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CHIKYU MAIL NEWS Vol. 102, June 26th 2008

This mail news service provides you with information
about the Deep Sea Drilling Vessel "Chikyu" and
science and technology for the IODP Earth exploration.

CHIKYU HAKKEN WEB SITE
http://www.jamstec.go.jp/chikyu/
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[JAMSTEC Press Release]
June 25, 2008
The Deep-Sea Drilling Vessel CHIKYU
Projected measures for the damages on Azimuth Thruster and
future schedule
http://www.jamstec.go.jp/e/about/press_release/20080625/index.html
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The Deep-sea Drilling Vessel Chikyu, operated by the Japan Agency
for Marine-Earth Science and Technology (JAMSTEC: Yasuhiro Kato,
President), carried out a Drydock Survey, including repair and
maintenance work from February until April this year at the Sasebo
Shipyard, Sasebo Heavy Industries Co., Ltd in Sasebo City, Nagasaki
Prefecture. During the survey, some cracks and chips were discovered
on the teeth of some of the Azimuth Thruster (360 degree swiveling
propellers used to maintain ship's position during drilling operations) gears.

JAMSTEC and outside experts investigated the cause and found
that several factors are involved, including design and manufacture,
the gear material, and the assembly and adjustments made to the
thrusters. Projected future preventative measures include the use
of improved materials, designing, and manufacturing, and more careful
assembly and adjustment. Therefore, all six gears will be completely
replaced with new ones.

We anticipate that the gear change will be completed by January 2009,
and Chikyu will conduct IODP (the Integrated Ocean Drilling Program*1)
riser drilling after completing test drilling in the Sea of Kumano, off the
coast of the Kii Peninsula.

[Appendix: Damage Assessment and projected solutions]
Damaged areas were carefully analyzed with technical advisers who
identified the following areas:
- The vertical shaft (pinion) gear teeth might contact and induce
cracks in the wheel gear teeth,
- Lack of strength in the internal shear stress or existing impurities
in the gear may have caused the cracks.
The following measures will be taken, in consideration of other possible
factors: 
- Modify the shape and round off the corners of the pinion gear's
teeth to avoid contact with the wheel gear,
- Assemble and adjust gear teeth carefully,
- Modify the design to decrease internal shear stress of the gear
and enhance internal strength,
- Advance methods to increase carburizing depth,
- Improve the quality of gear material to avoid the inclusion
of impurities.
Therefore, all six existing gears will be replaced by new ones
with the new modified design.

[Reference: Damages of Azimuth thruster]
The CHIKYU installs a computer system called Dynamic Positioning
System (DPS) to control the power and direction of thruster so
that the CHIKYU can maintain a constant position for the deep-sea
drilling with 6 Azimuth thrusters (3 on the bow and 3 on the stern:
propeller diameter is 3.8m) which is used worldwide.
Damage has been identified on 3 out of 6 wheel gears and one of
those was replaced. It was the first overhaul inspection of Azimuth
thruster since the CHIKYU's delivery in July 2005.

See more about the news;
http://www.jamstec.go.jp/e/about/press_release/20080625/index.html

Contacts:
(For Chikyu)
Takeo Tanaka, e-mail: cdex@jamstec.go.jp
Manager, Planning and Coordination Department
The Center for Deep Earth Exploration (CDEX)
Japan Agency for Marine-Earth Science and Technology

(For Publication)
Noriyuki Murata, e-mail: press@jamstec.go.jp
Manager, Planning Department Press Office
Japan Agency for Marine-Earth Science and Technology

*1: Integrated Ocean Drilling Program (IODP)
The Integrated Ocean Drilling Program (IODP) is an international
marine research drilling program dedicated to advancing scientific
understanding of Earth by monitoring and sampling subseafloor
environments. Through multiple platforms, preeminent scientists
explore IODP principal themes: the deep biosphere, environmental
change, and solid earth cycles. IODP has started since October 2003
led by Japan and the USA. IODP now has 21 member countries.

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CHIKYU HAKKEN web site introduces you to every
aspect of the Deep Sea Drilling Vessel "Chikyu" and
science and technology for the IODP Earth exploration.
http://www.jamstec.go.jp/chikyu/

The Integrated Ocean Drilling Program (IODP) is an
international marine research drilling program dedicated
to advancing scientific understanding of the Earth by
monitoring and sampling sub seafloor environments.
IODP drilling operations aboard the Chikyu are managed by
JAMSTEC through CDEX, Japan Implementing Organization.
http://www.iodp.org

"CHIKYU HAKKEN" means Discover the Earth in Japanese.
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