Analysis of the Use of Electric and Hybrid Drives on SWATH Ships

energies

Article Analysis of the Use of Electric and Hybrid Drives on SWATH Ships

Andrzej Łebkowski * and Wojciech Koznowski *

Department of Ship Automation, Gdynia Maritime University, Poland Morska St. 83, 81-225 Gdynia, Poland * Correspondence: [email protected] (A.Ł.); [email protected] (W.K.)

Received: 2 November 2020; Accepted: 7 December 2020; Published: 8 December 2020

Abstract: The article presents issues related to the possibility of using electric and hybrid systems to drive Small Waterplane Area Twin Hull (SWATH) vessels. Ships of this type have significantly less sway and heave compared to monohull crafts and catamarans. Thanks to the synergistic combination of the hydrodynamic properties of SWATH hull and electric drive systems, they can be an interesting proposition for use in transport of passengers and offshore wind farms service crews. The paper presents comparative test results of an electric drive system powered by Hybrid Energy Storage System, which are a combination of systems consisting of batteries (BAT), hydrogen fuel cells (FC) and diesel generators (D). For the presented configurations of propulsion systems, mathematical models taking into account the hydrodynamic resistance of the hull of the vessel have been developed and implemented in the Modelica simulation environment. The tests carried out for various configurations of the drive system have shown reduced energy consumption by the DIESEL-ELECTRIC drive system (by approx. 62%), as well as the reduction of harmful greenhouse gas emissions to the atmosphere (by approx. 62%) compared to the conventional DIESEL drive.

Keywords: electric vehicles; electric ships; electric marine propulsion; electric hybrid systems

1. Introduction The restrictions related to the emission of harmful gases to the atmosphere related to transport [1–4] contribute to the development of environmentally friendly technologies. In order to achieve this task, an effort related to the use of ecological drive systems [5], including electric and hybrid [6,7], is undertaken. Thanks to the use of low-emission drive systems, the level of energy consumption is reduced, as well as the amount of poisonous exhaust gases emitted to the natural environment [8,9]. The exhaust gases emitted by the internal combustion engine include those that can be classified as harmless to the health of living organisms (oxygen O2, nitrogen N2, hydrogen H2); poisonous to living organisms (carbon monoxide CO, HC hydrocarbons and their derivatives, nitrous oxides (monoxide and dioxide), sulphur oxides (monoxide, dioxide, trioxide), soot and smoke (PM), ashes, heavy metals, other solid substances and heavy organic compounds) harmful to the environment and favouring the development of the greenhouse phenomenon in the atmosphere (carbon dioxide CO2, methane CH4, ammonia NH3, nitrous oxide N2O) [10,11]. Another factor contributing to the reduction of energy consumption and the amount of poisonous exhaust gases emitted to the atmosphere by ships is the use of hull structures with low hydrodynamic drag [12,13] or optimization of the hull shape in terms of minimizing motion resistance [14,15]. In practice, one can come across innovative structures limiting resistance, such as, a catamaran with an air cushion [16], multihull crafts with various float configurations [17,18], numerous designs of SWATH type vessels [19–21] and various innovative structures employing hydrofoils [22–29]. Anti-collision systems [30–34] and methods of optimal ship steering [35–40] are also used as another way of minimizing the ship energy consumption.

Energies 2020, 13, 6486; doi:10.3390/en13246486 www.mdpi.com/journal/energies Energies 2020, 13, 6486 2 of 26 Energies 2020, 13, x FOR PEER REVIEW 2 of 27

BearingBearing in in mind mind the the comfort comfort of of people people working working and and transported transported by by sea, sea, parallel parallel efforts efforts are are made made toto develop develop a a ship ship hull hull structure with the greatest possible stability in wave. The The minimum minimum level level of of accelerationacceleration that shouldshould bebe metmet byby sea sea vessels vessels in in order order to to ensure ensure the the comfort comfort of travelof travel according according to ISO to ISO6954: 6954: 2000 2000 is 0.2 is g0.2 for g thefor crewthe crew and and passengers passengers and and 0.4 g0.4 for g anfor experienced an experienced crew crew [41]. [41]. TheThe above above criteria are certainly metmet byby SmallSmall WaterplaneWaterplane Area Area Twin Twin Hull Hull (SWATH) (SWATH) vessels. vessels. Due Due to tothe the stable stable position position of this of typethis type of ships of inships wave, in theywave, can they be usedcan be in hydrographicused in hydrographic surveys, passenger surveys, passengertransport, transport, public utility public services, utility o ffservshoreices, wind offshore farms wind and farms others. and others. WithWith the the development development of of tools tools for for modeling modeling the the hydrodynamic hydrodynamic drag drag of the of theship’s ship’s hull hull[42], [the42], designthe design of the of SWATH the SWATH type type underwent underwent modifications modifications [21] [from21] from the 1st the generation 1st generation developed developed in the in 1970s,the 1970s, consisting consisting of two of struts two struts and two and torpedo-sh two torpedo-shapedaped floats floats through through the SWATH the SWATH II (four II (fourstruts, struts, two torpedoes)two torpedoes) [43], [SWATH43], SWATH III (four III (four struts, struts, four four torp torpedoes),edoes), up up to tothe the SWASH SWASH (one (one central central strut strut and and largelarge torpedo, torpedo, with with two two small small side side floats) floats) (Figure (Figure 11)) andand finallyfinally toto vesselsvessels usingusing hydrofoilshydrofoils underunder itsits hullhull like like the the HYSWATH HYSWATH [[44].44].

FigureFigure 1. 1. ComparisonComparison of of hull hull shapes shapes of of various various vessel vessel types: types: ( (aa) )MONOHULL, MONOHULL, (b (b) )CATAMARAN, CATAMARAN, ((cc)) SWASH, SWASH, ( d) SWATH I,I, ((ee)) SWATHSWATH II, II, ( f(f)) SWATH SWATH III. III.

SWATHSWATH type type vessels vessels are are built built on on the the basis basis of oftw twoo submerged submerged floats floats connected connected by struts by struts to the to platformthe platform above above the waterline. the waterline. Thanks Thanks to this, to they this, have they a havehull with a hull a withsmall awaterline small waterline area, which area, minimizeswhich minimizes the contact the contact area with area the with sea the surface. sea surface. Minimizing Minimizing the area the of area the ofship the having ship having contact contact with thewith water the water surface surface has a hasvery a verybeneficial beneficial effect e ffonect reducing on reducing the wave the wave resistance resistance of the of ship’s the ship’s hull. hull. At theAt thesame same time, time, basing basing the structure the structure on two on twosubmerged submerged torpedoes torpedoes results results in very in veryhigh highstability stability at high at operatinghigh operating speeds speeds and andsignificant significant waves waves on onthe thehigh high seas. seas. Unfortunately, Unfortunately, the the use use of of submerged submerged torpedoestorpedoes increases increases the the total total wetted wetted surface surface area area an andd increases the frictional resistance. Thanks Thanks to to this,this, SWATH SWATH ships ships achieve achieve very very high high stability stability at athigh high operating operating speeds speeds and and significant significant waves waves on the on high seas [12,21,45]. Additionally, they have a large, wide and flat platform that can be used for

Energies 2020, 13, 6486 3 of 26

Energies 2020, 13, x FOR PEER REVIEW 3 of 27 the high seas [12,21,45]. Additionally, they have a large, wide and ﬂat platform that can be used for transportation ofof goodsgoods oror to to install install specialized specialized equipment. equipment. Examples Examples of of SWATH SWATH vessel vessel structures structures are areshown shown in Figure in Figure2. 2.

(a) (b)

Figure 2.2. SampleSample photosphotos of of SWATH SWATH ships: ships: (a) SWATH(a) SWATH GEN. GEN. I [46 ],I ([46],b) SWATH (b) SWATH GEN. II GEN. [47], (cII) SWATH[47], (c) SWATHGEN. III [GEN.48], (d III) SWATH[48], (d) GEN.SWATH IV–SWASH GEN. IV–SWASH [49]. [49].

The article analyzes the possibility of using an electric propulsion system system for for a a SWATH SWATH type vessel powered by HybridHybrid EnergyEnergy StorageStorage System,System, consistingconsisting of:of: a chemical-based energy store (rechargeable batterybattery packs—BAT),packs—BAT), aa hydrogenhydrogen fuelfuel cellcell (FC)(FC) andand aa dieseldiesel engineengine generatorgenerator (D).(D). Based on the operational data from the actual SWATH SWATH ship, simulation models were developed for which the conventional internal combustion en enginegine propulsion system was replaced with an electric one powered by Hybrid Energy Storage SystemSystem (HESS). The advantage of using electric main propulsion ofof the the ship ship is theis possibilitythe possibility of reducing of reducing the energy the consumptionenergy consumption and emission and ofemission poisonous of poisonousgases into thegases atmosphere. into the atmosphere.

2. Operational Operational Properties of SWATH VesselsVessels Increased stabilitystability of of SWATH SWATH vessels vessels on the on wave the comparedwave compared to monohull to monohull ships, and ships, the possibility and the possibilityof reducing of the reducing emission the ofemission harmful of gases harmful into gase thes atmosphere into the atmosphere from the from diesel the propulsion diesel propulsion system, system,have a positive have a net positive eﬀect onnet the effect possibility on the of possibility their implementation. of their implementation. SWATH ships areSWATH characterized ships are by characterizedsmall waterplane by small area, thankswaterplane to their area, streamlined thanks to shape their andstreamlined small area shape struts and supporting small area the struts wide supportingand spacious the structure wide and of thespacious main deck structure on two of submerged the main deck hulls on similar two tosubmerged torpedoes. hulls It is similar estimated to torpedoes.that the SWATH It is estimated type vessels that have the SWATH a waterline type area vessel thats ishave half a the waterline size of monohullarea that is vessels half the of similarsize of monohulldisplacement. vessels SWATH of similar struts displacement. are characterized SWATH by streamlinedstruts are characterized shapes, thanks by streamlined to which the shapes, wave thanksresistance to which of such the a vesselwave resistance is much lower of such than a vessel in a classic is much monohull. lower than The in presence a classic ofmonohull. the supports The presencehas an eﬀ ofect the on supports reducing has the an volume effect ofon thereducing ship’s the hull volume and the of area the ofship’s itscontact hull and with the seaarea waves. of its Ascontact a result, with the sea energy waves. transferred As a result, by the the energy waves tran to thesferred hull isby lower, the waves and theto the ship hull itself is lower, becomes and more the shipstable. itself At thebecomes same more time, thestable. space At availablethe same ontime board, the ofspace a SWATH available vessel on board is much of a larger SWATH compared vessel tois muchmonohull larger vessels. compared Unfortunately, to monohull placing vessels. the load-bearingUnfortunately, elements placing of the the load-bearing SWATH structure elements completely of the SWATHunder the structure water surface completely increases under the totalthe water wetted surfac areae of increases vessel and the increases total wetted the frictional area of vessel resistance, and whichincreases in turnthe frictional translates resistance, into increased which consumption in turn translates of energy into increased used to propel consumption the ship. of Onenergy the otherused to propel the ship. On the other hand, when the torpedo-shaped hulls are submerged, they act as stabilizers, using the phenomenon of an exponential decrease in wave influence with increasing

Energies 2020, 13, 6486 4 of 26

Energies 2020, 13, x FOR PEER REVIEW 4 of 27 hand, when the torpedo-shaped hulls are submerged, they act as stabilizers, using the phenomenon of an exponential decrease in wave influence with increasing depth. An important element when depth. An important element when designing a SWATH vessel is the selection of the appropriate designing a SWATH vessel is the selection of the appropriate width between the supports. The spacing width between the supports. The spacing of supports influences the ship’s stability related to the ofaction supports of heeling influences moments the ship’s from stabilitywind and related the mo tovement the action of the of heeling transported moments cargo from and windpassengers. and the movementFigure 3 shows of the an transported example of cargo a vessel and of passengers. the SWATH Figure II type,3 shows called an M/V example FOB SWATH of a vessel 4, which of the SWATHbelongs IIto type, the calledfamily Mof/V sister FOB SWATHvessels built 4, which at Danish belongs Yachts to the A/S. family These of sister ships vessels are currently built at Danish used Yachtsmainly A to/S. operate These ships offshore are wind currently farms used [50]. mainly to operate offshore wind farms [50].

FigureFigure 3. SWATH GENERATION II–MII–M/V/V FOB SWATH 4, IMO 9672947, (former SEA STORM) STORM) [51]. [51].

TheThe operationaloperational datadata of an exemplary FOB FOB SW SWATHATH vessel vessel was was taken taken from from the the shipowner shipowner [52]. [52 ]. TableTable1 1presents presents exemplary exemplary parameters parameters of of M M/V/V FOBFOB SWATHSWATH 2,3,4,52,3,4,5 andand 6.6.

Table 1.1. SpeciﬁcationSpecification of M/V M/V FOB SWATH 2,3,4,5 and 6 [52,53]. [52,53].

ParameterParameter Description Description Parameter Parameter Description Description NameName M M/V/V Fob Fob Swath Swath 2-3-4-5 2-3-4-5 Engines Engines 2 × 1213 2 1213 kW kW MAN MAN V12-1650 V12-1650 × OwnerOwner OOffshoreﬀshore Windservice Windservice A/S Waterjets Waterjets 2× Hamilton 2 Hamilton HM721 HM721 × Built 2014–2015A/S /2020 Gear 2 Hundested GI50 × Type SWATH Generator 2 80 ekW KOHLER/John Deere Built 2014–2015/2020 Gear 2× Hundested× GI50 Classiﬁcation DNV-GL 1A1 HSCLC CREW R1 Service speed 20–22 kn HullType and Superstruct. Aluminum SWATH Generator Max. speed 2 × 80 23–24 ekW kn KOHLER/John Gross Tonnage 243 Fuel tankDeere 36,000 L NetClassification Tonnage 73DNV-GL 1A1 HSCLC Service Fuel speed consumpt. 20–22 approx. kn 323 L/h Length Overall 25.70CREW m R1 Operating time 24 h Breadth 10.60 m Freshwater 4000 L Hull and Aluminum Max. speed 23–24 kn Draft max CAT 1.80 m Crew 4 DraftSuperstruct. max SWATH 2.40 m IP 24 Gross Tonnage 243 FuelCrane tank 36,000TMP750K, L max. load 1.47 t (5 m) Net Tonnage 73 Fuel approx. 323 L/h The SWATH propulsion system is most oftenconsumpt. located in submerged torpedoes and partially in the supportsLength Overall together with 25.70 ballast, m fuel and freshwater Operating tanks. Classic24 h propellers or water jet drives are used as propulsors. Both designs can be driventime by internal combustion engines located on the Breadth 10.60 m Freshwater 4000 L Draft max CAT 1.80 m Crew 4

Energies 2020, 13, 6486 5 of 26 vessel’s deck and transmitting the driving torque through the Z-type drive with bevel gears or directly by engines located in the torpedoes and transmitting the driving torque through the propeller shaft or belt transmissions. In some constructions, gearboxes between the drive motor and the propeller are used to increase the eﬃciency of the drive system. The location of the drive system components has an obvious impact on the dimensions of the struts, which translates into the value of the wave resistance of the vessel. An important aspect is also crew access to the propulsion system components and the possibility of service. The employed propulsion systems make it possible to accelerate these ships to speeds of up to 25 kn. SWATH type crafts are characterized by very good wave stability and resistance to rolling even in diﬃcult sea conditions and wave height reaching several meters. Table2 presents a summary of the design parameters of Monohull/Catamaran/SWATH ships.

Table 2. Comparison of design parameters of Monohull/Catamaran/SWATH craft types.

SWATH SWATH Parameter Unit Monohull Catamaran SWATH I SWATH II III IV Torpedoes (ﬂoats) - 0 0 2 2 3 1 Strut - 0 0 2 4 4 3 Hull - 1 2 0 0 0 0 Strut breadth m - 2.50 0.61 0.65 0.65 0.87 Strut length m - 25.40 15.73 9.10 9.14 15.74 Length Overall LOA m 25 25 25 25 25 25 Beam Overall BOA m 11 11 11 11 11 11 Waterline Beam BWL m 10.50 11.00 8.67 8.67 8.67 8.38 Waterline Length LWL m 22.37 23.38 15.75 15.59 15.59 15.74 Draft m 1.40 1.50 2.71 2.71 2.71 4.10 Displaced volume m3 190.91 173.42 171.31 157.03 158.88 70.17 Displacement t 195.87 177.93 175.76 161.11 163.01 71.99 Wetted area m2 231.08 229.02 314.82 302.01 308.41 161.55 Waterplane area coeﬀ. - 0.844 0.559 0.106 0.053 0.053 0.108 Total resistance (at 24 kn) kN 139.00 171.65 165.65 159.88 157.95 138.59 Total Power (at 24 kn) kW 2451.72 2119.27 2921.71 2819.97 2785.95 2444.54

In order to reduce energy consumption for ship motion, it is proposed to use an electric propulsion system powered by HESS. The use of an electric propulsion system can contribute to an increase in its overall efficiency, which would consequently translate into a reduction in energy consumption for ship propulsion and the amount of exhaust gases emitted into the atmosphere. The electric drive system, including the main electric machine, is characterized by smaller dimensions compared to the conventional internal combustion engine. Moreover, the use of energy storage in the form of HESS, and in particular electrochemical batteries, contributes to the even distribution of the ship’s weight. Thanks to the use of the power grid on the ship, it is possible to arrange the elements of the electric propulsion system in different places of the ship, ensuring optimal use of space. Moreover, in order to increase the ship’s operability, it is possible to use containerized, interchangeable energy stores, which can be easily installed onboard the vessel. Several configurations of propulsion systems were analysed: DIESEL (ship powered only by an internal combustion engines); BAT-D (vessel powered by electric motors powered by battery electricity storage and diesel generating sets); BAT (ship powered by electric motors powered only by battery electricity storage); FC-BAT-D (vessel powered by electric motors powered by hydrogen fuel cell and battery electricity storage with diesel generating sets), FC-BAT (vessel powered by electric motors powered by hydrogen fuel cell and battery electricity storage).

3. Modeling

3.1. Mathematical Description An important element influencing the operational properties of a marine craft is the optimal selection of the propulsion system. The above issue should be resolved on the basis of the tasks the vessel will perform, the future navigation area and operational requirements. An essential element Energies 2020, 13, 6486 6 of 26 when choosing a propulsion system is to determine the total resistance associated with a moving ship, and on this basis, with the known efficiency of propellers, it is possible to determine the power necessary to propel the ship under specific environmental conditions (ship speed, sea state, wind strength, sea currents). The total resistance of a moving ship is related to the external and hydrodynamic forces acting on the hull. The magnitude of these forces depends mainly on the speed of the ship, as well as its geometrical dimensions and shape. The estimated value of the resistance of every ship can be determined by a dependence taking into account the following values: wave resistance, frictional resistance, pressure resistance and additional resistance: RTOT = Rw + R f r + Rp + RADD (1) where: RTOT—total ship resistance; Rw—wave resistance; Rfr—frictional resistance; Rp—pressure resistance; RADD—additional resistance. There are many studies in the literature explaining the individual components of Equation (1) and the method of determining the total resistance of the ship [26,54–57]. However, it should be remembered that the parameters that are taken into account when determining the total resistance of a SWATH vessel are more complicated and must take into account more components related to the geometrical dimensions of the SWATH hull, such as: dimensions of torpedoes and supports, spacing of torpedoes, draft, superstructure height and others [12]. Taking into account the appropriate coefficients, the total resistance of a SWATH type vessel can be expressed by the relationship:

1 2 1 2 R = ρw v Cw + C + Cp C Ω = ρw v C Ω (2) TOT 2 · · · f r · ADD · 2 · · · TOT ·

3 where: ρW—density of water (kg/m ); v—SWATH speed (m/s); Cw—wave resistance coefficient (-); Cfr—frictional resistance coefficient (-); Cp—pressure resistance coefficient (-); CADD—additional resistance coefficient (-); Ω—wetted area of the hull (m2). Depending on the shape of the hull of a SWATH type ship, the percentage share of particular types may change with the change of the speed of the vessel. The wave resistance Rw, related to the formation of waves from the moving hull, due to the slender structure and streamlined shape of the supports is small and, at low speeds, it can amount to 10 to 20% of the total resistance. At higher speeds, the wave resistance can be as high as 50% of the total resistance. The percentage share of the frictional resistance Rfr in the total drag of a SWATH vessel can be as high as 70 to 90% due to the large, wetted area of this type of craft in relation to monohull vessels. The pressure resistance Rp, caused by the turbulence of the water flowing around the ship’s torpedo floats, depends mainly on their shape and the ship speed. Usually, the value of the pressure resistance for SWATH ships is small and amounts to few percent of total resistance. The value of additional resistance RADD is mainly influenced by: aerodynamic resistance; appendage resistance of protruding parts such as rudder, propellers, fins, etc.; resistance due to fouling of the hull with seaweed; resistance resulting from deterioration of weather conditions; resistances in shallow waters and in channels which are negligibly small. The value of additional resistances can be initially estimated on the basis of:

RADD = Rair + Rap + Rh f + Rac (3) where: Rair—aerodynamic drag (kN), dependent on the speed of the ship and the force of the wind acting on the surface of the ship’s hull; Rap—appendage resistance (kN), shows the inﬂuence of various hull appendages such as propeller, rudders, keels, skegs, thrusters, stabilizer ﬁns, and exposed propeller shafts; Rhf—hull fouling resistance (kN); Rac—atmospheric conditions resistance (kN), dependent with the state of the sea. Energies 2020, 13, x FOR PEER REVIEW 7 of 27

= + + + RADD Rair Rap Rhf Rac (3)

where: Rair—aerodynamic drag (kN), dependent on the speed of the ship and the force of the wind acting on the surface of the ship’s hull; Rap—appendage resistance (kN), shows the influence of various hull appendages such as propeller, rudders, keels, skegs, thrusters, stabilizer fins, and exposed propeller shafts; Rhf—hull fouling resistance (kN); Rac—atmospheric conditions resistance Energies(kN), dependent2020, 13, 6486 with the state of the sea. 7 of 26 Aerodynamic drag value Rair under normal weather conditions does not exceed 2 to 5% of the total drag. The value of appendage resistance Rap, depending on the used components and drive Aerodynamic drag value Rair under normal weather conditions does not exceed 2 to 5% of the system, can be up to about a dozen percent of total resistance (bow thrusters 1–5%, shaft covers 4– total drag. The value of appendage resistance Rap, depending on the used components and drive 8%). Depending on the frequency of surveys of the ship’s hull and the water temperature in the area system, can be up to about a dozen percent of total resistance (bow thrusters 1–5%, shaft covers 4–8%). in which it is operated, the value of resistance related to fouling of the hull, Rhf, may be from 0.2 to Depending on the frequency of surveys of the ship’s hull and the water temperature in the area in 0.5% of the total resistance. The most unpredictable and difficult to determine resistances are related which it is operated, the value of resistance related to fouling of the hull, Rhf, may be from 0.2 to 0.5% to fluctuating hydro-meteorological conditions. Changes in wind speed and the resulting wave may of the total resistance. The most unpredictable and difficult to determine resistances are related to lead to increased heeling, dive, rocking and flooding the sides and decks. They can also decrease the fluctuating hydro-meteorological conditions. Changes in wind speed and the resulting wave may efficiency of the propeller and increase the resistance to motion. For SWATH vessels, despite the fact lead to increased heeling, dive, rocking and flooding the sides and decks. They can also decrease that they are very resistant to unfavorable weather conditions, in extreme conditions the value of the efficiency of the propeller and increase the resistance to motion. For SWATH vessels, despite resistance related to hydro-meteorological conditions may reach a value of up to 25% of the total the fact that they are very resistant to unfavorable weather conditions, in extreme conditions the resistance. value of resistance related to hydro-meteorological conditions may reach a value of up to 25% of the Based on the knowledge of the total resistance value RTOT and assuming the overall efficiency of total resistance. individual elements of classic ship structures, at the level of: free running propeller efficiency (0.35– Based on the knowledge of the total resistance value RTOT and assuming the overall efficiency of 0.75), rotational efficiency (1–1.07), the shaft line efficiency (0.9–0.99), hull efficiency (0.95–1.05) individual elements of classic ship structures, at the level of: free running propeller efficiency (0.35–0.75), [12,58–60], it is possible to determine the power value of PM (electric motor/internal combustion rotational efficiency (1–1.07), the shaft line efficiency (0.9–0.99), hull efficiency (0.95–1.05) [12,58–60], engine) motors used to drive the SWATH type vessel. For SWATH type units, the ranges of the it is possible to determine the power value of PM (electric motor/internal combustion engine) motors presented coefficients may be slightly wider, depending on the shape of the structure and the number used to drive the SWATH type vessel. For SWATH type units, the ranges of the presented coefficients of torpedoes and struts. To determine the power of the propulsion engine, it is necessary to know the may be slightly wider, depending on the shape of the structure and the number of torpedoes and struts. drive train efficiency, which consists of: To determine the power of the propulsion engine, it is necessary to know the drive train efficiency, which consists of: R ⋅v P = TOT M RTOTη ⋅η v (4) PM = ·H (4) η ηH · where: PM—power of drive motor (kW); RTOT—total resistance (kN); v—SWATH speed (m/s); η— where: PM—power of drive motor (kW); RTOT—total resistance (kN); v—SWATH speed (m/s); η—drive drive train efficiency; ηH—SWATH hull efficiency. train efficiency; ηH—SWATH hull efficiency. Figure4 4 shows shows the the value value of of individual individual resistances resistances related related to to the the motion motion of of a a SWATH SWATH II II vessel. vessel.

Figure 4. Resistance related to a moving SWATH IIII vessel.vessel.

The Holtrop and Multihull methods [61] implemented in FREE!Ship Plus software were used to estimate the total resistance and the necessary drive power for vessels of similar dimensions namely MONOHULL, CATAMARAN, SWATH I, SWATH II shown in Figure5, SWATH III, and SWATH IV a.k.a. SWASH, the parameters of which are presented in Table2. The presented test results and characteristics are approximate in order to maintain the same calculation methods to enable comparative tests. Energies 2020, 13, x FOR PEER REVIEW 8 of 27 Energies 2020, 13, x FOR PEER REVIEW 8 of 27 The Holtrop and Multihull methods [61] implemented in FREE!Ship Plus software were used to estimateThe the Holtrop total resistance and Multihull and the methods necessary [61] driv implemene powerted for in vessels FREE!Ship of si milarPlus software dimensio werens namely used to MONOHULL,estimate the total CATAMARAN, resistance and SWATH the necessary I, SWATH driv eII power shown for in vesselsFigure of5, SWATHsimilar dimensio III, and nsSWATH namely IVMONOHULL, a.k.a. SWASH, CATAMARAN, the parameters SWATH of which I, are SWATH presented II shown in Table in Figure 2. The 5,presented SWATH testIII, andresults SWATH and characteristicsIV a.k.a. SWASH, are approximatethe parameters in of order which to are main prestainented the in sameTable calculation2. The presented methods test toresults enable and comparativecharacteristics tests. are approximate in order to maintain the same calculation methods to enable Energiescomparative2020, 13 ,tests. 6486 8 of 26

FigureFigure 5. 5.GeometricGeometric shape shape of ofthe the SWATH SWATH II IIhull hull in in FREE!ship FREE!ship [61]. [61]. Figure 5. Geometric shape of the SWATH II hull in FREE!ship [61]. FigureFigure 66 shows shows the the approximate approximate results results of of calculat calculationsions of of the the total total resistance, resistance, depending depending on on the the vesselvessel Figurespeed speed for6 forshows the the above-mentioned above-mentionedthe approximate ships.results ships. The of The calculat pr presentedesentedions dependencies of dependencies the total resistance, show show that that depending the the hull hull of on of the the SWASHSWASHvessel speed craft craft has for has thethe the lowestabove-mentioned lowest resistances resistances inships. in the the speedThe speed pr rangeesented range from from dependencies 0–14 0–14 [kn] [kn] to to show24–30 24–30 that[kn], [kn], the while while hull in of in the the speedspeedSWASH range range craft of of 14–24has 14–24 the [kn] [kn]lowest the the MOresistances MONOHULLNOHULL in thevessel vessel speed performs performs range frombetter. better. 0–14 [kn] to 24–30 [kn], while in the speed range of 14–24 [kn] the MONOHULL vessel performs better.

FigureFigure 6. 6. ApproximateApproximate plot plot of ofthe the relationship relationship of oftota totall resistance resistance versus versus longitudinal longitudinal speed speed for for MONOHULL,MONOHULL,Figure 6. Approximate CATAMARAN, CATAMARAN, plot ofSWATH SWATH the relationship I, I, SWATH SWATH IIof II,, SWATH total resistance III, SWATH versus IV–SWASHIV–SWASH longitudinal ships. ships. speed for MONOHULL, CATAMARAN, SWATH I, SWATH II, SWATH III, SWATH IV–SWASH ships. FigureFigure 77 shows shows the the results results of the of demand the deman for propulsived for propulsive power of MONOHULL, power of MONOHULL, CATAMARAN, CATAMARAN,SWATHFigure I, SWATH 7 SWATHshows II, SWATH theI, SWATH results III, SWATH II, ofSWAT the IV–SWASH Hdeman III, SWATHd vessels.for IV–SWASHpropulsive vessels.power of MONOHULL, CATAMARAN,SWATH I, SWATH SWATH II I, and SWATH SWATH II, SWAT III ships,H III, thanks SWATH to the IV–SWASH ballast tanks, vessels. can change their draft. This allows them to be operated in two modes: with submerged ﬂoats, as SWATH ships and with ﬂoats

partially surfaced, in catamaran mode. Figure8 shows the results of calculations of total resistance for the two operating modes of SWATH type vessels with torpedoes submerged (draft max 2.40 m) (SWATH I, SWATH II, SWATH III) and surfaced (draft max 1.80 m), in catamaran mode (SWATH I cat, SWATH II cat, SWATH III cat). Energies 2020, 13, x FOR PEER REVIEW 9 of 27

Energies 2020, 13, 6486 9 of 26 Energies 2020, 13, x FOR PEER REVIEW 9 of 27

Figure 7. Approximate plot of the relationship of required drive power versus longitudinal speed for MONOHULL, CATAMARAN, SWATH I, SWATH II, SWATH III, SWATH IV–SWASH vessels.

SWATH I, SWATH II and SWATH III ships, thanks to the ballast tanks, can change their draft. This allows them to be operated in two modes: with submerged floats, as SWATH ships and with floats partially surfaced, in catamaran mode. Figure 8 shows the results of calculations of total resistance for the two operating modes of SWATH type vessels with torpedoes submerged (draft max 2.40 m)FigureFigure (SWATH 7. 7. ApproximateApproximate I, SWATH plot plot II, of ofSWATH the the relationship relationship III) and of of surequir requiredrfaceded drive drive(draft power power max versus versus1.80 m), longitudinal longitudinal in catamaran speed speed formode for (SWATHMONOHULL,MONOHULL, I cat, SWATH CATAMARAN, CATAMARAN, II cat, SWATH SWATH III cat). I,I, SWATHSWATH II, II, SWATH SWATH III, III, SWATH SWATH IV–SWASH IV–SWASH vessels. vessels.

FigureFigure 8. 8.ApproximateApproximate plot plot of thethe relationshiprelationship of of total tota resistancel resistance versus versus longitudinal longitudinal speed speed for SWATH for SWATHI, SWATH I, SWATH II and SWATHII and SWATH III ships III depending ships depe onnding ﬂoat on submerged float submerged/surfaced/surfaced mode. mode.

FigureFigure 9 9shows shows the the results results of of the the demand demand for for propulsive propulsive power power for for SWATH SWATH I, I,SWATH SWATH II IIand and SWATHSWATH III III vessels vessels for for two two modes: modes: with with torpedoes torpedoes su submergedbmerged and and partially partially surfaced surfaced in incatamaran catamaran mode. mode. The SWATH II design was selected for further analysis on the basis of the determined thrust characteristics and the vessel’s motive power demand. Due to the shape of the torpedoes and the separation of the struts, this structure is more rigid and requires less power in the catamaran operation Figure 8. Approximate plot of the relationship of total resistance versus longitudinal speed for mode than the SWATH III type structure. On the other hand, in the range of higher speeds, exceeding SWATH I, SWATH II and SWATH III ships depending on float submerged/surfaced mode. 15 knots, the total resistance generated by the hull of the SWATH II type ship is slightly higher than the SWATHFigure III type9 shows vessel. the results of the demand for propulsive power for SWATH I, SWATH II and SWATH III vessels for two modes: with torpedoes submerged and partially surfaced in catamaran mode.

Energies 2020, 13, 6486 10 of 26 Energies 2020, 13, x FOR PEER REVIEW 10 of 27

Energies 2020, 13, x FOR PEER REVIEW 11 of 27 FigureFigure 9. Approximate 9. Approximate plot plot of theof the required required propulsionpropulsion power power versus versus longitudinal longitudinal speed speed for SWATH for SWATH I, − I, SWATHdescription II and of SWATH the properties III ships of depend the DC/DCing on powerfloat submerged/surfaced electronic converter, mode. taking into account the SWATH IIconstant and SWATH value of III the ships average depending load of the on on-board float submerged receivers,/ surfaced mode. − description of the properties of the fuel cell related to the maximum load and consumption of 3.2. Model ofThe a HybridSWATH SWATH II design II was Powertrain selected for further analysis on the basis of the determined thrust characteristicsthe energy and contained the vessel’s in the motive hydrogen power fuel dem andand. its efficiency, Due to the shape of the torpedoes and the Usingseparation− thedescription Modelicaof the struts,of the programming propertiesthis structure of the environmentis hydrogen more rigid tank and (withrelated requires Modelicato its parametersless power Energy such in Storagestheas volume catamaran of library and operationhydrogen mode than in the the tank, SWATH hydrogen III type pressure, structure. On the other hand, in the range of higher speeds, Modelica− Standardship’s speed Library) regulator [62 with], anda block vessel for setting operations the route dataof passage gathered (set speed from on individual the MarineTra ffic exceeding 15 knots, the total resistance generated by the hull of the SWATH II type ship is slightly website [63],sections a mathematical of the route), model of a SWATH II ship with an diesel propulsion system has higher than the SWATH III type vessel. been developed.− power Subsequently management system, the model including of the control electric of the propulsion flow and consumption system poweredof power between by HESS hybrid individual energy sources (generating sets, fuel cell, electric energy storage), energy3.2. stores Model has of a been Hybrid developed, SWATH II Powertrain modeling the rechargeable battery packs (BAT); hydrogen fuel cell − auxiliary generator for the DIESEL system, providing power supply at the level of a constant (FC) and internalUsingaverage the combustion Modelicaload value programmingof engine on-board (D). receivers, environment (with Modelica Energy Storages library and TheModelica mathematical− a measurementStandard Library) model system was[62], tasked and developed withvessel the operations recording on the basisdataof all gathered electrical of theavailable fromand mechanical the MarineTraffic elements parameters of website the of Modelica standard[63], library a mathematicalthe above-mentioned and the model elements of adevices SWATH developed and II shipadditionally with and an/or dieselperforming modified propulsion the by functions thesystem authors has of beenconverting taking developed. intoall account the propertiesSubsequentlyparameters and the correlations model related of to the energy electric between consumption, propulsion devices COsystem as2 emissions well powered as and parameters by fuel HESS costs. hybrid and energy catalog stores data has of real devices.been Figures developed,The two10– configurations18modeling show the the rechargeableof basic drive blockssystems battery were of the pack mo mathematicaldeled:s (BAT); the hydrogenfirst with model a fuel DIESEL cell with (FC) engine a and description (Figure internal of the combustion engine (D). functions10) performed. and the second hybrid DIESEL-ELECTRIC (Figure 11) with the use of HESS in combination with batteriesThe mathematical and hydrogen model fuel cells.was developed on the basis of the available elements of the Modelica standard library and the elements developed and/or modified by the authors taking into account the properties and correlations between devices as well as parameters and catalog data of real devices. Figures 10–18 show the basic blocks of the mathematical model with a description of the functions performed. The developed mathematical model includes such elements as: − dynamics of the mechanical structure of the ship’s hull expressed on the basis of the geometrical shapes of the ship and its mass, − description of the characteristics of internal combustion engines related to the generated power, torque and energy consumption (fuel) depending on the operating point (rotational speed, load), − description of the characteristics of the electric power generators related to the supplied mechanical power and the generated power at a specific efficiency defined by the efficiency map, − description of the properties of the electricity storage taking into account: cell temperature and related physicochemical properties such as maximum load current and operating voltage (SOC), − description of the properties of the inverter-motor electric drive system, taking into account: the efficiency of the inverter and the motor, the allowable load and power curve (torque, power, rotational speed, current, voltage), − ship’s propellers with a certain constant efficiency value, − gearboxes with a specific ratio and efficiency,

Figure 10.FigureModel 10. Model of a Diesel-Propellerof a Diesel-Propeller SWATH II IIpowertrain powertrain developed developed in Modelica. in Modelica.

Energies 2020, 13, x FOR PEER REVIEW 12 of 27 block; reduction gear block; propeller block; auxiliary power generator block and a transition route block. Configuration of the hybrid propulsion system DIESEL-ELECTRIC (DE) with HESS mathematical model implemented in the Modelica environment allows performing research depending on the selected structure of the electric power sources. Possible configurations include: battery electricity storage with diesel generating sets (BAT-D), as well as hydrogen fuel cell and battery electricity storage with diesel generating sets (FC-BAT-D). When selecting a given power sources combination, the individual masses of propulsion system components [65–68], automatically update the total ship mass, which affect the overall energy consumption of the ship [69–73]. The modeled drive system consists of: two generating sets with a power of 1200 kW each; electricity storage system (two parallel packages of 220 LiFePO4 300 Ah cells connected in series, with a total capacity of 422.4 kWh and a weight of 4400 kg); two electric motors with a nominal power of 1022 kW; DC/AC converter with a nominal power of 20 kW feeding the ship power grid; two hydrogen tanks, with capacity of 37.44 m3 each, and rated pressure 200 bar, containing 549 kg of hydrogen at a mass of 10,200 kg; and 14 PEM hydrogen fuel cells with a nominal power of 85 kW and a weight of 256 kg each. Based on the above parameters, the total weight of the ship was determined for each configuration at: D 118.4 t; BAT-D 119.1 t; FC-BAT-D 135.88 t. The elements of the hybrid propulsion system (Figure 11) of the DIESEL-ELECTRIC type are presented in the form of blocks modeling: the SWATH II hull block with the forces acting on it; block of two generating sets; electric energy storage block which includes two battery packs; on-board equipmentEnergies 2020, power13, 6486 supply unit included in the Power Management System (PMS); inverter module11 of 26 and electric motor block, gearbox block; propeller block; the transition route block.

Energies 2020, 13, x FOR PEER REVIEW 13 of 27

For the second configuration of DE, seven different configurations of drive systems were analyzed, including: BAT-D with SOCON-OFF = 15–85%, BAT-D with SOCON-OFF = 10–90%, BAT-D with SOCON-OFF = 40–60%, BAT-D with SOCON-OFF = 30–70%, BAT with SOCON-OFF = 15–85%, FC-BAT-D with SOCON- OFF = 15–85%, and FC-BAT with SOCON-OFF = 15–85%. The proposed designation of SOCON-OFF = 15– 85% means that the charging and discharging thresholds for BAT energy storage were chosen at 15% SOC and 85% SOC, respectively. This means that when the battery State Of Charge (SOC) drops below 15%, the BAT energy storage will be connected to the generator to supplement its energy and if the SOC exceeds 85%, the charging process will halt. The structure of the internal combustion engine block is presented in Figure 12. The basis for modeling the engine operation is the characteristic of the maximum torque depending on the rotational speed, and the Brake Specific Fuel Consumption (BSFC) characteristic describing the fuel consumptionFigureFigure 11. 11. of ModelModel the engine of of a ahybrid hybrid depending Diesel-Battery-Electric Diesel-Battery-Electric on the power SWATH delivered, SWATH II II powertrain powertrain all presented developed in Figure in Modelica. 13.

Tests were carried out for two types of drive systems DIESEL (D) and DIESEL-ELECTRIC (DE). For the drive type D, one power train configuration consisting only of diesel engines was analyzed.

FigureFigure 12.12. Model of a MAN V12-1650 diesel engine developeddeveloped inin Modelica.Modelica.

Figure 13. MAN V12-1650 engine curves [53].

Energies 2020, 13, x FOR PEER REVIEW 13 of 27

For the second configuration of DE, seven different configurations of drive systems were analyzed, including: BAT-D with SOCON-OFF = 15–85%, BAT-D with SOCON-OFF = 10–90%, BAT-D with SOCON-OFF = 40–60%, BAT-D with SOCON-OFF = 30–70%, BAT with SOCON-OFF = 15–85%, FC-BAT-D with SOCON- OFF = 15–85%, and FC-BAT with SOCON-OFF = 15–85%. The proposed designation of SOCON-OFF = 15– 85% means that the charging and discharging thresholds for BAT energy storage were chosen at 15% SOC and 85% SOC, respectively. This means that when the battery State Of Charge (SOC) drops below 15%, the BAT energy storage will be connected to the generator to supplement its energy and if the SOC exceeds 85%, the charging process will halt. The structure of the internal combustion engine block is presented in Figure 12. The basis for modeling the engine operation is the characteristic of the maximum torque depending on the rotational speed, and the Brake Specific Fuel Consumption (BSFC) characteristic describing the fuel consumption of the engine depending on the power delivered, all presented in Figure 13.

Energies 2020, 13, 6486 12 of 26 Figure 12. Model of a MAN V12-1650 diesel engine developed in Modelica.

Energies 2020, 13, x FOR PEER REVIEW 14 of 27

The engine is controlled by setting the desired RPM to the RPM demand input. This value is limited to a maximum of 2200 RPM. Then it is transferred to the input of the PID controller of the engine speed. The value of the torque signal from the output of the PID controller is limited based on the torque characteristics in the torque limiter block, and then it controls the engine torque block corresponding to the actual torque generated by the crankshaft. The mechanical power of rotation measured by the power meter block is the basis for measuring the amount of fuel consumed by the engine based on the BSFC curve. The instantaneous fuel consumption value in kg/s is available at the INST_FUEL output of the engine model; it is also integrated to obtain the total value of fuel consumed by the engine, expressed in kilograms (FUEL output). The value of the total mechanical energy generated by the motor expressed in kWh is available at the KWH output. The block directly cooperating with the internal combustion engine in the BAT-D configuration is the generator block shown in Figure 14. It is modeled by an electrical machine identical to the one used to drive the propeller, with the difference that it works in the generator mode as a synchronous generator, at the output of which is connected a rectifier circuit producing a direct current, used to charge the electricity store. FigureFigure 13. 13. MANMAN V12-1650 V12-1650 engine engine curves curves [53]. [53].

Figure 14. Model of a generator set developed in Modelica. Figure 14. Model of a generator set developed in Modelica.

The generator block operation is controlled by the Demand power input, to which the required electrical power is supplied. Based on the current value of the voltage at the SUPPLY output terminals permanently connected to the energy store, the value of the output current is determined, taking into account two restrictions. The first is related to the generator rated current, which is limited by the current limiter. The second limitation, which results from the possibility of overloading the generator at too low rotational speed, resulting e.g., from the recent start of the internal combustion engine driving the generator, or from the drop in speed as a result of engine overload. In this case, the hysteresis overload safety will limit the generator current to zero for the duration of the rotational speed hysteresis system action. The current supplied to the SUPPLY output, created by the generator, causes the flow of electricity to the storage, measured with an electrical power wattmeter. Power measurement is used to calculate shaft load. At the same time, depending on the generator rotational speed, the efficiency

Energies 2020, 13, x FOR PEER REVIEW 15 of 27 map of the generator-rectifier system is taken into account, which is the basis for the generator block operation. The diagram of the electric energy storage block is shown in Figure 15. In its central place there is a model of a LiFePO4 battery with a capacity of 300 Ah, developed on the basis of a battery model fromEnergies the2020 Modelica, 13, 6486 EnergyStorages library. The introduced modifications to the battery model13 of 26 included the implementation of the cell load characteristics depending on temperature and SOC.

Energies 2020, 13, x FOR PEER REVIEW 16 of 27

Energies 2020, 13, x FOR PEER REVIEW 16 of 27 FigureFigure 16. 15. Model ModelModel of of ofa PEMelectrical electrical hydrogen energy fuel store cell developed developed in in Modelica. Modelica.

The energyindividual released energy by systems,the fuel cell,such expressed as GEN1 ,in GEN2, joules, FC is counted(fuel cell), in theDC/DC Fuel converterEnergy block. and Thismotors value MOT1 is then and converted MOT2 intogenerators an energy are value connect expresseded through in kWh the available corresponding at the KWH DC output junctions, and intodistributed a mass around value of the hydrogen perimeter fuel of theconsumed. energy stor Theage mass block. of Eachconsumed of the hydrogen,device groups: available generators, at the outputfuel cells H2_KG, and engines, is calculated has its on own the measurementbasis of the calorific system value for the of electrichydrogen power and theflowing total throughefficiency this of thegroup, fuel with cell. the values available on the P_FC, P_GEN and P_CONS connectors. The value of the total energyFigure consumed 17 shows by athe diagram DC/DC of converter the hydrogen and drive pressure motors vessel expressed model. inThe kWh model is available represents on two the tanksKWH_CONS with a rated connector. pressure pn equal to 20 MPa and rated capacity mn equal to 549 kg of hydrogen. The modeledThe fuel cellvariable block isshowed the pressure in Figure in 16the models tank p aexpressed stack of fuel in MPa,cells with changing a specific according power torating the relationship:and efficiency. The base model to determine the efficiency was a 30 kW PEM Ballard FCveloCity MD fuel cell, with a total efficiency of 30%. The fuel cell model works in two states, controlled by the 𝑚 𝑚∙𝑝 Enable input. Starting the module energizes𝑝 the SUPPLY output with a specific rated power(5) 𝑚 calculated in the FC power block, through the flow of the current forced by the FC current block, where:appropriate mn–rated to the capacity actual voltageof the tanks level in at kg SUPPLY H2, mf–mass terminals. of H 2[74]. consumed by the fuel cell in kg, pn–rated pressure of the tank in MPa. Figure 16. Model of a PEM hydrogen fuel cell developed in Modelica. Figure 16. Model of a PEM hydrogen fuel cell developed in Modelica.

The energy released by the fuel cell, expressed in joules, is counted in the Fuel Energy block. This value is then converted into an energy value expressed in kWh available at the KWH output and into a mass value of hydrogen fuel consumed. The mass of consumed hydrogen, available at the output H2_KG, is calculated on the basis of the calorific value of hydrogen and the total efficiency of the fuel cell. Figure 17 shows a diagram of the hydrogen pressure vessel model. The model represents two tanks with a rated pressure pn equal to 20 MPa and rated capacity mn equal to 549 kg of hydrogen. The modeled variable is the pressure in the tank p expressed in MPa, changing according to the relationship:

𝑚 𝑚∙𝑝 𝑝 (5) 𝑚 FigureFigure 17. ModelModel of of a a 20 20 MPa MPa compressed compressed hydrogen hydrogen storage tank developed in Modelica. where: mn–rated capacity of the tanks in kg H2, mf–mass of H2 consumed by the fuel cell in kg, pn–ratedDue pressureto the fact of thethat tank fuel in cells MPa. are supplied with hydrogen directly from the pressure tank, without the participation of pumps, taking into account the requirements of fuel cells related to the minimum fuel pressure at the inlet of 0.8 MPa, the hydrogen tank model block is equipped with a system comparing the pressure in the hydrogen tank with the set minimum pressure. If the pressure in the tank is above the minimum pressure, the comparison system transmits the FUEL PRESENT signal to the fuel cell, which allows the cell to operate.

Figure 17. Model of a 20 MPa compressed hydrogen storage tank developed in Modelica.

Energies 2020, 13, x FOR PEER REVIEW 17 of 27

The model of the ship’s hull with its resistances is shown in Figure 18. The main modeled element is the hull mass block, the value of which is automatically calculated before starting the simulation,Energies 2020 ,based13, 6486 on the defined type of propulsion system. 14 of 26

Figure 18. Model of the ship’s hull and hull resistance components developed in Modelica. TheFigure developed 18. Model mathematical of the ship’s model hull and includes hull resistan suchce elements components as: developed in Modelica.

Thedynamics mass block of the is mechanicaldirectly related structure to the ofRTOT the hull ship’s resistance hull expressed force block, on the the basis value of of the which geometrical is the − sum ofshapes the hydrodynamic of the ship and and its aerodynamic mass, resistances (1). The value of the total aerodynamic drag Rair is deriveddescription from of the the drag characteristics equation: of internal combustion engines related to the generated power, − torque and energy consumption (fuel) depending on the operating point (rotational speed, load), 𝜌∙𝐴 ∙𝐶 ∙𝑣 description of the characteristics of the𝑅 electric power generators related to the supplied mechanical(6) − 2 power and the generated power at a specific efficiency defined by the efficiency map, where: ρ—air density in kg/m3, A—frontal area of the ship’s surfaced part, expressed in m2, Cd— description of the properties of the electricity storage taking into account: cell temperature and coefficient− of aerodynamic drag, v—apparent wind velocity in relation to the ship’s hull, expressed related physicochemical properties such as maximum load current and operating voltage (SOC), in m/s. description of the properties of the inverter-motor electric drive system, taking into account: − The value of total hydrodynamic resistance is taken from the Resistance table containing the the efficiency of the inverter and the motor, the allowable load and power curve (torque, power, results of the simulation of hull resistances depending on the ship speed. Additionally, the ship’s hull rotational speed, current, voltage), block has two outputs. The first one, the DISTANCE output, provides the value of the distance ship’s propellers with a certain constant efficiency value, traveled− by the vessel in km. The second SOG output (Speed over Ground) allows for one to read the gearboxes with a specific ratio and efficiency, value− of the longitudinal speed of the vessel in km/h. description of the properties of the DC/DC power electronic converter, taking into account the − All parameters of the modeled elements and devices presented in the diagrams are recorded by the measuringconstant valuesystem, of the which average additionally load of the on-boardperforms receivers,conversion functions related to energy description of the properties of the fuel cell related to the maximum load and consumption of the consumption,− CO2 emissions and fuel costs. energy contained in the hydrogen fuel and its efficiency, 4.1. Simulationdescription Results of the properties of the hydrogen tank related to its parameters such as volume of hydrogen in the tank, hydrogen pressure, The comparative analysis for the developed models of DIESEL and DIESEL-ELECTRIC ship’s speed regulator with a block for setting the route of passage (set speed on individual propulsion− systems has been carried out in the Modelica environment using the actual route of the M/V FOBsections SWATH of the 4, route),IMO 9672947 [52] as available from the MarineTraffic website [63]. 2. Thepower simulation management was carried system, out including in the OpenModelic control ofa the environment, flow and consumption using the DASSL of power solver between with a variableindividual step with energy a maximum sources (generating length of 100 sets, s and fuel a cell, maximum electric energysimulation storage), duration of 300,000 s. auxiliary generator for the DIESEL system, providing power supply at the level of a constant The− following solver options were used: Root Finding, Restart After Event as well as coloredNumericalaverage load Jacobian. value of on-boardThe maximum receivers, integration order of 5 was selected. Figurea measurement 19 shows systemthe registered tasked withspeed the profile recording of the of allM/V electrical FOB SWATH and mechanical 4, which parameters was used ofas thea − test profileabove-mentioned for all the analyzed devices configurations and additionally of performingthe propulsion the functionssystem inof the converting developed all SWATH parameters II ship model.related Selected to energy test consumption, route covers COa period2 emissions of approximately and fuel costs. 82 h (3 days, 10 h) and is associated with the ship tasks including leaving the port, traveling to the vicinity of offshore wind farm towers, The two configurations of drive systems were modeled: the first with a DIESEL engine (Figure 10) and the second hybrid DIESEL-ELECTRIC (Figure 11) with the use of HESS in combination with batteries and hydrogen fuel cells. Energies 2020, 13, 6486 15 of 26

The DIESEL propulsion system (D) was implemented on the basis of two identical systems installed in each of the SWATH II torpedoes, which include: a diesel engine with a nominal power of 1200 kW, reduction gear and a propeller [64]. Additionally, in order to provide power to the electric on-board devices, the use of an auxiliary diesel generator with a power of 18 kW was adopted. The structure of the modeled SWATH type diesel propulsion system consists of blocks such as: SWATH II type ship hull block modeling the hull form with the forces acting on it; internal combustion engine block; reduction gear block; propeller block; auxiliary power generator block and a transition route block. Configuration of the hybrid propulsion system DIESEL-ELECTRIC (DE) with HESS mathematical model implemented in the Modelica environment allows performing research depending on the selected structure of the electric power sources. Possible configurations include: battery electricity storage with diesel generating sets (BAT-D), as well as hydrogen fuel cell and battery electricity storage with diesel generating sets (FC-BAT-D). When selecting a given power sources combination, the individual masses of propulsion system components [65–68], automatically update the total ship mass, which affect the overall energy consumption of the ship [69–73]. The modeled drive system consists of: two generating sets with a power of 1200 kW each; electricity storage system (two parallel packages of 220 LiFePO4 300 Ah cells connected in series, with a total capacity of 422.4 kWh and a weight of 4400 kg); two electric motors with a nominal power of 1022 kW; DC/AC converter with a nominal power of 20 kW feeding the ship power grid; two hydrogen tanks, with capacity of 37.44 m3 each, and rated pressure 200 bar, containing 549 kg of hydrogen at a mass of 10,200 kg; and 14 PEM hydrogen fuel cells with a nominal power of 85 kW and a weight of 256 kg each. Based on the above parameters, the total weight of the ship was determined for each configuration at: D 118.4 t; BAT-D 119.1 t; FC-BAT-D 135.88 t. The elements of the hybrid propulsion system (Figure 11) of the DIESEL-ELECTRIC type are presented in the form of blocks modeling: the SWATH II hull block with the forces acting on it; block of two generating sets; electric energy storage block which includes two battery packs; on-board equipment power supply unit included in the Power Management System (PMS); inverter module and electric motor block, gearbox block; propeller block; the transition route block. Tests were carried out for two types of drive systems DIESEL (D) and DIESEL-ELECTRIC (DE). For the drive type D, one power train configuration consisting only of diesel engines was analyzed. For the second configuration of DE, seven different configurations of drive systems were analyzed, including: BAT-D with SOCON-OFF = 15–85%, BAT-D with SOCON-OFF = 10–90%, BAT-D with SOCON-OFF = 40–60%, BAT-D with SOCON-OFF = 30–70%, BAT with SOCON-OFF = 15–85%, FC-BAT-D with SOCON-OFF = 15–85%, and FC-BAT with SOCON-OFF = 15–85%. The proposed designation of SOCON-OFF = 15–85% means that the charging and discharging thresholds for BAT energy storage were chosen at 15% SOC and 85% SOC, respectively. This means that when the battery State Of Charge (SOC) drops below 15%, the BAT energy storage will be connected to the generator to supplement its energy and if the SOC exceeds 85%, the charging process will halt. The structure of the internal combustion engine block is presented in Figure 12. The basis for modeling the engine operation is the characteristic of the maximum torque depending on the rotational speed, and the Brake Specific Fuel Consumption (BSFC) characteristic describing the fuel consumption of the engine depending on the power delivered, all presented in Figure 13. The engine is controlled by setting the desired RPM to the RPM demand input. This value is limited to a maximum of 2200 RPM. Then it is transferred to the input of the PID controller of the engine speed. The value of the torque signal from the output of the PID controller is limited based on the torque characteristics in the torque limiter block, and then it controls the engine torque block corresponding to the actual torque generated by the crankshaft. The mechanical power of rotation measured by the power meter block is the basis for measuring the amount of fuel consumed by the engine based on the BSFC curve. The instantaneous fuel consumption value in kg/s is available at the INST_FUEL output of the engine model; it is also integrated to obtain Energies 2020, 13, 6486 16 of 26 the total value of fuel consumed by the engine, expressed in kilograms (FUEL output). The value of the total mechanical energy generated by the motor expressed in kWh is available at the KWH output. The block directly cooperating with the internal combustion engine in the BAT-D configuration is the generator block shown in Figure 14. It is modeled by an electrical machine identical to the one used to drive the propeller, with the difference that it works in the generator mode as a synchronous generator, at the output of which is connected a rectifier circuit producing a direct current, used to charge the electricity store. The generator block operation is controlled by the Demand power input, to which the required electrical power is supplied. Based on the current value of the voltage at the SUPPLY output terminals permanently connected to the energy store, the value of the output current is determined, taking into account two restrictions. The first is related to the generator rated current, which is limited by the current limiter. The second limitation, which results from the possibility of overloading the generator at too low rotational speed, resulting e.g., from the recent start of the internal combustion engine driving the generator, or from the drop in speed as a result of engine overload. In this case, the hysteresis overload safety will limit the generator current to zero for the duration of the rotational speed hysteresis system action. The current supplied to the SUPPLY output, created by the generator, causes the flow of electricity to the storage, measured with an electrical power wattmeter. Power measurement is used to calculate shaft load. At the same time, depending on the generator rotational speed, the efficiency map of the generator-rectifier system is taken into account, which is the basis for the generator block operation. The diagram of the electric energy storage block is shown in Figure 15. In its central place there is a model of a LiFePO4 battery with a capacity of 300 Ah, developed on the basis of a battery model from the Modelica EnergyStorages library. The introduced modifications to the battery model included the implementation of the cell load characteristics depending on temperature and SOC. The individual energy systems, such as GEN1, GEN2, FC (fuel cell), DC/DC converter and motors MOT1 and MOT2 generators are connected through the corresponding DC junctions, distributed around the perimeter of the energy storage block. Each of the device groups: generators, fuel cells and engines, has its own measurement system for the electric power flowing through this group, with the values available on the P_FC, P_GEN and P_CONS connectors. The value of the total energy consumed by the DC/DC converter and drive motors expressed in kWh is available on the KWH_CONS connector. The fuel cell block showed in Figure 16 models a stack of fuel cells with a specific power rating and efficiency. The base model to determine the efficiency was a 30 kW PEM Ballard FCveloCity MD fuel cell, with a total efficiency of 30%. The fuel cell model works in two states, controlled by the Enable input. Starting the module energizes the SUPPLY output with a specific rated power calculated in the FC power block, through the flow of the current forced by the FC current block, appropriate to the actual voltage level at SUPPLY terminals. [74]. The energy released by the fuel cell, expressed in joules, is counted in the Fuel Energy block. This value is then converted into an energy value expressed in kWh available at the KWH output and into a mass value of hydrogen fuel consumed. The mass of consumed hydrogen, available at the output H2_KG, is calculated on the basis of the calorific value of hydrogen and the total efficiency of the fuel cell. Figure 17 shows a diagram of the hydrogen pressure vessel model. The model represents two tanks with a rated pressure pn equal to 20 MPa and rated capacity mn equal to 549 kg of hydrogen. The modeled variable is the pressure in the tank p expressed in MPa, changing according to the relationship:

(mn m f ) pn p = − · (5) mn where: mn–rated capacity of the tanks in kg H2, mf–mass of H2 consumed by the fuel cell in kg, pn–rated pressure of the tank in MPa. Energies 2020, 13, 6486 17 of 26

Due to the fact that fuel cells are supplied with hydrogen directly from the pressure tank, without the participation of pumps, taking into account the requirements of fuel cells related to the minimum fuel pressure at the inlet of 0.8 MPa, the hydrogen tank model block is equipped with a system comparing the pressure in the hydrogen tank with the set minimum pressure. If the pressure in the tank is above the minimum pressure, the comparison system transmits the FUEL PRESENT signal to the fuel cell, which allows the cell to operate. The model of the ship’s hull with its resistances is shown in Figure 18. The main modeled element is the hull mass block, the value of which is automatically calculated before starting the simulation, based on the deﬁned type of propulsion system. The mass block is directly related to the RTOT hull resistance force block, the value of which is the sum of the hydrodynamic and aerodynamic resistances (1). The value of the total aerodynamic drag Rair is derived from the drag equation:

2 ρ A Cd v R = · · · (6) air 2 where: ρ—air density in kg/m3, A—frontal area of the ship’s surfaced part, expressed in m2, Cd—coeﬃcient of aerodynamic drag, v—apparent wind velocity in relation to the ship’s hull, expressed in m/s. The value of total hydrodynamic resistance is taken from the Resistance table containing the results of the simulation of hull resistances depending on the ship speed. Additionally, the ship’s hull block has two outputs. The ﬁrst one, the DISTANCE output, provides the value of the distance traveled by the vessel in km. The second SOG output (Speed over Ground) allows for one to read the value of the longitudinal speed of the vessel in km/h. All parameters of the modeled elements and devices presented in the diagrams are recorded by the measuring system, which additionally performs conversion functions related to energy consumption, CO2 emissions and fuel costs.

4. Simulation Results The comparative analysis for the developed models of DIESEL and DIESEL-ELECTRIC propulsion systems has been carried out in the Modelica environment using the actual route of the M/V FOB SWATH 4, IMO 9672947 [52] as available from the MarineTraffic website [63]. The simulation was carried out in the OpenModelica environment, using the DASSL solver with a variable step with a maximum length of 100 s and a maximum simulation duration of 300,000 s. The following solver options were used: Root Finding, Restart After Event as well as coloredNumerical Jacobian. The maximum integration order of 5 was selected. Figure 19 shows the registered speed profile of the M/V FOB SWATH 4, which was used as a test profile for all the analyzed configurations of the propulsion system in the developed SWATH II ship model. Selected test route covers a period of approximately 82 h (3 days, 10 h) and is associated with the ship tasks including leaving the port, traveling to the vicinity of offshore wind farm towers, maneuvering there and finally returning to the home port. The maximum speed during the journey under the given route did not exceed 20 kn. Figure 20 shows the demand for power from drive motors necessary to drive a SWATH II ship along a given test route, shown in Figure 19 using the vessel’s longitudinal speed controller. Figure 21 shows the consumption of energy contained in the fuel for individual types of drive systems of the SWATH II ship. Additionally, for the BAT-D hybrid system, the test results for various configurations of the electricity storage related to the setting of charging and discharging thresholds depending on the SOC are presented. Energies 2020, 13, x FOR PEER REVIEW 18 of 27

Energies 2020, 13, 6486 18 of 26 Energies 2020, 13, x FOR PEER REVIEW 18 of 27

Figure 19. Ship transition route speed profile of a SWATH II type ship.

Figure 20 shows the demand for power from drive motors necessary to drive a SWATH II ship along a given FiguretestFigure route, 19. 19. Shipshown Ship transition transitionin Figure route route 19 using speedspeed the prof proﬁle vessel’sile of of a a SWATHlongitudinal SWATH II IItype type speed ship. ship. controller.

Figure 20 shows the demand for power from drive motors necessary to drive a SWATH II ship along a given test route, shown in Figure 19 using the vessel’s longitudinal speed controller.

EnergiesFigure 2020, Figure13 20., x FORPropulsion 20. PEER Propulsion REVIEW power power during during the the tested tested transition transition route of of SWATH SWATH II IItype type vessel. vessel. 19 of 27

Figure 21 shows the consumption of energy contained in the fuel for individual types of drive systems ofFigure the SWATH 20. Propulsion II ship. power Additionally, during the for tested the tranBAT-Dsition hybrid route of system, SWATH the II testtype results vessel. for various configurations of the electricity storage related to the setting of charging and discharging thresholds dependingFigure 21on shows the SOC the are consumption presented. of energy contained in the fuel for individual types of drive systems of the SWATH II ship. Additionally, for the BAT-D hybrid system, the test results for various configurations of the electricity storage related to the setting of charging and discharging thresholds depending on the SOC are presented.

FigureFigure 21. Time 21. Time plot plot of consumedof consumed fuel fuel energy, energy, dependingdepending on on the the selected selected configuration conﬁguration of powertrain: of powertrain: Diesel,Diesel, BAT-D BAT-D (15–85), (15–85), BAT-D BAT-D (10–90), (10–90), BAT-D BAT-D (30–70), (30–70), BAT-D BAT-D (40–60),(40–60), FC-BAT-D FC-BAT-D (15–85). (15–85).

Figure 22 shows the waveforms of the state of charge of the energy storage (SOC) cooperating with generating sets. The characteristics are presented for the adopted four switch-on and switch-off thresholds for charging the energy storage: SOCON-OFF = 15–85%, SOCON-OFF = 10–90%, SOCON-OFF = 30– 70%, SOCON-OFF = 40–60%. The presented values were recorded by the measuring system during the simulation tests.

Figure 22. BAT energy store State Of Charge plot, depending on the selected configuration of powertrain: BAT-D (15–85), BAT-D (10–90), BAT-D (30–70), BAT-D (40–60).

Figure 23 presents the changes in the HESS battery voltage for the four selected charge-discharge threshold values. At the start of simulation, the SOC of the battery is equal to 1, which explains the high initial peak in all four cases. During the course of simulation, the higher voltage peak-to-peak values can be observed in the wider threshold cases, such as BAT-D (10–90) configuration, compared to smaller differences of BAT-D (30–70) case, caused by deeper discharging and charging.

Energies 2020, 13, x FOR PEER REVIEW 19 of 27

Energies 2020, 13, 6486 19 of 26 Figure 21. Time plot of consumed fuel energy, depending on the selected configuration of powertrain: Diesel, BAT-D (15–85), BAT-D (10–90), BAT-D (30–70), BAT-D (40–60), FC-BAT-D (15–85).

FigureFigure 22 shows 22 shows the the waveforms waveforms of of the the state state ofof chargecharge of of the the energy energy storage storage (SOC) (SOC) cooperating cooperating with generatingwith generating sets. sets. The The characteristics characteristics are are presented presented for the the adopted adopted four four switch-on switch-on and andswitch-off switch-o ﬀ thresholdsthresholds for charging for charging the the energy energy storage: storage: SOC SOCON-OFFON-OFF == 15–85%,15–85%, SOC SOCON-OFFON-OFF = 10–90%,= 10–90%, SOCON-OFF SOC =ON-OFF 30– = 30–70%,70%, SOC SOCON-OFFON-OFF == 40–60%.40–60%. The The presented presented values values were were recorded recorded by the by measuring the measuring system systemduring the during the simulationsimulation tests.tests.

FigureFigure 22. BAT 22. energyBAT energy store Statestore OfState Charge Of Charge plot, depending plot, depending on the selectedon the selected conﬁguration configuration of powertrain: of BAT-Dpowertrain: (15–85), BAT-D BAT-D (10–90),(15–85), BAT-D BAT-D (10–90), (30–70), BAT-D BAT-D (30–70), (40–60). BAT-D (40–60).

FigureFigure 23 presents 23 presents the the changes changes in in the the HESS HESS batterybattery voltage voltage for for the the four four selected selected charge-discharge charge-discharge thresholdthreshold values. values. At theAt the start start of of simulation, simulation, thethe SOCSOC of of the the battery battery is isequal equal to to1, which 1, which explains explains the the high initial peak in all four cases. During the course of simulation, the higher voltage peak-to-peak high initial peak in all four cases. During the course of simulation, the higher voltage peak-to-peak values can be observed in the wider threshold cases, such as BAT-D (10–90) configuration, compared values can be observed in the wider threshold cases, such as BAT-D (10–90) conﬁguration, compared to to smaller differences of BAT-D (30–70) case, caused by deeper discharging and charging. smallerEnergies diﬀ erences2020, 13, x FOR of BAT-D PEER REVIEW (30–70) case, caused by deeper discharging and charging. 20 of 27

FigureFigure 23. BAT 23. BAT energy energy store store voltage, voltage, depending depending onon the se selectedlected configuration conﬁguration of powertrain: of powertrain: BAT-D BAT-D (15–85),(15–85), BAT-D BAT-D (10–90), (10–90), BAT-D BAT-D (30–70), (30–70), BAT-D BAT-D (40–60). (40–60).

BasedBased on theon the examination examination ofof the the waveforms waveforms in Figu in Figuresres 21–23, 21 it– can23, be it concluded can be concluded that the picked that the pickedthreshold threshold level level of ofcharge/discharge charge/discharge of the of theelectr electricityicity storage storage has little has littleeffect e ﬀonect the on total the totalenergy energy consumption for the adopted test route. consumption for the adopted test route. Figure 24 shows the emission of carbon dioxide and other harmful substances into the atmosphere, linked to the fuel consumption of the SWATH II vessel. Carbon dioxide emissions by combustion engines were estimated on the basis of the assumption that 3.08 kg of CO2 is generated from one kilogram of diesel after combustion [75].

Figure 24. CO2 emission depending on the selected drivetrain configuration: DIESEL, BAT-D (15–85), BAT-D (10–90), BAT-D (30–70), BAT-D (40–60), FC-BAT-D (15–85).

Figure 25 shows the costs related to fuel consumption of a SWATH II ship depending on the selected configuration of the drive system. The operating costs of a given drive system were estimated on the basis of the unit fuel consumption and the adopted market prices: diesel oil USD 328/ton [76], electricity USD 0.14/kWh [77], hydrogen USD 16.51/kg [78].

Energies 2020, 13, x FOR PEER REVIEW 20 of 27

Figure 23. BAT energy store voltage, depending on the selected configuration of powertrain: BAT-D (15–85), BAT-D (10–90), BAT-D (30–70), BAT-D (40–60).

Energies 2020, 13, 6486 20 of 26 Based on the examination of the waveforms in Figures 21–23, it can be concluded that the picked threshold level of charge/discharge of the electricity storage has little effect on the total energy Figureconsumption 24 shows for the adopted emission test of route. carbon dioxide and other harmful substances into the atmosphere, Figure 24 shows the emission of carbon dioxide and other harmful substances into the linked to the fuel consumption of the SWATH II vessel. Carbon dioxide emissions by combustion atmosphere, linked to the fuel consumption of the SWATH II vessel. Carbon dioxide emissions by engines were estimated on the basis of the assumption that 3.08 kg of CO2 is generated from one combustion engines were estimated on the basis of the assumption that 3.08 kg of CO2 is generated kilogramfrom of one diesel kilogram after of combustion diesel after combustion [75]. [75].

FigureFigure 24. CO 24.2 COemission2 emission depending depending on on the the selected selected driv drivetrainetrain configuration: conﬁguration: DIESEL, DIESEL, BAT-D BAT-D (15–85), (15–85), BAT-DBAT-D (10–90), (10–90), BAT-D BAT-D (30–70), (30–70), BAT-D BAT-D (40–60), (40–60), FC-BAT-D FC-BAT-D (15–85). (15–85).

FigureFigure 25 shows 25 shows the the costs costs related related to to fuel fuel consumptionconsumption of of a aSWATH SWATH II IIship ship depending depending on the on the selectedselected conﬁguration configuration of the of the drive drive system. system. The The operating operating costs of of a agiven given drive drive system system were were estimated estimated on the basis of the unit fuel consumption and the adopted market prices: diesel oil USD 328/ton [76], on the basis of the unit fuel consumption and the adopted market prices: diesel oil USD 328/ton [76], electricity USD 0.14/kWh [77], hydrogen USD 16.51/kg [78]. electricityEnergies 2020 USD, 13, x 0.14 FOR/ kWhPEER REVIEW [77], hydrogen USD 16.51/kg [78]. 21 of 27

FigureFigure 25. 25.Comparison Comparison of of operating operating costs costs of of a SWATHa SWATH II vessel II vessel on aon given a given test test route, route, depending depending on the on adoptedthe adopted conﬁguration configuration of the of drive the drive system: system: DIESEL, DIESEL, BAT-D BAT-D (15–85), (15–85), BAT-D BAT-D (10–90), (10–90), BAT-D BAT-D (30–70), (30– BAT-D70), BAT-D (40–60), (40–60), FC-BAT-D FC-BAT-D (15–85). (15–85).

The flow of energy between its sources, namely the BAT energy storage, FC hydrogen fuel cells and generating sets D, and electricity consumers and the main electric drive, is shown in Figure 26.

Figure 26. Plot of power flow between battery (BAT), generators (D), fuel cell (FC) and propulsion system.

5. Discussion The analysis of the obtained test results of various configurations of the SWATH II drive system showed that the use of a DIESEL-ELECTRIC hybrid drive system may significantly reduce the operating costs of the vessel, as well as the amount of exhaust gases emitted to the environment, when compared to the drive type DIESEL. In addition to the development of a mathematical model Energies 2020, 13, x FOR PEER REVIEW 21 of 27

Figure 25. Comparison of operating costs of a SWATH II vessel on a given test route, depending on

Energiesthe2020 adopted, 13, 6486 configuration of the drive system: DIESEL, BAT-D (15–85), BAT-D (10–90), BAT-D (30–21 of 26 70), BAT-D (40–60), FC-BAT-D (15–85).

The ﬂowflow of energy between its sources, namely thethe BAT energy storage, FC hydrogen fuel cells and generating sets D, and electricity consumersconsumers andand thethe mainmain electricelectric drive,drive, isis shownshown inin FigureFigure 2626..

Figure 26. 26. PlotPlot of power of power flow flowbetween between battery battery (BAT), gene (BAT),rators generators (D), fuel (D),cell (FC) fuel and cell propulsion (FC) and propulsionsystem. system. 5. Discussion 5. Discussion The analysis of the obtained test results of various configurations of the SWATH II drive system The analysis of the obtained test results of various configurations of the SWATH II drive system showed that the use of a DIESEL-ELECTRIC hybrid drive system may significantly reduce the showed that the use of a DIESEL-ELECTRIC hybrid drive system may significantly reduce the operating costs of the vessel, as well as the amount of exhaust gases emitted to the environment, operating costs of the vessel, as well as the amount of exhaust gases emitted to the environment, when compared to the drive type DIESEL. In addition to the development of a mathematical model when compared to the drive type DIESEL. In addition to the development of a mathematical model based on actual operating data, the research also includes the development of models for electric drive system components such as inverters, drive motors, power electronic converters, electricity storage, hydrogen tanks and hydrogen fuel cells. The length of the test route was about 580 nm and it was not a problem to cover it for DIESEL, BAT-D and FC-BAT-D drive systems. The maximum range achieved by the vessel for the BAT configuration was 7.2 nm and for FC 181.2 nm. In order for the given route to be covered only on battery power, using the LiFePO4 cell technology with the energy density of approx. 100 Wh/kg, the mass of the energy storage would have to be approx. 350 tons, and using Li-Ion cells with a density of 200 Wh/kg—169 tons, and for upcoming cells with a density of 1000 Wh/kg—about 34 tons [79]. Based on the analysis of the waveforms related to consumption of energy contained in fuel, the state of charge of energy store and the voltage at energy store terminals (Figures 20–22), it can be concluded that the adopted SOCON-OFF level of discharge and charging of the electricity storage has little effect on the total energy consumption for the adopted test route. Taking into account the influence of the SOC charge level on the cell life parameter called SOH (State Of Health), it is recommended to adopt a configuration of at least SOCON-OFF = 15–85%. Adopting the SOCON-OFF = 10–90% configuration causes the energy store to operate within extreme limits that may shorten the SOH lifetime of the energy store. On the other hand, assuming too narrow operating range of the energy store, e.g., SOCON-OFF = 40–60%, the number of generators starts will be greater than for the energy store operation range at the level of SOCON-OFF = 10–90%. Therefore, assuming a certain level of operation SOCON-OFF of the energy store, the operational situation of the ship should be calculated, taking into account the ship’s route and the stops schedule. Energies 2020, 13, 6486 22 of 26

The obtained test results confirmed the expectation of reduced fuel consumption used to propel the ship. Specific Energy Consumption (SEC) expressed in kilowatt hours kWh per nautical miles Nm was correspondingly for the configuration type: DIESEL 236.24 kWh/nm; BAT-D (10–90) 177.94 kWh/nm; BAT-D (15–85) 177.97 kWh/nm; BAT-D (30–70) 178.17 kWh/nm; BAT-D (40–60) 179.11 kWh/nm; BAT (15–85) 58.51 kWh/nm; FC-BAT-D (15–85) 179.05 kWh/nm; FC-BAT (15–85) 70.42 kWh/nm. Thus, the lowest SEC value was obtained for the BAT configuration 58.51 kWh/nm (percentage difference to DIESEL system ( 75.23%), then FC-BAT 70.42 kWh/nm ( 70.19%) and then − − in order with slight differences, BAT-D configurations 177.97 179.11 kWh/nm ( 24.67 24.18%), ÷ − ÷ − FC-BAT-D 179.51 kWh/nm ( 24.21%) and finally, DIESEL 236.24 kWh/nm. − For DIESEL and BAT-D configurations, the efficiency of the drive system is largely dependent on the efficiency of the internal combustion engine (η), which depends on the engine operating point (Figure 13). The engine operating point depends on its load, which is simply a resultant function of the set engine rotational speed, the ship’s loading condition and hydro-meteorological conditions (canopies, waves, sea currents). If a powerful engine is only slightly loaded, its efficiency will be low. On the other hand, if the same engine is loaded in the optimal range of its operation, i.e., approximately 85–90% of the rated power, for example by driving a generator as in the BAT-D configuration (η 41.5%), then the value of its average efficiency will be significantly higher than ≈ when the engine is operated in the DIESEL drive system (η 24.5%) on the same route. ≈ The emission of poisonous gases and carbon dioxide into the atmosphere is related to the consumed energy (Figure 24). Along with the reduction of fuel consumption, the CO2 emission was reduced and it amounted to: DIESEL 62.30 kgCO2/nm; BAT-D (10–90) 46.80 kgCO2/nm; BAT-D (15–85) 46.81 kgCO2/nm; BAT-D (30–70) 46.86 kgCO2/nm; BAT-D (40–60) 47.11 kgCO2/nm; BAT 5.66 kgCO2/nm; FC-BAT-D (15–85) 41.46 kgCO2/nm; FC-BAT (15–85) 0.11 kgCO2/nm [80]. The highest value of CO2 emission reduction was obtained for the system powered mainly by FC-BAT hydrogen fuel cells (15–85) 0.11 kgCO /nm ( 99.82%), due to the fact that generation of electricity from hydrogen gives no emission 2 − of CO . This was followed by BAT 5.66 kgCO /nm ( 90.91%), FC-BAT-D (15–85) 41.46 kgCO /nm 2 2 − 2 ( 33.45%) systems; BAT-D (10–90) 46.80 kgCO /nm ( 24.87%); BAT-D (15–85) 46.81 kgCO /nm − 2 − 2 ( 24.86%); BAT-D (30–70) 46.86 kgCO /nm ( 24.78%); BAT-D (40–60) 47.11 kgCO /nm ( 24.38%). − 2 − 2 − It should be noted that the FC-BAT-D propulsion system uses hydrogen fuel cells, with power of one unit is not large (85 kW). In order to provide propulsion for the SWATH II type vessel, at least a dozen of them should be used only with hydrogen fuel cells. The maintenance and operation of hydrogen tanks may also be a problem. In addition, the cost analysis showed that the operation of the FC-BAT-D propulsion system is significantly more expensive compared to both DIESEL, BAT-D and BAT systems (Figure 25). The ship’s cost per mile (CPM) in DIESEL is USD 6.64/nm; in BAT-D (10–90) is USD 5.16/nm; in BAT-D (15–85) USD 5.17/nm; in BAT-D (30–70) is USD 5.17 USD/nm; in BAT-D (40–60) is USD 5.20/nm; in BAT (15–85) is USD 14.63/nm; in FC-BAT-D (15–85) is USD 34.47/nm; in FC-BAT (15–85) is USD 96.32/nm. The lowest cost of operation in relation to the DIESEL configuration was obtained for the following configurations: BAT-D (10–90) at 5.16 USD/nm ( 22.25%), BAT-D (15–85) at − 5.17 USD/nm ( 22.23%), BAT-D (30–70) at 5.17 USD/nm ( 22.15%), BAT-D (40–60) at 5.20 USD/nm − − ( 21.75%). The remaining systems generate higher unit costs in relation to the CPM index, respectively: − BAT (15–85) at USD 14.63/nm (+220.23%); FC-BAT-D (15–85) at USD 34.47/nm (+518.95%); and FC-BAT (15–85) at USD 96.32/nm (+1450.18%).

6. Conclusions The use of the DIESEL-ELECTRIC hybrid drive system to drive the SWATH II type craft can significantly contribute to the reduction of operating costs as well as the amount of exhaust gases emitted into the environment. The obtained test results confirmed that thanks to the appropriate configuration of the electric drive system and the appropriate selection of parameters (SOCON-OFF), it is possible to extend the SOH life of the batteries. Energies 2020, 13, 6486 23 of 26

The use of a hybrid drive system with electrical components allows for optimal placement of elements on board the ship, which translates into an increase in the level of safety for the crew and transported goods. The use of hybrid propulsion enables the adaptation of vessels by shipowners to increasingly stringent environmental protection regulations. The operation of the internal combustion engine in its optimal load range in a hybrid system, such as BAT-D, has a positive effect on the increase of the average value of its efficiency, in relation to the DIESEL configuration, which entails a reduction in fuel consumption and emission of exhaust gases into the atmosphere. The advantages of using a DIESEL-ELECTRIC hybrid drive, and in particular the possibility of temporary shutdown of diesel engines, allows local reduction of exhaust gases emissions to zero, especially in zones where exhaust emissions and noise from internal combustion engines are not desired.

Author Contributions: Conceptualization, A.Ł. and W.K.; computations, A.Ł. and W.K.; methodology, A.Ł. and W.K.; experimental verification, A.Ł. and W.K.; writing text of the article, A.Ł. and W.K.; review and editing, A.Ł. and W.K.; visualization, A.Ł. and W.K.; supervision, A.Ł. and W.K. All authors have read and agreed to the published version of the manuscript. Funding: The project is financed from the Ministry of Science and Higher Education program named “Regionalna Inicjatywa Doskonało´sci”in the years 2019–2022, project number 006/RID/2018/19, the sum of financing 11 870 000 PLN. Conflicts of Interest: The authors declare no conflict of interest.

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