" S e i r y u - m a r u " - Tr a i l i n gSuction Hopper Dredger With
Oil Recovery System
SHUHO YANO*1
TAKANORI WATANABE*2
NAOTO MIYAKE*3(e) Capable of functioning as a disaster control center.
(f) Integrated high-grade automated control system fordredging, land discharge, ship steering, oil recoveryand engine room.

1. Introduction
The Seiryu-maru is a highly advanced multifunctional
high-capability trailing suction hopper dredger with oil recovery system unparalleled anywhere in the world. She isequipped with three outstanding functions: dredging capableof environmentally-friendly leveled dredging by thin layers; oil recovery capable of handling low- to high-viscosity
oil in the open sea, and accident control capable of prompt
response in the event of an accident. This vessel was ordered from Mitsubishi Heavy Industries, Ltd. (MHI) by theChubu Regional Bureau of the Ministry of Land, Infrastructure and Transport (MLIT) in November 2003, and its
building was completed at MHI's Kobe Shipyard & Machinery Works in March 31, 2005. Since then, she has been
engaged in dredging work in Nagoya Bay. She has replaced
the first-generation Seiryu-maru, a trailing suction hopper dredger with oil recovery system built in 1978. Although
she has succeeded to the name of the former Seiryu-maru,
which became well known for her operations such as in theoil leakage accident of the Nakhodka, the new Seiryu-maru
is an outstanding vessel unparalleled in the world withregard to her basic concept and component systems.

3. Dredging system and layout
The dredging system is based on adoption of the world's
largest-class wide span drag head which permits highaccuracy leveled dredging without left-over, excessive orstripe dredge.
A monobloc type drag head 7.2 m in width was selected to obtain a high leveling effect. With this dredger,
the drag head is divided into four sections, making it
possible to follow the sea bed undulations, thus preventing water suction caused by such unevenness, which is a
shortcoming of the wide span monobloc type drag head.
In actual dredging operations, highly accurate dredging
with a high mud concentration has been realized. A recycling system that returns the water in top of the mud
hold to the drag head has also been adopted to upgrade
dredging efficiency.
Adoption of the wide span drag head has resulted in ahull layout that can accommodate the aft center drag system. A side drag dredge normally has two drag arm systems,
but this dredger has one system equipped with one dredging pump. In addition, this dredger does not operate thedischarging pump and the recycling pump simultaneously,
enabling the number of pumps to be reduced as the samepump is used for the two purposes. Accordingly, the numbers of dredging pipes and recycling pipes on the dragladder have been reduced to half, facilitating maintenance.
The aft center drag system also has the advantage thatthe dredged line is shown exactly by the ship's wake, further improving dredging accuracy.
When the aft center drag system is used, the crew's
quarters are often positioned in the fore section in consideration of ship hull trimming and drag ladder maintenance.
This dredger, however, is intended to operate in high sea
areas for oil recovery and other emergency activities, andaccordingly the crew's quarters are located in the aft sections, ensuring comfort for the crews in view of vibration,
pitching and rolling of the ship. Additional measuresagainst vibration and noise were also taken to ensure thecrew's comfort.

2. General description(1) Principal particulars
Length (o.a.):104 mLength (p.p.):
96.0 mBreadth (moulded): 17.4 m
Depth (moulded): 7.5 m
Draft (moulded):
5.6 m
Gross tonnage:
4 792 tons
Trial speed (max.): 13.5 knots(2) New technologies and systems used on this dredger(a) A dredging system capable of highly accurate leveled dredging and a new type drag head.
(b) An environmentally-friendly land discharging system and a high-grade dredge recycling system which
promotes both environment protection and dredging
efficiency upgrading.
(c) Oil recovery scoop and oil collection system excellingin rough sea operation.
(d) Oil recovery scoop capable of handling low- to highviscosity oil.
*1 Shipbuilding & Ocean Development Headquarters*2 Kobe Shipyard & Machinery Works*3 Seiryo Engineering Co., Ltd.

HITOSHI KUMAMOTO*1
TAKESHI OGAWA*2

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 1 (Jan. 2006)

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Fig. 1 Wide span drag head
Dredge surface undulations can be reduced, and prevention ofexcessive dredging effect can also be expected.

Fig. 2 Water jet type oil collection device and oil recovery device
These increase the efficiency of oil recovery in rough sea conditions.

4. Oil recovery system

5. Disaster control system

With regard to the oil recovery system, effective measures were devised and mounted on this dredger to promote
efficiency of oil recovery equipment in rough seas, collection of floating oil, recovery of high viscosity oil, and others.
For oil recovery, a device capable of recovery operationin rough seas with wave height of 2.5 m was developed.
This device was realized by improving the whirlpool typeoil recovery scoop as follows:(1) Increased height of the suction port.
(2) Increased capacity of the jet water in the lower sectionof the oil recovery scoop for suction force upgrading.
In order to improve the recovery efficiency, an oil collection system using a water jet was developed and mounted
on this ship for the first time in the world. Conventionally,
the recovery efficiency declines as the oil after entering
the recovery equipment flows away under the effect of retreating waves or as the oil accumulated in front of therecovery equipment runs off. This oil collection system withwater jet has drastically improved the oil collection performance as effective oil collection is made possible by optimal
combination of jet power and direction. This system is extremely simple to operate compared with the conventionaloil boom and similar systems, and it is safe in relation toship navigation as no structure is in contact with the sea
water surface. Also, following the experience of emergencydispatch to the oil spill accident of the Nakhodka, the skipper type high-viscosity oil recovery equipment wasdeveloped and is mounted on this dredger, enabling oil tobe scooped and recovered by means of a cage.

In addition to the dredging and oil recovery functions,this dredger also has an disaster control function. Built for
the MLIT, the vessel is provided for the first time with ahelicopter deck for the purpose of transporting disaster
control personnel and emergency materials at the time oflarge-scale disasters. This dredger accommodates TV conference and disaster control rooms provided with the latest
information and communication technology equipment
having audio-visual support functions such as accident information collection, information distribution and accident
prevention documentation.

Shuho Yano

Hitoshi Kumamoto

6. Conclusion
Asia is now believed to be on the brink of miraculous
economical development, and the present 21st century has
been called the century of Asia. Accordingly, Japan's ports
are becoming increasingly important, and the role of thisdredger in port and harbor improvement and environmental preservation is likely to be highly significant.
As mentioned above, this dredger is an excellent multifunctional vessel featuring a hitherto unseen combinationof dredging capability, oil recovery capability and maritime
disaster control capability. She is expected to contributeactively in the future not only to port and harbor improvement and maintenance but also to combating problems suchas sea contamination and pollution.
Lastly, MHI wishes to express its deep appreciation
to all those who have generously cooperated in the conception and realization of this unique multiplex task boat.

Takanori Watanabe

Takeshi Ogawa

Naoto Miyake

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 1 (Jan. 2006)

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