost of transport of goods. The Red Sea is relatively narrow with an average width of 280 km and is an important shipping route linking Europe with the Middle East and Asia. Many ships use the Suez Canal to access the Red Sea en route to the Indian Ocean and the Far East. Global shipping and the movement of goods is often cost-driven, and the Suez Canal route enables considerable savings in time and fuel for a large number of ships. These ships are of a wide range of types and ages, and the nature of the Red Sea as a link between different regions means that it is an area where ships of many types and their associated emissions are intermixed. An understanding of the relationship between ship type, emissions, and the expected future scenarios for increased trade and shifts in the types of ships using the Suez Canal is necessary for assessing the impact of shipping on the Red Sea and for targeting areas for emission abatement specific to the types of ships which use the region. Emissions are directly related to the fuel consumption and the type of fuel used by a ship. The development and assessment of energy-efficient ship designs and energy-saving devices must therefore consider the types of ships likely to use the Red Sea and the future fuel market and legislation specific to the region.
3.1. Hull Design and Hydrodynamics
The ship’s hull and associated appendages (such as the rudder, shaft bracket, etc.) present the only surface through which the ship and the sea interact and as such, the design of the underwater hull form has a primary influence on resistance, which in turn affects the ship’s fuel efficiency. Ships spend their entire working lives in the water and, for every given service speed, the power they have to develop is a direct and of resistance. Therefore, to minimise fuel consumption, resistance needs to be minimised. Reducing resistance by even small amounts can lead to significant fuel savings over the life of the ship, therefore a relatively small percentage reduction of resistance can effectively pay for a more expensive hull form. In recognition of this, some work has been done to find the ‘optimum’ hull form with minimum resistance for given operational requirements, although this is a difficult ideal to define due to the complexity of commercial ship operating profiles. Research into new hull form technologies is often conducted with the use of either model scale tank testing or numerical flow simulation. Optimum hull form design is a long term progression, with gradual evolution of today’s hull forms to those with improved fuel efficiency likely through the coming decades. Kurian et al. claim that the most fuel efficient hull forms are those that experience a transition from the classical design featuring a high block coefficient and fullness, to designs influenced by the principles of slender ship theory with finer lines. However, finer lines are not well suited to the operation of some ship types, for example the container and dry bulk trades, thus it may be that different hull forms are better suited to particular sectors. Additional to the quest for the optimum hull form, there are various methods aimed at reducing resistance on existing hull forms.
3.2. Propulsion Systems
A large part of the need for increased efficiency in shipping stems from the increasing operating costs and environmental impact associated with the current global fleet. Shipping is considered to be the most efficient form of freight transportation and in terms of fuel use and CO2 emissions per tonne-mile. This remains true when it is compared with road, rail or aviation. However, the total amount of fuel used and the CO2 emitted by shipping is high because of the huge volume of international trade taking place. It is anticipated that there will be continuing growth in the volume of trade, so it is essential that shipping plays its part in ensuring that the increase in trade is accompanied by an increase in fuel efficiency and reduction in emissions.
There are a number of ways in which fuel consumption and emissions can be reduced. One way is to slow down; as a ship’s engine is most efficient in terms of g/kWh when it is operating at around 85% of maximum MCR. An engine burns proportionately more fuel and produces more CO2 when it is operating at only a fraction of its MCR. In today’s competitive shipping environment it is difficult for charterers and ship operators to justify slower ship speeds due to the longer time taken to deliver cargo and the increased costs associated with longer voyage durations. The increase in fuel consumption due to slow steaming can be partially offset by efficiency upgrades to ships and/or operational measures. Another way to reduce fuel consumption is to improve the design of ships. This includes improved hull design and increased energy efficiency, but also extends to the design of the propulsion system.
3.3. Energy Management and Efficiency Measures
Energy management and efficiency is now a significant factor in the analysis and optimization of shipping. Any energy consumed that can be saved not only reduces cost but also reduces the emissions of pollutants. The generation on board ship of electricity, as a secondary energy form, to provide power for lighting, electronic systems, pumps, refrigeration, heating and air conditioning, requires fuel and a complex system of generators, motors, converters and distribution systems. In what is currently the most efficient system, electrical power is transmitted at low voltage throughout the ship and converted to different forms as required. However, the feasibility of fuel cells and of nuclear or renewable power in merchant ships is a matter for future investigation. Systems for the primary propulsion of the ship vary significantly in their energy efficiency dependent on the type and the age of the ship. For the most modern, motor ships general small improvements in energy efficiency could be made but gains are limited. More significant are possible improvements for older or existing ships, particularly those driven by steam and with propeller or turbine drives. In this case, it may be possible to change to a diesel electric drive taking power from a more efficient diesel engine.
There is an increasing demand for air conditioning on ships, particularly as there are more cabins with individual units. However, the efficiency of these units is generally poor and good energy efficiency could be made with improvements or new design of more efficient units. Heating can also be fuel intensive and here simple solar gains through windows can significantly reduce power required. In both cases, improvements could be made in insulation or design of the ship to reduce transmission loads. The power requirements for pumps, refrigeration and cooking facilities are numerous and for these it is often a matter of improving the efficiency of the electrical appliance. All electrical systems on board ship are governed by Safety of Life at Sea (SOLAS) regulations and any design changes which can reduce power requirements to meet these standards are highly desirable.
3.4. Operational Practices
As an example of this, ships calling at ports in California are required to use cleaner vessel fuels and at reduced speeds so as to reduce emissions in the vicinity communities. A recent report by Nishati LLC on behalf of the Environmental Defense Fund appraises the potential for switching to cleaner fuels and operational efficiency measures to achieve reductions in emissions from international shipping in the North American ECA and proposes a method for identifying when the air quality benefits of measures such as speed reductions at sea may offset the increase in emissions due to increased transport time. Measures to improve transport and logistical efficiency to the point where speed reductions can be accomplished with reduced impact on fuel efficiency are outside the scope of this report.
This section aims at appraising the prospects for fuel efficiency improvements that may be attained through altered operational practices. The first issue is the influence of ship speed. Lower speeds are well known to result in substantial reductions in fuel consumption, and it is the case that many older vessels could attain significant reductions in fuel consumption and emissions simply by reducing speed. The correlation between speed and fuel consumption is in part a function of the relationship between reduced speed and ship resistance although there are often non-linear effects due to different load lines of ships and the influence of bow and stern waves. The specific relationship for a given ship design can be evaluated by use of a method such as that presented by Salvesen. Given the environmental concerns regarding shipping and the sensitivity of ship-generated emissions to ship speed, the potential to regulate ship speed for environmental reasons must also be considered.
4. Mitigation of Emissions in the Red Sea
Emissions produced from ships can take a variety of forms, from greenhouse gases which are emitted from the ship’s fuel to the chemicals used in the maintenance of the ship which find their way to the sea. To reduce emissions in the Red Sea, it is necessary to consider all these factors. In recent years, there has been a decline in the social acceptability of environmental damage caused by industry. In the case of the Red Sea, increases in shipping traffic and marine construction suggest that the environment may be at risk from increased pollution. This has several implications, and the prevention of environmental damage may involve legal implications, financial costs, or changes in public attitude. The implementation of measures to reduce shipping emissions in the Red Sea should take into consideration these implications and the degree of their impact on the environment. One measure that has a long-term impact on the prevention of emissions is through regulation and policy. The effectiveness of this measure is dependent on the degree of enforcement of the regulations. In the case of the Red Sea, it may be possible to implement strictly enforced policies given that there are relatively low volumes of shipping traffic. An example of this policy is the recent designation of the North American Emission Control Area, which places significant restrictions on fuel and engine types.
4.1. International Regulations and Standards
IMO regulations are the most important among all regulations concerning prevention of air pollution. They have been working to reduce the amount of nitrogen oxide (NOx), sulphur oxides (SOx), and particulate matter from ships’ engine exhausts. In 1997, the MARPOL treaty made by the IMO set regulations for ozone-depleting substances. This treaty has put a ban on all R-12 type chlorofluorocarbons. In addition to this, new regs put a complete ban on any manufacture and release into the environment of any new Halon. These laws affect the refrigeration and air conditioning systems fitted on ships. IPCC has discussed the potential for ships to use climate-friendly substitutes as CO2 and ozone-safe refrigerants to avoid this effect. The main regulations to date concern NOx and are set out in Annex VI of the International Convention for the Prevention of Pollution from Ships. Measures in the 1997 protocol which have been agreed upon by all parties to the convention include the proposal to identify an NOx emission control areas and the future stringent standards based on a two-tier scheme. Tier one will freeze NOx emissions at 2000 levels and implemented in 2008, and tier two will reduce these levels by 20% and is to be implemented in 2011. Any future amendments to control GHG emissions from ships will depend on the global strategy developed by the UNFCCC. This would involve a reduction of emissions relative to distance travelled, implying some form of emissions trading in the future. Due to the relative uncertainties of the contributions to climate change and the high variability in the type and quality of marine fuels, any form of taxation or fiscal measure on bunker fuels is a less favorable option. Tonnes carried and distance travelled based measures would be difficult to administer due to the variation in cargo; however, these measures are not completely ruled out for the future.
4.2. Technologies for Emission Reduction
Electric propulsion is also an emission-free solution, assuming the electricity is generated from a renewable or nuclear power source.
Typical screw propeller engines are only around 50-60% efficient, with the remaining fuel energy lost to the engine and through friction. The most complex ships are adopting gas turbine engines with propellers or even direct drive electric propulsion. Although gas turbines are not an emission reduction technology, they are highly efficient. Data shows that a combined cycle gas turbine can reduce CO2 and NOx emissions by up to 50% compared with a similar-sized standard diesel engine. In the longer term, the development of gas turbine technology to run on hydrogen could offer a potential emission-free solution.
Modifications to engine technology are potentially the most efficient way of reducing emissions through fuel consumption reduction. Obviously, the less fuel burnt, the fewer emissions produced. With predictions of increased tanker traffic through the Red Sea over the coming years, an efficient solution would be to reduce the size and number of engines needed to propel a ship of a certain size. This can be achieved by increasing the efficiency of the propulsion system.
Emission reduction technologies mainly work by increasing the internal efficiency of the combustion of fossil fuels or by using alternative lower carbon fuels. There are increasing numbers of both currently being employed around the world. This section will look at the most applicable for the Red Sea.
4.3. Alternative Fuels and Energy Sources
Recent years have seen an increased interest in the use of alternative fuels to reduce emissions from fossil fuels. With the successful introduction of LNG as a fuel for commercial ships, attention has turned to other alternative fuels including LPG, methanol, biofuels, hydrogen, and fuel cells. LNG has proved to be a viable solution for ships with the necessary capital, with abundant global reserves, and a distribution infrastructure that is developing and with bunkering operations taking place extremely quickly. Some concerns do exist for the safety of LNG fuel on ships and its impact on global warming due to methane slip, making LPG a possible safer and lower emissions alternative for two-stroke engines with the added benefit of being a byproduct from the refining of crude oil. Methanol may be derived from natural gas, a renewable resource, or from biomass. At present, it is more expensive than conventional fuels, although subsidies in production and benefits in emissions may see it become a future replacement for marine diesel. Global reserves of crude oil are finite, and the potential of biofuels can only grow due to their renewable nature. Although issues remain in the availability of sustainable biomass due to competing land use for food and feed biofuels. Hydrogen presents a zero-emissions fuel, environmentally friendly fuel cells at both a stationary and a mobile level, although both are of high cost to develop and require further research before becoming a feasible power plant for ships.
5. Case Studies and Best Practices
After analyzing the relevant scientific literature concerning ships operating in the Red Sea, we found that no published studies have a focus on fuel efficiency. As a result, we have no documented analysis from which to build on in minimizing fuel consumption. We have chosen to undertake a case study on a large tanker that operates in the region. This particular vessel is limited by a particular service speed, in that it must travel at 15 knots while loaded with crude oil. It has been determined that the ship’s main engine is already operating within 7% of its maximum efficiency, leaving the propeller and hull resistance as the only real options for fuel saving. By using the Energy Ship software developed by Marintek for the European Union, the ship’s hull resistance can be calculated and a rough estimate of fuel consumption can be determined. Following this, a CFD analysis using tools such as Fluent can be used to accurately predict the effects of modifications to the hull without risking an costly trial and error period with the ship. An example of such an alteration would be to increase the bulbous bow size, or even completely change the bow to an X-bow. Results of the CFD analysis can then determine the validity of such modifications. With fuel prices constantly escalating in real terms, it is important that additional fuel through slow steaming is not seen as a solution to the problem, but rather a last resort. By being able to predict and quantify the savings of some of the aforementioned devices, it can be clear whether they are a genuine long term solution to the owner of the ship.
5.1. Successful Ship Designs for Fuel Efficiency in the Red Sea
It would be beneficial to draw from past case studies and alter successful ship design features to cater for specific geographic requirements. The Suezmax class of oil tankers offers a good base for such design work. These vessels have to escort through the Suez Canal and therefore have been designed for similar environmental conditions as those found in the Red Sea. A case study of how to optimise a Suezmax tanker design for fuel efficiency in the Red Sea is through the CFD analysis of a new propeller design. A simple change in propeller design can offer vast savings in fuel. With a tailored approach to low risk, minor changes and a fast payback, it is an attractive fuel saving solution. A CFD analysis showed that changing the owners fixed pitch 16% skewed propeller from a standard 4 blade design to a 5D design with the same pitch, would result in a 4.2% reduction in required delivered power for the same service speed.
Further tests taken place to assess this new propeller design’s performance using the unsteady RANS solver on STAR-CCM+ software, simulating the ship’s transit through the specific Suez Canal operational profile, found that there would be a 7.1% reduction in power and 6.5% reduction in fuel consumption. These test results show a clear benefit in changing the propeller design when fuel consumption results in cost savings of less than a year with a new built ship. The propeller design changes often come with no increase in build costs and so for Suezmax tankers built for service in the Red Sea, it seems illogical to ignore the potential fuel savings from specific propeller design changes and it should be factored into each new build specification.
5.2. Implementation of Emission Reduction Strategies
The concept of reducing emissions from ships has received much attention recently, with the International Maritime Organization (IMO) adopting regulations which require all contracting parties to Annex VI of the MARPOL Convention to establish and maintain a National Plan to address air pollution from ships, and to develop the Energy Efficiency Design Index (EEDI) which provides a specific value of CO2 emissions in grams per ship’s capacity-mile, and is required to be reduced for future ship generations. To cater for the EEDI, ship owners are provided with the option to employ efficient designs and technologies to power their ships. This has seen an increasing trend of slow steaming, which refers to the practice of operating a ship at a speed lower than its design speed but with significant energy reduction. Efforts were made to design and construct specifically for the Red Sea, with Ghenaa and El Madina (1998) being two Egyptian-built ROROs which employed the assistance of an Overseas Development Assistance (ODA) loan, with aims of providing safe and reliable transport of goods and passengers between ports in Egypt and KSA, and to revitalize Egypt’s maritime connection with the outside world. ODA had stipulated that the ships be environmentally friendly and have minimum impact. This resulted in the development of a RORO type unique to the Red Sea with a design focused on reduced emissions and increased accessibility. However, a downside to this approach is that it restricts technological options, and there is potential for opportunity loss if no feasible designs or technologies are found.
