Marine transportation sector, responsible for 3% of the global emissions of Carbon Dioxide. Without effective measures within the next decade, the contribution will become the major source of air pollution by 17%. International Maritime Organization (IMO) Tier III emission regulations will in effect for recreational ships, less than 500 gross tonnage (GT) and greater than 24 m load line length (LLL) after 2021. The regulation affects more than 52% of the current yachting market which raises concerns over Selective Catalytic Reduction (SCR) influencing the market negatively. The purpose of this study is to investigate the yacht market by retrofitting 2 models with promising powering and propulsion systems under certain load profiles. The retrofit study indicates an extensive applicability potential with improving feasibility and promises more cost-effective and long-term viable solutions rather than centralizing SCR and similar gas-after treatment solutions which do not improve upon the needed technology to encourage a sustainable future.

Increasing concerns on environmental issues and limited supply of non-renewable fuels have enforced all sectors including transportation such as automotive, railway, aviation and marine which accounts for 28.2% greenhouse gas (GHG) emissions to be reduced 80% by 2050 compared to 1990 levels for EU [1], [2]. With latest fuel efficiency improvements in railway and increasing number of electric and hybrid cars which currently makes up 4% of new registration, the level of emission levels is expected to decrease [3]. Under measures already in place, land transport is expected to consume 43 MTOE (million tonnes of oil equivalent) less energy per year in 2030 than it did in 2010. Yet ships and planes in Europe will consume 19 MTOE more fuel annually in 2030 than they did 20 years earlier [4], [5]. The growth in these two sectors can undo almost half of the already insufficient progress made by cars, rail and inland navigation. Maritime industry moves more than 90% of global trade by volume, making it an essential part of the world economy [6]. Although shipping is the most energy-efficient mode of mass cargo transport, with only a smaller contribution of almost 3% to the global emissions of carbon dioxide [7]. Without effective measures within the next decade, shipping and aviation will become major sources of air pollution with an estimated contribution of 17% and 22% by 2050 [8].

A particular range in yachting sector has been the blind spot for regulators due to its minor contribution to GHG emission levels, therefore fell behind regarding the innovation on sustainability until its current contribution projected to increase with shipping and aviation as mentioned above. (IMO) Marine Pollution (MARPOL) Annex VI Tier III Emissions Regulations was agreed to be in effect for recreational ships, less than 500 (GT) and greater than 24 m (LLL), defined in this report as ‘large yachts’, Tier III legislation implementation was delayed to 2021 due to an amendment during IMO MEPC 66 in April 2014. The Tier III emission standards will reduce the nitrogen oxide emission limits by 70% (2g/kWh) for large yachts with power rating greater than 130 kW in designated Emission Control Areas (ECAs) [9]. With North America, United States Caribbean, Baltic and North Sea will be joining Emission Control Areas (NECAs) by 2021 and discussions about including Mediterranean Sea hasn’t concluded but it was supported by 6 European countries makes the Tier III regulation inescapable. This potential interest due to the high proportion of large yachts operating in Mediterranean Sea (64%). The size distribution of total delivered vs. in-build yachts in 2018 indicates 30-40 m yachts cover 52% market share which is in Tier III regulation parameters. As the data excludes the sail and large yachts greater than 40 m but less than 500 GT and large yachts between 24-30 m, the market share is expected to be significantly higher [10]. This represents more than 52% of yachting market getting affected by the regulation. The current large yachts market is comprised with just below 500 GT limit to avoid the same and further regulations and certifications appointed by IMO which is likely to be soften with the implementation of this regulation. 

The current conventional diesel and diesel electric propulsion systems are not sufficient enough to achieve desired emission levels without the installation of gas-after treatment systems [9]. The auxiliary engines used on large yachts typically less than 130 kW, meaning they do not need to comply Tier III. One possibility to comply Tier III is the use of auxiliary gensets to power the vessel via electric propulsion motors. Within a NECA these gensets will be operational while the main propulsion engines certified for Tier II are switched off. These gensets are expected to be less than 130 kW so do not need to compliant with Tier III, would provide low power enabling the yacht to achieve very low speeds. It is expected that not being able to access the yacht’s top speed in NECA regions would be unacceptable to many large yacht customers [9]. Therefore, the only commercially feasible solution to comply Tier III is to use SCR units. An optimized SCR system is a similar size to the engine, urea storage tanks need to be fitted close to the system which will take up more engine room space and further reduce the space needed for maintenance [9]. In order to equilibrate the additional required space in the engine room (13), either the guest accommodation space (1 out of 4 cabin) would have to be reduced or tender garage space, which would have a severe impact on the sale price of these yachts and reduce the profit margin. Tier III compliant engines are expected to cost up to circa twice the price of Tier II engines. Moreover, the significant mass of the SCR system will result in a change to centre of mass of the vessel and the fuel consumption and maximum speed of the vessel (approximately 5% reduction in top speed) and the vibrations associated with the SCR systems on large yachts are yet to be determined [9]. Although the SCR system will bring unquestionable negative impacts on more than 52% of the yachting market, it offers the most cost-effective method to comply Tier III. In July 2018, International Council of Marine Industry Associations (ICOMIA) appointed Ricardo UK to postpone the IMO Tier III regulations for the second time to 2030. But it was resulted with a rejection from IMO. Ricardo UK study indicates some contractions by excluding a full cost-effectiveness study on hybrid with SCR system, fully electric with latest battery installation and various energy storage mechanism with efficient fuel cells.

Currently, there are many promising sustainable systems which are being investigated and considerably used in transportation sector such as diesel electric, full electric and fuel-cell powering and propulsion systems. With the continuous increment in the rate of emission standards has been getting close to a point where it can only be achieved by eliminating the use of non-renewable fuels and inefficient models of producing energy. The enforcement drove the emission free technological advancements as of producing or storing energy more efficiently for longer ranges suggest focusing on ultimate system would be logical in the sense of using and improving on it. Electrification of vehicles is a growing topic with many examples from different industries. In the automotive industry, as of 2020 Tesla Motors starts selling Roadster 2.0 which has 1000 km range with a single charge, it will be the only electric and sports vehicle featuring this range [11]. The achievement occurred after Tesla acquired Maxvell Technologies in May 2019 and started producing their 21700 battery cells which they started using in their cars. It has 20% more energy density compared to Panasonic 18650 cells, making Tesla the only company with lowest cost and highest energy per Li-ion cell to date [12], [13]. With the increasing number of electric vehicles from other brands the electric automotive market is growing. Moreover, there are many car companies whichcurrently offer fuel-efficient hybrid and hydrogen powered cars [14]. A 4-year project 60 m fully electric ferry Ellen funded by European Commission (EC) has launched in January 2020. The ferry carries 31 cars and 198 passengers and boasts 15 knots between 38 km apart harbours [15]. The increasing number sustainable ferries didn’t stop with fully electric system, but hybrid and hydrogen-power ferries operate for extended range missions. Today, there are many 100-passenger hydrogen-power Zemships in Hamburg which are started to go into service in 2008 [16]. Greenline Yachts produces hybrid with fully electric mode small yachts [17]. Feadship launched 83.5 m diesel-electric superyacht in 2015 which offers 30 tonnes of Li-ion batteries with a fuel saving of 30% [18]. 

These latest implementations and advancements in existing technologies brings the sustainable future closer each year. This study focuses on providing an applicational analysis of diesel electric, diesel electric with SCR system, fully electric and hydrogen powered powering and propulsion systems feasibility by retrofitting 36 m and 44 m large yachts which have to comply Tier III if built after 2021. These systems are tried to fit in within the allowable range to no minimize the customer space in models. 2 models usage provides a wide spectrum of the large yacht market. In addition, the study provides economic feasibility, complications, comparison, and estimation of long-term viable solution for 30-40 m yacht market.

1.     Material and Method

The following models were used: 36 m wooden (planning hull) and 44 m steel (semi-displacement) motor yachts which are described as model 1 and 2 respectively in the rest of the report [19], [20]. These models were built and launched. Their CFD, real fuel consumption, house power demand data and weight analysis have been considered and filtered for appropriate usage. A conservative engine and house demand profile was used for models as shown in Table 1. 3 out of 4 modes of power state were indicated as docking, cruising, manoeuvring and night anchor in which docking was excluded due to power is supplied from shore. As indicated in Table 1, models were considered to spend 90 days on sea (24.6% online) and rest of the year docked at a marina which was completely ignored. Annual engine hours were set to be 360 which was taken as an average for planning and semi-displacement hulls for 30-40 m large yacht market [9]. Manoeuvring is the most energy consuming mode and it was taken as 0.5 hours to be conservative side. All the relevant calculations are mentioned in the appendix section.

    Table 1 Modes of State

ModesDailyMonthlyAnnually
Cruising (Hour)4120360
Manoeuvring (Hour)0,51545
Night Anchor (Hour)19,55851755
Total247202160

All modes require auxiliary load, on the other hand propulsion load is only required in cruising and manoeuvring modes. Cruising time is equivalent to the distribution profile in Table 2. Table 2 propulsion load profile is used to calculate daily fuel consumption and kWh which was later used to obtain efficiencies and economic compensations for models. 70% online time at 70% load represents the optimum engine speed for conventional diesel and diesel electric systems.

 Table 2 Propulsion Load Profile (Cruising)

Load RangesOnline Time (%)Online Time (Hours)
1070,28
2000
3000
4050,2
5030,12
6050,2
70702,8
8000
9000
100100,4
Total1004

1.1       Energy Storage System (ESS)

There are many battery technologies available for experimental and applicational use today. Thus, the wide spectrum and promised technologies which are not commercially available were ignored. A research has been made to find the cheapest, durable, lightest and highest in energy and voltage capacity and lowest self-discharge rate used to date. The Li-ion technology provides the optimum parameters from the following: Maintenance, longevity, charging, safety, sustainability and cost. Currently, Tesla 21700 cell production offer minimum cost per kWh in the market and when slightly altered in favour of energy capacity with decreased life cycle which is sufficient enough to provide optimum specifications for diesel electric and fully electric under a usage indicated in Table 1 as follows: 

Table 3 Battery Specification

SpecificationOriginalAlteredUnits
Height7070mm
Radius15.515.5mm
Volume5283352833mm3
Weight7070g
Nominal Voltage3.74.2V
Nominal Charge5.755.75Ah
(P) Capacity0,021270,02415kWh
Energy Density0.87750.996Wh/m3
Specific EnergyDischarge Rate0.322100%0,34570%kWh/kg
Life Cycle 2000500Charge
Estimated Cost150150$/kWh

The discharge rate (DOD) of the batteries original condition conservatively assumed to be 100% and reduced to 70%, making the models requiring more battery cells, increasing cost and life cycle. Therefore, the current life cycle is expected to be significantly higher.

1.2       Volume and Weight 

Model’s current engine room and fuel tanks weights and volumes were noted. A statistical research has been made to obtain minimum displacement and local maximum fuel tank volume in class. The additional volumes were added, and minimum displacement and engine room weight were subtracted to calculate the additional allowable weight and volume which can be added to the models. Emergency generator was excluded. All the relevant calculations mentioned in the appendix section.

1.3       Hotel Demand

AC Load analysis was used to calculate daily kWh with modes of power indicated in Table 1. The house demand was set to be fixed for all types of systems. AC load analysis was calculated with 98% heat and 10% efficiency loss to be on the conservative side. 2  of LG Neon2 solar panels were installed onboard to provide additional energy which was subtracted from the daily kWh of hotel demand [21]. The following Table 4 was used to calculate the daily kWh from time data given Table 1.

                             Table 4 Hotel Demands

 Model 1Model 2
Cruising (kW)48,187,9
Manoeuvre (kW)61,5131,8
Night Anchor (kW)24,637,0
Solar Panels (kW)2,82,8
Total (kWh/day)772,71115,8

1.4       Conventional Diesel

Conventional diesel system which was already installed in the models was used. 

1.4.1  Fuel Consumption

The original engine performance and fuel consumption (litre/hr) data were used to calculate total fuel consumption (litre) of conventional diesel propulsion system with dedicated propulsion loads. House demand was used to calculate the daily fuel consumption from installed synchronous generator sets at variable loads. The heat losses and efficiency drops were accounted, and final demands were used. Therefore, daily fuel consumption of the entire model was obtained. The current installation does not comply Tier III releasing less than 9.2 g/kWh of  [9]. Installed auxiliary and emergency generators are exempted due to low power rating and purpose of use. Relevant documentation is mentioned in the appendix section.

1.4.2  Cost

The daily fuel consumption was multiplied with 90 days of same operation and annual fuel consumption was obtained. Then obtained annual fuel consumption multiplied with average price of Euro Diesel Fuel price (1.28 €/litres) at marinas in 2020 [22]. The initial cost of the model’s main engines and auxiliary equipment were noted to be used when comparing it with other systems. 

1.5       Diesel Electric

CFD analysis was used to calculate individual daily kWh of the models with a 70% reduced propulsion load profile as indicated in table 2. Reduced maximum speed was essential to offer minimum daily kWh possible and optimum overall efficiency. Therefore, it was also calculated for current conventional diesel installation for comparison.

1.5.1  Fuel Consumption

In order to select the required kW for genset, 70% reduced maximum propulsion load and hotel load were added and divided by desired number of generators. The power (kW) of the generator were increased by 10% and the nearest generator in the Caterpillar product book was selected [23]. The propulsion and hotel demands were added through 5 power modes: Night anchor, manoeuvring, silent cruising, optimum cruising, and maximum cruising. Night anchor has no propulsion load and hotel demand was taken from AC analysis. Manoeuvring includes 10% propulsion load and hotel demand which is substantially required by bow thrusters. Silent cruising requires no generators to operate for the specified time mentioned in 2.5.3. Silent cruising has its own maximum speed and low speed which is primarily for docking. Optimum cruising requires installed genset to operate at their highest kW per minimum fuel consumption (optimum speed) which is 75% load per generator and deliver power to electric motors and house. Maximum cruising required all generators to operate at 90% load and deliver power to electric motors and house. In order to calculate the fuel consumption, 5 modes of power were summarized to 2 generator modes and time spent on each which are optimum and maximum operation. The optimum includes night anchor, manoeuvring, silent and optimum cruising whereas maximum operation includes only maximum cruising. Through the 2 generator modes, total fuel consumption was calculated. The achieved fuel saving must be more than 70% which is sufficient enough to make SCR unnecessary. If the required saving was not achieved, a smaller SCR system may be integrated corresponding to saved fuel []

1.5.2  Electric Motor

Electric motors were selected as Twin 97.5% efficient 800 kW Siemens three-phase squirrel for both models. Highest possible voltage was selected to minimize heat losses. Single electric motor was used to supply the propulsion load. With the introduction of electric motors presumably being azimuth thrusters eliminating rudders and minimising required engine room space. Relevant documentation is mentioned in the appendix section.

1.5.3  Energy

The generators total operating time for each mode was calculated in 2.5.1 which was roughly assumed to make generators completely unneeded throughout the night. By assuming batteries are being charged and not used when generator is operating, the amount of time batteries can run the models were subtracted by the generator’s operation time and daily kWh and how many cells needed were calculated.

1.5.4  Volume and weight

Volume and weight of the battery cells were 10% increased due to bedding and integration of the system and electric motor’s weight were noted. The allowable volume, and weight which is calculated in 2.2 was subtracted from the total installed weight. The final installed volume and weight were calculated. It should be noted that the installed volume onboard is only the battery packs and generators. Smaller SCR system’s weight and volume were noted.

1.5.5  Cost

The efficiency improvement was calculated by obtaining the percentage difference between diesel electric and conventional diesel daily fuel consumption. As the diesel electric system is heavier and more expensive but consumes less fuel than conventional diesel, compensation calculation was carried out to calculate the number of years it will take for models to pay for initial price by saving fuel. Initial and continuous compensation was calculated in 2 methods: First method ignores half of battery charging prior to departure from the marina which has to be charged with generators. The reason its half charged is to prevent excessive degeneration caused by stress when either the battery is fully charged or empty. The second method includes charging prior to departure. Due to the electricity price (0.4 €/kWh) which was selected from the most expensive is still being significantly lower (67%) than diesel fuel price, ensures that considerable amount of savings can be made [24]. A cheaper SCR system price was noted [9].

1.6       Fully Electric

Model’s CFD analysis was used to calculate 3 profiles of daily kWh with 100%, 70%, and 60% reduced propulsion loads. The load reduction was offered to give comprehensive understanding of optimization between initial cost compensation and life cycle of the batteries which was mentioned in 2.1. Single electric motor was selected through the same process mentioned in 2.5.2.

1.6.1  Energy

The daily kWh (propulsion and hotel) was calculated with 70% DOD for each profile and divided by battery cell capacity to obtain the number of cells needed on models. With the number of cells known, the allowable weight calculated in 2.2 was used to obtain the number of days models can be on sea in each profile without being charged. This method was used to avoid excessive weight. Table 2 and number of sea days was used to calculate range of the models. 

1.6.2  Volume and Weight

Fully electric system eliminates all the generators, main engine and fuel tanks. Due to 21700 cells having very high energy density, the models don’t have problem accommodating cells in volume wise. Therefore, the elimination of mentioned equipment and minimum displacement in class created the maximum allowable weight only for batteries and electric motor. The number of batteries, range and total kWh was found from the allowable weight. Volume and weight of the battery cells were 10% increased due to bedding and integration of the system. By and large, the total added weight and volume were arranged to not exceed the allowable values which are indicated in Table 5.

1.6.3  Cost

The lifecycle of the battery cells and initial and continuous cost compensation by electricity usage over diesel fuel were calculated. If the lifecycle was lower than the cost compensation the load profile was marked to be not feasible in terms of cost-effectiveness. 

1.7    Hydrogen Powered

Hydrogen requires enormous amount energy and volume to store primarily due to its low volumetric energy density for pressurized conditions. Second way to store hydrogen is in liquefied state and it has 2-fold more energy density than pressurized tanks. But liquefying requires hydrogen gas to be cooled down to about -253 °C, it needs pre energy and which requires additional auxiliary generators [25]. Associated risks with liquid hydrogen can be more hazardous such as self-pressurization, heat leaks, sloshing and flashing. Hydrogen at 500 bar pressure was selected due to its relatively easiness for storage and cost. Although hydrogen is liquefied, it has 78.3% lower brake energy density (1.1 kWh/L) compared to diesel fuel but has a greater specific energy (33.33 kWh/kg) by 64%. The high-pressure hydrogen can be stored latest IV carbon-composite tanks. The 200 kW Solid Oxide Fuel Cells (SOFC) currently features more than 65% efficiency in converting hydrogen’s theoretical energy to electricity [26]. Therefore, the current fuel tank should be enlarged by 4.6-fold if its desired to achieve the same range. Due to the unreal enlargement, allowable volume was used. The liquefied version can achieve 3-fold greater volumetric energy density, yet the available technology is not mature enough. The same electric motor was used as in 2.5 and 2.6. The fuel tank was multiplied with hydrogen’s brake energy density to attain model’s total kWh. Total kWh was distributed to the propulsion load profile indicated in Table 2. 

1.7.1  Fuel cell

Hydrogen fuel cells directly convert chemical energy in hydrogen to electricity and release water and useful heat as by products which is in the range clean energy. Since all the SOFC components are solid, as a result, there is no need for electrolyte loss maintenance and also electrode corrosion is eliminated [27]. Since SOFCs are operated at high temperature, expensive catalyst such as platinum or ruthenium are totally avoided.   The required fuel cell power rating was selected to be equivalent to maximum propulsion load and hotel load. Bloom Energy offers the highest capacity fuel cells (200 kW) commercially available which was used to obtain the number of cells. 

1.7.2  Volume and weight

While the hydrogen fuel tank covers the usual space while the fuel cells are just 43 each. The hydrogen powered Solid Oxide fuel cell system does not require battery or generator. Therefore, installation; high pressurized fuel tanks, fuel cells, electric motors and the fuel were noted for allowable volume and weight calculations whether it’s in the limits.

1.7.3  Cost

The total price (14.8 €/kg) of the fuel tanks were calculated which is 19% cheaper than diesel fuel [28]. Although the fuel price differs, the initial price should be greatly higher due to electric motors, high pressured tanks and fuel cells which were noted for compensation.

The explained procedures were followed for both models and results were noted to be analysed. 

2.     Results and Discussion

Each section carries out specific and individual calculation. Allowable volumes, weights, constant hotel loads, and 100%, 70%, 60% reduced propulsion loads, and corresponding daily kWh and maximum speeds are given in Table 5.

      Table 5 Specifications

 Model 1Model 2
Allow. Vol.58638,582745
Allow. W.80,390,392,8127,6132,6138,4
Hotel7721115
Propulsion543331872726569032572629
Total6206396034996806,143733745,2
Max. Speed221614171514

Where volume is in litre, weight in tonnes, loads are in kWh/day and maximum speeds in knots.

2.1       Conventional Diesel Results

The original system includes 2 x C32.2 main engines and 2 x C4.4 generators in both models with different power ratings. Main engines performance and fuel consumption data was integrated to load profile mentioned in Table 2 with 100% load in Table 5. The generators provide power via synchronous and nonsynchronous variable loads depending on the demand in Table 4. The optimum daily fuel consumption was selected and calculated in Table 6. Main engines comply Tier II and release approximately 9.2 g/kWh of. The introduction of SCR unit requires up to 13  additional space in engine room [9]. Model 1 has already a small beach club, therefore accommodation space should be minimized. Model 2 offers a reduction in 60  beach club area which is likely to cause 5.2 metre tender to be smaller or removed. These negative effects of a SCR unit are expected to cause an uncertainty for large yacht customers. 

Table 6 Conventional Fuel Consumption

 Model 1Model 2
Main Engines (litre/day)1967,041823,36
Generators (litre/day)204,73312,30
Total (litre/day)2171,772135,66
Daily Cost (€)2779,862733,65

2.2       Diesel Electric Results

The 70% reduced load profile was calculated for conventional diesel and diesel electric. Due to silent mode offering a reduced propulsion load to enable the models to cruise on batteries, there is a slight decrease in daily kWh compared to Table 5. Accurate generator selection was the essential part of making the system efficient. The generator’s power was selected by the sum of maximum power and house load at any given time. The maximum power was divided by 3 and power per each generator was attained. The following generators were selected CAT C18 465 kW and 565 kW at 1800 rpm and 50 Hz respectively [23]. Their optimum speed was obtained by the highest kW per fuel consumption which formed the cruising speed of the models.

Table 7 Diesel Electric Modes & Genset

kWh/dayModel 1Model 2
Rest531,09796,50
Silent302,12255,12
Optimum Thrust2484,012600,80
Maximum Thrust567,66639,62
Manoeuvre33,9672,72
Optimum Mode 3351,183725,14
Maximum Mode  567,66639,62
Total3918,844364,76

In each mode, residual energy was set to be the subtraction between optimum power and used power in which the batteries can be charged and used later for stated purposes. Therefore, batteries cannot be charged during maximum mode as the residual power is minor. Table 7 was used to perform fuel consumption calculation for diesel electric models and following fuel consumption results were obtained in Table 8.

 Table 8 Fuel Consumption Comparison

 Model 1Model 2
Diesel Electric (litre)1044,71294,6
Conventional Diesel (litre)1200,01550,7
Fuel Efficiency Achieved (%)14.216,51

As shown above, the model with greater house load but similar propulsion load has greater efficiency which can be achieved due specific fuel consumption point, not possible for conventional diesel gensets operating at various loads. The mentioned fuel saving can provide advantageous reduction in SCR unit installation due to SCR system prices are dependent on kW installed: 100k $/MW [9]. A reduction in fuel consumption is equivalent to reduction in installed kW due to GHG emission are calculated in grams per kW. Therefore, an SCR system will cost 18k $ and 25k $ less respectively. A smaller SCR unit presumably has smaller urea tank required. Due to locating electric motors outside the hull, the overall installed volume was improved 8.8% and 6,72% compared to conventional diesel with SCR unit. Shafts and motors are outside the hull and number of total engines was decreased by one with lower power rating and operating at optimum speed due to which additional SCR system’s vibration and noise levels are expected to be minimized. Batteries contributing greatly, the total weight increased by 14,000 and 25,000 kg. The batteries are primarily the cause of high initial price and increased weight. If the batteries are charged 15 out of total 90 days when docked at marina, the cost compensation is 5% and 27% earlier compared to not charging. For model 1, it’s 9.74 and 11.9 years whereas, and model 2 has 9.72 and 13.35 years. The difference occurs as a result of model 2’s 15% more installed battery cells which will be charged 67% cheaper than diesel fuel each time as indicated in 2.5.5. By and large, diesel electric installation can comply with Tier III emission standards with lower cost of ownership that compensates in given years. In addition to fuel saving, diesel electric propulsion system is broadly simplified in terms of maintenance.  

2.3       Fully Electric Results

Daily loads indicated in Table 5 are increased by 70% DOD charge which is essential to prolong the battery life cycle. Due to increase in voltage capacity life cycle are expected to decrease which should be minimized by maximum 70% state of charge. Days are calculated according to how many battery cells can be installed onboard given load per day. At given loads and usage, range is the total distance achieved before requiring charge. The initial cost is the subtraction between installed and uninstalled equipment which refers the additional cost for retrofitting. 

        Table 9 Fully Electric Results

 Model 1 
 Profile 1Profile 2Profile 3 
Days3,95,56,4 
Range241,0267,0288,7 
Initial Cost1059735853506703806 
Compensation51.112.19.8 
Life Cycle14.820.824.1 
FeasibilityNot FeasibleFeasibleFeasible 
Model 2
 Profile 1Profile 2Profile 3
Days5,38,610,5
Range310,2437,1501,8
Initial Cost113315731769576398
Compensation162.2912,98,9
Life Cycle20,332,839,9
FeasibilityNot FeasibleFeasibleFeasible

Where range is in nautical miles, initial cost in Euros, compensation and life cycle in years. 

Compensation is a calculation to present how many years it will take for system to pay for itself. Life cycle is how many years it will take for battery cells to degenerate to minimum 80% state of charge with 400 Dynamic Stress Test (DST) at 25 °C [29]. Feasibility presents whether the life cycle is higher than the compensation duration. Contrarily, the battery cells capacity wouldn’t efficiently be replaced before they compensate which wouldn’t be financially advisable. In both models’ profile 2 and 3 achieve minimum 2-fold rate. Second decisive part in arranging the battery cell specification is to achieve a life cycle value close the refit time (minimum 20 years) of the models which would make it feasible. During a comprehensive refit, battery cells can be replaced. In this case, the compensation time is equivalent to owner’s use time. The total use day and range indicated in Table 9 suggest that the models cannot achieve long cruises therefore may subject to negative effects of not getting classification’ certificates and transatlantic cruises. Although Model 1’ installed weight suggests a change in model’s hull which was initially planning. The range difference occurs more as a consequence of model 1 being planning hull (high speed and low range) and model 2 being semi-displacement (flexible to lower speeds and longer range). In addition to already reduced speeds the increase in weight is expected to cause a shift in model’s hull to semi-displacement and a reduction in indicated top speed. Consequently, the results suggest that a long range (long range for planning) and high speed is not practicable with similar planning hull usage due to significant weight of the batteries. Accompanying the current installation, the models can achieve small cruises as indicated in Table 9. Model 1 profile 3 and model 2 profile 2 and 3 can offer average charter experience which is usually 7 to 10 days anywhere in the world [30]. In this case, the models are expected to complete their range otherwise total use day can be extended if its lower than the propulsion load profile indicated in Table 2. The current installations would increase the sale price with not sufficient payback period. In addition to models not fitting the large yacht market specifications due to lower range and speed, the technological implementations and complications in terms of safety and longevity are yet to be comprehensively investigated. However, models are applicable for low profile local and charter use and they can comply with all emission regulations which may result decrease in taxation.

2.4       Hydrogen Powered

With allowable volume used as a fuel tank for pressurized hydrogen, the total range with same load profile is greater than fully electric system. Therefore, range comparison was made between hydrogen and conventional diesel. The following comparison was made at 15 and 12 knots of speed which were originally selected as cruising speed for conventional diesel.

                  Table 10 Hydrogen Range Comparison

 Model 1Model 2
Enlarged Hydrogen Tank (nm)4911067
Original Diesel Tank (nm)5022126

Their weights (only hydrogen) are 1063 and 1500 kg in total. Model 1 features similar range due to high allowable volume which makes model out of planning hull region. Accordingly, model 1 comparison is not valid for planning as mentioned in 3.3. Although enlargement in hydrogen fuel tanks Model 2 doesn’t achieve desired range as it requires 2-fold increase in addition to increase in allowable volume which is not valid. As the results suggests hydrogen is required to be stored in liquefied state which greatly improves volumetric energy density if same range is needed. If it’s to be compared to fully electric with same specifications in Table 9, following fuel tank enlargements should be made as in Table 11. 

           Table 11 Hydrogen Volumetric Space Comparison

 Model 1Model 2
Profile 1 (%)47,712,9
Profile 2 (%)40,016,2
Profile 3 (%)41,619,7

Although an increase in required volume, hydrogen has greatly low weight per kWh compared to fully electric. There are many practical complications in hydrogen storage and fuel cell technology. The production and transportation of hydrogen is not equally distributed around the world and fuel station are not well-located around marinas which can cause ununiformly price jumps, making hydrogen unreliable. Initial cost is estimated to be significantly high due to fuel cells and carbon composite pressurized fuel tanks. SOFCs have some disadvantages in existence for deteriorating the performance which is essential for Model 1. The cells operate at high temperatures, so the materials used as components are thermally challenged. The complex fabrication has significant problems resulting in high price. Although the indicated complications, it requires less maintenance and more cost-effective than Proton Exchange Membrane (PEM) cells in long term. 

All the mentioned systems currently achieve Tier III emission standard with either limited range, a required hull model shift, high sale price or with the introduction of SCR unit. The conventional diesel installation results in negative effects in large yacht market whereas the diesel electric, fully electric and hydrogen powered models offer high initial price, lower cost of ownership and emission free solution which are expected to be optimized if technological adaptation occurs. The high cost equipment, significant development effort of these systems can be reduced with accurate and wide adaptation and involvement. Fully electric system can be conveniently adapted for average charter purposes in local regions where higher savings can be made as a result of price difference between electricity and diesel fuel. Hydrogen powered systems can be improved on an optimized SOFCs for large yacht profiles. Adaptation of these systems likely to cause improvements on current specifications and price decrease.

3.     Conclusion

In this study, currently available conventional diesel, diesel electric, fully electric and hydrogen powered powering and propulsion systems and use of SCR unit were investigated over the implementation of IMO Tier III  emission standards which was agreed to be in effect for recreational ships, less than 500 gross tonnage (GT) and greater than 24 m (LLL), after January 2021. The conclusion of this study may be summarized as follows:

  • Conventional diesel systems with an SCR unit comply Tier III  emission standards but result in significant weight, volume, price and maintenance difficulty. Tier III compliant engines are expected to cost up to circa twice the price of Tier II engines which creates an uncertainty about customer acceptance of increased cost, lost space and performance.
  • Diesel electric systems with smaller SCR unit comply emission standards and result in favourable specifications in terms of volume, lower cost of ownership, vibration and noise levels and convenience for maintenance. 
  • Fully electric systems comply emission standards without any use of combustion engines and do not release GHG emissions. A retrofit study of 2 large yachts suggests that these systems are compatible for average use and feasible for certain applications. Results indicates inapplicability for planning hulls, limited range, low maximum speed, significantly higher initial price which compensates within the customer’s use time. Fully electric system offers the cheapest running cost among all. A wide adaptation of these systems can result in an incentive factor for improvements on current specifications and price reduction in terms of economy of scale.
  • Hydrogen powered systems comply emission standards and it offers longer ranges than fully electric systems but also highest in initial cost. Volumetric energy density comparison indicates to be lower than diesel fuel source which requires additional space to achieve the same range. Although hydrogen price is ununiformly distributed, it offers less running cost than conventional diesel and diesel electric systems. 

To summarize, the large yacht retrofit study indicates an extensive applicability potential with improving feasibility and promises more cost-effective and long-term viable solutions rather than centralizing on SCR and similar gas-after treatment solutions which do not improve upon the needed technology to encourage a sustainable future.

Future Research

As a result of uncertainty with the collected and calculated data in this study, it is believed that a computer simulation and accurate data collection especially on hydrogen powered should be performed. Due to lack of fuel cell and hydrogen storage costs, the compensation calculation for 3.4 was not extensively performed. This study hopefully provides a greater level of clarity for the growing number of sustainable powering and propulsion system in transportation sector. Understanding today’s technological capabilities should contribute tomorrow’s involvements.

Acknowledgements

The author would like to thank Dr Rosemary Norman for the supervision and improvements on this study. The study was also supported by Yusa Demir, Kemal Eyvaz and Erdinç Kuşcu who helped with model’s data. Special thanks to my fellow students Ritik Raj, Isaak Hall and Nicholas Voltis who reviewed and motivated this study. 

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Author: Ramazan Mengi

Purpose of the dissertation: Newcastle University Stage 3 BEng Marine Technology and Small Craft Technology Final Dissertation for Graduation, 2020 5th of July

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