Offshore Technology

Offshore Technology
OMAE 2008
Underwater Vehicles:
Propulsion: The Schottel
Arctic shipping: Arctic
“Neumayer III”:
Ocean energy: Rexroth rises
Ice barriers: Ice Protection
Maritime robots for survey
and security 3
Sauna at the South Pole
Ship Design:
Drilling in Ice
8
6
Combi Drive: suited to offshore application 10
to the Power Take-Off
12
knowledge at DNV informs
risk management 14
Structures
16
Hydac: Condition monitoring Pipeline monitoring: Hydroof oil systems
13
carbon sensor systems
19
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ISSN 1436-8498
Maritime robots for
survey and security
UNDERWATER VEHICLES Maritime investigations, measurements and inspections with autonomous underwater vehicles (AUV) are a core element of ATLAS Elektronik to discover the
underwater resources for economic use as well as for the protection of maritime facilities. The
operation under extreme and difficult environmental conditions requires the use of robots of
the newest technology with high degree of automation and extreme navigation accuracy.
Willi Hornfeld
E
conomic use of the seas and
oceans as well as protection of
the ports and their access has a
top-ranking position – the maritime
market has reached world-wide an
enormous order of magnitude. In this
market a German company in general
has not only a strong position, but in
some special maritime engineering
fields even a top place. In this environment the substantial target areas of the
German maritime technologies are:
The strongly growing and important market segments such as oil and
gas production from the sea bottom,
underwater mining, exploration and
exploitation of gas hydrates, etc..
Maritime Homeland Security, one
of the highest priority missions around
the world with the strategic objectives
Prevent terrorist attacks within and
terrorist exploitation of the national
domain
Reduce the countries vulnerability
to terrorism within the maritime domain
Protect the population centres, critical infrastructure, maritime borders,
ports, coastal approaches, and the
boundaries and seams between them
Protect the marine transportation
Minimize the damage and recover
from attacks that may occur in the maritime domain as either the lead federal
agency or a supporting agency.
One of the core elements for a Maritime
Homeland Security is the protection of
harbours, a razor edge of danger.
Sea Ports and Sea Lanes are the primary gateways for global trade and
commerce. Ports are the nerve centers
of the international supply chain network. Operational drop-outs of any of
such critical hubs and bottlenecks will
hence generate consequential damages
on a truly global scale.
The European Sea Ports Organisation
(ESPO) determines that “the Eu- Fig. 1: ATLAS’ UUV family
Schiff & Hafen | June 2008 | No. 6
3 Special
SPECIAL | OFFSHORE TECHNOLOGY
Parameter
SeaFox
Length [m]
1.3
Width [m]
Ø 0.4 (max)
Weight [kg]
40
Speed [ktd]
•max
6
•min
0.5 (backwards)
Diving depth [m]
300/600
Payload [kg]
5
Obstacle avoidance
yes
Hover capability
yes
Tab.1: SeaFox parameter
Parameter
SeaWolf
Length [m]
2.0
Width [m]
Ø 0.5 (max)
Weight [kg]
110
Speed [kts]
max
8
min
Minus 0.5
Turn radius
<3m
Diving depth [m]
3 to 300
Payload [kg]
> 30
Fig.2: The SeaFox family
ropean Union without its seas port
cannot act directly. The entire foreign
trade of the community and nearly
half of their domestic trade are almost
conducted via the more than 1,000 sea
ports in the coastal member states of
the European Union.”
Obstacle avoidance
yes
Autonomous underwater vehicles
Hover capability
yes
Navigation
INS + DVL + (D)GPS +
pressure sensor + compass
Maritime investigations, measurements
and inspections with autonomous underwater vehicles (AUV) are a core element of the above mentioned market
and growth fields. The fundamental
pre-condition is however the ability for
precise acting in unknown waters as
well as the technologies for the protection of maritime facilities (e.g. inspection of berthing areas, piers and ship
hulls) under extreme and difficult environmental condition. This requires
the use of robots of newest technology
with high degree of automation and
extreme navigation accuracy with high
manoeuvrability.
Such unmanned underwater vehicles are
one of the main product areas of ATLAS
Elektronik. The company has been developing and delivering such vehicles for
military and commercial applications for
about thirty years. Current products to be
noted are the SeaFox, the SeaWolf and the
SeaOtter Mk II.
The development of these AUVs respectively HAUVs (Hybrid Autonomous Underwater Vehicles) happens under consistent attention of as far as possible synergies
between the individual systems. Beyond
that the underwater vehicles are based substantially on dual use, i.e. they are designed
for military and commercial missions, with
that due to better serial production figures
for the basic systems, a more attractive
price for the customer can be reached. This
philosophy shows Fig.1, the ATLAS UUV
(Unmanned Underwater Vehicles) family
which includes not only the Autonomous
Tab. 2: SeaWolf parameter
Parameter
SeaOtter Mk2
Length [m]
3.45
Width [m]
.90
Height [m]
.48
Weight [kg]
1000
Speed [kts]
•max
8
•optimal
4.0
•min
0.5 (backwards) hover
Diving depth [m]
5 to 600
Duration [h]
24 @ 4 kts
Obstacle avoidance
Yes
Hoover capability
Yes
Navigation
MARPOS II
(INS+DVL+DGPS+CTD+ pressure sensor) & CML
Tab.3 : SeaOtter parameter
TYPICAL USERS OF UUV´S
Defence Forces
Coast Guard
Maritime Administration
Customs and
Immigration
Port Authorities
Environmental Agencies
Commercial Operators
Maritime Scientific Institutes
Special 4
Schiff & Hafen | June 2008 | No. 6
Underwater Vehicles (AUV) but also Remotely Operated Vehicles (ROV).
A further characteristic of the here
discussed underwater vehicles is their
modularity which, depending on the
specific payload capacity, will be realized by the possibility of plug and
play integration of quasi any payload.
Finally all ATLAS UUVs can be mission-specifically equipped by the user
with a fiber-optic cable (FOC), so that
a wide-band, real time transmission to
the surface of all sensor and status information can take place. Such hybrid
AUVs (HAUVs) will open wider and
completely new application areas.
The UUVs SeaFox, SeaWolf and SeaOtter are characterised by most different
users and several areas of application.
With other the following applications
are standing in the centre:
Mine counter measure
Damage assessment
Intelligence
Rapid environmental assessment
Route survey
Maritime border control
Waterways and port surveillance
Passenger terminal protection
Maritime science.
The following features are, depending
upon payload capacity, realized or will be
realized in the systems:
Autonomous or operator supported inspection and classification of all kinds
of underwater areas, structures and objects
Adaptive autonomy in relation of the
mission
On line data link via fibre optic cable
on request (hybrid)
Operation in confined and tidal
areas
Inspection sensors of latest technologies
in underwater vehicles
Navigation/positioning of highest accuracy
Standard interfaces for simple integra-
tion of customer specified sensors and
software (plug and play)
High-performance multi sensor image
processing on board or in the surface
console
100% inspection of selected object assured
CAD base inspection on request
CAD object data creation during the inspection
Alarm function in relation to the identified anomaly
Prepared for team operation
Object oriented mission planning and
control.
The UUV SeaFox is a small and lightweight (see Tab. 1) vehicle with an endurance of more than one hour. The
vehicle is available in several configurations from the military systems (SeaFoxC
for mine disposal and SeaFoxI and T
for inspection and training) till the
modular one IQ, predominately used
for commercial survey missions.
Thanks to this modularity, missionadapted sensor suits with e.g. 360° and
side looking sonar as well as a tiltable TV
system are installable as shown in Fig. 2.
The HAUV SeaWolf is a multirole system for all kinds of underwater inspection and anomaly identification.
The propulsion philosophy is comparable with the Seafox (four main propellers and one vertical thruster). Due to a
special adjustment of the main motors
a high efficiency was achieved.
The vehicle is equipped with the latest
sensor and software technologies and
therefore able to inspect autonomously even very complex 3D objects.
For real time data transfer, the SeaWolf can
be connected with the control console by
a fibre optic cable. In this case the mission
will be executed autonomously but with a
real time data transfer.
SeaWolf achieves versatility and flexibility of mission and payload configuration by using plug and play modules
for software, electronic and sensor devices within a generic architecture.
The vehicle’s basic payload is a side
scan and obstacle detection sonar as
well as a TV camera with LED illumination.
For operation in water with low visibility a three dimensional high frequency
multibeam sonar and/or a laser projection unit are additional available. The
navigation is of a very high accuracy and
based on an IMU with DVL and differential GPS. Therefore the use of an acoustic
positioning system is not necessary.
Due to its relatively low weight, the system
is easy to operate and applicable from all
kind of vessels or from the shore.
Fig.3: SeaWolf configurations
Fig.4 : SeaOtter Mk II
The mission planning, control and
evaluation is done from a portable console, the same as used for the SeaFox.
Tab.2 shows the SeaWolf parameter
and Fig. 3 the system configuration.
The HAUV SeaOtter Mk II is based on
the proven MARIDAN 600 and the SeaOtter Mk I, which have been in operations throughout the world. Due to the
design and the flexible payload concept, the system is easily adaptable to
various military and commercial missions.
The SeaOtter Mk II also offers the benefit
of a real time data transfer to the operator
consol through the fibre optic link option.
The standard version of the vehicle
is equipped with side scan sonar, a
multi-beam echo sounder, a sub-bottom profiler, obstacle avoidance sonar,
a TV camera and a precise navigation
system.
Due to its serious payload compartment (approx. 150 kg) the vehicle can
per plug and play be adapted to nearly
all kinds of required missions from
scientific till maritime security applications.
Tab. 3 gives the SeaOtter Mk II figures
and Fig. 4 an impression of the design.
Willi Hornfeld
ATLAS ELEKTRONIK GmbH, Bremen
[email protected]
www.atlas-elektronik.com
Schiff & Hafen | June 2008 | No. 6
5 Special
SPECIAL | OFFSHORE TECHNOLOGY
Sauna at the South Pole
RESEARCH STATION “NEUMAYER III” Germanischer Lloyd’s Business Segment Oil and Gas
offers its wide range of services all over the world. Just recently the experts also conquered
the ‘sixth continent’: they certify the new research station “Neumayer III”
N
ot a single ray of sunlight penetrates the darkness of the polar
winter night. The thermometer
drops below 50°C as storms whip across
the icy landscape. In this environment,
buildings must be designed to withstand
extremely hostile climate conditions.
Materials must be selected carefully and
the functional fitness of elements must
be tested in realistic simulations.
A house in Antarctica: In December
2006, Germanischer Lloyd received an
order from the Alfred Wegener Polar
and Marine Research Institute (AWI) in
Bremerhaven, Germany, to certify the institute’s new research station “Neumayer
III” in Antarctica. Even for an experienced classification society, this project
is rather challenging. The station, named
after the German polar explorer Georg
von Neumayer (1826 to 1909), will consist of a structure supported by sixteen
hydraulically operated posts. By moving
up and down on these support legs, the
building will adjust continuously to the
changing level of the snow surface. As a
consequence, the research station will
not gradually disappear under masses of
snow, as its predecessor did.
Submerged in ice
After 15 years of operation, the current
Neumayer station has sunk twelve metres deep into the ice and will have to
be abandoned in the near future. Built
in 1992, the tube-type structure was state
of the art at the time. But the two steel
tubes that form its outer shell have been
deformed over the years by the movement of the shelf ice and the constantly
increasing load of snow. Today, the once
elliptical shape of the station is no longer
discernible. Time and again, bolts burst
with a loud bang, unable to withstand
the weight of tons of snow bearing down
on the station. The engineering concept
of the new station consists of a building
to be erected on top of a platform above
the snow surface. The building will accommodate rooms for research and operations as well as living quarters.
To construct this unique facility, a pit eight
metres deep will have to be excavated for
the foundations of the hydraulic support
pillars of the station. Later on, the pit will
also be used as a parking area for tracked
vehicles and snowmobiles. A workshop,
the hydraulics centre, exercise rooms and
food stores will be located directly below
the cover of the pit. The station itself will
be positioned on stilts six metres above
snow level so even high winds and dense
snowfall will not cause any major snowdrifts. The two-story building will be standing on a platform 68 by 24 metres large
and provide space for common rooms, a
kitchen, an infirmary and operating theatre, 15 bedrooms with 40 beds, as well as
twelve laboratory and office rooms. Nine
so-called “overwinterers” – scientists, physicians and technicians – will have nearly
twice as much space for their work as in the
subterranean station “Neumayer II”. For
leisure, there will be a lounge with a bar
and a sauna. Once the basic structure has
been completed, a protective shell 120 mm
thick with a blue, white and red coating
– the colours of the AWI – will be placed
on top of it to reduce wind loading. The
roof offers enough space to accommodate
a chamber for helium sounding balloons,
as well as antennas and other measuring
equipment.
Certified containers
Assembly of the “Neumayer III“ in
Bremerhaven
Special 6
Schiff & Hafen | June 2008 | No. 6
AWI-employees at the underwater
acoustic measuring station “Palaoa“
The entire building itself will be assembled
from containers certified by Germanischer
Lloyd. GL has many years of experience
in container certification. Today, the society certifies up to 360 000 containers each
year. After the design review, GL subjected
the thermally insulated containers to spe-
The model shows the hydraulic posts of the garage level
cial tests to check their fitness for transport.
Those tests included stackability, as well as
loading and unloading strength, which ensured that the containers were taken safely to
Antarctica aboard a Danish freighter. Now,
the GL experts main task is to review the
documentation for safety-relevant equipment for the entire station – including evacuation and survival systems, fire extinguishing and fire alarm systems, automation and
alert systems. “Due to the exposed location,
the system as a whole has to meet the most
stringent reliability requirements,” says An-
BACKGROUND:
ANTARCTICA
The Antarctic Zone comprises the land
and sea areas of the South Pole region.
It covers a surface of approximately 12.5
million square kilometres. 98 percent of
this area is permanently covered by ice.
The continent of Antarctica is located in
the centre of the region. The Antarctic
was explored by various scientists and
seafarers from 1920 onwards.
The continent is characterized by an
extreme climate: It is the coldest, driest
and most wind-ridden part of the earth.
There have been reports of temperature readings as low as – 89 °C and wind
speeds exceeding 300 km/h. According
to CONMAP (Council of Managers of
National Antarctic Programs), there are
currently more than sixty active research
stations on the continent.
dreas Mäscher, project manager of GL. “In
this respect we can draw on our experience
in offshore installations.”
The AWI order also includes tests of the
energy supply systems as well as the acceptance inspection of a combustion engine-based cogeneration plant at the manufacturer site. “Supplying the station with
heat and energy is a particular challenge,
considering the extreme climate conditions
– low temperatures, large quantities of
snow, high winds,” Andreas Mäscher emphasizes. Thanks to more efficient generation of heat and electricity in the cogeneration plant, the future station will need only
30 percent more polar diesel (diesel plus
kerosene) than its predecessor although
it is twice as large and will be exposed to
greater wind loading.
GL conducted the component acceptance tests for both, the diesel-operated
generator and the hydraulically operated
stilts. Last year, the lifting units were tested under low-temperature conditions to
ensure flawless operation in the extreme
temperature environment (+4 to -50° C)
of Antarctica.
In November 2007, the components were
loaded onto the Danish freight vessel “Naja
Arctica”, which reached the Antarctic Atka
Bay on schedule in mid-December. However, a sea ice barrier of several metres
thickness prevented the vessel from moving
ahead. The research icebreaker “Polarstern”
was appointed to free a navigation channel
to the ice edge and helped “Naja Arctica”
to reach her planned unloading position at
the edge of the ice shelf only in mid-January 2008. Despite the one-month delay, the
construction of Neumeyer Station III moved
rapidly ahead in good weather conditions.
In only eight weeks, the entire steelworks of
the underground garage section with 16 hydraulically operated posts as well as the first
floor of the future station were erected. The
unfinished building is intended to be used
as a store room for construction equipment
and materials until the next Antarctic summer. The completion of the new station is
scheduled for spring 2009. Then, a GL surveyor will join the construction site at 70°
40.8‘ south and 8° 16.2‘ west, 6.5 km away
from the old station, to inspect the construction of the Neumayer III station and
conduct the acceptance tests.
The new research station, which will
cost about 36 million euros, is designed
for a service life of at least 25 years. The
Alfred Wegener Institute, the operator
of “Neumayer III”, will continue its research activities in Antarctica, recording
important meteorological data and taking measurements of the earth’s magnetic field as well as atmospheric readings of climate-relevant gases. GL will
continue to keep an eye on the station
as well, says Andreas Mäscher: “There
are plans for periodic inspections of the
structure and its equipment.”
Germanischer Lloyd, Hamburg
www.gl-group.com
Schiff & Hafen | June 2008 | No. 6
7 Special
SPECIAL | OFFSHORE TECHNOLOGY
Drilling in ice
SHIP DESIGN The challenge for discovering Arctic oil and gas reserves will be to find solutions to
produce gas and oil with the highest safety and environmental standards. For ice going drill vessels the Hamburg Ship Model Basin (HSVA) has done various innovative frontier developments.
Karl-Heinz Rupp, Walter L. Kuehnlein
I
t is estimated that the Arctic
contains more than one third
of the world’s undiscovered
oil and gas reserves. Although
some developments have already
occurred, the region remains
one of the last energy frontiers.
But the region is also one of the
most difficult areas in the world
to work at, due to its remoteness,
the extreme cold, dangerous sea
ice and its fragile environment.
Big energy companies are preparing to go into the Arctic, they
are taking measures in order to
ensure that they will operate
safely and responsibly.
This is not the first run to the
Arctic. Petroleum companies
entered into the Arctic already
half a century ago. Experiences
from past Arctic developments
show the potential hazards of
further exploration. A key challenge will be developing and
deploying solutions, which are
currently at the cutting edge of
technology. The Arctic Ocean is
the only major sub-basin of the
world’s oceans that has only occasionally been sampled by deep
sea drilling. Today the properties
of the Arctic Ocean are being
focussed upon by both researchers and commercial oil and
gas drilling companies. Research
core drilling is of great impor-
tance for the researchers because
it allows them to increase their
knowledge about that large ice
covered area. And of course the
present high prices for energy
make it profitable to explore for
reserves and to produce energy
even in the ice covered waters of
the High North.
Drilling operations in ice have
been already carried out at the
ice border with “open water drill
ships“, mainly with the support
of icebreakers (e.g. “Joides Resolution” with “Maersk Master”).
Some drill ships are reinforced
for operation in ice, but this reinforcement is limited to the
strengthening of the ship structure
and does not include the propulsion and operational outfitting.
An ice-breaking drill ship should
be capable of keeping its position
so that the drilling operation can
be continued, also when it is surrounded by drifting ice.
Existing
designs
concepts
Some of the challenges which
a drill ship in ice will experience, have been already described in 1983 (Dynamic
Response of a Moored Drill
ship to an Advancing Ice
Cover, T. Kotras, A. Baird, E.
Corona, Poac 83, Volume 3,
Fig.1.: The cross section shows the sloped side of
the HSVA drill ship design with ice accumulated
Special 8
and
Schiff & Hafen | June 2008 | No. 6
page 433, Helsinki, Finland,
1983):
“The ability of a vessel to stay
within a prescribed operational
radius is greatly enhanced when
impacting ice in a head-on condition. Beam-on collisions cause
excursions from two to five times
larger as those occurring head-on.
The ability of a drill ship to
quickly yaw into a heading inline with the advancing ice is
directly related to the maximum
excursion seen.
In the Bering Sea, an unassisted drill ship may not be capable
of year round operation during
the heavy ice periods, ...“.
Almost 30 years ago, in 1980, a
drill-platform from Gulf Canada
(Conical Drilling Unit) was tested in ice by HSVA. It was found
that the rig could operate in an
environment up to about one
meter level ice thickness. This
platform, the “Kulluk“, was kept
in position with a mooring system. The shape of the platform
was circular in the plan view
and the section was similar to
an asymmetrical sandglass. The
turret was placed in the centre of
this floating island. This platform
was not suitable for being moved
over a long distance at sea.
In the last decade improvements in manoeuvrability and
ice breaking performance have
been achieved by applying
azimuth propulsors. Nowadays several ice going and ice
breaking vessels, e.g. icebreakers, supply vessels, tankers and
multi-purpose container vessels are equipped with this type
of propulsion system.
New technical developments
In 2000 contracted the AlfredWegener-Institut (AWI) in
Bremerhaven Germany (www.
awi-bremerhaven.de) the Hamburgische-Schiffbau Versuchsanstalt (HSVA) to carry out a
draft design study for an Arctic
Drilling Research Vessel with
dynamic positioning capabilities in ice. The project was entitled “Aurora Borealis”.
Drifting ice may change in both
in speed and direction. Furthermore the ice conditions vary
from easy to heavy (e.g. ice
ridges), therefore the drill ship
must be able to keep position
within a very narrow margin. All
of these requirements, as well as
the technological developments
described above have been taken
into consideration for HSVA’s
conceptual design for the “Aurora Borealis”.
The technical features of the
HSVA design are:
Fig.2: Side view of “Aurora Borealis“ with two moonpools
(as designed by HSVA)
Low ice resistance of the drill
ship at both bow and stern. This
was achieved with an optimized
icebreaking hull shape, similar
to that of an icebreaker.
High ability to turn the vessel
in ice in order to follow changes
in ice drift. This was achieved by
implementing a strong slope at
the side of the vessel (see cross
sections). This hull shape allows the vessel to break ice over
the entire ship length. In order
to break the ice the azimuth
propulsors deliver the required
thrust for turning the drill ship.
The vessel is able to operate in
ice without icebreaker assistance
up to very severe ice conditions,
far above of the capabilities of
all existing ice going drill vessels.
With icebreaker assistance the
operational limits of the drilling
vessel can be further extended.
Consequently, the HSVA
design is the first design world
wide, which will allow drilling
in ice with a dynamic positioning, i.e. no fixed mooring system
will be required.
The HSVA design study for “Aurora Borealis” has been presented
in several publications and presentations since 2001. The figures
1 and 2 are from: European Polar
Board (EPB), Aurora Borealis “A
long term European Science Perspective for Deep Arctic Ocean
Research 2006-2016”, June 2004.
Logistics in ice management
In addition to the technological
improvements, the logistics in
ice management are also of great
importance.
The use of modern satellite ice
and weather data are a first step
for obtaining information about
the ice conditions ,ice drift speed
and drifting direction over a large
area. Closer to the drill ship, ice
drift speed and direction can
be detected by sensors installed
on board of the drill vessel. The
ice thickness can be measured
with electro magnetic ice thickness measurement devices and
together with visual ice observations, severe ice conditions can
be detected and traced, and the
potential danger to the drill ship
can be calculated and predicted.
An example for excellent ice
management was the core drilling research work of “Vidar Viking” in 2004 close to the North
Pole. “Vidar Viking” was built
as an ice breaking supply vessel
and was equipped with a drilling
rig. The vessel alone was not able
to keep position during drilling in the Arctic ice, although
it is equipped with a dynamic
positioning system (DP) for ice
free waters. Manual DP in ice
was only possible in well managed ice. The Russian nuclear
icebreaker “Sowjetski Sojus“ and
the Swedish Icebreaker “Oden“
broke the drifting ice into small
pieces (well managed ice).
Fig. 3: The vessel is rotated around the centre of the turret
using the thrust of the azimuth propulsors
Tests with a moored drilling
vessel in drifting ice
HSVA has tested several drilling,
production and storage vessels in
managed and in well managed
ice. In these tests the ice drift is
supposed to hit the vessel under
different angles. Such “oblique
towing tests” generate large deviations to the vessel’s position
and the corresponding loads in
the mooring systems. During
the last few years HSVA has designed and/or optimized several
of these vessels and consequently
HSVA has gained a tremendous
amount of expertise for such
highly complex systems in ice.
As an example: From 2006 until
2008, HSVA carried out several
ice model testing campaigns for
a moored drilling vessel for the
Norwegian engineering company LMG Marin in Bergen and
Statoil (now StatoilHydro). The
tests demonstrated the excellent
ice breaking capabilities of the
unit in level ice of up to 1.60m
thickness, in ice ridges and in ice
rubble fields. The main target of
the investigations was to develop
a concept for enabling the vessel
to follow the ice drift change in
order to keep the vessel within
the range of the lowest ice resistance and therefore within the
defined operational working
area. The pictures 3–6 give an
overview of several ice scenarios
which have been tested.
Fig. 4: The propeller wash is a useful tool for breaking ice or to
wash ice away from the vessel
Fig. 5: Track behind the drill ship after an ice drift course
change of 20°
Dr. Karl-Heinz Rupp,
Dr. Walter L. Kuehnlein
Hamburg Ship Model Basin
(HSVA), Hamburg
[email protected]
[email protected]
www.HSVA.de
Fig. 6: Tests in broken irregular thick ice
Schiff & Hafen | June 2008 | No. 6
9 Special
SPECIAL | OFFSHORE TECHNOLOGY
The Schottel Combi Drive:
suited to offshore application
PROPULSION Schottel which develops, designs, manufactures and sells propulsion and
manoeuvring systems with power ratings of up to 30 MW for vessels of all
types and sizes set new standards for the manoeuvrability in the
early 1950s with their Schottel Rudderpropeller (SRP).
The SCHOTTEL Combi Drive (SCD) combines the main technical and economic criteria of both mechanical Rudderpropellers and pod drives.
S
chottel builds combi drives both in
a twin-propeller version and as a
ducted single-propeller system, at
present covering a power range from 2,100
to 3,300 kW. In contrast to pod drives with
an electric motor inside the underwater
pod, the motor in the Combi Drive is integrated vertically into the support tube of
the Rudderpropeller. Neither an above-water gearbox nor a cardan shaft is required,
making the system extremely compact and
easy for the shipyard to install in the vessel
with very low space requirements.
Since the market launch, 16 of these innovative propulsion systems have already
successfully entered everyday service. Three
double-ended ferries built for Fjord1
Fylkesbaatane in Norway by the shipyard
Aker Brattvaag AS are each equipped with
four gas-electric powered Schottel Combi
Drives of type SCD 2020 in twin-propeller
configuration (4 x 2,750 kW). The ferries
operate between Bergen and Stavanger.
An ecological and safety-oriented concept
The SCD has a promising future in the offshore sector. The Norwegian Ulstein Verft,
for example, has chosen it as the propulsion system for two platform supply vessels of type PX105. These 4700 dwt ships
with the distinctive Ulstein X-Bow™ were
built for the shipping company Bourbon
Offshore Norway IS KS, a subsidiary of the
French Group Bourbon, based in Marseille.
With their new bow, they are “highly-developed, large and reliable multifunctional
platform supply vessels, which distinguish
themselves particularly in terms of fuel
consumption, good sea-going characteristics, positioning, speed, stability and loading capacity”, as the shipyard emphasizes.
Both vessels are equipped with two
SCD 2020 twin-propeller systems (max.
2,700 kW). The decision to combine a
diesel-electric propulsion concept with
an azimuth drive system means a significant improvement to the performance of
Special 10
Schiff & Hafen | June 2008 | No. 6
the vessels. The concept allows flexible
power distribution and offers a higher
degree of redundant safety. The lower fuel
consumption also makes the PSVs more
environmentally friendly.
The shipping company had stipulated that
the vessels were to be equipped in accordance with the requirements of the DNV
Clean Design Class. This means that
the equipment had to meet strict
criteria with regard to its environmental impact. BP Norway, the
operator, also stressed that the
ecological and safety-related
concept of the new vessels had
played a decisive role in the
awarding of the contract.
The economic expectations
of Bourbon Offshore Norway
with regard to these two innovative vessels were quickly confirmed
with the result that the company has
meanwhile placed a further order with
Ulstein Design for the design and technical equipment of four more vessels of the
same type, also with Schottel SCD 2020
Combi Drives. The construction contract
was awarded to Zhejiang Shipbuilding Co.
Ltd. in Zhejiang, China. The shipyard will
be delivering the vessels in late 2009 or
early 2010.
Both Neptune Offshore in Norway and EDT
on Cyprus have ordered two further vessels
of the same design in the meantime.
US owners such as Otto Candies LLC in
New Orleans, a major offshore shipping
company in the Gulf of Mexico, are also
focussing on this innovative propulsion
concept. For two of its new offshore supply
vessels, built by Dakota Creek Industries
(DCI), the company has chosen the Combi
Drive. The ships are each to be equipped
with two SCD 2020 systems (2 x 2,250 kW
and 2 x 2,500 kW).
Following the successful market launch of
the twin-propeller version, intensive market research culminated in the decision to
introduce a ducted variant of the SCD.
Ducted variant of the SCD
While the twin-propeller SCD is mostly
used in vessels with an operating profile
in the transit range at medium to high
speeds, the ducted propeller operates at
its best in the lower speed range and at
static thrust. Especially for vessels with
an operating profile characterized by dynamic positioning (DP) and partial-load
operation, the ducted variant represents
a particularly efficient solution.
Anchor Handling Tug Supply vessels
(AHTS), seismic research vessels, cable
ships and other work vessels are ideally
suited to this propulsion solution. This
presupposes, of course, that the vessels
are equipped with a diesel-electric propulsion system. This is usually the case
with cable ships or seismic research vessels; AHTS vessels, however, are still an
exception – and not always with good
reason, as investigations have shown.
Side view of a new Offshore Supply Vessel for Otto Candies LLC in New Orleans
A diesel-electric propulsion system is
endowed with a power management system that ensures that only the currently
required power is generated and distributed to the various units in the vessel.
The connected generators always run at
the optimum operating point. In combination with a ducted fixed-pitch propeller, as in the Schottel Combi Drive,
such a system offers very high efficiency,
especially in the low-load range.
In a diesel-electric fixed-pitch system, the
required thrust is regulated via the electric motor speed (frequency control).
The connected generators run at the optimized operating point – as does the
fixed-pitch propeller if designed accordingly. Furthermore, for low to medium
vessel speeds, a well-designed fixed-pitch
propeller with frequency control is more
efficient at the rated speed than a controllable-pitch propeller.
The trend towards diesel-electric powered
vessels has sharply increased over the last
few years. This is due to the fact that particularly work vessels in offshore operations
are becoming ever more complex. Moreover, the leading seafaring nations in this
segment, such as Norway or the USA, are
enforcing more restrictive environmental
and climate protection measures.
Above all in harbours, the amount of pollutants emitted by conventional diesel engines is considerable, due to operation in
the unfavourable partial-load range. Under
the working title of “Green Tug”, dieselelectric concepts for harbour tugs have for
the first time now been developed in the
USA for the harbours in Los Angeles and
Design: MMC Ship Design & Marine Consulting, Ltd, Poland
Houston. For example, in Los Angeles it
is planned to allow tugs to operate only
under battery power in the city area of the
harbour. In the outer area of the harbour,
the batteries can then be recharged via the
generators. If such plans are implemented
– and there are many arguments in their
favour – the Schottel Combi Drive undoubtedly represents the optimal propulsion
solution for harbour tugs meeting these
requirements.
Schottel GmbH
Spay/Rhein
www.schottel.de
The platform supply vessel “Bourbon Mistral“ has already fulfilled the shipping
company´s economic expectation in just a short space of time.
Photo: Tony Hall
Increased economic efficiency
The space saved by the diesel-electric concept, together with the flexible design of
the vessel’s interior (the SCD requires no
space-intensive shaft lines), result in a substantial increase in the usable volume. This
is of particular importance with such complex vessels as AHTS, and increases their
economic efficiency.
These arguments convinced the shipowner
Great Offshore Ltd., based in Mumbai, India, so that it ordered for the first time a
150 t anchor handling tug with diesel-electric propulsion and two ducted SCD 3030s
(2 x 3,300 kW) from Bharati Shipyard Ltd.
in Mumbai. The newbuilding is scheduled
to go into service at Great Offshore at the
end of 2008.
Schiff & Hafen | June 2008 | No. 6
11 Special
SPECIAL | OMAE 2008
Wave ernergy utilisation
Rexroth rises to the Power Take-Off
UTILIZING OCEAN ENERGY One of the main challenges at the concept of ocean power stations
which extract power from ocean energy lies in devising a suitable “power-take off“ system for
converting the kinetic energy of the water into electrical power
Nik Scharmann
E
xperts tell us that within a few decades, innovative systems for the
sustainable use of ocean energy may
generate as much electricity as 150–200
nuclear power stations.
On the one hand the important advantages
of utilizing ocean energy here is that around
two third of the world‘s inhabitants live in
coastal regions. The close proximity of ocean
power stations to consumers simplifies the
infrastructure and minimizes power losses.
On the other hand ocean energy is always
available: tides, currents, and – to a certain
extent – sea swells are ever present, thus enabling more long-term planning. As a result,
ocean power stations are a much better option for providing the base load of the electricity networks.
A number of companies are currently working on different concepts for large-scale facilities that will extract power from this renewable energy source. The main challenge lies
in devising a suitable “power-take off“ system for converting the kinetic energy of the
water to electrical power while ensuring that
generation costs remain competitive. The
development of the plants and the necessary
PTOs is only in its infancy, but Rexroth is
already supporting numerous projects with
tailored solutions, just as it did for wind
energy a few decades ago. These solutions
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Schiff & Hafen | June 2008 | No. 6
are based on Rexroth hydraulic components
and cross-technology systems, which have
already proven extremely robust and reliable
in a range of maritime applications.
The ocean energy industry currently consists of two main sectors: tidal energy and
wave energy.
Tidal energy
Tidal power stations use the energy of currents to power rotors – be they tidal or natural sea currents. Water has a density one
thousand times greater than air and can thus
generate significant power even from low
flow velocities. This requires specifically tailored solutions.
The diameter of underwater rotors does not
have to be large for them to be able to con-
Mechanic Power-Take-Off
duct energy effectively. Even at low speeds,
the forces acting on the entire system are
significant. Rexroth is currently pursuing a
development concept that adopts the generator gearbox technology employed in the
wind energy sector, an area in which the
company has established itself as a worldleading supplier for renewable energies.
Research is also being conducted into the
use of hydraulic converters. This simple yet
highly robust concept transforms rotary
motion into hydraulic flow, which powers
an adjustable hydraulic motor for the generator with great efficiency. A slow-running
radial piston motor with constant displacement is employed on the pump side. It
generates a volumetric current based on the
rotor speed. A fast-running axial piston dis-
placement motor is connected on the motor side, which can be fitted directly to the
generator shaft. The motor-generating set is
then operated directly at mains frequency.
There is no need for elaborate control electronics or frequency converters. It is also
possible to implement a continuous transmission ratio. The system can thus be used
to quench short-term peak demand while
also enabling long-term adaptation to the
changing current flow rates throughout the
tide cycle. A pitch system is not required.
Since the displacement motors employed
can be operated in dual-quadrant mode, it
is even possible to reverse the direction of
the rotor when the tide changes. It is not
necessary to rotate the system. Another advantage of this system is the positioning of
the gearbox components: while the highly
robust radial piston pump is installed under water, the motor-generating set remains
above water.
However, the high level of flexibility of a
hydrostatic power train over a mechanical
gearbox results in lower efficiency overall. It
is not yet clear which power train technology
will eventually prevail, but it will certainly
depend on the activities of the plant suppliers. Increased efficiency, particularly in the
case of the fast-running displacement motors, could result in the hydraulic concept
gaining the upper hand.
Wave energy
Fluid technology is particularly well suited
to meeting the requirements of wave energy utilization. In a system with a nominal
power of 150 kW, travel speeds will gener-
Hydrostatic Power-Take-Off
ally range between 1 and 2 m/s at forces of
500 kN to 1 MN. It should be noted that
the maximum forces and speeds do not
correlate: high travel speeds are usually the
result of small waves over short periods,
while high forces are produced by high
waves over longer periods.
The challenge for the PTO is posed by the
specific attribute of waves: within a wave period, the input power of the machine fluctuates twice between zero and the maximum
value. A typical wave period lasts 10 s, i.e.
0.1 Hz; the main frequency is between 50
and 60 Hz. This effectively requires a transmission ratio of i = 500-600. Furthermore,
the power of a wave increases approximately with the square of the significant wave
height. As a result, a power ratio of 1/100 can
soon develop between the lower and upper
operating window of the WEC (wave energy
converter).
to catch the eye: the more efficiently a PTO
converts the energy, the more electricity
is produced. However, the target variable
that will ultimately overshadow all activities is the cost of electricity generation in
c/kWh. As well as the afore mentioned
system efficiencies, this index also incorporates the facility costs, including operating and maintenance costs, as well as the
service life of the installed systems. Only
a comprehensive optimization of all variables will lead to the minimization of electricity production costs.
The development of a WEC and PTO that
generates competitively priced electricity
under the described conditions is a challenge which the entire industry is currently
tackling with great vigor.
Efficiency is not everything
Nik Scharmann
Bosch Rexroth AG, Lohr a. Main
From a technical point of view, the efficiency of the PTO is the first target variable
[email protected]
www.boschrexroth.com
Condition monitoring of oil systems
HYDAC | One customer of Hydac AS com-
petent clientele is Maskindynamikk AS in
Spjelkavik, which develops complete solutions for periodic and continuous monitoring of rotating machinery with varying
loads. Maskindynamikk has extensive experience with vibration analysis and have now
implemented Hydac’s particle counter if oil
cleanliness should be monitored as well.
The hydraulic market shows great interest
in monitoring oil cleanliness through online particle counting, relative humidity
and pressure measurements. This makes
it possible to use condition based maintenance instead of periodic solutions. The
advantages are many, but of course to have
maximum up-time on the machinery to a
minimized price is the most important one.
The fear of choosing an alarm point which
could be wrong has been one of the most
difficult obstacles in the way of condition
based maintenance. If it is able to define
what is „normal“ it is also possible to define
Example: Thruster systems for ships are a very good example of a system which is
interesting to monitor. Both the manufacturers and the ship owners are very interested in online monitoring of the condition of the thruster system. If the monitoring
system is approved by a classification society, it is possible to reduce the amount of
visual inspections of these systems.
what is irregular. With continuous signals
Maskindynamikk’s system is able to „learn“
and define what is normal and one is able
to use all logic ( „OR“, „AND“, „THEN“ etc.)
commands to interconnect different signals which give the basis for the alarm. This
means an alarm triggers only if it’s real and
important to act upon.
HYDAC International GmbH,
Sulzbach/Saar
[email protected]
www.hydac.com
Schiff & Hafen | June 2008 | No. 6
13 Special
SPECIAL | OFFSHORE TECHNOLOGY
Arctic knowledge at DNV
informs risk management
ARCTIC SHIPPING DNV has class notations covering the entire spectrum of cold climate operations ranging from control of icing in open waters to ice-breaking abilities in temperatures
as low as -55˚C and in recognition of the rapidly changing physical and business environment in
the Arctic. This offers now greater flexibility in winterisation notations.
Wendy Laursen
A
s recently as two years ago, it was estimated that the north-eastern Arctic
shipping route would be open for
most of the year in ten to 15 years time, but
the latest Norwegian research predicts that
this may happen earlier than that. Icebergs
forming in the region, some weighing over
six million tonnes, are the largest moving
objects on earth.
Johan Tutturen, DNV business director for
tankers, presented research results at the
Mare Forum, Athens, in March 2008 that
quantified the value of the most important
risk control options for Arctic shipping.
Based on a shuttle tanker project intended
for operation in Arctic waters, the research
used known risk elements from worldwide
operation but added additional risk elements for both cold climate and ice.
The project revealed that redundant propulsion offers a 6 % reduction in the likelihood of accidents involving collision,
grounding, fire and explosion. Use of an
automatic identification system and electronic chart display as well as information
systems offer a further 6 % reduction. Setting high standards in bridge resource management and the selection and training of
crew can reduce risk by 44 % and minimising noise and vibration levels when travelling through ice can reduce risk by a further
12 %.
Previous studies have shown that ships
built with additional DNV class notations
for nautical and bridge safety experience
risk reductions of nearly 50 %. Most accidents at sea are caused by human error
and harsh climatic conditions can result
in poor quality rest, reduced alertness and
concentration and poor speech intelligibility. The main objective of DNV’s NAUT notation is to reduce the risk of human failure
in bridge operations by specifying requirements for workplace design, equipment
standards and operational procedures.
“There are many types of mitigating measures that can be introduced to reduce cold
stress and they should be considered as
safety investments,” says Tutturen. “It all
boils down to risk management: identify-
ing the hazards, measuring specific risk elements and the way they interact and then
evaluating and implementing control options.”
Oil and gas recovery in the Arctic is increasing and DNV undertakes feasibility studies and concept evaluations for these cold
climate activities. They use integrated risk
management tools that assess the total investment risk over the full project life cycle.
Factors such as component reliability and
production profiles are used to develop
forecasting models and the use of probability distributions in simulation model
input parameters allows uncertainty and
variation to be used in the development
of a quantified risk picture for any revenue
stream.
“It is vitally important that ship owners contemplating Arctic operations are
aware of the possible challenges connected with their intended trading patterns. Our research capability, extensive
experience and state-of-the-art simulation techniques bring value to these of-
“Arctic Discoverer“ will be trading out of Hammerfest close to the Barents Sea. The vessel is managed by K Line and classed to DNV.
Special 14
Schiff & Hafen | Juni 2008 | Nr. 6
Photo: DNV
ten multi-billion dollar decision making
processes,” said Tutturen.
Once a project is live, DNV can assist with
quality control, maintenance and repair
evaluations. Vessel category and availability can be an important consideration and
limited accessibility for remedial action if
incidents occur means extra planning effort is essential for safe Arctic operations.
The protection of Arctic and sub-Arctic environments has been of increasing importance in recent years. Petroleum and shipping companies are facing rising demand
for environmental safety. DNV participates
in baseline studies and environmental
monitoring. Their environmental risk
analysis approach gives decision makers a
transparent and efficient tool for identifying and quantifying risk due to accidental
oil spills. It includes probabilistic oil drift
modelling and toxicity and impact assessments on sensitive environmental resources. Their contingency planning toolkit
includes an electronic map interface for oil
spill response operations that is distributed
in real time to all involved parties.
More tanker operators are looking to venture
into the Arctic as a means of shortening voyage times from Europe to Japan and the US.
“Allowing for changing climatic conditions
is an important consideration on a day-today basis for ship operators but I believe that
operating flexibility will grow in importance
in the future,” said Tutturen. “This is already
the case with the newbuildings we are involved in. Hull fatigue damage accumulation is about twice as rapid in North Atlantic
conditions compared to the comparatively
more benign environment of traditional
LNG routes, for example, and there is an increasing trend amongst owners to specify 40
years of fatigue life in the North Atlantic to
ensure trouble free operation in these more
demanding cold climates.”
Traditional open water accidents such as
groundings and collisions are more likely
to occur in cold climates. Fires are responsible for 10 % of all fatalities at sea and fire
fighting in severe weather is more complicated and therefore more likely to cause
critical damage. In addition to this, new
sources of accident are introduced in cold
climates. Ice may damage a vessel or force
it aground. Icebergs and ice floes can cause
serious damage to a vessel in the zone between open sea and solid ice and sea spray
can lead to severe icing and damage from
the clogging of vents and the freezing of
pipes.
Extra notations
DNV has been delivering standards for
ice class shipping since 1881. Currently,
over 1900 vessels carry DNV ice class
notations, including the four highest
specification LNG carriers in operation.
They incorporate Finnish and Swedish
Maritime Authorities’ rules in their Baltic
specifications and although unified International Association of Classification
Society rules are under development,
DNV’s extra notations offer a greater
depth of operational security based on
extensive experience and intimate local
knowledge. Safe ship operations require
more than just ice strengthening of the
ship’s structure and propeller, says Tutturen, and DNV has developed technical
standards for all ship’s equipment and
structures where reliability is important.
DNV’s latest Winterised notations have
been expanded effective 1 January 2008.
The notations recognise that some vessels spend shorter times in cold climates
than others and the expanded rules define
three different levels of cold climate safety
design. Each has separate designations for
temperature in material selection and extreme temperature performance. Nevertheless, emergency features relating to escape
exits, lifeboats, towing and evacuation play
an important part in all notations.
The highest level, Winterised Arctic, is
for ships such as ice breakers that are
operating in the harshest cold climate
conditions and the notation calls for redundant propulsion. “A loss of power in
extremely low temperatures can quickly
lead to a critical situation and freezing of
water and vital parts in the engine room
may reduce the possibility of a re-start.
Ideally, a blackout period longer than
ten minutes should be avoided,” says
Johan Tutturen. “Emergency generators
should be located in a tempered location to avoid starting problems at low
temperatures and additional heating arrangements ensure that temperatures in
the engine room are maintained above
freezing point during a blackout.”
Winterised Basic and Winterised Cold cater
for vessels operating in cold climates on a
seasonal basis. Winterised Basic includes
anti-icing precautions for communication
and navigation equipment, sea chests,
fire fighting capacity and some vents and
valves. Winterised Cold specifies additional requirements including temperature
protection for equipment and spaces, stability under ice loads and the use of low
temperature steel for some of the structures
above the waterline.
Vessels travelling in the Arctic tend to try
and follow the same ice channel as each
other to navigate a path of least resistance
and often the most favourable ice conditions will be close to shore. In practice,
though, ships may sometimes operate under heavier ice conditions that those stipulated for their ice class. As well the safety
risks associated, this can bring vessels into
contact with the Russian authorities.
“Arctic Discoverer“ will be crossing the
Northern Atlantic where the weather
condition will create challenges Photo: DNV
DNV’s established relations with Russian
institutions, means that they can offer valuable assistance in meeting local regulations.
In Russian waters, it may be necessary for a
vessel to have an ice passport. This is not
a building standard but a description of
safe operating modes for a particular vessel
based on how the ship is actually built. It
is based on the ship’s structure, hull lines,
dimensions, displacement, propulsion
power, propeller thrust, age and the state
of the shell plating.
DNV contributes actively to the development of technical and operational codes
and directives for offshore petroleum activity in the Arctic and they proactively maintain their position at the forefront of research and risk management solutions for
cold climate business. Over the next three
to six years their strategic research initiatives are focusing on extreme ice shipping
and human responses to the associated
cold, noise and isolation. They will also research best practice emergency evacuation
from ships and platforms in the Arctic and
work on achieving a greater understanding
of the ever-changing Arctic environment
from a risk acceptance perspective.
Wendy Laursen
Det Norske Veritas
[email protected]
www.dnv.com
Schiff & Hafen | June 2008 | No. 6
15 Special
SPECIAL | OFFSHORE TECHNOLOGY
Ice protection structures
ICE BARRIERS For over 25 years IMPaC Offshore Engineering has gained substantial
knowledge and experience in numerous ice engineering projects. One area of special expertise
is the design of ice protection structures.
Joachim Berger
T
he increasing demand for
hydrocarbons
requires
offshore exploration and
production drilling activities
in ice infested areas. In shallow
water areas like the North Caspian Sea, purpose-designed ice
protection structures also called
ice barriers can lead to solutions
that provide technical and economical advantages compared
to field developments without
ice protection measures.
For the protection of offshore
production facilities in shallow water areas permanent ice
barriers made from rock or
concrete structures are often
the appropriate solution. For
drilling exploration facilities,
which usually have to change
their location after they have
sunk the well, ice barriers made
from steel are mostly the better
solution as they are easier to install and de-install.
Ice barriers can also be used to
protect offshore wind parks or
harbour installations.
Advantages
Ice barriers allow designing
of an exploration platform or
other offshore facility for re-
duced ice loads. The ice load reduction is a function of the type
and number of ice barriers.
Less expenditure for the protected platform requires additional costs for the design
construction, installation and
operation of the ice barriers.
However ice barrier structures
also considerably improve the
conditions under which supply of the offshore unit is possible. In some cases platforms
can only be operated during
the winter season with ice barriers in place. Also during the
non-ice season ice barriers can
improve the platform supply
conditions by reducing wave
heights in the vicinity of the
offshore installation. Thus, ice
barriers can considerably extend the availability of the platform with large positive effect
on the overall economics of the
offshore field operation.
Ice barriers can also be required
to facilitate evacuation of the
crew from the platform under
ice conditions. Production on
offshore platforms has to be
stopped under extreme environmental conditions where rubble
ice piles prevent the emergency
Fig. 1: Drilling unit with driven piles as ice protection structure
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Schiff & Hafen | June 2008 | No. 6
evacuation of personnel. Therefore, ice barriers whilst protecting the integrity of the offshore
platform structure also increase
the availability of the platform’s
production, thus improving the
economics of the project.
Requirements
An ice protection structure has
to be a simple, yet robust structure as it is exposed to harsh environmental conditions and has
to withstand large ice loads. The
main requirement on ice barriers
is a high technical reliability at a
minimum material expenditure.
For the protection of mobile
units like offshore exploration
drilling rigs the de-installation
and re-use of an ice barrier are
also of importance.
Full compliance with environmental protection requirements
is mandatory for all ice barriers.
Determination
loads
of
design
The technical reliability of
an ice protection structure is
strongly dependent on the correct ice load. In some cases especially in deeper water areas
the hydrodynamic forces due to
waves and current can become
the dominating load situation.
Deterministic methods are
mostly applied to predict the
ice loads as the data basis for a
probabilistic approach is often
insufficient.
When the ice protection structure is of simple geometry analytical methods can be applied
to establish the ice loads. When
the shape of the ice barrier is
too complicated for analytical
methods ice model tests have
to be carried out.
In practice, the prediction of
ice loads is not the major challenge but the determination
of realistic full-scale ice conditions from which the ice loads
will be derived. The uncertainty
in the ice load conditions and
the lack of full-scale data often
require a conservative design
approach and do not allow full
design optimisation of the ice
barrier structure.
Due to the lack of ice data
satellite imaging has been utilised to determine ice conditions. The satellite images allow a fairly good estimate of
the ice coverage and the thickness of sheet ice. But in many
Fig. 2: Ice protection piles, view from drilling unit
Fig. 3: Drilling unit with barge type ice barriers to protect against excessive ice loads
cases the dominating ice loads
for an ice protection structure
result from the interaction
with pressure ridges, which
cannot be identified from the
satellite pictures. In such cases
field observations and surveys
are of particular importance.
Driven piles as ice protection structure
Driven piles have been used as
ice protection means at the first
two exploration sites of a mobile drilling barge, which has
been operating since 1998 in
the shallow water areas of the
North Caspian Sea. The piles
also serve as berthing and mooring piles for the supply vessels.
The optimum pile arrangement has been determined in
ice model tests. The main parameters influencing the ice
load reduction for a given ice
thickness are pile diameter
and pile spacing. With the optimised pile arrangement the
ice loads could be reduced by
60 percent compared to the solution without any piles.
Simple pontoons as ice protection structures
As a larger number of wells
had to be drilled as originally
Fig. 4: Design options for optimised barge type ice barriers
structures
anticipated the piles have been
replaced at later sites by pontoons, which have the advantage of easy re-usage.
After de-ballasting and refloating the ice barrier barge
can be towed to the next exploration site of the drilling
unit. At the drilling site the
ice barrier barge needs to be
ballasted with sea water in
order to create sufficient sliding resistance. In some cases
concrete can be used as fixed
ballast. However, due to draft
limitations fixed ballast cannot always be used. Due to
the simple geometrical form
of the barge type ice barriers
the ice loads could be established by analytical methods.
However, for establishing the
minimum number of ice barrier barges and their optimal
arrangement relative to the
drilling unit ice model tests
have been carried out.
In future, ice model tests may
only be required for verifications purposes as latest developments of computer models
allow a relatively good analytical simulation of the interaction of drifting ice with ice
barriers of different arrangement.
Fig. 5: Ice barrier structure providing shelter for a supply
vessel
Schiff & Hafen | June 2008 | No. 6
17 Special
SPECIAL | OFFSHORE TECHNOLOGY
Fig. 6: Sketch of a light-weight ice barrier © IMPaC
Purpose-designed ice protection barges
Various types of barges have
been developed by IMPaC
aimed to optimise performance as an ice barrier.
The vertical wall design has
been compared to sloped
walls with different slope angles. For sheet ice the sloped
surface has advantages but often the interaction with pressure ridges is the dominating
load scenario for which the
slope angle of the wall is of
lesser importance.
Ice protection barges with
one vertical long wall have
advantages during site installation and de-installation or
when the barge needs to be
moored in a harbour or yard
for inspection purposes. During operation the vertical wall
normally facing towards to the
drilling unit has the advantage
of providing a berthing and
mooring place for marine
boats and barges.
Sloped walls also have the advantage of smaller local ice
loads compared to vertical
walls. The weight of the steel
shell of a barge type ice barrier
strongly depends on the size
and distribution of the local
ice loads. The smaller the ice
load exposed area considered
in the stress analysis the larger
the local design ice load to be
applied. The distribution of
the local ice loads including
so-called “ice background pressures” acting on the sloped or
vertical shell usually leads to a
vertical stiffening of the shell.
For economical reasons plastic deformations of the outer
steel plate and the stiffening
bulb profiles are normally accepted while stresses in frames
and bulkheads have to remain
within the elastic range.
In Figure 5, a barge type ice
barrier with one sloped and
one vertical wall is shown,
providing shelter for an ice
breaking supply vessel.
While the local ice loads have a
large impact on the design of the
steel shell the global ice loads
usually dictate the overall height
and bottom width of barge type
ice protection structure.
The ice barrier has to provide
sufficient sliding and overturning resistance. In very
shallow water areas sliding
failure is more of a risk than
overturning.
When the seabed is of the
non-cohesive type (sand)
the overall design of the ice
barrier is weight driven. The
larger the contact pressure
from the bottom plate to the
top layer of the seabed, the
larger the sliding resistance of
the ice protection barge. The
sliding resistance can be further improved by using skirts.
Spray ice could also be used
to increase the weight of the
barrier. The larger weight of
the barrier structure leads to
larger sliding resistance.
When the seabed is of the cohesive type (clay) the footprint
of the ice barrier becomes important while the weight has
less impact on the sliding resistance. At sites with cohesive
seabed material, underwater
berms or backberms can lead
to an improvement of the sliding resistance.
Light-weight ice protection
structure
Fig. 7: Light-weight ice barrier with accumulated rubble ice and
indicated ice drift direction
Special 18
Schiff & Hafen | June 2008 | No. 6
IMPaC has developed a light
weight ice barrier structure,
which is based on the idea
that the broken ice pieces will
be collected and the mass of
the accumulated rubble ice
contributes to the overall resistance of the barrier.
The principle of the lightweight ice barrier can be seen
in Figure 6. It shows the first
stage of the interaction with
drifting ice in early winter
when relative thin ice has
failed at the sloped wall and
the broken ice piece start to
accumulate.
Various ice model tests have
been carried out to verify the
function of the light-weight
ice barrier. The ice model
tests were also performed to
measure the ice forces acting on the structure during
the different phases of the
interaction with drifting ice
features. Also the mass of the
accumulated ice was determined which allowed checking the sliding stability of the
light-weight barrier structure.
Figure 7 shows the situation
after the light-weight ice barrier has been filled-up with
rubble ice.
The research project was supported by the German Federal
Ministry of Education and Research.
Outlook
Future exploration and production activities in the North
Caspian Sea and other ice infested shallow water areas will
require a considerable amount
of ice protection structures,
which need to be designed,
built and operated.
IMPaC Offshore Engineering
will continue to play a leading
role in the realisation of these
projects and also in the future
development of new ice protection technologies.
Joachim Berger
IMPaC Offshore Engineering
Hamburg
[email protected]
www.impac.de
Hydrocarbon sensor systems
PIPELINE MONITORING To improve detection efficiency and to eliminate the need to introduce
additional potential pollutants to underwater pipeline systems CONTROS has developed a new leak
detection method, a “Hydrocarbon Sniffer System”, called HydroC™.
Daniel Esser
T
he global demand for energy challenges the offshore
oil & gas industry to go for
deeper regions and the arctic
areas. However, environmental
awareness and concern puts the
focus on effective and reliable
monitoring systems to avoid leaks
and spills of harmful fluids.
Subsea production systems are
getting more and more common
for these applications. Globally
subsea pipelines and production
systems are becoming a major
concern as authorities are less tolerant to leaks of polluting material into the marine environment.
In this respect, the ability to detect
and also to locate any leakage of
oil or gas to the surrounding water and environment is of utmost
importance to safeguard a green
and healthy planet.
At a depth of 3,000 meters operation of a subsea production
installation is a great challenge
and a high risk. Not only are the
costs for deep sea installation
high, but the risk for the environment is evident – is it possible to
detect or repair a leak?
Subsea field development and
long pipeline transport may be
the only alternative to develop a
deep sea installation; if sufficient
water depths, infrastructure on
the seafloor can be advantageous.
However, in Arctic areas where
the surface ice and iceberg conditions can be problematic. Subsea
processing is regarded as an efficient way to safe energy; reduce
the use of chemicals and to reduce
discharge of produced water.
In the past three main methods
of subsea leak detection have
been used for leaks where obvious visual signs of large leaks
such as bubbles, large clouds,
etc. are either not present or have
failed to locate these problems.
These three main methods used
are fluorometric measurement,
pig-systems (not useable for all
types of pipelines of today) and
passive acoustics, which listen
for ultrasound created by fluid
leaking under pressure.
The systems mostly used these
days for permanent monitoring
or pipeline inspection by ROV
(Remotely Operated Vehicle) or
AUV (Autonomous Underwater
Vehicle) seem all to have disadvantages in detecting very small
and non visible oil or gas leaks.
In an effort to find new leak detection methods that improve
detection efficiency and also
eliminate the need to introduce
additional potential pollutants to
pipeline systems, CONTROS has
been working on a “Hydrocarbon
Sniffer System” called HydroC™
for the last five years. This unique
system which is now available
has a worldwide patented optical
analysing system. Hydrocarbon
molecules diffuse through a special membrane (which keeps the
water out) and enters into the detector chamber. The adsorption
of light in gas leads to change
of intensity which is measured
electronically. The HydroC™ can
detect the higher order chain
of hydrocarbons or just CH4 if
Methane is of primary interest;
which is a huge advantage as CH4
is the smallest molecule in nearly
every crude oil and natural gas.
A system can consist of one HydroC™ or an array of sniffers, current meters and other instrumentation required covering a large
subsea installation or an area of
manifolds. This HydroC™ system is unaffected by turbidity or
other interferences such as H2S
or any other gaseous substances
in the environment. This system
was developed specifically to allow fast, real-time and in-situ detection of dissolved and gaseous
hydrocarbons/methane in water,
whatever the source. It has been
successful used in hydrocarbon
surveys and pipeline inspections
to water depth up to 3,000 metres worldwide.
The very high sensitivity (down
to 30 nmol/l) of the HydroC™
Monitoring of critical paths and pipelines
system also makes it ideal for
the detection of methane seepage from the seabed. Here it is
also widely used for the exploration and the production process
of methane hydrates in different projects around the world.
CONTROS is also partner of the
German Gashydrate Organisation (www.german-gashydrate.
org) where another CONTROS
HydroC™ instrument for CO2
detection is used for the CO2
sequestration process, which
has become an important topic
for the international oil companies. The calibrated HydroC™
(Hydrocarbon or CO2) plug &
play system records data either
internally or externally in units
of hydrocarbon or methane concentration. By careful logging
around an area of leakage from
a pipeline, the seabed or a manifold, an estimate of the amount
of leaking gas or oil can be made
directly. HydroC™ is in use by
several pipeline inspection companies and CONTROS has close
cooperation with the leading
ROV manufacturers to equip
their inspection ROV’s with the
latest leak detection technology.
In summary CONTROS provides
offshore pipeline inspection
and long term monitoring solutions. HydroC™ leak detection
product line, field experience
and advanced data management
systems meet demanding regulatory requirements and enhancing
safety during production from
subsea production systems.
Daniel Esser
CONTROS Systems &
Solutions GmbH, Kiel
[email protected]
www.contros.eu
Schiff & Hafen | June 2008 | No. 6
19 Special
Oil and Gas: a new perspective
Your business is oil and gas – and our business is your safety. From industrial plant to pipelines, from planning to maintenance,
whether its advice, testing or certification you require: Germanischer Lloyd Oil and Gas (GLO) is your reliable serviceprovider
when it comes to verification, certification and quality assurance for your systems – anywhere in the world. Our range of services revolves around the safety and health of people, the protection of the environment, and the securing of investments.
Welcome to GLO, your partner for the utmost safety, on- and offshore.
Germanischer Lloyd Industrial Services GmbH
Oil and Gas
Steinhöft 9 · 20459 Hamburg, Germany
Phone +49 40 36149-750 · Fax +49 40 36149-1707
[email protected] · www.gl-group.com/glo