Developing a new methodology for evaluating diesel electric propulsion

Transcription

1 Journal of Marine Engineering & Technology ISSN: (Print) (Online) Journal homepage: Developing a new methodology for evaluating diesel electric propulsion E Sofras (PhD Candidate) & J Prousalidis (Ass. Prof.) To cite this article: E Sofras (PhD Candidate) & J Prousalidis (Ass. Prof.) (2014) Developing a new methodology for evaluating diesel electric propulsion, Journal of Marine Engineering & Technology, 13:3, 63-92, DOI: / To link to this article: Published online: 23 Nov Submit your article to this journal Article views: 522 View Crossmark data Citing articles: 2 View citing articles Full Terms & Conditions of access and use can be found at

2 Developing a new methodology for evaluating diesel - electric propulsion E Sofras, PhD Candidate, National Technical University of Athens (NTUA), GREECE J Prousalidis, Ass. Prof., National Technical University of Athens (NTUA), GREECE In this paper a methodology for the design of ships with a diesel-electric propulsion system, according to the All Electric Ship concept is presented. Taking into account that there is no long and extensive relevant experience for all ship types, diesel-electric propulsion should be selected after careful consideration and thorough evaluation of many technical and economic parameters. This paper offers a step-by-step procedure towards this direction; the discussion is enriched by a case-study of a ship type, where the selection of the proper propulsion system is not straightforward as many parameters have a substantial impact. INTRODUCTION Worldwide concern about air quality, greenhouse gas emissions, and oil supplies has led to stricter emissions regulations and fuel economy standards, as well as to exploration of alternative propulsion systems. In the context of alternative propulsion systems, application in ships of the electric propulsion concept, according to which the propeller is driven by an electric motor, was enabled by the development of Power Electronic Converters about two decades ago. Extending the electric propulsion concept, the modern concept of All Electric Ship (AES) includes the incorporation of multiple independent sources of power generation, as well as extensive electrification of main and auxiliary energy consuming systems (propulsion subsystem, oil/water/ballast/ cargo pumps, ventilation fans, oil/cargo heaters, distillers, purifiers, navigation subsystems, general ship loads, etc.) See 1,2,3,4,5,6,7,8,9. This transition from the traditional diesel mechanical system, where the main engines operate only with liquid fuels (Marine Diesel Oil or Heavy Fuel Oil) towards electrical systems, leads to several advantages such as increased manoeuvrability, precise and smooth speed control, high reliability and redundancy, reduced machinery space, and low noise and pollutant emission levels. Furthermore, a careful approach in the design of an AES can result in significant savings in running and maintenance costs 10. In addition, in podded propulsion schemes (in which the propeller and its driving electric motor are both located in a compact unit underneath the vessel s hull), the shaft system of the vessel is completely eliminated. In an AES, considering that all sub-systems are controlled via electronic control units, an overall control centre can be established, offering increased monitoring and control capabilities. This function is enabled by a central electric Power Management System (PMS), often referred to as Electric Power Management and Control System (EPMACS) 11, 12, 13,14,15,16. Thus, the manufacturers of the electric power system (or even of key components) become the system integrators for the entire vessel. As a consequence of the development of ship design concepts, marine electrical networks are becoming very different from those previously encountered ashore or aboard. In the framework of AES design, the power generation units (marine diesel engines, gas turbines and possibly fuel cells in the future), optimized to operate for maximum fuel economy and minimum pollutant emissions, are still crucial for the overall propulsion efficiency 10,17,18. Taking into account the appealing advantages offered by the AES concept, i.e. a clean, safe and efficient means of waterborne transportation, this paper presents a method to evaluate AES designs from a techno-economical point of view. Thus, it is shown that via the developed methodology the circumstances, under which the AES design can be fairly profitable, can be clearly identified. Moreover, it is shown that the selection of the proper propulsion system must be based on a thorough technoeconomical analysis where certain parameters having a substantial impact must be taken into account. As a casestudy a special ship type, namely a small passenger ship with special features is considered. Within this frame, under certain circumstances, the electric propulsion can be a beneficial solution. Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 63

3 BACKGROUND Typical diesel-electric propulsion plants configurations The selection of the diesel-electric propulsion plant mainly depends on the type of vessel from which are originated the specifications related to dynamic positioning, high redundancy, safety and comfort on navigation, high reliability etc. To this end, the main configuration types are categorized according to the type of vessel as follows 19, 20, 21 : LNG carriers A typical diesel-electric propulsion configuration of LNG vessels (Fig 1) consists of two high speed electrical motors of about 600 or 720 rpm and a reduction gearbox with two input terminals and one output, whereas the rated power of the installed alternator is around 40 MW. The main requirement for such a vessel is the high redundancy, and the equipment for that configuration is a VSI (voltage source inverter) converter with 24-pulse PWM (pulse width modulated), a supply transformer and an electric propulsion motor. In contrast to all other service loads, where asynchronous motors are used, both synchronous and asynchronous motors can be exploited for the propulsion of LNG carriers. The main advantages of Diesel-electric propulsion for the complicated and heavy plant configuration of this ship type consist in high propulsion power with high drive - motor efficiency and low harmonic distortion. Offshore support vessels Platform Supply Vessels (PSV), Anchor Handling/Tug/ Supply (AHTS), Offshore Construction Vessel (OCV), Diving Support Vessel (DSV), Multipurpose Vessel etc. are included in the broad category of offshore support vessels. The main requirements of dynamic positioning and station keeping capability impose the exploitation of diesel-electric propulsion plant along with variable speed motor drives and fixed pitch propellers. In modern applications (Fig 2) frequency converters with an active front end are used, which give specific benefits in the space consumption of the electric plant, as it is possible to eliminate the heavy and bulky supply transformers. On the other hand, the electric motor is an induction (asynchronous) motor which is stiff, simple design and cost competitive and ensures, in most cases, a long lifetime with a minimum of breakdown and maintenance. The advantages of such a system are the decreased requirements for space and weight, and elimination of supply transformer. On the other hand, the use of harmonic filters for decreasing the THD (total harmonic distortion) is necessary. Cruise vessels High reliability and redundancy are the main requirements of a propulsion system intended for cruise vessels, as well as that onboard comfort is a high priority allowing only low levels of noise and vibration from the ship machinery. A typical diesel-electric propulsion configuration for cruise vessels (Fig 3) consists of VSI type converter with 24-pulse PWM technology, supply transformers and a synchronous slow speed electric motor of about 150 rpm. The advantages of such a system are the high redundancy and reliability, the high drive and motor efficiency and the low noise and vibration. On the other hand, the major disadvantage is the complexity of the propulsion plant. Fig 1: Diesel-electric configuration of an LNG vessel 21 Fig 3: Diesel-electric configuration of a cruise vessel 21 Fig 2: Diesel-electric configuration of a PSV 21 Fig 4: Diesel-electric configuration of a RoPax vessel Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014

4 RoPax vessels The requirements for a cruise liner are also valid for a RoPax. A representative configuration (Fig 4) consists of high speed electric motors (900 or 1200 rpm), geared transmission, frequency converters of VSI type with 12-pulse PWM technology, supply transformers with two secondary windings and an induction motor for propulsion motor. The advantages of such a system are the robust and reliable technology, the lack of need for THD filter, while among the disadvantages are the large space requirements and the increased weight of the total installation. RoRo vessels In this case (Fig 5) an electric propulsion motor running on two constant speed levels (medium and high, respectively) along with a controllable pitch propeller (CPP) provides a high reliable and compact solution with low electrical plant losses. The main equipment for this plant is a power electronic converter and an induction motor with no supply transformer. The advantages of such a system are the high reliability, the low losses and the low THD. On the other hand, using a controllable pitch propeller is recorded as a disadvantage. METHODOLOGY ON HOW TO DESIGN A DIESEL-ELECTRIC VESSEL The study of a vessel with diesel-electric propulsion plant differs in many ways from the corresponding of a vessel with conventional propulsion. Thus, in the case of the conventional propulsion plant, the electric energy system and the propulsion one are essentially two separate parts of the vessel design. On the other hand, in the case of a vessel with diesel-electric propulsion plant, the electric and the propulsion systems are strongly interrelated and should be evaluated on a common basis during the design, taking into account techno-economic criteria, emissions, feasibility issues etc. Considering that, as of today, the literature in design methodology of ships with electric propulsion is fairly poor, this paper aims at providing a detailed relevant procedure. As a contribution to the design, a simplified flowchart with the main studies related to the design of the Diesel-electric propulsion plant is presented in Fig 6. Furthermore, a more detailed flowchart, showing all the steps which should be followed during the design phase of a vessel with Dieselelectric propulsion, is shown in Fig 7. Fig 5: Diesel-electric configuration of a RoRo vessel 21 Fig 6: Basic parts of the design phase of a vessel with Dieselelectric propulsion CASE STUDY The methodology presented in the previous section has been applied to a small passenger ferry with carrying capacity 150pax. Via this method the feasibility of the Diesel-electric propulsion from both technical and economical point of view is investigated. The study is presented in a succinct manner next. Owner s requirements and specifications The following requirements concerning design and technical details of the vessel as well as the evaluation of investment have been set by the ship owner: 1. The Length Over All (L.O.A) of the vessel should be L min. = 50 m up to L max. = 56 m. 2. The journey duration should be one hour and a half (1.5 h). 3. The ship service speed will be 20 knots. 4. The vessel carrying capacity should be 150 pax seated at air type seats. 5. A bow thruster should be arranged. 6. A small pantry for the crew should be arranged. 7. Two passenger bars should be arranged 8. All the enclosed crew and passenger areas should be fully air conditioned. 9. The ship will be sailing exclusively on the day (daily cruises). Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 65

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7 Fig 7: Flowchart for design a vessel with Diesel-electric propulsion 10. The crew should / should not have the capability to overnight on board. 11. Commission of main and auxiliary engines of dual fuel type. 12. The number of crew on board should be 10 persons. 13. The number of scheduled trips per day should be six (6). 14. The days of trading per year should be 300 days (under normal conditions with no damages or any other imponderable factor). 15. The net price ticket per person should be 15 euro. 16. The acquisition cost of machinery will be covered by a bank loan. 17. The cost of construction excluded the machinery will be funded by equity. Length over all: Length between perpendiculars: Breadth mld: Depth mld: Design draught mld: Table 1: Main particulars of the under study vessel m m 9.00 m 3.50 m 2.80 m 68 Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014

8 18. The latest SOLAS rules and regulations should be applied. 19. The construction should be conform to an IACS register rules and regulations. Taking into account the owner s requirements, the main particulars which have been selected for the under study vessel at the preliminary design, are shown in Table 1. Brief hull description The vessel has been designed according to SOLAS regulations for passenger vessels and as a result a full breadth double bottom has been arranged from Fr.15 up to Fr. 83, see Fig 8. The hull is divided in 11 watertight compartments having a minimum length according to the subdivision length given by SOLAS reg6 Ch.II-1. The watertight bulkheads are extended up to the main deck, as well as that at the bulkheads fitted at frames 7,15 and 24 openings at the center of the bulkhead have been arranged so that the crew members can pass from one compartment to another during ship operation. The above mentioned openings can close tightly using steel water tight sliding doors in order to maintain the watertightness and construction integrity of the bulkhead. Those water-tight doors are can be remotely controlled from spaces above main deck. Engine room, propulsion motor room, generator room, auxiliary machinery room and steering gear room are arranged at the aft part of the vessel between frames aft Fr.35. The generators have been arranged in such a way that, in case of two compartment flooding there will be one compartment Fig 9: Tank Top Arrangement intact containing at least one diesel generator which can supply the electric loads of the vessel. In the case that the vessel uses LNG as fuel for both conventional and diesel-electric propulsion then two LNG tanks are arranged in the compartment between Fr.35 Fr.45 inside B/5 line. The bow thruster room is arranged at the fore part between frames (83 92), while the fore peak tank is located in front of the bow thruster room. The double bottom is divided in small tanks, using longitudinal bulkheads, containing the bunker fuel oil, the fresh water, the lub oil and any other usefull consumable for the ship operation. Outside the hull at the aft part, a skeg has been arranged in order to separate the sea water flow between the two propellers improving their efficiency. Two propeller shafts exit the hull at fr. 11 and they are supported using two V- brackets. Behind the propellers, two semi-spade hydrodynamic rudders have been arranged. Fig 8: General Arrangement Propulsion and energy system Regarding the propulsion and energy generation of the vessel 19,20 the following two alternative solutions have been considered and examined in detail. The first alternative (see Fig 9 and 10), which will be mentioned hereinafter as conventional propulsion, comprises a typical propulsion system including two main diesel engines (internal combustion reciprocating engines) connected to the propeller shaft through reduction gears, arranged inside the engine room. Moreover, the electric energy generation system comprises three main diesel generators. The second alternative (see Fig 9 and 11), which will be mentioned hereinafter as diesel-electric propulsion, includes 5 auxiliary diesel generators producing electrical energy in 6600V and one harbour diesel generator producing electrical energy in 440V. The auxiliary diesel generators are connected to the main switchboard, which is divided into two sections for higher redundancy. Two variable speed induction electric propulsion motors in line with two frequency converters with an active front end Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 69

9 Fig 10: Typical propulsion and energy system of Conventional Propulsion Fig 11: Typical propulsion and energy system of diesel-electric Propulsion are connected and fed directly from the Main Switch-Board (MSB) and the propeller shafts are connected to the propulsion motors through reduction gears. The auxiliary engines and the propulsion motors in this solution are arranged in the engine and generator room, while the main switchboard is inside in the generator room, too. The main and auxiliary engines selected in all alternative solutions (with the exception of the low power generators) are of the dual fuel type, which means that the engines can operate with either liquid fuels (such as heavy fuel oil, light fuel oil, marine diesel oil and marine gas oil) or with gas fuel such as methane (LNG). V (knots) EHP(kW) SHP(kW) BHP(kW) Table 2: Final SHP and BHP per each velocity Fig 12: SHP-V graph for the under study vessel The number and the rated power of each main or auxiliary engine have been selected according to propulsion prediction study and detailed electric load balance analysis. Estimation of SHP and BHP The SHP and BHP for the range of velocities as calculated in the conventional propulsion are summarised in Table 2 and Fig 12, respectively. 70 Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014

10 Fig 13: Power flow in a simplified Diesel electric system 19 Energy demand for diesel-electric propulsion A typical diesel electric propulsion system power flow is illustrated in Fig 13, where a prime mover rotates the electric generator shaft and the electricity produced, distributed through the main switchboard, the transformer and the frequency converter to the electric propulsion motor. The shaft of the electric motor is connected directly or sometimes through gearbox (depending on the electric motor rounds) to the propeller shaft of the vessel. The power losses in the components between the prime movers shaft and the electric motor shaft are both mechanical and electrical producing heat and temperature increase in the equipment and its surrounding. The overall electrical efficiency of the system could be derived from the following formula: Equation 1: η = p pout in where P in can be expressed as a function of P out and P losses according to the formula: Equation 2: pin = pout + plosses For each of the components the electrical efficiency can be calculated, while typical values at their rated power are given next: Generator: η= Switchboard: η = Transformer: η = Frequency converter: η = Electric motor: η = Hence, the overall efficiency of a diesel-electric system from diesel engine shaft to electric propulsion motor shaft is normally 0,875 0,926 at full load and depends on the loading of the system. The required shaft power (P out ) for the under study vessel taken from Table 2 at the speed 20 knots is kw; therefore, using the overall efficiency for the diesel-electric system the intake power (P in ) is: p in pout = = 4240kW η This intake power will be used at the electrical balance analysis in order to determine the total energy demand including the electrical power dedicated to propulsion. Selection of diesel generators After elaborating the electric load analysis for both type of propulsion alternatives (conventional and diesel-electric) and for all three main operating conditions as described below, the number and the rated capacity of the Diesel generators are selected in order to meet the highest power demands. Sea-going condition: referring to the operating condition where the vessel is sailing with the service speed of 20 knots with full load of passengers and therefore a large number of electric consumers most of them in full load are in operation. At the diesel-electric propulsion, the intake power (Pin) is 4240 kw as calculated in the previous section (the power demands for the propulsion have also been included in the electrical balance analysis). This explains the big difference between the total required power at sea-going condition in conventional and diesel-electric propulsion. Rest-in-port (idle) condition: referring to the condition, where the vessel is resting in port without passengers, only vital consumers (such as auxiliary machinery for the generator, lights in predefined areas, ventilation in generator room etc.) operate. In this condition, no intake power has been included in the electric balance analysis of a diesel-electric vessel and at a first reading the total required power between the two propulsion systems would be expected to be almost the same. However, this is not correct because the engine auxiliaries and the machinery space ventilation auxiliaries of the two propulsion systems have different nominal power, with the Diesel electric system having higher power values. In order to make this clearer, a part of the in port electric balance analysis including the auxiliary machinery and the ventilation is given in Table 3. Maneuvering condition: referring to the condition where the vessel is approaching port. In this operating condition, the vessel sails at low speed, while most of the consumers operate in partial load. In this condition, the operation of the bow thruster motor must be considered, too. At the Diesel electric propulsion the intake power corresponding to a vessels speed of 13 Knots for the maneuvering has also included in the electrical balance analysis. Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 71

11 REST IN PORT CONDITION FOR THE CONVENTIONAL PROPULSION AUXILIARY MACHINERY Total number of consumers (N) Nominal Efficiency (η) Absorbed nominal Installed Number of consumers in use (N') Load factor (fs) Operation MAIN COOLING S.W PUMP MAIN JACKET COOLING F.W PUMP D.O TRANSFER PUMP D.O DE LAVAL L.O DE LAVAL AIR COMPRESSOR BALLAST PUMP BILGE PUMP FIRE PUMP OILY WATER SEPARATOR SEWAGE PUMP SLUDGE PUMP GEAR BOX L.O PUMPS STERN TUBE L.O PUMP C.P.P HYDRAULIC PUMP HYDROPHORE UNIT VACUUM SYSTEM Table 3: Part of the In Port electrical balance analysis for the two propulsion systems 72 Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014

12 AUXILIARY MACHINERY Total number of consumers (N) Nominal Efficiency (η) Absorbed nominal Installed Number of consumers in use (N') Load factor (fs) Operation BIOLOGICAL UNIT SPRINKLER SYSTEM STEERING GEAR HOT WATER BOILER HOT WATER CIRCULATORS SUB TOTAL 23.7 VENTILATION Total number of consumers (N) Nominal Efficiency (η) Absorbed nominal Installed Number of consumers in use (N') Load factor (fs) Operation E/R SUPPLY FAN E/R EXHAUST FAN GEN. ROOM SUPPLY FAN GEN. ROOM EXHAUST FAN STEERING GEAR ROOM SUPPLY FAN CO2 ROOM EXHAUST FAN SUB TOTAL 9.3 Table 3: Part of the In Port electrical balance analysis for the two propulsion systems (continued) Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 73

13 REST IN PORT CONDITION FOR DIESEL ELECTRIC PROPULSION AUXILIARY MACHINERY Total number of consumers (N) Nominal Efficiency (η) Absorbed nominal Installed Number of consumers in use (N') Load factor (fs) Operation MAIN COOLING S.W PUMP MAIN JACKET COOLING F.W PUMP D.O TRANSFER PUMP D.O DE LAVAL L.O DE LAVAL AIR COMPRESSOR BALLAST PUMP BILGE PUMP FIRE PUMP OILY WATER SEPARATOR SEWAGE PUMP SLUDGE PUMP STERN TUBE L.O PUMP C.P.P HYDRAULIC PUMP HYDROPHORE UNIT VACUUM SYSTEM BIOLOGICAL UNIT SPRINKLER SYSTEM STEERING GEAR HOT WATER BOILER Table 3: Part of the In Port electrical balance analysis for the two propulsion systems (continued) 74 Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014

14 AUXILIARY MACHINERY Total number of consumers (N) Nominal Efficiency (η) Absorbed nominal Installed Number of consumers in use (N') Load factor (fs) Operation HOT WATER CIRCULATORS SUB TOTAL 30.7 VENTILATION Total number of consumers (N) Nominal Efficiency (η) Absorbed nominal Installed Number of consumers in use (N') Load factor (fs) Operation PROPULSION MOTORS ROOM SUPPLY FAN PROPULSION MOTORS ROOM EXHAUST FAN GEN. ROOM SUPPLY FAN GEN. ROOM EXHAUST FAN STEERING GEAR ROOM SUPPLY FAN CO2 ROOM EXHAUST FAN SUB TOTAL 23.3 Table 3: Part of the In Port electrical balance analysis for the two propulsion systems (continued) Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 75

15 CONDITION SEA GOING REST IN PORT MANEUVERING TOTAL REQUIRED POWER (kw) DIESEL GENERATORS (2 238 ekw ekw) GENERATOR TOTAL CAPACITY (kw) AVAILABLE LOAD PERCENTUAL (%) Table 4: Selection and loading of main diesel generators (conventional propulsion) CONDITION SEA GOING REST IN PORT MANEUVERING TOTAL REQUIRED POWER (kw) DIESEL GENERATORS AVAILABLE (5 1014kW kW) GENERATOR S TOTAL CAPACITY (kw) AVAILABLE LOAD PERCENTUAL (%) Table 5: Selection and loading of Main Diesel generators (Diesel-electric propulsion) Fig 14: Comparison graph of cabling weight for the two propulsion systems Fig 16: Comparison diagram of the E.E.D.I. index for the conventional propulsion Fig 15: Comparison graph cabling weight per category Fig 17: Comparison diagram of the E.E.D.I. index for the Diesel-electric propulsion 76 Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014

16 The conclusive results of the electric balance analysis and the selection of diesel generators results for both type of propulsion systems are summarised in Tables 4 and 5. Cabling weight After rating the cables of the electric grid, the total cabling weight is estimated and presented in Figs 14 and 15. It is worth noting that the total cabling weight of the electric grid of the vessel with Diesel electric propulsion is about twice of that of conventional propulsion. Energy Efficiency Design Index (E.E.D.I) The Energy Efficiency Design Index has been calculated for the conventional propulsion using the guidelines of IMO in MEPC.1/Circ Furthermore, and in order to make a comparative analysis between the two types of propulsion, the proposed methodology from the Centre for Maritime Technology and Innovation on Nr report for the calculation of EEDI of the Diesel-electric vessel has been used. In all cases, the fuel type considered was either liquid (HFO, LFO, MDO and MGO) or gas (LNG). The results and the extracted conclusions are presented in Figs 16 and 17. By inspecting Figs 16 and 17, the following conclusive remarks are drawn: 1. The best solution, concerning the E.E.D.I., is to use gas as fuel for both types of propulsion. The value of E.E.D.I. is significantly smaller than that with the next highest price corresponding to HFO. 2. The E.E.D.I. of the diesel-electric propulsion when using liquid fuels is slightly better (about 10 grco 2 /GT*Knot less) than that of the conventional propulsion, except when using LNG as fuel, where the two indexes are exactly the same. 3. The E.E.D.I. of both types of propulsion for the under study vessel are significantly higher compared with E.E.D.I. of other types of vessels. The only type of vessel with similar E.E.D.I. is that of yachts. The main reasons for this high differentiation are mentioned here below: a. the under study vessel (like yachts) has very low capacity, a parameter which is at the denominator of the E.E.D.I calculation formula and, hence, increase dramatically the index. b. the under study vessel has very high installed power - in relation to her size - for the propulsion in order to achieve high speed. The installed power of main and auxiliary engines is presented at the numerator of the E.E.D.I. formula and increases the index. As a final result, it can be argued that the under study vessel with either type of propulsion is a rather polluting ship due to her high service speed and low transport work. Techno-economic analysis In order to evaluate which one of the two propulsion systems are more profitable 24, 25, 26 for the under study vessel, a techno-economic analysis has been performed. The following techno-economic parameters have been calculated for both types of propulsion using as variable parameter the type of the fuel (see Table 6 as a typical example) and the cost of: Net Present value (NPV) (see Fig 19) Internal rate of return on investment (IRR) (see Fig 20) Discounted payback period (DPB) (see Fig 21) Present worth cost (PWC) (see Fig 22) In addition, the CAPEX (CAPital EXpenditure) and OPEX (OPerational EXpenditure) indices have been calculated for both types of propulsion, (see Fig 18). The criterion of economic performance in the technoeconomic analysis is the difference in Net Present Value (NPV) of the investment between that of the conventional propelled vessel (NPV conventional ) and that of the Diesel-electric propelled vessel (NPV Diesel-electric ). Where Δ (NPV)>0, then the conventional propulsion is considered to be more profitable than the Diesel-electric propulsion. Techno-economic scenario In order to evaluate the techno-economic analysis for the under study vessel the following scenario has been considered. The total investment cost is assumed to be the cost for the delivery of the vessel. This cost is divided in two categories. The first category is the cost for the construction and acquisition of the hull and any other relative equipment and is assumed equal to (This price has been derived from a vessel with similar dimensions and type). This cost will be covered with own funds and it is assumed to be constant for both types of propulsion (conventional and Diesel electric). The second category is the cost of the acquisition and construction of the electromechanical and propulsion systems. This cost has been analyzed thoroughly for both types of propulsion operating either in Diesel or in gas mode, while a typical example for this analysis is given in Table 7. This cost will be covered exclusively by a loan of 20 years duration. The initial annual incomes are derived from the passengers carried on board, assuming 300 days trading per year, 6 trips per day and 75% average booking capacity. The net ticket price per passenger after deducting any taxation has been assumed to be 15. The annual costs are assumed to be the cost of the fuel and lubricating oil plus the cost of the machinery maintenance plus the crew pay roll. Therefore, the net initial annual net incomes (f t ) are the initial annual incomes minus the initial annual costs. Hence: ft = (300days x 6trips per day x75% x 15 Euro x 150 pax) (C CREW +C FUEL +C L.O +C MAIN. ). For every other year of the period of the techno-economic analysis the annual incomes are calculated from the initial Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 77

17 t C CREW C MAIN. C FUEL C L.O f t A t L t A Lt I Lt Δ Lt F t F t /(1+i) t (F t /(1+i) t ) Table 6: Typical summarising table for NPV, IRR, DPB and PWC calculation of the conventional propulsion operating in L.S Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014

18 t C CREW C MAIN. C FUEL C L.O f t A t L t A Lt I Lt Δ Lt F t F t /(1+i) t (F t /(1+i) t ) NPV IRR 0,4387 DPB 3,061 Table 6: Typical summarising table for NPV, IRR, DPB and PWC calculation of the conventional propulsion operating in L.S 380 (continued) Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 79

19 t C CREW C MAIN. C FUEL C L.O A Lt C t C t /(1+i) t (C t /(1+i) t ) PWC Table 6: Typical summarising table for NPV, IRR, DPB and PWC calculation of the conventional propulsion operating in L.S 380 (continued) 80 Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014

20 CONVENTIONAL PROPULSION (DIESEL MODE) ACQUI- SITION MAINTE- NANCE OPERATION M.D.O) OPERATION LSM.G.O) OPERATION LS180) OPERATION LS380) A MAIN PROPULSION ENGINES & REDUCTION GEARS /year /year /year /year /year TYPE QUANTITY FUEL L.O FUEL L.O FUEL L.O FUEL L.O MAIN ENGINE: WART- SILA 6L34DF 2700kW PROPULSION LINES & REDUCTION GEARS TOTAL TOTAL TOTAL TOTAL TOTAL B DIESEL GENERATORS TYPE QUANTITY OPERATING IN M.D.O CAT GEN SET C9 269bkW (238ekW) 440V 60Hz CAT GEN SET C44 86bkW (76ekW) 440V 60Hz TOTAL TOTAL Table 7: Typical summary table for cost analysis of the conventional propulsion (diesel mode) Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 81

21 CONVENTIONAL PROPULSION (DIESEL MODE) ACQUI- SITION MAINTE- NANCE OPERATION M.D.O) C EMERGENCY DIESEL GENERATOR TYPE QUANTITY OPERATING IN M.D.O CAT GEN SET C44 113bkW (99ekW) 440V 60Hz TOTAL TOTAL 3895 D ELECTRIC MOTORS NOMINAL POWER (kw) QUANTITY TOTAL Table 7: Typical summary table for cost analysis of the conventional propulsion (diesel mode) (continued) OPERATION LSM.G.O) OPERATION LS180) OPERATION LS380) 82 Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014

22 CONVENTIONAL PROPULSION (DIESEL MODE) ACQUI- SITION MAINTE- NANCE OPERATION M.D.O) E TRANSFORMERS TYPE QUANTITY MAIN: 440/220 V DRY TYPE 32kVA EMERGENCY: 440/220 V DRY TYPE 16kVA TOTAL 7000 F POWER CABLES NOMINAL CROSS SECTION LENGTH (m) 3 x 1, x 2, x x x x x x x x TOTAL Table 7: Typical summary table for cost analysis of the conventional propulsion (diesel mode) (continued) OPERATION LSM.G.O) OPERATION LS180) OPERATION LS380) Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 83

23 CONVENTIONAL PROPULSION (DIESEL MODE) ACQUI- SITION MAINTE- NANCE OPERATION M.D.O) G LOAD CIRCUIT BREAKERS RATING (A) QUANTITY AEG MC167N A ICU =25kA (bow thruster) TOTAL 1582 Table 7: Typical summary table for cost analysis of the conventional propulsion (diesel mode) (continued) OPERATION LSM.G.O) OPERATION LS180) OPERATION LS380) 84 Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014

24 CONVENTIONAL PROPULSION (DIESEL MODE) ACQUI- SITION MAINTE- NANCE OPERATION M.D.O) OPERATION LSM.G.O) OPERATION LS180) OPERATION LS380) H AUTOMATIC CIRCUIT BREAKERS FOR D/G AND PANELS TYPE QUANTITY AEG MCL408N A =35kA ICU =35kA AEG MCL258N A =35kA ICU =35kA AEG MCL258N A =35kA ICU =35kA AEG MCL168N A =30kA ICU =30kA AEG MCL128N A =25kA ICU =25kA AEG MCL128N 60-80A ICU =25kA TOTAL GRAND TOTAL Table 7: Typical summary table for cost analysis of the conventional propulsion (diesel mode) (continued). Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 85

25 annual incomes considering a ticket net price inflation rate of 0.04 and deducting the annual costs considering also relative inflation rates. Hence: Annual Incomes at year t=(initial annual net incomes) (1+Ticket net price inflation rate) t 1 Annual Fuel cost at year t=(initial Fuel cost) (1+Fuel cost inflation rate) t 1 Annual L.O cost at year t=(initial L.O cost) (1+L.O cost inflation rate) t 1 Annual maintenance cost at year t= (Initial maintenance cost) (1+main.cost inflation rate) t 1 Annual crew pay roll at year t= (Initial crew pay roll) (1+crew pay roll inflation rate) t 1 The annual tax deduction (A t ) considering linear deduction is: Equation 3: A t = Investment Cost Tax Deduction Period The annual sinking fund considering equal annuity through the years is: Equation 4: A ( ) = L CRF N, i Lt L L Whereas the CRF is: Equation 5: ( L ) NL ( 1+i ) CRF= i 1+i L L FUEL NL TYPE OF FUEL IN $/MT IN /MT LS380 (1) LS180 (2) LS MGO (3) MDO (4) Table 8: Fuel cost (bunker price Singapore on 11/12/13 (source: NOTES 1) LOW SULPHUR FUEL IFO380(RMG380,RMH380) WITH SULPHUR CONTENT 1% 2) LOW SULPHUR FUEL IFO180(RME180,RMF180) WITH SULPHUR CONTENT 1% 3) LOW SULPHUR MARINE GAS OIL (DMA,DMX) WITH SULPHUR CONTENT 0,1% 4) MARINE DIESEL OIL (DMB,DMC) Where: i L is the Loan interest rate and, N L is the loan payback period The loan interest through the year t is: Equation 6: I Lt =r L L t The rest of the loan (L t ) at the beginning of the year t, is: Equation 7: L t+1 =L t A Lt +I Lt The reduction of the loan at year t is: CONVENTIONAL PROPULSION MAINTENANCE INFLATION RATE 0.04 FUEL INFLATION RATE 0.04 LUBRICATING OIL INFLATION RATE 0.04 TICKET NET PRICE INFLATION RATE 0.04 CREW SALARY INFLATION RATE 0.04 TOTAL SEATING PERSONS 150 AVERAGE BOOKING CAPACITY 75% DAYS PER YEAR TRADING 300 TRIPS PER DAY 6 INITIAL NET TICKET PRICE 15 INITIAL ANNUAL NET INCOME NUMBER OF CREW 10 AVERAGE CREW SALARY 1500 TOTAL INVESTMENT (DIESEL MODE) TOTAL INVESTMENT (GAS MODE) PERIOD OF CONSTRUCTION (years) 2 LOAN PAYBACK PERIOD (years) 20 PERIOD OF ECONOMIC ANALYSIS (years) 30 LOAN INTEREST RATE 0.07 MARKET INTEREST RATE 0.12 TAX DEDUCTION PERIOD (linear deduction) Na (years) 20 CAPITAL RECOVERY FACTOR (N L.r L ) SALVAGE VALUE Table 9: Economic parameters and data for elaborating techno-economical analysis for the conventional propulsion 86 Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014

26 Equation 8: ΔL t =A Lt I Lt The net cash flow at year t is: Equation 9: F t =f t A Lt Whereas the initial net cash flow F 0 is: Equation 10: F 0 = (Investment cost covered with own funds) period of construction (1+i M ) where: i M is the market loan rate The CAPEX is given by the following equation: Equation 11: CAPEX=IC i t ( 1+ it ) n ( ) 1+ i 1 t n where: IC is the investment cost, i t is the discount rate and n is the lifetime of the investment Equation 12: OPEX = AFC + ALOC +AMMC + AHMC+ACC+APC where: AFC is the annual cost for fuel consumption (referred as C FUEL in Table 9) ALOC is the annual cost for lubricating oil consumption (referred as C L.O in Table 9), AMC is the annual machinery maintenance cost (referred as C MAIN in Table 9) AHMC is the annual hull maintenance cost ACC is the annual crew salary and provision cost (referred as C CREW in Table 9) APC is the annual premium cost The present worth of the life cycle cost is used to make economical comparisons between investments and can be expressed from the following general equation: Fig 18: CapEx and OpEx comparison diagrams Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 87

27 Fig 19: NPV diagrams Fig 20: IRR diagrams Fig 21: DPB diagrams Equation 13: PWC = PWC C + PWC OM where: PWC C is the present worth cost of capital and, PWC OM is the present worth cost for operation and maintenance Equation (14) can be expressed in more detail: 88 Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014

28 Fig 22: PWC diagrams Equation 14: c PWC = t ( 1+i ) t t t where: C t is the operation cost plus the annual sinking fund and, i t is the discount rate. The cost of the fuel types used for the calculation is depicted in Table 8 Finally all the economic parameters and data for performing the techno-economic analysis are summarised in Tables 9 and 10. According to Figs 18 to 22, the most profitable investment, as expected, is the vessel with the conventional propulsion operating in fuel L.S 380, while the worst one is when using marine diesel oil or marine gas oil as fuel for both conventional and diesel-electric propulsion. Hence the conventional propulsion for the given type of vessel seems to be the best solution (ΔNPV>0) except when using LNG as fuel. In this latter case, the diesel-electric propulsion and the conventional propulsion are very close to each other, as derived from the diagram in Fig 22. This is another proof that in this case study, the Diesel-electric propulsion with the use of DF engines comparing to conventional propulsion with main Diesel engines operating only on DIESEL ELECTRIC PROPULSION MAINTENANCE INFLATION RATE 0.04 FUEL INFLATION RATE 0.04 LUBRICATING OIL INFLATION RATE 0.04 TICKET NET PRICE INFLATION RATE 0.04 CREW SALARY INFLATION RATE 0.04 TOTAL SEATING PERSONS 150 AVERAGE BOOKING CAPACITY 75% DAYS PER YEAR TRADING 300 TRIPS PER DAY 6 INITIAL NET TICKET PRICE 15 INITIAL ANNUAL NET INCOME NUMBER OF CREW 10 AVERAGE CREW SALARY 1500 TOTAL INVESTMENT (DIESEL MODE) TOTAL INVESTMENT (GAS MODE) PERIOD OF CONSTRUCTION (years) 2 LOAN PAYBACK PERIOD (years) 20 PERIOD OF ECONOMIC ANALYSIS (years) 30 LOAN INTEREST RATE 0.07 MARKET INTEREST RATE 0.12 TAX DEDUCTION PERIOD (linear deduction) Na (years) 20 CAPITAL RECOVERY FACTOR (N L.r L ) SALVAGE VALUE Fig 23: Δ (NPV) diagram Table 10: Economic parameters and data for elaborating techno-economical analysis for diesel-electric propulsion Volume 13 No 3 Dec 2014 Journal of Marine Engineering and Technology 89

29 Diesel mode, is profitable and substantially advantageous, from the techno-economical point of view, when using exclusively LNG as fuel. It is noted that a typical example is the modern LNG carriers with dual fuel auxiliary engines operating in gas mode. At this point, it should be mentioned that the Diesel mechanical propulsion with the introduction of two-stroke Dual Fuel main engines operating on gas should be further evaluated and compared with some concrete advantages of Diesel electric propulsion with four-stroke Dual Fuel engines, such as high redundancy of power. Those twostroke engines have passed successfully the manufacturer s shop tests with very good results in fuel consumption and furthermore a few cargo vessels (not yet delivered to the ship owners from the shipyards) have been ordered with these engines. On the other hand, for some type of vessels (like small passenger vessels or ropax ferries or cruise vessels) the use of 2-stroke engines is prohibitive mainly due to the high height of the engine and the low clear height of the engine rooms. Thus, up-to-date, the diesel-electric propulsion on gas mode seems to be the best alternative. SUMMARY OF RESULTS AND DISCUSSION The results of both types of propulsion are tabulated in Table 11 so that critical factors such as weight, emissions, cost etc. can be easily compared. Thus, the electric propulsion for the vessel considered seems to be less technically and economically competitive than the conventional propulsion for the following reasons: The cabling weight at the Diesel-electric propulsion is about twice the cabling weight at the conventional propulsion. Furthermore, it is noted that in the Diesel-electric propulsion case, there are five (5) Diesel Generators operating at medium voltage, while in the conventional propulsion case there are two (2) Diesel Generator of low voltage. This implies that the Diesel-electric propulsion require heavier electromechanical equipment. This fact is against to the payload of the vessel as well as to the effort, especially at high speed vessels to reduce the lightship. CONVENTIONAL PROPULSION DIESEL-ELECTRIC PROPULSION CABLING WEIGHT kgr kgr ELECTRIC POWER FACTOR LOADING OF GENERATORS SEA GOING IN PORT MANEUVERING SEA GOING 91% 83% IN PORT 78% 82% MANEUVERING 76% 79% H.F.O L.F.O E.E.D.I M.G.O M.D.O L.N.G CAPEX DIESEL MODE GAS MODE L.S OPEX (for the first year) L.S L.S M.G.O L.S M.D.O L.N.G Table 11: Summary table 90 Journal of Marine Engineering and Technology Volume 13 No 3 Dec 2014