Mitsubishi Heavy Industries Technical Review Vol. 53 No. 2 (June 2016)
58

7,000 Vehicle Class Post-Panamax Energy-saving
Pure Car and Truck Carrier “IRIS LEADER”

S h i p & O c e a n E n g i n e e r i n g D e pa r t m e n t ,Shipbuilding & Ocean Development
Division,C o m m e r c i a l Av i a t i o n & Tr a n s p o r ta t i o nS ystems

In preparation for the opening of the new Panama Canal, the expansion of which started in
2007, new-generation post-Panamax PCTC (pure car and truck carriers) are beginning their maiden
voyages. Iris Leader, completed in December 11, 2015, is a new-generation post-Panamax
energy-saving car carrier owned by Nippon Yusen Kabushiki Kaisha. Its conceptual design andhull form development was undertaken by Mitsubishi Heavy Industries, Ltd. (MHI), and thefollowing basic and detailed design and shipbuilding was handled by Imabari Shipbuilding Co.,
Ltd. This paper presents the latest new-generation post-Panamax PCTC as achievements of these
efforts by the two companies.

|1. Features of new-generation energy-saving car carrier1.1

Principal particulars and general arrangement

Table 1 and Figure 1 show the principal particulars and general arrangement of Iris Leader.
The principal dimensions of the car carrier were determined in consideration of a carrying
capacity of approximately 7000 vehicles, and a 34.8 m-beam was adopted, which is somewhat
smaller than the post-Panamax maximum beam of 160 ft (approximately 49 m) allowable forpassing through the new Panama Canal. The length of the car carrier was set to less than 200 m to
avoid the additional requirements for navigating in specified routes in Japan.
Based on these properly determined principal dimensions, despite the increased carrying
capacity, Iris Leader can reduce the amount of ballast sea water for maintaining the stability
performance of the vessel in comparison with existing Panamax car carriers. Furthermore, the latest
hull form does not require a significant increase in the power of the main engine.
Four of the twelve car decks are liftable decks under which passenger vehicles, heavy-duty
vehicles such as construction machines, and long cargo, etc., can be loaded. This achieves a cargohold that can flexibly handle variations of transported cargo.
The rampway in the hold uses jumping slopes arranged in a straight line, resulting in a
reduction of the cargo handling time. Pillars in the hold structure are arranged in a single line, andthe car hold structure under the embarking deck adopts a newly developed structural form where no
conventional transverse bulkhead for securing the structural strength is used. For this reason,vehicle maneuverability in the hold is significantly improved.
Table 1
Ship classification
Country of registration
Overall length(m)Breadth(m)Depth(m)Full load draft(m)Car capacity(RT)Ship speed(kt)Dead-weight capacity (t)Gross tonnage

NKJapan
199.99
34.80
38.07
10.60
7,125
20.2
20,85370,826

Specifications of Iris Leader
Main engine type
Main engine maximum output
Generator
Diesel driven
Turbocharger driven
Vehicle deck
Liftable deck
Shore rampway design loadStern(t)Middle of vessel (t)7UEC60LSE-Eco-A2
13,800 kW x 105 min-1(Total) 4,180 kW
4 sets
1 set
12 layers
4 layers
150
20

Mitsubishi Heavy Industries Technical Review 53 No. 2 (June 2016)
59Figure 1 General arrangement

1.2

Energy-saving and global environmental-protection technologies

Figure 2 shows the energy-saving and global environmental-protection technologies
equipped on Iris Leader.
As a result of the introduction of these technologies, Iris Leader attains energy saving ofapproximately 30% per a transported vehicle in comparison with existing Panamax car carriers.

Figure 2(1)Energy-saving and global environmental-protection technologies

Inverter-controlled cooling sea water pump system
The central cooling system (CCS), which is the main engine cooling system, uses aninverter-controlled sea water pump that can control the pump speed and amount of pumped sea
water responding to the sea water temperature in order to reduce electricity consumption.
Figure 3 shows the structure of the inverter-controlled cooling sea water pump system.

Mitsubishi Heavy Industries Technical Review 53 No. 2 (June 2016)60

The control valve opening range is automatically adjusted so that the cooling fresh watertemperature becomes constant, and therefore varies in response to the sea water temperatureand the ship thermal load. The fresh water temperature control valve opening signal is input tothe control panel, the sea water pump speed is increased or decreased in response to the sea
water temperature and the ship thermal load, and the pump discharge flow amount is
continuously and optimally controlled. This keeps the opening of the fresh water temperature
control valve within a certain range and attains energy saving.

Figure 3(2)Inverter-controlled cooling sea water pump system

Mitsubishi VTI (variable turbine inlet) system
The service schedule of a ship is determined in response to seaborne cargo traffic. In
some cases, where there is little seaborne cargo traffic, navigation at a reduced speed occurs.
While a ship is navigating at a reduced speed, the main engine operates under a low loadcondition where the scavenging air pressure of the main engine decreases, resulting in loweringof the main engine operating efficiency. For maximizing and optimizing the efficiency during
navigation at a reduced speed and under a low load condition, the variable turbine nozzle of theVTI (variable turbine inlet) turbocharger is installed to the exhaust gas inlet and changes thenozzle throat area. This results in improvement in fuel efficiency of 2 to 3 g/kWh. The VTIsystem has a simple and easy-to-maintain structure where the turbocharger main unit with avarying mechanism that switches the nozzle in two steps to reduce the nozzle area is used toincrease the scavenging air pressure supplied to the main engine. Figure 4 shows the nozzle
opening and closing mechanism of the VTI.

Figure 4

Mitsubishi VTI (variable turbine inlet) system

Mitsubishi Heavy Industries Technical Review 53 No. 2 (June 2016)
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Windscreen reducing wind resistanceIris Leader is equipped with a windscreen that reduces the wind resistance caused by
opposing wind from the front and the diagonal-front of the vessel. There is a concern that ascreen installed in the near-front of the wheelhouse may affect the view from the wheelhouse.
The windscreen equipped on Iris Leader, however, adopts a shape that minimizes the adverse
effect on the view while maintaining the resistance reduction effect. Figure 5 shows a bird's
eye view of the windscreen.

Figure 5Windscreen reducing wind resistance(4)

Post-Panamax hull form equipped with reaction rudder with bulb
The hull form of the vessel was developed using the towing tank in the Fluid Dynamics
Research Department of the MHI Research and Innovation Center with the full use of MHI's
hull from development technologies and technological expertise accumulated over many years.
In addition, a reaction rudder with a thin blade cross section was adopted as additionalenergy-saving equipment to further reduce rudder resistance and obtain a reaction effect of therudder. Furthermore, the rudder bulb was installed at the rear of the propeller boss cap with theaim of enhancing the propulsive efficiency. Iris Leader was built before the enforcement of theIMO EEDI (Energy Efficiency Design Index) regulations. However, the statement of fact reportissued by the classification society verified that Iris Leader attains an EEDI that is more than
10% less than the reference line of the regulatory requirements.
(5) Mitsubishi hybrid turbocharger
Iris Leader is equipped with a Mitsubishi hybrid turbocharger that recovers the exhaustgas energy of the main engine during navigation. Figure 6 shows a cross-sectional view of thehybrid turbocharger unit. The hybrid turbocharger, a turbocharger combining an MET
turbocharger and a high-speed motor/generator directly connected to its rotor shaft, feeds
pressurized combustion air to the engine in a manner similar to a conventional turbocharger andsimultaneously serves as a plant that generates electricity using exhaust gas energy.
Furthermore, the generator can be used as an electric motor to accelerate combustion air supply
instead of the auxiliary blower when the engine operates under a low load condition. In suchcases, the required power is lower than that of the auxiliary blower and a higher energy-saving
effect can be attained.

Figure 6

Mitsubishi hybrid turbocharger

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Mitsubishi Air Lubrication System (MALS)
Iris Leader is equipped with the Mitsubishi Air Lubrication System (MALS) in order toreduce main engine fuel consumption through a reduction in the frictional resistance of sea
water on the vessel during navigation. MALS is a mechanism that blows air from the bottom ofthe vessel and carpets it with small bubbles to reduce resistance during navigation. In this case,the application target is car carriers with relatively fine hull form and smaller flat bottom. The
sea trial results, however, showed an expected effect of MALS and verified its effectiveness.
Figure 7 shows the wakes generated when MALS is used and when it is not. This figure showsthat when MALS is used, the bubbles blown from the bottom at the bow flow along the bottom
surface to the stern without leaking out to the side and are released from the stern edge.

Figure 7(7)MALS wakes

Environmental-protection fuel tank
The fuel tank is located at the bottom and is enclosed by the ballast water tank on thebottom outer panel side to reduce the risk of a fuel spill in the case of external damage to thebottom of the hull. This tank layout satisfies IMO regulations for the prevention of sea pollution
by oil and contributes to environmental protection.