The First Hybrid CRP-POD
Driven Fast ROPAX Ferryin the WorldNAOKI UEDA* 1
AKIRA OSHIMA* 2
TAKASHI UNSEKI* 3
SHIGETOMO FUJITA* 3SHINGEN TAKEDA* 3
TOHRU KITAMURA* 4

A fast ferry equipped with the world's first hybrid CRP-POD propulsion system having the same effects as contrarotating propellers (CRP) has been developed by combining an electric pod propulsion unit and conventional diesel
propulsion system. With this system, energy is saved by more than 13% as compared with the conventional twin shafts
and propellers system, contributing to a reduction of operation costs and of CO 2 emission. Two ferries, named
HAMANASU and AKASHIA, adopting this system were delivered to Shin Nihonkai Ferry Co., Ltd. at the end of June
2004. Excellent propulsion performance of the hybrid CRP-POD system was confirmed not only by the trial Maximum
speed of 32.04 knots (59.3 km/h) but also by the vessels' operational record. They have been in commercial operation
between Maizuru and Otaru since July 2004, and the previous one-way cruising time of 29 hours has been shortened to20 hours. They are two of the fastest ro-pax ferries in the world.

1. Introduction

2. Outline of the Principal Particulars

More than 20 fast ferries of the 30 knot class are operating in the world at present. Those fast ferries
consume a greater amount of fuel and have very highoperation costs, while cruising economy, CO 2 emissions
and other environmental effects are also serious problems in need of solution.
The world's first hybrid CRP-POD driven system
Fig(FigFig.. 1 ) installed in the HAMANASU and AKASHIA is a
21st century-oriented propulsion plant featuring energy
saving of more than 13% of the conventional level, enhanced cruising economy, and low environmental impact.
This paper reports an outline of the new ferry, mainlywith reference to the novel propulsion system

The principal particulars of the ship are shown inTable 1
1.
To enhance the propulsion performance, the overall length is 224.82 m, surpassing the 200 m mark forthe first time in Japan. It is the longest ferry in theworld.
The main engine for propulsion and the main generator engines for supplying power to the pod are twounits each of 12V46C manufactured by Wartsila, andthe pod propulsion unit is Azipod (R) of ABB, adopted
in view of its past record and reliability.

Table 1 Main specifications

Fig. 1 CRP POD propulsion system*1 Shipbuilding & Ocean Development Headquarters*2 Nagasaki Research & Development Center, Technical Headquarters*3 Nagasaki Shipyard & Machinery Works*4 Shimonoseki Shipyard & Machinery Works

Lengthoverall(m)224.82Main
engineBreadth(m)26.00

Maximum-1
output 12 600 kW x 500 min

Depth(m)

20.4

Main
generator
engineDraft(m)7.40

Maximum
12 600 kW x 514 min-1
outputGross tonnage (t)InternationalJapanese

34 18 1
16 810

Auxiliary
generator
engineTrial maximum
speed(kn)

32.04

Maximum
2 910 kW x 720 min-1
outputPassengercapacity(persons)

820

Podpropulsion
unit

AZIPOD Type 21

Vehicle capacity

158 vehicles of
12 m length; 65
passenger cars

Normaloutput(kW)

17 600Wartsila
12V46C x 2 units

Wartsila
12 V 46 C x 2Daihatsu
8DK32C x 1unit

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 6 (Dec. 2004)

13. History of development

4. Outline of hybrid CRP-pod-driven propulsion

The pod propulsion unit is an azimuth type one driving a propeller directly coupled with a motor byincorporating the motor in a pod unit. This propulsion
unit is at the stern of the hull, and also the unit has afunction of rudder due to rotation. Thanks to its 360degree free rotation, excellent steering performanceis realized in harbor and pier operations, together withpowerful propulsion.
This compact system incorporating a propulsion motor in the pod was jointly developed by European
electric manufacturer and shipyard in the early 1980s
for ice breakers.
The pod propulsion unit, a revolutionary system inthose days, has been employed in more than 70 vessels, but since it is an expensive system, it has beenused mainly in cruise passenger ships so as to makethe best of its features, including excellent steering
performance, vibration and noise suppressing effect,and high flexibility of inboard layout.
MHI initially promoted investigation into applications of pod propulsion unit aiming at large cruise
ships and LNG carriers. From around 2000, efforts
have been concentrated on development of a novel propulsion plant using the pod unit as part of campaign
to reinforce the competitive power of ferries and ro-roships which belong to the main strategic category forMHI.
As a result, it has been found that the "CRP-POD
propulsion system," combining the conventional propeller propulsion system with pod propulsion, issufficiently economical and competitive in general merchant ships.
In Europe, too, intensive studies have been madeto apply the hybrid system in ferries as an applicationof the pod propulsion unit. In April 2002, MHI started
joint research with ABB, an active manufacturer whichis enthusiastically developing this concept.

Generally speaking, large ferries have twin shafts andpropellers arranged symmetrically to the center line because propeller diameter are limited due to limitation ofdraft, and because plural independent propulsion plants
are needed to assure the safety of passengers in case oftrouble. For a ship adopting the twin shafts and propellers, the propeller shaft is generally exposed from thestreamlined hull, and is supported by bossing and brack2 This is known as the "shaft bracket
ets as shown in Fig. 2.
system," and the additional resistance may occupy 10 percent of the total resistance.
As shown in Fig. 3
3, in this ship, the pod propulsion
unit is located immediately behind the coaxial line of themain propeller of one shaft, and two propellers are arranged like one set of contra-rotating propellers. The main
propeller is a controllable pitch propeller, and is driven
directly by two sets of medium speed diesel main engines
by way of reduction gears with clutch and intermediate
shaft. The pod propeller positioned behind is an electric
propulsion unit driven by an electric motor in the pod,using electric power from the power generation plant.
As a result, two sets of propellers can be installed without any appendages such as shaft bracket, and theresistance performance is significantly improved as compared with the conventional twin shafts ship. In addition,
rotating the adjacent propellers in opposite directions
could realize high propulsion efficiency by reducing tangential water flow. (It is called contra-rotating propellers,
CRP, effect.)
This pod propulsion unit has a larger loss of energy
conversion due to electric propulsion as compared withmechanical driving. This demerit is compensated by lowering the distribution rate of electric propulsion. Thus,by combining the pod propulsion with conventional mechanical drive propulsion plant, the concept of CRP isrealized, and is accordingly called as hybrid CRP-POD
driven propulsion.

Fig. 3 CRP POD propulsion system

Fig. 2 Conventional twin shafts ship (shaft bracket system)

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Technical Review Vol. 41 No. 6 (Dec. 2004)

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Conventional four-engine twin shafts diesel direct drive system

GG

12V 46B
16V 46B

Main engine: 53.17 MW
Main generator: 3.75 MW
Shaft generator: 2.50 MW
Total: 59.42 MW

G 1250kW
G 1250kW
G 1250kW

16V 46B
12V46B

Fuel consumption: 220 tons/day

Energy saving effect of 13%Hybrid CRP POD propulsion system

12V 46C

12V 46C

Main engine: 25.20 MW
Main generator: 24.40 MW
Auxiliary generator: 2.76 MW
Total: 52.36 MW

G

2760kW G

12V 46C

12V 46C

G

Fuel consumption: 193 tons/day
Fig. 4 Plant comparison

Fig. 4 compares the conventional mechanical drive
twin-shafts system and the hybrid system, and showsthat the energy saving effect is as high as 13%.
This plant has the same redundancy as a twin-shafts
ship because the two driving systems are completely independent.

As a result, along with the effect of optimization oflength, residual resistance decrease of 22% is realized
as compared with the 30-knot ro-ro ship developed by
MHI in 1998, as shown in Fig. 66.
Since the main propeller operates in the wake of thehull, it is important to incorporate a design that reduces
generation of cavitation and propeller fluctuation pressure. The essential design points for the pod propeller
are avoidance of tip vortex generated from the main propeller, and strength on the fluid force in pod steering
condition. The pod propeller was designed jointly withABB, and perfect verification was achieved.
In the design of both propellers to harmonize with eachother as the CRP, numerical calculation by CFD and model
verification were executed repeatedly. In numerical calculation, the Navier-Stokes equation was solved in the propeller
running state, the flow to the propulsion unit was calculated, the propeller fluid force designed by UQCM (unsteadyquasi-continuous method), a numerical propeller calculation
method used for years at MHI, was put back to a CFD modelby the multiblock lattice structure theory, and a theoretical
calculation of high precision was performed.

5. Technical subjects in development: The subject ship
: 30 kn Ro-ro ship (200m long)

Residual resistance coefficient

5.1 Propulsion performance
At the beginning of the development, using the experimental tank at MHI's Nagasaki Research &Development Center and the depressurized towing tankof MARIN in the Netherlands, which is noted for its
achievements in pod-driven ships, the resistance andpropulsion performance, and propeller fluctuation pressure were investigated.
On the basis of the findings obtained, a hull model
for minimizing the resistance at design speed was developed by utilizing computational fluid dynamics (CFD),
and this was verified at the Nagasaki R&D Center experimental tank. Fig
Fig.. 5 shows an example of hull side
waveform by CFD.

Service speed of 30 kn Ro-ro ship
Navigation speedof the subject ship

-22%

0.30

0.31

0.32

0.33

0.34

0.35

0.36

0.37 0.38

Froude number (non-dimension speed)

Fig. 5 Waveform calculation by CFD

Fig. 6 Comparison of residual resistance (main hull only)

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 6 (Dec. 2004)3

20.00: +35-T: -35-T

15.00
10.00

DT=2.95

Ad=2.73

Ad=2.98
DT=3.425.00
0.0-5.00-20.00Fig. 7 Pressure and streamline vector calculationof pod surface-10.000.00
10.00
Normal seagoing (CRP mode)

20.00

20.00
15.00

Rudder angle: 0 degree

DT=2.43

Ad=2.46

Ad=2.39

10.00
DT=2.41
5.00
0.0-5.00-20.00-10.000.00
10.00
Pod propeller thrust only

20.00

20.00
Fig. 8 Example of cavitation observation in
depressurized towing tank

15.00
10.00

500.0

X (M)

Ad=3.90

DT=4.03

5.00

400.0
300.0

Ad=3.27

Dead slow
navigation

Slow
down

Reverseand stop

180-degree
head turning

0.0
-5.00
-20.0020.00
0.00-10.00
10.00
Main propeller thrust only (pod steering)

200.0
100.0
Stern fixing

Fig. 9 Turning performance (model test)

0.0
Quay

-100.0-200.0-300.0-100.0 0.0 100.0
300.0
500.0
Harbor steering result Y (M)

700.0

900.0

Fig. 10 Simulation of harbor operation (model test)

Fig. 7 shows an example of calculation of pressure
distribution and speed vector on the pod surface in thepropeller running state.
Fig. 8 is an example of cavitation observation using a
depressurized towing tank. In the sea trial, the cavitation of actual ship was observed, and the results ofestimation were verified.
5.2 Steering performance
The pod propulsion unit features high steering performance. In the hybrid system, steering variations
combined with the conventional propulsion system may
be considered. Fig. 9 shows three modes of turning trackchart: CRP mode, pod alone, and main propeller alone.
In the main propeller alone mode, the pod propeller idles
and the pod functions as a rudder.
Fig. 10 shows a track of turning-round motion by bow
thruster and pod 90-degree steering from the dead slow
ahead in the model test. The turning motion is completed

in a state close to in-situ head turning motion, and safeand prompt steering is realized in narrow waters in harbor or at piers.
The ship has an automatic control system that maintains the output balance of pod and main propellers in
the optimum state, and during normal navigation it ispossible to operate in CRP mode to accelerate and decelerate the pod and main propellers at the same time by asingle main engine telegraph lever. In harbor operation,by changing to the maneuvering mode, the pod and main
propellers can be operated independently. The wing operation panel in the wheelhouse includes remotecontrollers for regulating the thrust of the main propeller, thrust and steering of the pod, and operation of thebow thruster. Although the sense of maneuvering is different from that of existing ships, it can be learned in ashort time, and excellent maneuverability has been demonstrated in actual navigation.
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Technical Review Vol. 41 No. 6 (Dec. 2004)4

5.3 Structural strength and vibration countermeasure
Greatest attention has been paid to the strength design of structures for supporting the weight of the pod
installed at the end of the stern, generated thrust by
pod propeller, and large turning force generated during
1 shows an FEM analysis model ofturning motion. Fig. 1
11the stern section including the pod support structure, inwhich the fitting portion of the support structure andhull is shown finely in the mesh size corresponding to
the plate thickness.
To minimize noise as required in a passenger ship,vibration mode and local vibration were investigated byfull ship FEM model. This ship has four main sources ofvibration of different frequencies, namely the main engine, main generator engine, pod propeller, and main
propeller. The dominant vibration source is the main
propeller, for which vibration countermeasures have been
carefully chosen and applied. The effect of vibration countermeasures has been confirmed that correspond exactly
to prior estimations at the sea trial.
5.4 Layout of propulsion plant
The prime movers of the propulsion plant are two sets
each of 12V46C of Wartsila in both the mechanical driving system and the electric propulsion system, with aview to common use of maintenance parts.
The power generation plant also has one auxiliary
power generation engine to assure electric power in port.
A total of three generators can supply power to the highvoltage power distribution board at 6 600 V.
As measures to restore stability in damage case, theseprincipal facilities are installed in three independent compartments: the generator room, the generator engine room,

Naoki Ueda

Akira Oshima

Fig. 11 FEM model of pod support structure

and the main engine room. The space behind the main engine room is effectively utilized as the passenger car deck.
The pod room located immediately below the stern ofthe car deck accommodates the pod steering unit, its
hydraulic unit, and cooling unit, while the stern of eachdeck has a sheer that accommodates the slip ring compactly without projecting to the car deck. In addition,
the cooling unit and slip ring of the pod are of limited
height as specially ordered.

6. Conclusion
The hybrid CRP-POD propulsion system allows theHamanasu and Akashia to achieve excellent performancein terms of both propulsion efficiency and maneuverability. The performance was confirmed by the vessels'
operational record since June 2004. This innovative propulsion system could be applied to other kinds of vessels
e.g. large container carrier and/or LNG carriers.
The authors highly appreciate the pioneer spirit andthe advices with operational experience of those vessels'owner, Shin Nihonkai Ferry Co., Ltd.

Takashi Unseki

Shigetomo Fujita

Shingen Takeda

Tohru Kitamura

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 41 No. 6 (Dec. 2004)

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