Study of the sizing of the propulsion and storage system for an hybrid/electric ferry for the Ligurian Natural Parks

Marco Bianucci 1, Luca Baruzzo 2, Marco Ferrando 2,3 Silvia Merlino 1 1 Istituto di Scienze Marine ISMAR-CNR, Forte Santa Teresa, Pozzuolo di , 19032 Lerici, (IT) [email protected] 2 Polo Universitario G. Marconi di La Spezia (Università di Genova), Via dei Colli n.90, 19121 La Spezia 3Università di Genova – DITEN, via all’opera Pia 11, 16145 Genova, Genova (IT)

Abstract

The Gulf of La Spezia is one of the widest and deepest of the whole Tyrrhenian coast, enclosed between two headlands and bordered by an amphitheatre of hills and mountains. Just outside the bay to the west, the pristine Cinque Terre National Park is one of the most important and beautiful natural Mediterranean areas. Human activity and especially viticulture, have helped to create a unique landscape in which the total de- velopment of the typical “stone walls” reaches the length of the famous Great Wall of China. All this to- gether with the characteristics of a crystalline sea, a great network of paths, has made the Cinque Terre an increasingly popular destination for Italian and foreign tourists. The project faces the needs of tourist trans- port within the Park of 5 Terre, the islands of the Portovenere Park and town and the connection with La Spezia, and has the specific objective of defining the “optimal” Electric Ferry boat of 24-meter equipped with state of the art technology, but commercial, as a function of the size of the electric propulsion engine and of the energy storage, according to the different routes and possible stages in the transport service.

Keywords: Ferry boat, hybrid Ferry, Ferry for natural parks

We consider the state of the art, but commercial, 1 Introduction technologies as hybrid engine, energy storage and The Gulf of La Spezia is one of the widest and photovoltaic system, and we select those that are deepest of the whole Tyrrhenian coast, enclosed best suited to the type of service that the ferry has between two headlands and bordered by an am- to do in this particular case. phitheatre of hills and mountains. Just outside the bay to the west, the pristine Cin- 2 Objectives and motivations que Terre National Park is one of the most im- Ferry boats and waterbuses undertake important portant and beautiful natural Mediterranean ar- people transport and provide connections in many eas. Human activity and especially viticulture, seaside touristic areas often close or inside marine have helped to create a unique landscape in natural parks. Pollution and noise are particularly which the total development of the typical “stone undesirable in these contexts [1]. walls” reaches the length of the famous Great Eco - Ferry aims at promoting a substantial reduc- Wall of China. All this together with the charac- tion of chemical pollution and noise, the reduction teristics of a crystalline sea, a great network of of operating costs of public/private transport com- paths, has made the Cinque Terre an increasingly panies, and social acceptance transport on water- popular destination for Italian and foreign tour- ways. The hybrid/electric propulsion of boats ists. equipped with state of the art “marine” high effi- The project aims at defining the “optimal” elec- cient photovoltaic (PV) panels has a lot of advan- tric/hybrid 24-meter Ferry boat, suitable for tour- tages if compared with the conventional endother- ist transport within the Park of Cinque Terre, the mic propulsion: islands of the Portovenere Park and the tourist cities in the surrounding area as La Spezia and Lerici.

1 • the great energy efficiency of the electric (variable speed permanent magnet synchronous motor guarantees reduced emissions in air generator coupled to the electric motor, fixed and in water, speed genset etc..) the optimal size and angular • electric energy can be obtained directly from velocity of the propeller , the kind of the batteries renewable resources, as wind and sun, avoi d- etc . However in this paper we will not go inside ing the use of fossil fuels, this quite technical topics, but we will limit ou r- • an on board high efficient PV plant during selves in illustrating the electric/hybrid general the summer gives a great contribution to the configurations we considered, with the aim of energy balance for the boat, proving the actual feasibility and convenience of • the strong reduction of noise and vib rations using a Ferry with electric propulsion in a real allows a superior comfort, specific case. • the high torque of the electric motor allows a 3 The routes better control, a quick response of the pus h- ing force and rapid and secure manoeuvres, We took into account all the possible routes for • higher torque means increased transport Eco-Ferry in terms of travel distance in miles and capacity without increasing the engine power speed. These routes are: (l ess energy needs and wasting), 1. La Spezia – Portovenere, 4.5 nm; • in general the customer’s energy cost 2. Portovenere - Terrizzo , 0.6 nm; (€/kWh) is lower when using an electric e n- 3. Palmaria Terrizzo - Palmaria Pozzale, 1.8 nm; gine than when using a standard endothermic 4. Portovenere - Cinque Terre, 11.5 nm; diesel engine, 5. Tour of the Islands (Palmaria, , ) , • electric engines are easily controlled by 6.3 nm. automatic devices and this allows a safer navigation. However all these advantages should be co m- pared with the high cost, the problems of reliabi l- ity, and the reduced capacity in terms of energy density of the electric energy storage systems today available. Actually if we compare the gr a- vimetric e nergy density of the gasoline, about 12 kWh/kg (or 10 kWh/Litre ), with that of the sta n- dard commercial Li-ion batteries, about 0.1 -0.2 kWh/kg [2], we see that the transition toward the electric mobility is still actually a challenge. Also if we take into account that the efficiency of an Figure 1: A satellite map of the La Spezia Gulf with the endothermic engine is only about 30%, we get 4k routes we are interested on. Wh/kg that is still more than one order of magn i- tude of that of the best batteries today available 4 The Boat on the market. On the other hand for the boats We considered a 24 m displacement boat , a typical often the weight of the en ergy storage is not so shuttle with a gunwale high and closed with high important and there are cases where the benefits flexibility since the Portovenere Park requests to of the electric mobility are so great that you are transport also a van for some special occasions . willing to accept some compromises, such as the Here some general technical features: limited cruising range. The small boats used as - Length overall and at waterline about 24 m tenders of yachts are an example in w hich the - Beam about 6 m electric mobility is taking hold. Here we want to - Height over the water line about 3 m assess the feasibility and convenience of using electric boats in a specific case: the ferry service - Draft at full load 1.5 m for the tourist around the La Spezia gulf. In this - Full loa d displacement (estimated) 70 t project we have studied many different config u- - Fuel tank 10.0 m3 rations with different technical details concerning - Fresh water tank 2.5 m 3 the 24 meters ferry, as the kind of the electric - Waste water tank 1.5 m3 engine (permanent magnet motor, variabl e reluc- 3 - Holding tank 1.0 m tance motor, synchronous /asynchronous motor etc..) the different “in series” hybrid systems

2

Figure 2: Lines plan of the selected hull form

Figure 3: Top view

Figure 4: Main Deck

Figure 5: Lower Deck

Figure 2 illustrates the lines plan of the selected According to the fact that the foreseen speed hull form, while in figures from 3 to 5 the range of the boat will be in the pre-planing proposed general arrangement of the ferry can be regime, a hull from the SSPA Systematic Series found. [3] was selected.

3 The shuttle should fall under the certification plus space for two wheelchai rs, there is a bath- according to the RINA classification as a passen- room, and going up four steps we find the bar area ger vessel under 24 m for coastal navigation. and finally the wheelhouse. Figure 6 shows a sketch of the boat concept, The lower deck is almost entirely a technical area which is characterized by a huge flat deck that (motors, genset and batteries) but the forward part covers the superstructure. This solution allowed where there is a place for passengers with 12 the maximization of the useful surface for the seats. Thus the total number of seats is 58 + 2. solar panels, accommodating a photovoltaic sy s- The Engine room scheme is presented in Fig. 7. tem of 17 kWp. Here we can see the two diesel engines coupled to electric generators; electric motors drive the shaft lines through a gearbox. 4.1 Boat energy requirements In Fig. 8 the graph “Propulsion power vs. speed” is illustrated; it was obtained taking into account both the hydrodynamic resistance and the overall efficiency of the entire power train system, in- cluding the choice of the propeller (see details in Appendix A and B ). The shape of this curve is Figure 6. Sketch of the proposed concept . typical for this kind of hull and shows that over The open space in the stern can be used to carry a 10-11 knots the total hydrodynamic resistance van. This space, if not used for the van, can be grows quickly. In fact at a speed of 10 knots ap- fitted with removable benches and so used for proximately 75 kW are required, while to reach passenger transport. To ensure a little shadow in 13 knots the power request grows over 280 kW. this area it is possible to open a curtain from the This means that a great attention must be devoted end of the superstructure deck. to the hull form selection and to the choice of the design speed, in order to minimize the fuel co n- sumption.

Figure 8. Propulsion power required to the Ferry for Figure 7: Particular of the Engine Room layout different speed ( V). The main deck is characterized by a large fully The Table 1 lists the travel times and the esti- glazed passenger area that guarantees 46 seats mated energy consumption for the various routes,

Tabel 1. travel times and the estimated energy consumption for the various routes, for different cruise speeds . 4 for different cruise speeds , without considering histogram in Fig. 10. Thus t he 17 kWp PV sys- the on board systems energy consumption. tem, from May to August (the months when tour- To avoid encumbering reading this article, we ism is at its maximum), gives about 8 0 kWh/day. moved in the appendix C the calculus of the size of the on board electrical s ystems. Here we report only the result. The maximum total power r e- quirement of the on board systems is about 1 7kW of which the main contribute stems from the air conditioning unit (cooling, dehumidifying and delivering fresh and clean air). Usually these systems are tuned at 50% of the maximum power, i.e. about 9-10 kW. The energy consumption is thus about 70-80kWh/day. Though this energy amount is not so small if compared with the propeller energy requirement to move the Ferry at the slow cruising speed Figure 9. PVGIS Estimates of long -term monthly solar (typical in the short connection routes ), we will irradiation on the horizontal plane for the La Spezia gulf not include it in the total energy balance of the (from http://re.jrc.ec.europa.eu/pvgis/ ). Ferry. This is because the energy consumption of This demonstrates that the PV system in average the on board systems is in average completely offsets the energy requirement of the on board offset by the energy production of the high effi- systems as air conditioning and services, signifi- cient marine 17kWp PV system. This fact is de m- cantly reducing the amount of batteries installed onstrated in the next section. on board and the energy supply cost s.

4.2 The contribute of the PV System Recently in the market are available the powerful marine PV panels that where originally designed for race boats like those of the famous sailor Gi o- vanni Soldini. The panels laminated with special plastic materials, open a new world of possible photovoltaic solutions hitherto unexplored, not access ible to standard solar panels. In fact in ma- rine applications lightness, flexibility, strength, power and resistance to harsh weathe r and envi- ronmental conditions are all very important (and

“hard”) requirements that are not met by the sta n- Figure 10: PVGIS estimates of solar electricity generation dard PV panels. in kWh/day for a 17kWp PV system made with crystalline The PV system we include in the present Ferry silicon cells placed around the La Spezia gulf (from project consists of almost 100 m2 of these light- http://re.jrc.ec.europa.eu/pvgis/). weight and flexible PV panels, realized with very Estimated losse s due to temperature and low irradiance: high efficient, completely black, back -contact 9.2% (using local ambient temperature). Estimated loss due to angular reflectance effects: 3.8%. Other losses cells. The efficiency of the panels is about 20%, (cables, inverter etc.): 14.0%. Combined PV system and the nominal power of the whole PV plant is losses: 24.9%. about 17 kWp . These panels have been placed on the top roof as in the layout in Fig. 3. Because the 2 5 The studied configurations weight of this panels is only about 2. 1 kg/m (compared to 15-20 kg/ m2 of the standard glass Apart the special 17 kWp PV system, we consi d- PV panels), adding these lightweight PV system ered the following possible cases : does not affect the stability of the boat. 1. 500 kWh of Li-Ion battery storage: only ele c- To evaluate the daily energy yiel d of the 1 7 kWp tric without genset for all the routes, PV system we must consider the local solar irr a- 2. 300 kWh of Li-Ion battery storage: only ele c- diation, the scheduled use of th e F erry and also tric without genset for slow speed cruising the season. The solar irradiation can be obtained and electric with genset (in series hybrid) for from the Geographical Information System tool fast cruising towards the farthest touristic l o- (http://re.jrc.ec.europa.eu/pvgis/ ) made available by the European Commission. The data are r e- cations (CinqueTerre), ported in Fig. 9. From these data we obtain the

5 3. 160 kWh of Li-Ion battery storage: only ele c- weight, volumes and cost s, we decided not to tric without genset for very short distances exceed 500 kWh of storage capacity . connections (Portovenere-Palmaria) and ele c- Wishing then check the possibilities with this tric with genset fo r the other routes. configuration, for different speeds we evaluated the range in terms of both time and distance (space), ta king into account the fact that, to ensure a longer life to the batteries , they should not be discharged over 80% of the full charge (that cor- responds to a energy quantity of 400 kWh). In Fig. 10 we show the range distances for differ- ent cruise speed, taking into account the max i- mum energy available of 400 kWh and without considering the energy consumption of the on board systems , that in average should be offset by  the energy production of the Solbian PV plant. We have therefore analyzed the various routes of in terest to check the validity of this configuration respect to our requirements.

First, we considered the 12 nm path length Porto- venere - Cinque Terre. Dividing the maximum Figure 9. A photo that shows the flexibility and the distance range of Fig. 5 by 12 nm for each cruise lightweight of the new PV panels laminated with speed, we get the results in the Fig. 11. plastic materials, realized for the race boats of the sailor Giovanni Soldini and recently available on the At a speed of 8 kn w e see that the route Portov e- market. nere - Cinque Terre, can be made 6 consecutive times until the battery discharge arrive s at 100 kWh (80% of the full charge); so 3 times round For the validation of these configurations we have trip, for a total of 9 hours. simultaneously taken into account several factors: • The energy balance and the propulsive power required by the boat at various speeds (see Fig. 3), without considering the on board sy s- tems energy consumption compensated by the Solbian PV [4] energy yield; • the connections routes both in terms of speed and in terms of duration ( see the table in the previous page).

Figure 11. Battery discharge starting from 500 kWh as a function of the number of rides and for different ferry speed for the Portovenere –Cinque Terre route.

At a speed of 11 kn the route can be made up to 3 times before recharging the batteries, so it would be advisable to recharge the batteries in Portov e- nere for one hour ( ensuring 80% of full charge) before any departure . In total we get 6 hours of journey and 3 for charging, i.e. 3 times round trip per day, as in the previous case (the difference lies Figure 10. Energy consumption vs d istance for different in the fact that we now need a break of an hour at speed. each return to Portovenere).

5.1 Case 1: a pure electric Ferry The second path considered is the tour of the In the first configuration we considered the boat Palmaria and Tino islands , which is normally powered only by the batteries . Based on the performed at low speed being a very short trip and

6 in coastal waters. The speed of about 8/9 knots requires a limited power, and with 400 kWh of energy available it is possible to make this path for all the day ensuring a departure every hour. In conclusion we can say that with a purely ele c- tric propulsion system it is always essential to limit the cruise speed, even for the longest trips. Notice that for a speed up to 11 kn the vessel requires a power less than 120 kW. From the economic point of view, also if you save money by using smaller motors , you pay a lot for the purchase of a large pack of 500 kWh of batt e- Figure 13 . Battery discharge starting from 300 kWh as a ries. In fact, c onsidering an average cost of 500 function of the number of rides and for different ferry speed for the Portovenere –Cinque Terre route. Euro per kWh, you arrive to a total cost of some 250,000 Euros for this battery package . Moreover As mentioned before, for longer trips at high also the weight is considerable: considering an speeds we must also use a genset. In particularly energy density of 100 Wh/kg we get a total for travelling at a speed of 12 kn we need two weight of 5t for the 500 kWh battery pack. systems (diesel engine coupled to an electric re- We must also take into account that even in this versible motor) of 125-130 k VA each, to cover a pure elect ric configuration a small endothermic power total demand of 215 kW o r so. generator systems (genset ) must be included in the on board equipment as emergency power source.

Figure 14 . Battery discharge starting from 300 kWh as a function of the number of rides and for different ferry Figure 12 . Battery discharge starting from 500 kWh as a speed for the islands tour. function of the number of rides and for different ferry This hybrid configuration allows for higher speed for the islands tour. speeds than the previous case, with a top speed of around 12 kn, and at the same time offers the 5.2 Case 2: a hybrid electric Ferry with convenience of purely electric vehicle at speeds of a large energy storage pack. around 8/9 knots. In this case respect to the previous one we reduce It should be noted tha t the savings in economic the on board battery energy storage to 300 kWh terms reducing the bat tery pack , is not enough to saving about 10 0.000 Euro and 2 tons as weight. cover the difference in cost for the purchase of However we must board a genset to supply energy generators of large size. Th is solution thus ap- for the farthest touristic locations (Cinque Terre) . pears to be relatively costly from an economic Repeating the steps of the previous case we get standpoint. the results in Figs 13 and 14. From Fig. 14 we see that in the case of the longest route, at high speed, 5.3 Case 3 and selected configuration: it would be necessary to recharge the batteries to a hybrid system with a medium each docking. At lower speeds it is possible to battery pack. perform also the return trip before having to r e- charge the batteries. The third case was found to be the most interes t- ing, for both lower costs and high versatility, for On the other hand, the to ur of the islands at lower the specific routes and services of our ferry. Here, speed is guarant eed for the entire working day. respect to the previous case, we reduce the on board battery energy storage to 160 kWh saving abo ut 70.000 Euro (170.000 Euro respect to the

7 first configuration) and 1.4 t as weight (3.4 t re- spect to the first case). To reduce the energy consumption it is assumed that the boat speed will be limited at 8 kn when using the batteries pack alone as source of power. According to Fig. 5, a t 6/8 kn the ferry has a range of 6/4 hours, that would allow a lot of co n- nection route combinations. However, the typical use of the Ferry with this hybrid propulsion sol u- tion has be en thought to be the following: in the morning the Ferry ensures a continuous service of Figure 16. Battery discharge starting from 160 kWh as a short dis tance connections (Portovenere -Islands), function o f the number of rides and for different ferry using only the batteries as source of power, until speed for the islands tour. discharging the batteries up to 20% (approx i- This configuration allows to not stop the Ferry mately) of the full charge. during the day to recharge the batteries. In the Then it takes a longe r round trip connection, as night, on the contrary, a full slow charge will be Portovenere – Cinque Terre - Portovenere, turning made via a plug in a proper chargi ng station. on the genset group as soon the speed exceeds 8 kn.

Figure 17. The batteries discharge -recharge phases during the day according to the use of the ferry as described in the Figure 15 . Battery discharge starting from 160 kWh as a text. function of the number of rides and for different ferry Notice that in this case the genset could work speed for the Portovenere –Cinque Terre route. always at constant speed and power . In fact, the During the cruising at 11 kn the genset group variable power required during the acceleration provides the necessary power for both propulsion phase towards speeds higher than 8 kn, as well as and the recharging of the batteries. Near the dest i- for the manoeuvres’ at docks/jetties, or for short nations the speed falls again below 8 knots and routes, will be fully managed by the battery sy s- the genset are turned off again in order to ma- tem. This means that to optimize the perfor m- noeuvre in the Park/harbour without polluting and ances we can avoid using the very complicate noise. technology behind a variable speed permanent Finally, in the last part of the day, the ferry might magnet synchronous generator coupled to the come back to travel for short distance conne c- electric motor [5], and we can use instead a co n- tions, using only the batteries, now re -charged stant speed genset working in the power/torque (see Fig. 17). According to this co nfiguration and point that maximizes the ef ficiency of both the use of the Ferry, the genset group is chosen to be endothermic engine and the generator . Using the made of two 115 VA generators, sized so as to genset in this way it makes convenient choosing maximize the efficiency and to allow the rechar g- as generator a good asynchronous brushless motor ing of the batteries during the navigation at fast or a variable reluctance motor optimized for co n- speed. In fact 70-75% of the maximum power is tinuous high speed rota tion, cost effective solu- often the best efficiency working range for an tions that guarantee high efficiency and reliability endothermic engine and 75% of 2x115 kVA is compared to permanent magnetic motors. about 170 kW, just the amount of power required to charge the batteries up to 80% of full charge, Acknowledgments starting from 20%, during the two hours travel The project is a collaboration bet ween the Insti- round trip Portovenere – Cinque Terre – Portove- tute of Marine Science (ISMAR) of CNR, the nere, and simultaneously provide the necessary Department of Electrical, Electronic, Telecom- power to the electric motors while the Ferry nav i- munications Engineering and Naval Architecture gates at a speed of 11 kn.

8 of t he University of Genoa, the Municipality an d- ratio as a function of Fr ∇. the Natural and regional Park of Portovene re and The range of variation of the systematically the Solbian Srl company. changed parameters is the following: ≤ ≤ Appendix A: t he vessel resistance. 0.5 Fr ∇ 3.5 0.4 ≤ Fr ≤ 1.1 The hull resistance has been evaluated bot h by the 0.4 < L/B < 7.5 NPL [A1] Systematic Series and by a towing tank test. A preliminary estimate of the vessel resi s- 1.72 < B/T < 10.21 tance has been performed by means of the NPL 4.47 < M c < 8.3 systematic series. The main characteristics of the ferry are as fol- The NPL Series, published in 1969, had the pu r- lows: pose to gather data on hull forms suited for high 7 ≤ V ≤ 14 [ Kn] speed. The series regards semi-displacement hull forms that were tested in a speed range corre s- 0.5 ≤ Fr ∇≤ 1.29 ponding to Froude numbers from 0.40 to 1.10. 0.4 ≤ Fr ≤ 0.54 The series hull forms derive from a parent hull L/B = 4.69 having the following characteristics: B/T =3.62 c • water lines with linear entrance, M = 5.75 • rounded stern sections, The NPL series was used to obtain the prelim i- • linear buttocks in the stern region, nary estimate of the bare hull resistance for the • center of buoyancy located aft of midship displacement of 60 tonnes, in which the skeg is perpendicular. included according to the suggested formulation. Results are illustrated in table A1 and Figure A2. From the parent hull four hull forms have been obtained, by means of an affine transformation. In this way B and T were changed maintaining the displacement unchanged and modifying only the B/T ratio. C To obtain the variation of M , each of the models has been tested at several draughts, and so 22 different hull forms were evaluated. In addition, other ten models hav e been generated by the se c- tional area curve deformation, in order to allow the assessment of the influence of the longitudinal position of the center of buoyancy on the resi s- tance. Tests results, processed using the ITTC ’57 Figure A2. Hull resistance vs the speed of the vessel. friction coefficient, are pres ented in terms of RR/∆

Figure A1. Body plan of the NPL parent model.

9 Vs V Fn Fn  RF RR RHULL RSKEG RTOT_HULL kn m/s - - kN kN kN kN kN 7 3,598 0,235 0,583 2,021 0,380 2,401 0,308 2,709 8 4,112 0,269 0,666 2,591 1,334 3,925 0,394 4,319 9 4,626 0,303 0,750 3,227 2,780 6,007 0,490 6,496 10 5,140 0,336 0,833 3,927 4,550 8,477 0,595 9,072 11 5,654 0,370 0,916 4,691 6,850 11,541 0,650 12,191 12 6,168 0,404 1,000 5,517 9,100 14,617 0,834 15,451 13 6,682 0,437 1,083 6,407 10,214 16,621 0,967 17,588 14 7,196 0,471 1,166 7,357 14,043 21,400 1,110 22,510 Table A1. Hull resistance of the proposed ferry obtained by means of the NPL systematic series These results have been compared with towing tank test results of a very similar hull; Table A2 ηA has been obtained by the authors through a and figure A3 illustrate this comparison. regression based on a collection of data from twin-screw hard-chine model tests made with and NPL TANK TEST without appendages. V RTOT_HULL RTOT_HULL Kn kN kN 7 2,7 3,4 8 4,3 4,7 9 6,5 6,4 10 9,0 8,1 11 12,2 11,0 12 15,5 16,1 13 17,6 21,0 Table A2. Comparison between NPL and towing tank test results To obtain the ferry total resistance the appendage Figure A3. Graphic comparison between NPL and towing and air resistance have to be added, according to tank test results. the formula: As regards the air resis tance, it has be en estimated using the standard formula [A3] : R = R + R + R (A1) T BH AP AA R= K1 ρ AV 2 (A4) AA 2 a T As regards the appendage resistance, it has been where: estimated using the Blount & Fox formula[A2], - K is the air resistance coefficient, (assumed which holds for Fr ∇>1.0; accordingly , the appen- value 0.6); ρ dage resistance was added only for the highest - a is the air density; velocities. - AT is the area of the projection of the above   water part of the vessel on a transversal plane; =1 − - V is the vessel speed. RAPP R BH 1  (A2) η  A Finally a 10% Sea Margin has been added to a c- where: count for adverse meteo-marine conditions . RBH is the bare hull resistance; Final results are resumed in Table A3 and in Fig . ηA is defined in the following equation A4. Table A3 includes values of the effective power required by the complete hull to the pr o- 1 pulsive system ( PE=RT*V). η = (A3) A 0.005Fr 2 + 1.05 ∇

10 V V Fr Fr ∇ RBH RAP RAA RT RT + SM PE kn m/s - - kN kN kN kN kN kW 7 3.598 0.235 0.583 3.37 0.045 3.42 3.76 13.52 8 4.112 0.269 0.666 4.67 0.059 4.73 5.20 21.39 9 4.626 0.303 0.75 6.36 0.075 6.44 7.08 32.75 10 5.14 0.336 0.833 8.11 0.093 8.20 9.02 46.38 11 5.654 0.37 0.916 10.98 0.112 11.09 12.20 68.99 12 6.168 0.404 1 16.07 0.85 0.133 17.05 18.76 115.70 13 6.682 0.437 1.083 20.99 0.967 0.157 22.11 24.33 162.54 Table A3: Calculated values of the Resistance component and effective power.

• n is the number of revolutions per second of the propeller • D is the propeller diameter • VA is the propeller advance speed As regards the expanded area ratio , a first value to obtai n a cavitation free propeller is given by the Keller formula [B3]: A ()1,03+ 0,3 ⋅Z ⋅ T E = + k (B5) ()+⋅−γ ⋅ 2 AO p A hpD V where: Figure A4. Graphic representation of the ferry resistance • Z is the propeller blade number components. 2 • pA is the atmpspheric pressure in N/m (101300 N/m 2) Appendix B: the propeller choice . • γ ⋅h is the hydrostatic pressure acting on The propeller choice has been performed by the propeller means of the Wageningen B systematic series • pV is the sea water vapour pressure in [B1]. N/m 2 (2339 N/m 2) The open water characteristics of a propeller are • k is a constant that assumes values co m- usually described in terms of thrust and torque prised from 0 for lightly loaded propellers coefficients and by the open water efficiency ; to 0,2 for heavily loaded propellers . these coefficients are defined as follows: The ferry propeller choice has been performed T K = using the polynomial formulation due to Ooster- T ρ ⋅2 ⋅ 4 veld and van Oossanen [B2], that use the follo w- n D (B1) ing equations: Q K = t u Q 2 5 sP  A  v ρ ⋅n ⋅ D =T ⋅⋅⋅() E ⋅ () (B2) KCJT∑ stuv, , ,     Z s, t , u , v D   A  J K O η = ⋅ T (B3) (B6) 0 π 2 KQ t u sP  A  v =Q ⋅⋅⋅() E ⋅ () as a function of the advance coefficient (a non KCJQ∑ stuv, , ,     Z dimensional speed coefficient) s, t , u , v D   A O  V (B7) J = A n⋅ D (B4) that hold for a Reynolds number 2 ∙ 10 . where: T Q Values of the C and C coefficients and • T is the propeller thrust in Newton s, t , u , v s, t , u , v • Q is the torque absorbed by the propeller of the s,t,u and v parameters are shown in Table • ρ is the water density ( 1025 kg/m 3) B1.

11 The propeller choice has been performed at the Appendix A, the required thrust and propeller design speed using three different values of the advance speed at the design speed can be eva- diameter in order to better explore the coupling luated: with the electric motor. R = T = ⋅( − ) For each of the selected values of the diameter the T VA V1 w (B9) 1− t maximum efficiency pitch ratio was selected, according to the procedure outlined below. allowing the determination of the value y of the Use is made of the auxiliary variable y: auxiliary variable at the design speed. For each considered value of the pitch ratio P/D, k T nD2⋅ 2 T the equilibrium value of the advance coefficient y ==T ⋅ = J2ρ⋅⋅ nDV 242 ρ ⋅⋅ DV 22 can be found intersecting the design value y with A A . the propeller curve. (B8) From this equilibrium value of the advance coef- that allows to eliminate the propeller number of ficient the propeller revolutions number can be revolution which is at this stage unknown. obtained together with the engine revolutions Having assumed suitable values for the propulsive using the reduction ratio i: coefficients [B4]: [] (B10) ∙ t=0.04 w=0.02 η =1.0 R ∙ ∙ 60 [] (B11) and using the RT resistance values obtained in The power absorbed by the propeller can now be

Tabel B1. Values of the coefficients of the B series polynomials

12 computed through the equilibrium K Q value that can be obtained in correspondence of the equil i- brium advance coefficient value.

= 2π ρ 3 PO kQ n D. (B12)

Among all the p ropellers tested we consider here only those of greater efficiency, namely: • PROPELLER 1 : D = 0 6. m ; Z = 4 ; P A = 2.1 ; E = 59.0 ; efficiency 0.60 D A O Figure B2. Curves relatives to the propeller 2 (D=0.8m). = With a gear reduction ratio of 3.741 we get the • PROPELLER 2 : D 0.8 m ; Z = 3 ; figures in Table B3 for propeller 2 .

2 P A V V T VA KT/J J nelica nmotore PB = E = 1.0 ; 0.35 ; efficiency 0.70 knots m/s kN m/s - - giri/sec RPM kN D AO 7,0 3,598 1,957 3,526 0,427 0,770 5,724 1284,83 10,097 8,0 4,112 2,709 4,030 0,452 0,760 6,628 1487,70 15,995 = 9,0 4,626 3,687 4,533 0,486 0,740 7,658 1718,89 25,619 • PROPELLER 3 : D 1.0 m ; Z = 3 ; 10,0 5,140 4,699 5,037 0,502 0,730 8,625 1936,04 37,269

11,0 5,654 6,355 5,541 0,561 0,710 9,755 2189,64 55,834

P A 12,0 6,168 9,790 6,045 0,726 0,660 11,448 2569,66 97,686 =1.0 ; E = 0.30 ; efficiency 0.75 13,0 6,682 12,777 6,548 0,807 0,640 12,790 2870,79 140,250 D AO Table B3. Data relative to the propeller 2 (D =0.8m). In Figures B1-B3 and in the corresponding Tables B2-B4 the characteristic curves and figures of each of the selected propellers are reported.

Figure B3. Curves relatives to the propeller 3 (D =1.0m). With a gear reduction ratio of 3.741 we get the

figures in Table B4 for propeller 3 . Figure B1. Curves relatives to the propeller 1 ( D =0.6m). 2 V V T VA KT/J J nelica nmotore PB With a gear reduction ratio of 3.031 we get the knots m/s kN m/s - - giri/sec RPM kN figures in Table B2 for propeller 1 . 7,0 3,598 1,957 3,526 0,427 0,850 4,148 931,12 9,977 8,0 4,112 2,709 4,030 0,452 0,840 4,797 1076,81 15,787

2 9,0 4,626 3,687 4,533 0,486 0,830 5,462 1226,01 23,836 V V T VA KT/J J nelica nmotore PB 10,0 5,140 4,699 5,037 0,502 0,820 6,143 1378,84 34,654 knots m/s kN m/s - - giri/sec RPM kN 11,0 5,654 6,355 5,541 0,561 0,800 6,926 1554,64 51,743 7,0 3,598 1,957 3,526 0,427 0,760 7,733 1406,24 11,890 12,0 6,168 9,790 6,045 0,726 0,750 8,060 1809,04 89,418 8,0 4,112 2,709 4,030 0,452 0,750 8,955 1628,56 18,739 13,0 6,682 12,777 6,548 0,807 0,730 8,970 2013,49 127,493 9,0 4,626 3,687 4,533 0,486 0,730 10,350 1882,33 29,762 10,0 5,140 4,699 5,037 0,502 0,720 11,660 2120,52 43,142 Table B4. Data relative to the propeller 3 (D =1.0m). 11,0 5,654 6,355 5,541 0,561 0,700 13,193 2399,22 64,162 12,0 6,168 9,790 6,045 0,726 0,640 15,741 2862,70 117,367 Table B2. Data relative to the propeller 1 ( D =0.6m).

13 Appendix C: the on board electric Lenght Width Height Volume balance. m m m m3 The on board electric balance of the installed MAIN DECK utilities is illustrated by the Table C1: main passen. 9 4 2 76 room

UTILITIES bar 2 4 3 22

PABSORBED steering room 2 3 3 15 N° Description kW LOWER DECK sec. passen. 1 AIR CONDITIONING 11.46 5 4 2 41 room 4 24V BATTERY CHARGER/INVERTER 0.75 Tabel C2. The sizes of the rooms considered for air condi- tioning. 5 NAVIGATION INSTRUMENT 1.4

6 GALLEY 1.0 We considered both the loss of thermal energy by irradiation toward outside, and the gain of thermal 7 PUMP 0.23 energy for solar radiation and greenhouse given 8 LIGHTS USERS 220V 1.0 from glazed surfaces. 9 OTHERS 2.86 For each room we evaluated also the contributions

TOTAL 18.70 due to the air changes per hour using the follow- ing formula which includes both the flow sensi- Tabel C1. On board electric balance of the installed utili- ties tive, i.e. related to a change in temperature, and the flow latent, related to a phase transition: As we can see the larger contribution is given by the air conditioning system, thus here we report qair = n ⋅V ⋅ ρ ⋅[c ⋅ (T − T )+ r ⋅ (y − y )] P out in e i only the detailed calculations concerning this part. (C1) To plan the air conditioning system it must be considered the operation place of the Ferry: the where: north Mediterranean sea, and the season: summer. - n is the number of air changes per hour; So that the typical values of the environmental parameter are given by: - V is the volume of the room; - ρ is air density = 1.2 kg/m 3; - Outdoor temperature: TOUT = 35°C; - cP is the specific heat of air = 1000 J/kg - Outdoor relative humidity: iOUT = 0.7; K; - Indoor temperature: TIN = 27°C; - r is the latent heat of phase change = - Indoor relative humidity: iIN = 0.5 2.5x10 6 J/kg;

In the main deck we have three zones: the main - ye is the outdoor relative humidity ob- passengers room, the bar and the steering room, tained from the psychrometric chart; while in the lower deck we have the secondary passengers room (see Table C2 for the sizes of - yi is the internal relative humidity ob- these rooms). tained from the psychrometric chart. For each room we have considered all the surfac- es, distinguishing between horizontal and vertical Finally, we also took into account the heat sources surfaces, opaque and transparent, submerged and in the rooms, that can be divided into two broad emerged taking into account also the materials categories: sources due to equipment such as they are made, the thickness and the correspond- lighting, appliances, computers, etc. and anthro- ing value of the thermal conductivity k. pogenic sources such as people inside the room It is important to stress that for the insulations of carrying out a certain activity. The thermal flow the external walls we considered standard mate- due to the equipment is equal to the absorption of rials for boat building while today special mate- power of them, while for the anthropogenic rials with exceptionally low thermal conductivity sources we used the following formulation: and high thermal inertia, are available, decreasing = ⋅ ( + ) the general energy requirements. qsorg _ antr n qlat _unit qsens _ unit (C2)

14 where: - n is the number of people;

- qlat_unit is the latent heat flow that depends on the activity of the people;

- qsens_unit is the sensible heat flow which depends on the activity of the people too.

At the end of these calculations, we got the ther- mal fluxes for the rooms of the main and lower decks reported in table B1. We see that total thermal flux is about 51kW, i.e. about 17400 Btuh (see Table C3).

Volume qtot m3 W MAIN DECK main passen. 76 29213 room bar 22 6199 steering room 15 6358 LOWER DECK sec. passen. 41 9350 room TOTALE 51120

Tabel C3.Thermal power needs for air conditioning.

15

References [1] E. Pecorari, S. Squizzato, A. Ferrari, G. Cuz- zolin, G. Rampazzo, WATERBUS: A model to estimate boats’ emissions in “water cit- ies” , Transportation Research Part D: Trans- port and Environment, 23 , August 2013, Pages 73-80, ISSN 1361-9209, http://dx.doi.org/10.1016/j.trd.2013.04.003 . [2] J. Van Mierlo, G. Maggetto, Ph. Lataire, Which energy source for road transport in the future? A comparison of battery, hybrid and fuel cell vehicles , Energy Conversion and Management, 47 , Issue 17, October 2006, Pages 2748-2760, ISSN 0196-8904, http://dx.doi.org/10.1016/j.enconman.2006.0 2.004. [3] Lindgren H. Williams A. “Systematic tests with small fast displacement vessels, in- cluding a study of the influence of spray strips”, Publication nr. 65 SSPA, Göteborg 1969. [4] For technical specifications of the Solbian PV panels see at http://www.solbian.com . [5] Notti E., Messina G., Sala A., Rossi C. New hybrid diesel electric propulsion system for trawlers. From “Final report of European Commission, JRC Scientific and policy reports, Information Collection in Energy Efficiency for Fisheries (ICEEF2011)”, Edited by Antonello Sala, Emilio Notti (CNR, ISMAR) Jann Martinsohn, Dimitrios Damalas (JRC), 2011. The report has been prepared under contract ICEEF Service Contract Nr. 256660. [A1] BAYLEY D. “The NPL high speed round bilge displacement hull series”, Maritime Technology Monograph No.4, The Royal Institution of Naval Architects, 1969. [A2] Donald. L. Blount and David L. Fox, “Small-Craft Power Prediction”, Marine Technology, Vol. 13, No. 1, Jan. 1976, pp. 14-45 [A3] G. Hughes, “The Air Resistance of Ships' Hulls and Superstructures”, Institution of Engineers and Shipbuilders in Scotland, 1932

16