1 INTRODUCTION

Split is a second largest city in Croatia that has

become popular tourist destination. It is located on

the south of Croatia in the region called Dalmatia.

Next to Split in the north-west direction the town

Solin is located. Next to Solin there is city of Kaštela.

Kaštela is the name for the agglomeration that

consists of seven small towns. Kaštela are located

along the coastline. At the end of Kaštela the airport is

located. The distance between the airport and Split is

approximately 25 km. During summer season the

traffic by state and local roads which lead from

airport to Split gets congested.

Area around the Split harbor, which is located in

Split center, contains bus terminal and train station.

This situation combined with only one access road,

leads to traffic congestion in the center of Split (Fig.1).

The consequence of increased traffic congestion is

the additional air pollution caused by vehicle exhaust

emission. The contribution to air pollution comes

from the personal cars, taxi transfers (by cars and

vans) and bus transportation (domestic and

international). Once situated one portion of tourist

explore the local towns. Trogir is popular town

located approximately 31 km from Split in north-west

direction. This transition leads through Solin and

Kaštela which additionally contributes to air

pollution.

To quantify mentioned statements statistics from

the Airport “Split” and Croatian company for

management, construction and maintenance of state

roads “Hrvatske ceste” is used. Also, for number of

tourist arrivals the statistic from Croatian bureau of

statistics is used. The overall number shows that there

is an increase in total number of airport passengers,

number of vehicles and tourist arrivals. Figure 2

shows the graph of total airport passengers from

January 2013 to March 2019. Figure 3 shows the

average summer daily traffic (measured from July 1

Maritime Green Solution for Traffic Congestion

M. Petković, M. Zubčić, M. Krčum & I. Vujović

University of Split, Split, Croatia

ABSTRACT: Traffic congestion is a wide problem in many tourist destinations. Airports are usually distant

from the city centers. Hence, road and rail traffic are widely used to connect airports and city centers. In this

paper, we propose zero-emission solution for connection between airport and the center at the example of

Croatian city Split. Since Split has become a popular tourist destination, the number of vehicles during summer

season increases. As a measure to decrease air pollution, in this paper the marine traffic by electric vessels is

proposed for the route Split – airport. Seven all-

electrical vessels are presented with their technical

characteristics. The idea is to have zero emission transfers by sea from the center of the Split to the airport. The

criteria for minimum cruising speed is set to 13 knots, which ensures that one crossing takes 30 minutes and

makes it competitive with other forms of transport.

http://

www.transnav.eu

the

International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 14

Number 1

March 2020

DOI:

10.12716/1001.14.01.11

to August 31

) from 2014. to 2017. Figure 4 shows the

total number or tourist arrivals for Split and Trogir in

2017. and 2018.

Figure 1. Split center traffic congestion in summer season

(source: Jutarnji List)

Figure 2. Number of airport passengers through months for

the period from January 2013. to March 2019

(source: Split Airport)

Figure 3. Average summer daily traffic – measured at the

entrance of Split – northwest (source: Hrvatske ceste)

Figure 4. Number of arrivals for Trogir and Split

(source: Croatian bureau of statistics)

To reduce road traffic in the area of Kaštela and

Split center which can be done by reduction of taxi

and rent-a-car transfers from Trogir to Split and from

airport to Split, in this paper alterative path is

proposed.

The transfer of tourist from airport to Split can be

done by electric catamaran. Electric catamaran is a

vessel whose propulsion and control system consist of

electric motors, battery packs, charge/discharge

controllers, inverters, photovoltaic panels and other

loads (lightning, navigation, communication).

The idea of marine transfers is not new. At the

airport there are stands at which one can find taxi

boats and rent-a-bots. The ferry port Divulje is

approximately 800 m from the entrance into the

building of the airport. The first catamaran line from

center of Split to Resnik (ferry port Divulje) will start

with May 1

2019. Figure 5 shows the catamaran that

will be used from center of Split to Resnik.

Figure 5. Catamaran that will be used for Split – Resnik line

(source: Catamaran line d.o.o. Split)

Length overall of this catamaran is 26.65 m, beam

9.00 m, draught 1.20 m and the capacity is 145

passengers.

This catamaran will reduce the number of vehicles

but its propulsion system is based on diesel-engine

technology. Electric catamaran would use the energy

from the electrical grid. Since electrical energy in

Dalmatia comes from five hydropower plants the

catamaran would use “green” energy.

2 ELECTRIC CATAMARAN – ELECTRICAL

SYSTEM

In this paper two electrical systems are presented.

Electrical system of electric catamaran presented by

Spagnolo (Spagnolo et al., 2012) and Sunaryo

(Sunaryo, Ramadhani, 2018). Figure 6a shows the

electrical system for catamaran presented by

Spagnolo (Spagnolo et al., 2012) and Fig 6b shows

electrical system presented by Sunaryo (Sunaryo,

Ramadhani, 2018).

Figure 6. Catamaran electrical system: a) Spagnolo b)

Sunaryo (source: Spagnolo et al., 2012 ; Sunaryo,

Ramadhani, 2018)

Components of electrical system are:

− Photovoltaic array

− Battery bank

− DC/DC converter (Boost converter)

− Charge/discharge controller

− MPPT (Maximum power point tracking)

− AC/DC converter

− DC/AC converters

− Electric motors

− Management control

− Grid supplier

− Other loads (lightning, navigation,

communication, accommodation)

Basically, systems from Fig. 6a and Fig. 6b are the

same. In Table 1 the characteristics of catamarans are

shown.

Table 1. Catamaran characteristics (source: Spagnolo et al.,

2012; Sunaryo, Ramadhani, 2018)

_______________________________________________

Characteristics Spagnolo Sunaryo

_______________________________________________

Length overall 14.00 m 12.64 m

Beam 5.50 m 5.39 m

Draft 0.9 m 0.7 m

Maximum speed 15 km/h ≈ 8 knots 11 km/h ≈ 6 knots

Cruising speed 8 km/h ≈ 4 knots 8 km/h ≈ 4 knots

Electric motor 2 x 8 kW (PMSM) 1 x 4.9 kW (DC)

PV array area ≈ 55 m

≈ 58 m

No. of PV panels 42 58

Panel W

Pmax (STC) 225 W 140 W

_______________________________________________

3 PROBLEM STATEMENT

The first commercial catamaran on the route Split –

Airport (Resnik) will start operating on May 1st 2019.

Out of season this catamaran will daily cross this

route 16 times and during season, number of

crossings will be 20. Figure 7 shows the route on

which the catamaran will operate (black line).

Figure 7. Geographical position of Trogir, airport, Kaštela

(thick red lines), Solin and Split with proposed catamaran

line Split – Resnik (Airport) (thick black line) (source:

Authors)

The distance according to Google Maps is

approximately 12 km (or 7.3 NM). It is stated that this

catamaran will make one crossing in 20 min with

average speed of 36 km/h (≈ 20 knots).

Getting to airport from the same starting point in

Split by car, takes approximately 30 min. But during

the summer season, the traffic congestion in Split

center will make this trip 30 to 45 minutes longer.

To compete with conventional transport, this

paper proposes electrical catamaran that can transfer

the passengers from center of Split to airport (Resnik)

in 30 min. To achieve this crossing time average speed

of the catamaran must be 24 km/h (≈ 13 knots).

From Table 1 it can be seen that electrical

catamarans presented cannot be taken into

consideration because their maximum speeds are

lower than 13 knots. In next section 1 passenger ferry,

1 air supported vessel and 3 electrical catamarans are

presented.

4 ELECTRICAL VESSELS – OVERVIEW

4.1 “Future of the Fjords”

“Future of the Fjords” is the first of its kind all-electric

passenger catamaran. It is designed to take 400

passengers on the 90 minutes, each way, trip twice a

day from Flam to Gudvangen (23 NM, nautical miles).

Hull is constructed from carbon fiber composite.

Electric propulsion, delivered by two 450 kW motors,

is powered from 1.8 MWh battery pack enabling

cruising speed of 16 knots. Ship is docked in

Gudvangen on a 40 m long and 5 m wide floating

glass fiber dock, housing a 2.4 MWh battery pack

providing the 20-minute fast charging capability for

the ship. This charging dock is connected to the local

grid network and charges up steadily throughout the

day.

100

Figure 8. Electric catamaran “Future of the Fjords”

(source: DNV GL)

Table 2. “Future of the fjords” Facts

_______________________________________________

Length 42 m

Width 15 m

Material Carbon fiber sandwich

Seats 400

Propulsion 2 x 450 kW

Battery 1800 kWh

Cruising speed 16 knots

Range 30 NM

_______________________________________________

4.2 “E/S Sjövägen”

It is an electric ferry which transports up to 150

passengers eight times a day on a 10 NM public

transport line. It is made out of sandwiched PVC

composite material and is ice reinforced. Electric

propulsion is provided by two 160 kW electrical

motors on double propeller system enabling cruising

speed of 10 knots. Its 500 kWh battery bank are fully

charged during the ferry’s overnight stay at the dock,

with two partial charging sessions during the day.

Figure 9. “E/S Sjövägen” electric ferry

(source: B/F Sjövägen)

Table 3. “E/S Sjövägen” Facts

_______________________________________________

Length 24.55 m

Width 7 m

Material PVC composite sandwich

Seats 150

Propulsion 2 x 160 kW

Battery 500 kWh

Cruising speed 10 knots

Range 12 NM

_______________________________________________

4.3 Electric ASV vessel “BB Green Airi El”

This ship is designed for short routes (5 – 14 NM) at

high speeds (30 knots). Its unique hull design, made

out of carbon fiber sandwich, based on ASV (Air

Supported Vessel) technology reduces hull water

resistance by 40%. Most of the vessel’s weight is

supported on a cushion of air provided by electric lift

fan system. Electric propulsion is provided by two

280 kW permanent magnet motor with additional 50

kW motor for ASV lift fan system. Ship is designed to

carry 400 kWh battery pack while for prototype vessel

half the battery pack will be used. For commercial use

recharging the battery in less than 30 minutes and

operating on hourly schedule may be possible.

Table 4. “BB Green Airi El” Facts

_______________________________________________

Length 20 m

Width 6 m

Material Carbon fiber sandwich

Seats 70

Propulsion 2 x 280 kW; 1 x 50 kW

Battery 400 kWh

Cruising speed 30 knots

Range 12 NM

_______________________________________________

Figure 10. “BB Green Airi El” electric ASV vessel

(source: BB Green)

4.4 Electric catamaran “Niko Nodilo”

This electric catamaran is designed to operate in

vulnerable environment. This ecologically sensitive

ship will replace the older fleet that operated as

ferries around the larger lake in the middle of the

“Mljet” National Park. Hull is made out of composite

sandwich material, 15 meters long and 5 meters wide,

carrying 54 passengers and 2 crew members. Electric

propulsion is provided by two 12kW permanent

magnet motors which enables cruise speed of 5 knots.

A 7.5 kW solar power plant, installed on the roof,

provides a daily autonomy of 8 hours at cruise speed

during the summer months. Power is provided by 50

kWh LiFePO4 battery pack charged by onboard solar

plant or onshore local grid.

Figure 11. “Niko Nodilo” electric catamaran

(source: Pomorac.Net)

Table 5. “Niko Nodilo” Facts

_______________________________________________

Length 15 m

Width 5 m

Material Composite sandwich

Seats 54

Propulsion 2 x 12 kW

Battery 50 kWh

Cruising speed 5 knots

Range 40 NM

_______________________________________________

101

4.5 “Solarwave solar catamaran”

This electric powered catamaran is designed to carry

50 passengers. It is made out of PVC sandwich E-glass

and is 17.8 meters long and 6 meters wide. Electric

propulsion is provided by two 9 kW electric motors

powered from 60 kWh battery bank. Approximate

power consumption at cruising speed of 6 knots is 12

kW/h. Charging is done by 10 kW onboard solar

power plant installed on the roof or connecting to

onshore local grid.

Figure 12. “Solarwave solar catamaran”

(source: Solarwave Yachts)

Table 6. “Solarwave solar catamaran” Facts

_______________________________________________

Length 17.8 m

Width 6 m

Material PVC sandwich

Seats 50

Propulsion 2 x 9 kW

Battery 60 kWh

Cruising speed 6 knots

Range 30 NM

_______________________________________________

For comparison in Table 7 the cruising speed,

battery capacity, no. of seats and total propulsion

power of all vessels are shown.

Table 7. Comparison of vessel characteristics

_______________________________________________

Cruising Propulsion Battery Seats

Speed [kW] capacity

[knots] [kWh]

_______________________________________________

Future of the Fjords 16 2 x 450 1800 400

E/S Sjövägen 10 2 x 160 500 150

BB Green Airi El 30 2 x 280; 400 70

1 x 50

Niko Nodilo 5 2 x 12 50 54

Solarwave solar 6 2 x 9 60 50

catamaran

_______________________________________________

5 SOLAR POTENTIAL

Croatian yearly sum of global irradiation for

horizontally mounted PV modules is shown on Fig.

13. Only global horizontally irradiation is taken into

consideration because in this paper it is assumed that

all PV panels are mounted on the roofs which are flat

and parallel to the ground or the sea surface.

Figure 13. Yearly sum of global irradiation (source:

Photovoltaic geographical information system)

Yearly average energy obtained by PV system

(Spagnolo et al., 2012; Omar, Mahmoud, 2019):

1234PV

E P PSH k k k k

= ⋅ ⋅⋅⋅⋅

(1)

where: E [kWh/year] – yearly average energy; PSH

[h/year] – peak sunshine hours; P

PV [kWh]– PV array

peak power; k

1 – coefficient for compensation for

temperature effect; k

2 – coefficient which takes stains

and wear into consideration; k

3 – coefficient that takes

the loss of DC circuits into consideration (PV array); k

– coefficient that takes DC/DC converter losses into

consideration.

Peak sunshine hours (Mahmoud, 2003):

year

PSH

(2)

where: E

year [(kWh/m

)/year] – yearly average solar

radiation intensity; G

o [W/ m

] – peak solar radiation

intensity (= 1000 W/m

For the route from Split (center) to airport (Resnik)

the targeted cruising speed is 13 knots. From Table 7

only two vessels fulfil this demand: “Future of the

Fjords” and “BB Green Airi El”. “Future of the

Fjords” does not have PV panels and from Fig. 8 it can

be seen that its design does not have flat surfaces that

would be suitable for PV array installation. “BB Green

Airi El” also does not have PV panels but it has

relatively flat roof that provides possibility for PV

array installation (Fig. 14).

Figure 14. “BB Green Airi El” with PV panels array on its

roof (source: Transport Research and Innovation Monitoring

and Information System)

Calculation of daily solar energy is made for “BB

Green Airi El” and “Future of the Fjords” regardless

102

of its roof design. In this paper it assumed that area of

PV array takes 70% of the overall surface (S=Length x

Width) of the vessel. For the calculation, SunPower’s

panel SPR-X21-345 is taken into consideration. The

area of one panel is 1.63 m

and its nominal power is

345 W (SunPower). Yearly average solar radiation

intensity for area of Kaštela is 1650 [(kWh/m

)/year]

(Fig. 13).

Coefficients from Equation 1: k

1=0.9; k2=0.9;

3=0.95; k4=0.95. In Table 8 the average solar energy

production for “BB Green Airi El” and “Future of the

Fjords” is shown.

Table 8. Solar energy production

_______________________________________________

S 70% S No. of E Eday (Batt.

] [m

] panels

kWh

year







kWh

day







capacity/Eday)

[%]

_______________________________________________

A 120 84 51 21229 58 14.5

B 630 441 270 112357 308 17.1

_______________________________________________

A= “BB Green Airi El”; B= “Future of the Fjords”

5.1 Energy consumption and economics

Table 9 shows the estimation of total energy

consumption of “BB Green Airi El” and “Future of the

Fjords” for one crossing. Total energy consumption is

the sum of the propulsion motors and the other loads

consumption (Krčum et al., 2018). For this calculation

the assumption is that 20% of total battery capacity is

consumed by other loads.

Table 9. Energy consumption

_______________________________________________

Cruising Split – Crossing Consumption [kWh]

Speed Resnik time

[knots] [NM] [min] Propulsion Other Total

Loads

_______________________________________________

A 30 7.3 15 152.5 80 232.5

B 16 7.3 27.6 414 360 774

_______________________________________________

A= “BB Green Airi El”; B= “Future of the Fjords”

With 20% assumption for other loads, from Table 9

it can be seen that “BB Green Airi El” needs charging

at both docks (one charge for one crossing). “Future of

the Fjords” needs charging at one dock (one charge

every two crossings).

The number of crossings is taken with assumption

that 30 minutes is enough time to recharge the

batteries for next one or two crossings. The number of

crossing along with number of seats gives the

maximum number of passengers per day (Table 10).

Also, it gives daily energy consumption. For basic

economic analysis, maximum number of passengers

per day along with the price of the one-way ticket is

the income. Total energy consumption is the item of

the expense calculation.

Table 10. Basic economic indicators for summer season

_______________________________________________

June 1

– No. Max. no. Total energy

September 30

of of consumption

No. of seats passengers per day

crossings per day [MWh]

_______________________________________________

“BB Green 20 70 1400 4.65

Airi El”

“Future of 16 400 6400 12.4

the Fjords”

_______________________________________________

6 CONCLUSION

With growing tourist sector, there is an increase in

road traffic between Split and the airport. The area

between Split and the airport, city of Kaštela,

experiences increase in air pollution. In this paper the

alternative path is proposed with the purpose to

decrease the road traffic and Split center congestion.

Marine traffic on this relation is not new but there are

no organized transfers for larger number of

passengers with economically eligible ticket prices.

From May 1

2019. The first organized transfers by

diesel catamaran will start with operation. To fully

exclude the air pollution from marine traffic, in this

paper the electric vessels are investigated. Overall

seven vessels are presented in the paper. To compete

with road traffic and new catamaran line the

minimum cruising speed of the electric vessel is set to

be 13 knots. From presented vessels two of them

satisfy this speed value. These vessels are two very

different vessels. They differ in cruising speed,

installed battery capacity, propulsion power, overall

dimensions and number of seats.

The conclusion itself is that there are commercially

available electric vessels for the rout Split – airport

(Resnik) with minimum cruising speed of 13 knots.

But the question is, are these vessels along with the

service they provide cost effective.

Depending on the energy consumption and

battery capacity there can be one charging station or

two charging stations. One charging station means

lower infrastructure costs and lower maintenance cost

but in the case of malfunctioning there is no backup

supply except if there are battery pack at the station.

The cruising speed, number of crossings, energy

consumption, number of seats, one or two charging

stations, charging stations with or without battery

pack are all items that should be taken into

consideration to optimize the vessel for the route Split

– airport (Resnik). Which in the end leads to another

conclusion that custom solution may be needed.

Economic cost-effectiveness of this proposal will

be subject of our future work.

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