offshore deck mating onto a pre-installed semi-submersible
TRANSCRIPT
Offshore Deck Mating onto a Pre-Installed Semi-submersible by Means of a Self-propelled Heavy Transport Vessel
James Lee, Steven Byle, and Alex Ran, Offshore Kinematics Inc., Houston, Texas
Michel Seij and Jan Wolter Oosterhuis, Dockwise Shipping B.V., Breda, Netherlands
Abstract
This paper presents a method for topsides floatover installation onto a pre-installed semi-
submersible hull under West African swell conditions using a Dockwise Heavy Transport Vessel
(HTV). Floatover has become an increasingly popular method of topsides installation. In random
seas, floatovers have generally converged upon minor variations of the High-Deck method, using
elastomer mating units to buffer impact loads and facilitate load transfer. Under swell condition,
having much larger heave and surge motions, floatovers have converged upon variations of the
Uni-Deck method. This system employs an additional hydraulic system to close the initial gap
and achieve initial contact and then again to complete final transfer and achieve separation. This
method, however, is not applicable for floatover to a semi-submersible, due to the small
waterplane area of the hull causing a sudden vessel draft change by a rapid vertical load transfer
action.
Former floatover methods are generally directed at compensation of relative movements between
the structures and absorbing the energy of their impacts. The present method, however, is
directed primarily at damping out the relative motions between the HTV and semi-submersible.
This is achieved by the simple application of friction into the fendering system. A relatively
small magnitude of friction force, strategically applied, greatly reduces relative motions between
the vessels. The floatover can therefore proceed using a conventional High-Deck type of
floatover method. The initial goal of this study was to demonstrate feasibility for swell condition
to a semis-submersible during the relatively mild installation season. However, the results of the
study indicate that the method could also be generally applicable to fixed structures.
Introduction
The need for the development of a floaotver installation method for floating structures has arisen
as a result of local content requirements in Nigeria and other parts of the West Africa. These
requirements may make it necessary to build TLP and Semi hulls locally for integration with
overseas fabricated topsides through a deck mating operation in West African swell
environments.
Floatover Deck Mating installations began in the 1980’s. Most early transfers of topsides to a
pre-installed jacket or a floating hull substructure were performed in sheltered waters. Over the
years the procedures have evolved to the point that floatover installations can now be
accomplished in open sea environments all over the world. While numerous floatover methods
have been proposed over the years, the industry has generally coverged upon variations on two
main methods: the High-Deck method for random wave applications and the Uni-Deck method
for swell conditions. So far, all open seas floatover installations have generally been limited to
fixed jacket installations and there has been no floating-to-floating deck mating installation in
West African swell environments. A list of floatover installations since 1990 in West Africa is
presented below in Table 1.
Table 1 - List of Deck Mating Installations in West Africa
Open Water Floatovers In West African Environments – Completed since 1990
Platform Name Company
Location
Installation Year
Method Deck No
Contractor Used Wt (st) Legs
1 Cobo Pambi Elf Angola Technip/ETPM 1996 UNI-DK 9,500 8
2 Epke Mobil Nigeria McDermott/ETPM 1997 Smart-Leg 4,100 6
3 Amenan Kpono TotalFinaElf Nigeria Saibos/Technip/Dockwise 2003 UNI-DK 11,200 8
4 East Area Gas GN ExxonMobil Nigeria Technip/Dockwise 2005 UNI-DK 18,000 8
5 East Area Gas GX ExxonMobil Nigeria Heerema/Dockwise 2007 UNI-DK 12,500 4
Non-swell environments, or random wave environments, typically refer to the offshore areas in
Southeast Asia and in the Gulf of Mexico. Swell environments are the typical offshore
environments in West Africa and in Australia. The main differences in a deck mating floatover
installation between a non-swell environment and a swell environment are the different
magnitudes of the relative motions prior to the deck load transfer operation. In a floating-to-
floating deck mating installation, the relative motions refer to the motions between the two
floating bodies. In a floating-to-fixed deck mating installation, the relative motions are the
motions between the vessel and the pre-installed jacket legs.
FIXED JACKET FLOATOVERS:
The following presents a comparison in a typical fixed jacket floatover with a deck weight of
15,000 MT under swell conditions versus random waves:
Swells and Relative Motion responses: Random Waves and Relative Motion Responses Wave height: 1.0 meter Wave height: 1.0 meter
Wave Peak period: 12.0 seconds Wave Peak period: 5.2 seconds
Wave heading to the bow: + 15 degrees Wave heading to the bow: + 45 degrees
Vessel surge motions: + 1000~1200 mm Vessel surge motions: + 100~200 mm
Vessel heave motions: + 1000~1200 mm Vessel heave motions: + 150~300 mm
The significant increases in vessel motion responses under swells are mostly due to long wave
lengths in association with long wave periods of swells. To conduct a floatover installation under
swells, one has to overcome the following three major challenges:
1 Surge Suppresssion: Utilize an anti-surge system and a centralizing system to reduce the
surge motions and to align the deck legs to the jacket legs so that the stabbing cones at the
deck leg bottoms could stab into the receptacles at the jacket leg tops within a design
tolerance.
2 Rapid Contact/Separation: The employed system has to provide a capacity to generate a
sufficient air gap instantly at the separation stage, typically 2 meters in 12 seconds, to avoid
excessive impact loading between the support tops on the vessel deck and the deck bottoms.
3 Vertical Travel: Allow sufficient vertical travel during the installation: a) during entry with
a slot with a sufficient air gap (> 1.5 meters); b) deflections of elastomer elements during
the load transfer operation; c) a sufficient air gap (> 1.5 meters) after the separation and
during the withdrawal operation.
In the Uni-Deck method, and other existing methods such as Smart-Leg method and ETPM
method, a number of large capacity and long stroke hydraulic cylinders are employed to perform
the vertical motion compensation and to minimize the vessel draft changes with a two-step
extension/retraction action. Prior to entry, the whole deck is lifted by these cylinders to provide
an air gap for clearances. During the load transfer operation, a large portion of the deck load
could be quickly transferred, within a swell cycle such as 12 seconds, from the floating vessel
deck to the jacket leg tops to eliminate the initial air gap at the beginning of the load transfer and
to instantly generate a large air gap at the final separation of the load transfer operation, at the
support tops on the vessel deck. In the surge direction in Uni-Deck method, stoppers and large
capacity winches could be used to reduce to relative surge motions within a design tolerance for
stabbing.
With the employment of a large number of high capacity active devices such as the hydraulic
cylinders in the Uni-deck method, the construction and maintenance costs are high.
FLOATING STRUCTURE FLOATOVERS:
Conducting a floatover operation to a pre-installed semi hull in swell conditions would face
different technical challenges comparing to the fixed jacket deck mating installation listed above.
Among these challenges, the relative motions in surge and heave directions and the small water
plane areas of the semi columns are the most critical ones. The major differences between the
two deck mating installations are:
1 Surge Motion Phasing: Phasing plays an important role in semi deck mating installation.
Relative motions in surge direction are heavily dependent on the relative longitudinal
positions between the vessel and the semi hull. At entry and withdrawal positions, the
relative surge motions become larger because of the different phasing between the vessel
and the semi. Therefore, the deck position on the vessel deck has to be designed with a
minimum phasing difference between the two floating bodies. Consequently, the relative
surge motions could be minimized during the load transfer operation. In general, the deck
should be placed at the middle of the vessel to minimize the phasing effects and to have
achieve an optimum use of the vessels ballast capabilities.
2 Heave Motion Phasing: In heave direction, the relative motions are also dependent on the
phasing of the two floating bodies in two ways: a) the semi and the vessel have different
pitch natural periods; therefore, the pitch phasing induced relative heave motions at
different column tops of the semi hull could induce additional relative heave motions; b) the
semi heave natural period is much longer than the vessel heave natural period; therefore,
the different phasing of the two floating bodies could also result in additional relative heave
motions. Further more, both floating bodies have large masses and added masses and the
phasing induced relative heave motions could be more difficult to be reduced comparing to
fixed jacket deck mating installation.
3 Waterplane Area: The small column surfaces of the semi hull provide a soft stiffness in
heave direction. The water plane area serves as a water spring to be in series with the
elastomer springs at column tops. Therefore, the requirement for elastomer elements should
be much more reduced comparing to fixed jacket mating installation. In addition, the
softness of semi hull in vertical direction prohibits a large amount of load transfer from the
deck supports to the column tops and would not allow generating an instant gap for the
separation used in Uni-Deck method or other existing methods under swell environments.
4 Vertical Travel: Both the vessel and the semi can adjust its drafts during the installation.
Therefore, there should be no vertical travel issues for the semi deck mating installation.
5 Lateral Stiffness and Mass: The pre-moored semi hull has less lateral stiffness by its
mooring system, but it has a large mass. The reduced stiffness reduces the lateral docking
force and the large mass could generate a large impact loading. The lateral docking force is
sensitive to the gaps between the semi hull and the vessel during the entry/withdrawal
operations. The less the gaps, the less the lateral docking forces.
Overall, the semi deck mating floatover installation faces few technical challenges except in the
heave direction due to the phasing induced heave motions between the two floating bodies. It is
clear, from the comparisons between the floating-to-floating deck mating installation and
floating-to-fixed deck mating installation listed above, that the Uni-Deck method and other
current existing methods for West Africa applications are unsuitable and unnecessary methods
for the intended semi deck mating floatover installation application. Therefore, an alternative
approach is needed.
An Alternative Approach with a Friction Fender System
Dockwise Shipping B.V. (Dockwise) and Offshore Kinematics, Inc. (OKI) have jointly
conducted an investigation to study the feasibility of performing a deck mating floatover
installation onto a pre-installed semi-submersible hull in West African swell environments. As a
key part of this joint study, a deck mating system has been developed for the intended deck
mating floatover installation. In this system, instead of focusing on motion compensations, the
motion reduction becomes the primary objective. The system, called Friction Fender (FF)
system, utilizes friction forces as the principal means to minimize or to eliminate, the relative
motions between the vessel hull and the semi hull prior to conducting the deck load transfer
operation. In fact, the transfer operation could be conducted in a static process to transfer the
deck load from the vessel deck to the semi column tops with little impact loading.
The FF system is a friction based motion reduction system which is based on three physical
principles: 1) the friction force is always acting at the opposite direction of a relative motion to
directly reduce the relative motion; 2) the friction based system is an energy dissipation device to
consume relative motion induced wave energy to indirectly reduce the magnitudes of relative
motions in all directions; 3) the pair of the action force and reaction force acting on each of the
two floating bodies produce a combined double effort to effectively reduce the relative motions,
both in surge and heave directions. As the relative motions are reduced to a minimum level, or
even the total elimination of the relative motions, the load transfer operation, both at initial
contacts and at final separation, could be conducted in a static process to reduce or to eliminate
the need for shock absorbing devices.
A typical semi hull with a design deck payload of 25,000 MT at design draft was selected as the
base semi hull model in this study, see Figures 1 and 2. Deck weight during transportation and
floatover installation is estimated to be 15,000 MT. Dockwise’s Black Marlin Heavy Transport
Vessel (HTV - 217.8m x 42.0m x 13.3m) was selected as the transport and floatover vessel for this
study, see Figure 3. Equipped with the FF system, motions of both floating bodies were
simulated in frequency domain and time domain calculations to determine the relative motions
with and without the engagement of these FFs.
Currently, a calculation tool to determine the motion reduction vs. friction forces in time domain
simulations for a floating-to-floating deck mating model is not available on the market due to its
complicated stick-slip effects at both floating bodies during the relative sliding at these friction
surfaces. Therefore, the calculations of friction induced motion reductions for semi deck mating
installation in this study are all based on frequency domain calculations. The frequency domain
calculations could only provide the required friction forces to totally stop the relative motions, or
called “lock-in” friction force, in surge and heave directions. Unfortunately, this could not
provide the actual motion reduction magnitudes vs. the applied friction forces.
An extension of this FF concept to fixed jacket deck mating floatover installation was also
briefly investigated in this study. A different approach of FF system application for a fixed jacket
mating installation is proposed based on the study results. In the deck mating installation, the
required anti-surge force to stop a vessel such as the Black Marlin HTV is relative small and well
within design capacities listed for the semi floatover installation. The required “lock-in” force in
heave direction for a Black Marlin size vessel could be very large and difficult to reach a total
“lock-in” condition. A limited and acceptable heave motion, with a complete “lock-in” condition
in surge direction, should be expected and the floatover operation should have the combination
of the proposed FF system and conventional shock absorbing devices.
Further studies illustrated that the FF system could be adjusted to suit applications under larger
swells. In Uni-Deck method, larger relative motions induced by larger swells have to be
compensated by longer stroke cylinders and larger capacity anti-surge devices with significant
potential cost increases. In FF system, a proportional increase in the friction forces by the FF
system could effectively reduce, or eliminate, the relative motions with a limited cost addition.
Currently, the installation window in West Africa is limited to a 5-month duration called the
“Installation Season”, from November 1 to March 31 of a year. During this period, the
“workability curve” is usually defined by the following formula: Hs x Tp^2 <= 150, Where, the
Hs is the Significant Wave Height in meter and the Tp is the Peak Wave Period in seconds
ranging from 10 seconds to 18 seconds. In the rest of the year, a typical “workability curve”
could be defined to be Hs x Tp^2 <= 240 with the Peak Wave Period in seconds ranging from 11
seconds to 20 seconds.
In this study, both environments, “installation season” criteria and “all-year-round” criteria, were
considered. Calculations were performed to illustrate that the FF system could be used to
conduct a semi deck mating installation and a fixed jacket deck mating installation in any time of
a year under West African environments.
Base Study Models, Environments and Assumptions
Pre-Installed Semi Hull. In this study, a typical semi with 4 columns and 4 pontoons was
selected and the semi hull is pre-installed with 8 mooring lines, 2 at each column, at 1,200 meter
water depth. The basic assumptions for the semi hull are:
The semi hull is suitable to support a maximum deck payload of 25,000 MT.
At the installation, the deck weight is at 15,000 MT.
The pre-installed semi is able to use its chain jacks for a limited lateral movement in
adjusting its heading towards swells.
The semi hull should be able to use its internal pumping system for the adjustment of its
drafts during the deck mating floatover operation.
A small crane barge could be standby to provide power to the chain jacks and to the
internal pumping system during the deck mating floatover operation.
The crane barge could also have an installed living quarter to provide man power for post
mating activities.
The basic configuration of the semi hull is illustrated in Figure 3. A MOSES 3-D panel model
was created for frequency domain and time domain calculations in this study. The basic data and
assumptions for the semi are listed below:
Pontoon size: 16m x 10m Column size: 16m x 16m x 40m
Total size: 78m x 78m x 40m Slot size for entry: 78m x 46m
Operational draft: 32m Displacement: 63,500 MT
Estimate steel WT: 13,730 MT VCG w/o deck: 16 m above semi keel
VCG w/ deck: 24.8 m above semi keel Water depth: 1,200 m
Operational draft: 32m Internal pumping capacity: 8,000 MT/hr
Mooring system stiffness: 8 MT/m (both in surge & sway) Number of mooring lines: 8 (2 per column)
Heavy Transport Vessel (HTV). Black Marlin (217.8m x 42m x 13.3m) from Dockwise fleet
was selected as the HTV for this study. The lightship weight of the vessel is 19,350 MT. At the
vessel entry operation, the draft is at 8 meters. A MOSES 3-D panel model was created for
frequency domain and time domain calculations in this study. A rigid vessel assumption is
assumed in all calculations. An isotropic view of this vessel model is illustrated in Figure 3.
Deck Properties. The deck weight at the deck mating floatover operation is assumed to be
15,000 MT with 8 support legs (1.83 m O.D. or 72” O.D.) in in-place condition, two supports at
each column top. The deck is assumed to be loaded out from the vessel side at a fabrication yard
with 4 skid beams onto the HTV deck. There are a total of 8 Deck Support Unit (DSU) installed
inside 8 skid shoes, two at each skid beam top with a stiffness of 25,000 MT/M and a maximum
stroke of 75mm. There are 8 receptacles (1.83 m O.D.) at column tops to the corresponding deck
legs as the permanent supports for the semi deck. Inside each receptacle, a Deck Mating Unit
(DMU) is installed with a stiffness of 18,750 MT/M and a maximum stroke of 100mm. The
DSUs and DMUs are designed to mitigate the potential impact loading during the deck mating
installation. Additional deck data and assumptions are listed below:
Overall sizes: 78m x 60m x 15m Wind projected area (side): 1,200 m^2
Wind area VCG: 12m above HTV deck Deck VCG: 8 m above column tops
Deck position during tow: bot. girder 5m above HTV deck Deck in-place position: bot. 1m above column top
Radii of gyrations: Rx = 10m; Ry = 25m; Rx = 25m in MOSES coordinate
The deck/vessel was modeled in MOSES as a rigid body with compression-only spring
connectors between the vessel and the semi. Isotropic views of this deck model are illustrated in
Figures 1 and 2.
Selected Environmental Conditions for Deck Mating Installation. As mentioned early, two
sets of deck mating installation environments were selected for the two different offshore
installation seasons in offshore West Africa. The environmental condition A represents the
conditions in conventional installation season from November 1 to March 31 of a year. The
swells during this season can be best described by a “workability curve” formula: Hs x Tp^2 <=
150. In this study, only one point at this curve was studied (Hs = 1.0 m and Tp = 12 seconds). In
addition to swells, associated random waves and winds are also included in the defined
environmental condition A.
The environmental condition B represents the conditions in non-conventional installation season
from April 1 to October 31 of a year, or called all-year-round installation criteria. The swells
during this season can be best described by a “workability curve” formula: Hs x Tp^2 <= 240. In
this study, only one point at this curve was studied (Hs = 1.4 m and Tp = 13 seconds). In
additional to swells, associated random waves and winds are also included in the defined
environmental condition B. The environmental condition B is considered as the primary
conditions in this study. Details of both environmental conditions are listed below:
Environmental Criteria A (November 1 to March 31)
Swell height and period: Hs = 1.0 meter, Tp = 12 seconds
(+/– 10.0 and 15.0 deg. wrt Moored Semi Slot)
Random waves: Hs = 0.5 meter, Tp = 4.5 seconds
(+/– 60 deg. wrt Moored Semi Slot)
Wind speed: 25 knots (all directions)
Environmental Criteria B (April 1 to October 31, or All-Year-Round)
Swell height and period: Hs = 1.4 meter, Tp = 13 seconds
(+/– 10.0 and 15.0 deg. wrt Moored Semi Slot)
Random waves: Hs = 1.0 meter, Tp = 5.2 seconds
(+/– 60 deg. wrt Moored Semi Slot)
Wind speed: 25 knots (all directions)
Interaction Consideration between Semi Hull and Vessel Hull. Both HTV and semi are large
floating bodies. Hydrodynamic interactions could influence the motion responses of both floating
bodies. However, under swell conditions with near zero heading, both floating bodies response in
defined orbital motions, mainly in three degrees of freedom (surge, heave and pitch) and little
motions in others (sway, roll and yaw). The potential motion interactions between the two bodies
could only be in heave and pitch directions. During the whole floatover installation operation, the
minimum distance between the HTV keel and the top of submerged pontoons is more than 12
meters during mating operation. Because of this large vertical distance between the two bodies
and the relative small heave motion amplitudes of both floating bodies under the design swells,
the motion interaction between the two bodies could be considered to be insignificant.
Therefore, there is no motion interaction consideration in this study.
Friction Fender: Functions, Design Criteria, Modeling and Assumptions
The Friction Fender system is the center piece of the proposed deck mating floatover installation
method. The basic function of this FF system in a deck mating installation is similar to a brake
system inside a car which is designed to stop the moving car. As the FF system is activated with
the engagement of two friction surfaces (each is mounted at one floating body), the applied
friction forces will directly cause the motion reductions of both floating bodies in surge and in
heave directions. Both relative displacements and relative velocities between the two floating
bodies should be reduced.
Each FF unit designed for the semi deck mating operation consists of two parts. One part is at a
vessel deck facing an inner surface of a semi column and another part is at the inner surface of a
semi column facing the vessel side. The part on the vessel deck is a pneumatic cylinder with a
convex shape friction surface at the tip of its piston. The part at the column inner surface is a
block with a concave shape friction surface to face the machined convex friction surface at the
piston tip. As the piston is extended with pressured air, the two friction surfaces slide against
each other to generate friction forces for the reductions of the relative motions both in heave and
surge directions. The basic configurations of the FF unit are illustrated in Figures 4(A), 4(B),
4(C) and 5. The concave and convex shapes at the sliding surfaces also provide additional
benefits to the deck mating operation: a) a built-in self alignment mechanism to align vertically
between the deck legs and the corresponding receptacles at semi column tops; b) the concave
friction surface with building-in anti-surge slopes in horizontal direction to further increase the
anti-surge force as the compression force increase from the pneumatic cylinders. The anti-surge
slopes are higher near the edges of the concave curve (producing equivalent friction coefficient >
0.4 in the defined configuration of this study) and near zero at the center.
The friction coefficient at the sliding surface of each FF plays an important role in the system.
The fiction coefficient first should be high and reliable. Further more, the materials at the sliding
surface should also be strong to take the expected high compression loads. Two types of
materials were investigated and considered to be suitable for the intended application. One
option is to use plastic material such as Thordon at the tip of the convex friction surface (Ref. 1).
The material was extensively tested and found to have a reliable friction coefficient about
0.2~0.3 in both dry and wet conditions and the material has an excellent property against
wearing. The only weak side of this material is its strength against compression loading. The
design load for such material is only about 2~3 ksi. If this material is adopted, a relative large
contact surface would be required. Another option is to use steels at both contact surfaces. One
side, the concave one, is common rolled steel surface with a low steel surface hardness. Other
side, the convex one, is made of a machined steel surface with much higher surface hardness
such as a Brinell Hardness Scale about 200 comparing to the rolled steel surface with a Brinell
Hardness Scale about 15. Such large surface hardness difference helps ensure the high friction
coefficient and prevent potential galling during the steel-to-steel sliding. With this configuration,
the sliding surface has a high static friction coefficient about 0.4~0.5, and it also provides the
desired strength to take the expected high compression loads. If the required compression force
is low, the Thordon material is recommended. If the compression load is high, such as in this
semi deck mating installation study, steel-to-steel application appears to have more advantages
over the plastic material. In this study, the friction coefficient at surge direction is assumed to be
0.5 including the slope induced anti-surge component and the friction coefficient at heave
direction is assumed to be 0.4.
In this application of the FF system, the basic design criteria for the two parts are summarized
below:
Part at vessel deck: Part at semi column inner surface Cylinder stroke: 600mm Size: 2.8m (W) x1.7m (D) x 7.5m (H)
Cylinder capacity: 430 MT Slope near 2 edges: 30.00 (long. component = 50%)
Surface curvature: R = 2.5 m Rubber Strip fenders: 600mm x 600mm x 7.5 m
Steel surface hardness: 200 (Brinell Scale) Surface Curvature: R = 2.5 m
Max. Sliding surface area: 600mm x 600mm Steel surface hardness: 15 (Brinell Scale)
Mini. Equivalent friction coefficient: 0.5 (surge) Max. Sliding surface area: 2.2m (W) x 7.5m (H)
Mini. Equivalent friction coefficient: 0.4 (heave) Size of the concave shape: 2.2m (W) x7.5m (H) x0.4m (D)
The part of FF on the semi column is designed to be a buoyant structure for an easy recovery
during post mating activities. A common air injection source, a compressor or a compressed
accumulator, for these pneumatic cylinders is recommended because a simultaneous engagement
/ disengagement action of all cylinders are the essential part of the FF system. The smooth and
easy engagements/ disengagements between these piston tips and these receptacles at the sliding
surfaces also improve the safety of the operation.
Wellspring Pneumatic Jack – A Better Alternative. Reliable and safe pneumatic cylinders
which satisfy the above listed design criteria are the essential part of the FF system.
Conventional pneumatic cylinders can be utilized in the FF system with some modifications. A
conventional pneumatic cylinder is typically made of three separate moving parts: an inner
cylinder, an outer cylinder and a pair of seal rings between the two cylinders. There are two
major concerns in using a conventional pneumatic cylinder as the cylinder in the FF system: 1)
the ability to take a large lateral load, induced by the friction forces; 2) the reliability of these
seals for repeated uses and under tough offshore environments. An alternative pneumatic
cylinder, called Wellspring jack developed by OKI, is introduced as a potential candidate.
Wellspring jack is made of conventional marine shock cells. As illustrated in the following
figure, a marine shock cell generally consists of an inner and outer cylinder segment sealed by an
elastomer annulus. The length of the annulus is designed to absorb the impact energy of ships
and other structures experienced during docking procedures. The cylinder deflects under loading
to deform the elastomer annulus.
Figure 6 - A Typical Marine Shock Cell
One application of the jack is to perform the function as a cylinder, either hydraulic or
pneumatic. Further, the design has a built-in shock absorption capacity and an automatic
retraction mechanism after the water or air is released. These advantages are achieved by
replacement of the sliding seal and wiper configuration of conventional fluid/air power systems
with an arrangement of elastomer expansion joints. As illustrated in Figure 7, the overall cylinder
is divided into multiple segments, called expansion joints. The expansion joints comprise an
inner and an outer cylinder segment. These segments are joined and sealed by an elastomer
annulus. The elastomer annulus deflects to permit relative movement between cylinder segments,
inducing extension of the expansion joint. The extension of the individual expansion joint is
combined in series to provide overall cylinder extension and force transmission. An important
distinguish figure of the Wellsping jack is that the cylinder has no moving parts. The unique
simplicity of this configuration and its proven long service life under severe offshore
environments provide the desired reliability for the FF application.
Figure 7 - Wellspring Jack with Two Expansion Joints
The fluid/air power transmition capacity of an elastomer annulus in a conventional marine shock
cell was tested and confirmed by OKI in 1999. A maximum loading capacity of over 1,500 s.
tons was achieved. Several expansion and retraction positions of the elastomer annulus were
tested with an internal design compression of 1,500 psi. Photos from that test are listed below
(Ref. 2):
Details of the proposed Wellspring jack as a pneumatic cylinder is illustrated in Figures 4 (A), 4
(B) and 4 (C) for semi deck mating application.
The application details for a fixed jacket deck mating installation are shown in Figures 8, 9,
10(A), and 10(B). At the piston tip, a 30 degree angle as a wedge shape is recommended in
combination with a concave surface at the center. This configuration helps to provide a large
anti-surge force in the early stage of a fixed jacket deck mating installation. After the initial
engagement and the applied surge “lock-in” compression forces at the jacket legs, it is expected
that the vessel should slide vertically against these jacket legs at the concave center of the piston
tips without any relative surge motions.
Key Configurations and Base Study Cases
Four critical configurations were studied. The first configuration is the pre-entry configuration
shown in Figure 11. The third configuration is the mating configuration where the deck mating
loads transfer operation should take place; see Figures 12 through 14 for details. The second
configuration is the one halfway between the pre-entry and the mating configurations. The last
one is the post-separation configuration with the completion of the load transfer operation at an
increased vessel draft, see Figures 15 and 16 for details.
Pre-entry Configuration. Figure 11 is an isotropic view of the pre-entry configuration. At this
position, the semi heading could be adjusted with small degrees by these pre-installed chain
jacks. The vessel bow is positioned towards to the coming swells (< +15 degrees) and the stern
faces the slot formed by the semi columns. Two winch lines are crossly connected to the two
back columns passing through two flip sheaves located at the two front column inner surfaces.
These flip sheaves could be released, after the stern passes the front two columns, to make the
two crosswire directly be connected to the padeyes at the back two columns. Two additional
wires are connected from the sides of the vessel near the bow to the two front columns. At the
connections of all wires to the padeyes on the semi columns, stretchers such as nylon ropes are
required to limit the impact loading inside these wires.
Three tugs are utilized for the entry operation. One tug is connected to the vessel stern to assist
the vessel entry by pulling the vessel stern slowly into the slot. Two more tugs are positioned at
sides near the bow to keep the alignment of the vessel towards the slot during the entry
operation. At vessel stern, two guide frames are installed at both sides of the vessel over the stern
to serve as the initial guidance as the barge stern contacts the wood/rubber fenders at the first two
FF units. There is a 200 mm gap between the fender surface and the barge side surface at each
side of the vessel. During the entry, one side of the vessel should be slide against the fender and
keep a 400 mm gap at other side, depending on the wind direction at the time of the entry.
Two stoppers will be installed at the sides of the vessel for the longitudinal positioning of the
vessel at the mating configuration. The stoppers are made of conventional marine shock cells to
act against the two front column surfaces. These two stoppers are designed to let the vessel stay
close to the final mating position longitudinally prior to the engagements of FFs. Once FFs are
engaged, the final alignment between the deck and semi columns should depend on the self-
centering mechanism of these FFs.
At the initial entry, the vessel mean draft is at 8 meters and the semi draft is at 32.83 meters to
keep a clearance of 2 meters under Environmental B criteria between the bottom tips of deck legs
and the tops of receptacles at column tops. During the initial entry, the maximum relative
displacement between the vessel and the semi is about 1.5 meters in heave direction mostly due
to the phasing induced pitch effects. As the vessel near its mating configuration, the maximum
relative vertical displacement is reduced to only about 0.9 meter.
Mating Configuration. As the vessel is near the final mating position, the stoppers should make
initial contacts to the front column surfaces. Air should be injected into these FFs through an air
compressor. Relative motions will start to be reduced as the compression forces increase at these
friction sliding surfaces. When the relative motions, both in surge and heave directions, are
reduced to a minimum level such as “lock-in” condition, mating operation should commence
immediately by ballasting the vessel down and deballasting the semi up to transfer the deck loads
from the supports on vessel deck to the supports at semi column tops. At this configuration, the
FFs should provide sufficient compression forces and the total friction force resulted from these
sliding surfaces should exceed the calculated “lock-in” force prior to the deck transfer operation.
It is assumed that the load transfer operation could be conducted in a static process if the applied
friction force exceeds the required “lock-in” force. As the relative motions, surge and heave, are
locked in, the sway motion is also limited by the stiffness of these FF units in the lateral
direction.
In real operation, a small heave motion, sliding up and down at these sliding surfaces, is a
welcome one. This small sliding acting could avoid a sudden move in vertical direction between
the deck and the vessel. The desirable small sliding motion can be easily controlled by the
measured air pressures inside these cylinders.
Post Separation Configuration. After the deck load is 100% transferred from the supports on
the vessel deck to the semi column tops, the vessel should be further ballasted down and the semi
should be deballasted up until a 2 meter air gap occurs between the deck leg bottoms and the
support tops at the vessel deck. When the desired clearance is achieved, FFs should be
disengaged with the release of air from all FFs simultaneously.
After the disengagements of all FFs, withdrawal operation should be commenced immediately
with the help of a tug from the vessel bow.
A list of total 26 study cases is in Table 2. Among the 26 cases, they are divided into three
groups: 8 cases for entry configurations; 8 cases for mating configuration cases; and 10 cases for
separation and exit configurations.
Analyses and Discussion of Results
Analyses and Results for Semi Deck Mating Floatover Installation. Hydrodynamic analyses
were performed to prediction the environmental loads and the relative motions of the vessel and
semi hull, as well as the interactions load between the two bodies and the loads on the friction
fenders during the floatover operation. The critical parameters come from the analyses are:
Six degrees of freedom motions of the vessel and the semi.
Relative motions between the vessel and semi during entry, mating and exit.
Contact loads between the vessel and the fenders on the semi during entry and exit.
Friction forces needed during mating to minimize/stop the relative motions between the
two floating bodies.
Potential theory and panel method were used to predict the hydrodynamics, such as the wave
frequency diffraction loads, mean drift loads, added mass and wave damping, on the two bodies.
Since the semi hull is relatively slender and transparent to the waves (i.e. wave diffraction from
the semi hull is insignificant), and its pontoons (from which the wave force in heave comes) are
far below the keel of the vessel, the hydrodynamic interactions between the two bodies are
assumed trivial and negligible. This means that the hydrodynamics of one body is calculated
without the presence of the other one. In all calculations, 1 in 100 highest values were reported.
In the hydrodynamic calculation, both the vessel and the semi hull were each divided into over
2,500 panels so that the panel sizes are small enough to ensure accurate result for waves with
relatively short wave length. A total of 30 wave frequencies, ranging from 3.0 to 31.0 seconds,
were selected to cover the frequency range where the wave energy exists. The analyses were
carried out for following critical stages of the operation:
1. The stern of the vessel is at the center of the first row of column (early stage of entry, see
Figure 11 )
2. The stern of the vessel is at the center of the second row of column (mid stage of entry)
3. The deck of semi is centered above the semi hull (final stage of entry and start of mating,
Figure 12)
4. The stern of the vessel is at the center of the first row of column (final stage of exit)
After the hydrodynamic calculation, the relative motions between the two bodies were computed
in frequency domain. The results are shown in Table 3. In order to check the impact of the swell
heading to the motions and impact loads, the results of 10 degree and 15 degree swell headings
are both listed in the Table.
Figures 17 through 20 are MOSES model plots to show different positions between the semi and
the vessel. Figures 21 through 23 illustrate the motion RAOs of the vessel in Surge, heave and
pitch directions from MOSES analyses.
In the Table 3, the maximum relative heave motions between the mating point on the deck in
entry phase decides the vertical clearance needed during entry (the deck height on vessel and the
vessel draft). The relative sway motions indicate if there is contact between the two bodies. If the
gaps between the two bodies are less than this values, then contact is expected and the contact
loads need to be predicted. Since the contact loads are non-linear, time domain analysis were
used to calculate the contact loads. In the simulation, a small time step (0.05 sec) was used to
ensure the accuracy of predicting the impact loads, and the duration of the simulation is 1 hour.
The contact loads showing in the table are for the configuration where there is 0.2 meter gap (at
each side of the vessel) between the vessel and the fenders at the semi hull, and there are fenders
between vessel and semi columns with a stiffness of 2,500 MT per meter. These loads should not
be a concern to the structures of the vessel and semi hull. The impacts can be further reduced by
increase the gap and make the fender softer.
In the mating stages, it is preferred to reduce the relative motions as much as possible between
the two bodies by the friction fenders for the transfer of deck from vessel to the semi hull. The
analyses indicate that (Table 3), to fully stop the relative motions (“lock-in” condition), the
required maximum friction force is 350 MT (at each column of semi by 3 FF units) for a 1.0
meter swell (Environment A), and 512 MT for a 1.4 meter swell (Environment B). These values
decide the design capacity of these pneumatic jacks that apply the normal loads to these FFs. The
entry and mating calculation results are summarized in the following table:
Table 4 - Maximum Motions and Required “Lock-in” Friction Forces
Environments Entry Motions & Lateral Docking Forces Mating Motions &”Lock-in” Forces
Surge/Heave (m) Force/Per FF (MT) Surge/Heave (m) Force/Per FF (MT)
A 0.65/0.51 310 0.31/0.65 350
B 1.2/0.87 400 0.53/1.08 512
During the exit, the main concern is the vertical clearance between the bottom of the semi deck
and the vessel. The relative heave motions shown in Table 3 determines how far the ballast (for
vessel) or de-ballast (for semi) are needed. A 2-meter clearance gap is recommended during the
withdrawal operation, see Figure 16 for details. From the results listed in Table 3, the maximum
relative heave motion reaches to 1.9 meters as the vessel at the last slot exit position, it is also
recommended to have a negative trim angle of the vessel, such as 1 degree, prior to this position
in order to have sufficient vertical clearance at the vessel deck support tops.
Analyses and Results for Fixed Jacket Mating Floatover Installation. For the fixed jacket
deck mating calculations, 2 different cases were calculated under both Environment A and
Environment B. The total “lock-in” forces at surge direction and in heave direction were listed
in Table 5.
Table 5 - Maximum Friction Forces under “Lock-In” Conditions At Jacket Legs Case
Environments
Lock-In Forces at Middle 4 Legs Lock-In Forces at Outer 4 Legs
No. Surge (MT/Leg)
Heave (MT/Leg) Surge (MT/Leg) Heave (MT/Leg)
1 A 68 324 74 743
2 B 78 488 80 1135
The results indicated the required “lock-in” friction force in surge direction is relative small to
completely stop a vessel such as the Block Marlin HTV, especially with a wedge shape design of
the sliding surfaces. However, the required “lock-in” heave force is large and the distribution of
the loading is different between the 4 middle legs and the 4 outer legs. The middle 4 legs require
much less anti-heave forces than the ones at the outer 4 legs. The reason is the vessel pitch
induced moment and the distance between the two outer legs in longitudinal direction is much
shorter than the length of the vessel. Because the compression force to produce the required
“lock-in friction force in heave direction exceeds the allowable loading capacity of the jacket
legs, the total “lock-in” in both surge and heave directions could not feasible. In a most like case,
there is only vertical motion at these sliding surfaces between the vessel and the jacket legs.
Conclusions and Recommendations
The primary objective of this study is to provide an alternative approach in deck mating floatover
installation under West Africa swells to a pre-installed semi hull. In the proposed system,
Friction Fenders utilize horizontal compression forces to generate friction force for the relative
motion reductions between the two floating bodies. The motion calculation results indicated that
a total of 1,400 MT friction force per column, 350 MT per FF, is sufficient to totally eliminate all
relative motions in both surge and heave directions. This required total force is much less than
the required total capacity of the hydraulic system to lift the whole deck (15,000 MT in this
study) used in the Uni-Deck method. In addition, the required friction is based on the vessel sizes
and not based on individual deck weight. Other advantages over the existing method are listed
below:
1. The impact loading is limited due the significantly reduced motions.
2. Continous operations without instant contacts and separations.
3. Total reversible operation at any time of the installation.
4. The reliability of the FF system without the need for maintanence.
5. The relative motions at the sliding surfaces could be easily contolled and adjusted.
In the application of FF system to a semi deck mating installation, a total “lock-in” condition is
recommended prior to the deck load transfer operation. Under this condition, the two floating
bodies, semi and vessel, would move together and the entire load transfer operation could be
conducted in a near static process to provide significantly improved operational safety,
comparing to the Uni-Deck or other existing methods.
The study further confirmed that the FF system could allow the extension of the installation
season from current 5 months of a year to a whole year round installation under West Africa
swells. The required capacity increase for the FF system is limited.
Due to the limitations of current computer software in dealing with friction induced stick-slip
effect under swells for relative motion reductions, this study only provided the results at both
ends to determine the friction induced motion reductions: a) at one end, the relative motions
without any friction force; b) the required friction force for a “lock-in” configuration with total
elimination of relative motions. The middle section of the friction effectiveness in relative
motion reduction will depend on the results of a model test in a model basin or a better computer
software to handle the friction forces in time domain simulations.
The second objective of this study is to extend the application of the FF system to a fixed jacket
deck mating installation under swells. The study results indicated that a different application
procedure for the FF system should be followed in which the surge motions could be “lock-in”
and limited heave motions should be allowed during the mating operation.
Overall, this study confirmed that the proposed deck mating system is a simple and effective
system for the applications in deck mating floatover installations under West Africa swell
environments. This system could provide applications for both the floating-to-floating deck
mating installations and the floating-to-fixed deck mating operations.
This study also recognizes that further development of this FF system is needed, especially in
two critical areas: a model test in a model basin for the system confirmation and the development
of a suitable computer software for the calculation of the friction induced motion reduction in a
time domain simulation. Planned further developments for the FF system described in this study
will include the actions in the following 4 areas:
Model Test in a Model Basin – A model basin test is planned to confirm the
effectiveness of the motion reduction mechanism in surge and heave directions by a
designed FF system for both a floating-to-floating deck mating installation and floating-
to-fixed deck mating installation. The results of the test could also be utilized to calibrate
the numerical calculations in a developed time domain simulation software.
Software Development – A development of a time domain calculation tool is planned as
a part of the whole FF system development. In the software program, the stick-slip effect
to both a floating-to-floating deck mating installation and a loading-to-fixed deck mating
installation will be considered.
Friction Coefficient Test – Further testing of steel-to-steel friction coefficients with
different hardness between the two sliding steel surface. Other materials with reliable and
high friction coefficient could also be selected for testing.
Wellspring Jack – Further testing and designs of Wellspring pneumatic jacks for the
application of the FF systems, suitable for both a floating-to-floating deck mating
installation and floating-to-fixed deck mating installation, will be considered.
Applicability to Other Structures – Further investigation into the application of the
presented concept to other floating and fixed structures such as TLP’s, SPAR’s, fixed
jackets and compliant towers.
Acknowledgements
The authors would like to acknowledge the management of both Dockwise and OKI for
permission to publish this paper. Special thanks to Jim Li, from Ocean Dynamics LLC, for his
contributions to this study.
References 1. John Montague, Steven Byle, OKI – “Friction & Wear Test Report”, August 2001 2. John Montague, Steven Byle, OKI – “Wellspring Hydraulic Test Report”, June 1999 SI Metric Conversion Factors Kip x 4.448222 E+00 = kN
s.ton x 8.896443 E+00 =kN in x 2.540000 E-02 = m ft x 3.048000 E-01 = m kts x 5.147733 E-01 = m/s
FF Activatioon
Frequency
Domain
Time
Domain
Headings:
Swell/Wave/Wind
(Deg.) Objectives
B1 Pre-Entry PositionDraft = 32.8 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 8.0 m
Trim = 0.0 Deg NO Yes NO 10/45/90
Semi and HTV Individual Motions: Surge, Sway, Heave, Roll, Pitch and Yaw
B2 Pre-Entry PositionDraft = 32.8 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 8.0 m
Trim = 0.0 Deg NO Yes NO 15/45/90
Semi and HTV Individual Motions: Surge, Sway, Heave, Roll, Pitch and Yaw
B3 Mid-Stage PositionDraft = 32.8 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 8.0 m
Trim = -1.0 Deg NO Yes NO 10/45/90
Semi and HTV Relative Motions: Surge, Sway, Heave, Roll, Pitch and Yaw
B4 Mid-Stage PositionDraft = 32.8 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 8.0 m
Trim = -1.0 Deg NO Yes NO 15/45/90
Semi and HTV Relative Motions: Surge, Sway, Heave, Roll, Pitch and Yaw
A1 Mid-Stage PositionDraft = 32.8 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 8.0 m
Trim = -1.0 Deg NO NO Yes 10/45/90
Docking forces between vessel sides and rubber
strip fenders
A1 Mid-Stage PositionDraft = 32.8 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 8.0 m
Trim = -1.0 Deg NO NO Yes 15/45/90
Docking forces between vessel sides and rubber
strip fenders
B5 Mid-Stage PositionDraft = 32.8 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 8.0 m
Trim = -1.0 Deg NO NO Yes 10/45/90
Docking forces between vessel sides and rubber
strip fenders
B6 Mid-Stage PositionDraft = 32.8 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 8.0 m
Trim = -1.0 Deg NO NO Yes 15/45/90
Docking forces between vessel sides and rubber
strip fenders
B7
Mating Position
No Load TransferDraft = 32.6 m
Trim = 0.0 Deg
Disengaged
PositionDraft = 10.0 m
Trim = 0.0 Deg NO Yes NO 10/45/90
Semi and HTV Relative Motions: Surge, Sway, Heave, Roll, Pitch and Yaw
B8
Mating Position
No Load TransferDraft = 32.6 m
Trim = 0.0 Deg
Disengaged
PositionDraft = 10.0 m
Trim = 0.0 Deg NO Yes NO 15/45/90
Semi and HTV Relative Motions: Surge, Sway, Heave, Roll, Pitch and Yaw
A3
Mating Position
No Load TransferDraft = 32.6 m
Trim = 0.0 Deg
Disengaged
PositionDraft = 10.0 m
Trim = 0.0 Deg NO Yes NO 10/45/90
Semi and HTV Relative Motions: Surge, Sway, Heave, Roll, Pitch and Yaw
A4
Mating Position
No Load TransferDraft = 32.6 m
Trim = 0.0 Deg
Disengaged
PositionDraft = 10.0 m
Trim = 0.0 Deg NO Yes NO 15/45/90
Semi and HTV Relative Motions: Surge, Sway, Heave, Roll, Pitch and Yaw
B9
Mating Position Deck
Load TransferDraft = 32.6 m
Trim = 0.0 Deg
Disengaged
PositionDraft = 10.0 m
Trim = 0.0 Deg Yes Yes NO 10/45/90
Determine required lock-in froces in surge and
heave directions
B10
Mating Position Deck
Load TransferDraft = 32.6 m
Trim = 0.0 Deg
Engaged
PositionDraft = 10.0 m
Trim = 0.0 Deg Yes Yes NO 15/45/90
Determine required lock-in froces in surge and
heave directions
A5
Mating Position Deck
Load TransferDraft = 32.6 m
Trim = 0.0 Deg
Engaged
PositionDraft = 10.0 m
Trim = 0.0 Deg Yes Yes NO 10/45/90
Determine required lock-in froces in surge and
heave directions
A6
Mating Position Deck
Load TransferDraft = 32.6 m
Trim = 0.0 Deg
Engaged
PositionDraft = 10.0 m
Trim = 0.0 Deg Yes Yes NO 15/45/90
Determine required lock-in froces in surge and
heave directions
B11
Separation Position
No Load TransferDraft = 30.0 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 10.0 m
Trim = 0.0 Deg NO Yes NO 10/45/90
Semi and HTV Relative Motions: Surge, Sway, Heave, Roll, Pitch and Yaw
B12
Separation Position
No Load TransferDraft = 30.0 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 10.0 m
Trim = 0.0 Deg NO Yes NO 15/45/90
Semi and HTV Relative Motions: Surge, Sway, Heave, Roll, Pitch and Yaw
A7
Separation Position
No Load TransferDraft = 30.0 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 10.0 m
Trim = 0.0 Deg NO NO Yes 10/45/90
Docking forces between vessel sides and rubber
strip fenders
A8
Separation Position
No Load TransferDraft = 30.0 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 10.0 m
Trim = 0.0 Deg NO NO Yes 15/45/90
Docking forces between vessel sides and rubber
strip fenders
B13
Separation Position
No Load TransferDraft = 30.0 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 10.0 m
Trim = 0.0 Deg NO NO Yes 10/45/90
Docking forces between vessel sides and rubber
strip fenders
B14
Separation Position
No Load TransferDraft = 30.0 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 10.0 m
Trim = 0.0 Deg NO No Yes 15/45/90
Docking forces between vessel sides and rubber
strip fenders
A9 Final Exit PositionDraft = 30.0 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 10.0 m
Trim = 0.0 Deg NO NO Yes 10/45/90
Docking forces between vessel sides and rubber
strip fenders
A10 Final Exit PositionDraft = 30.0 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 10.0 m
Trim = 0.0 Deg NO NO Yes 15/45/90
Docking forces between vessel sides and rubber
strip fenders
B15 Final Exit PositionDraft = 30.0 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 10.0 m
Trim = 0.0 Deg NO NO Yes 10/45/90
Docking forces between vessel sides and rubber
strip fenders
B16 Final Exit PositionDraft = 30.0 m
Trim = 0.0 Deg
Pre-Moored
PositionDraft = 10.0 m
Trim = 0.0 Deg NO No Yes 15/45/90
Docking forces between vessel sides and rubber
strip fenders
Note: Cases B1 through B16are for Environmental Condition B and Cases A1 through A10 are for Environmental Condition A.
Post S
epara
tion a
nd E
xit C
onfigura
tions
Mating C
onfigura
tion
Table 2 - Defined Calculation Cases for Environmental Condition A and Environmental Condition B
Semi Configuration HTV ConfigurationCase No.
Entr
y C
onfigura
tion
Swell: ≤ 10° Heading
Wave: ≤ 60° Heading
Swell: ≤ 15° Heading
Wave: ≤ 60° Heading
Swell: ≤ 10° Heading
Wave: ≤ 60° Heading
Swell: ≤ 15° Heading
Wave: ≤ 60° Heading
1. Entry Configuration (Maxima in 8 Cases)
Relative surge motion (m) 0.650 0.650 1.200 1.200
Relative heave motion at mating point (m) 0.489 0.505 0.851 0.865
Relative sway motion at the columns (m) 0.285 0.382 0.429 0.568
Relative roll (deg) 0.173 0.242 0.274 0.378
Relative yaw (deg) 0.103 0.134 0.160 0.200
Relative pitch (deg) 0.801 0.801 1.269 1.269
Contact load between vessel and semi (mt) 256 312 299 400
2. Mating Comfiguration (Maxima in 8 Cases)
Relative surge motion befor lock-in (m) 0.305 0.305 0.533 0.533
Relative heave motion at mating point lock-in (m) 0.633 0.647 1.057 1.084
Relative sway motion at the columns lock-in (m) 0.069 0.091 0.117 0.142
Relative roll lock-in (deg) 0.160 0.228 0.254 0.359
Relative yaw lock-in (deg) 0.086 0.112 0.150 0.184
Relative pitch lock-in (deg) 0.760 0.760 1.349 1.349
Required Lock-In Force at Each Column - 3 FF Units (mt) 350 360 500 512
Compression Force Per Column to Lock-In (μ-=0.4) (mt) 875 900 1250 1280
Surge motion of vessel and semi after lock-in (m) 0.205 0.205 0.349 0.349
Sway motion of vessel and semi after lock-in (m) 0.079 0.106 0.161 0.215
Heave motion of vessel and semi after lock-in (m) 0.518 0.524 0.827 0.836
Roll of vessel and semi after lock-in (deg) 0.196 0.257 0.456 0.595
Pitch of vessel and semi after lock-in (deg) 0.611 0.612 0.917 0.917
Yaw of vessel and semi after lock-in (deg) 0.053 0.071 0.080 0.104
3. Post Separation Configuration (Maxima in 10 Cases)
Relative surge motion (m) 0.461 0.461 0.831 0.831
Relative heave motion (vessel to bottom of deck) (m) 1.321 1.321 1.863 1.863
Relative sway motion at the columns (m) 0.161 0.222 0.249 0.334
Relative roll (deg) 0.221 0.293 0.325 0.417
Relative yaw (deg) 0.088 0.115 0.152 0.187
Relative pitch (deg) 0.853 0.864 1.259 1.265
Contact load between vessel and semi w/o deck (mt) 210 245 332 453
Environment A
(Swell: Hs=1.0 m, Wave: Hs=0.5 m)
Environment B
(Swell: Hs=1.4 m, Wave: Hs=1.0 m)
Summary of Deck-Semi Floatover Analyses
Table 3 – Summary of Deck-Semi Motions and Required Friction Forces
Figure 1 – Deck Configuration without Semi Hull (Isotropic View)
Figure 2 – Deck at Installed Configuration on Semi Hull
Figure 3 – Heavy Transport Vessel – Black Marlin
Winch (TYP)
Guide Frame
(TYP)
Stopper (TYP)
Figure 4 (A) – Friction Fender (FF) Part A – Wellspring Jack and Convex Sliding Surface
In Disengaged Position
Piston Sleeve
Convex
Sliding
Surface
Wellspring Jack w/ 2
Expansion Joints Inside
Skid to Support
Wellspring Jack
Figure 4 (B) – Friction Fender (FF) Part A – Wellspring Jack in Extended Position
Piston
Extension
Figure 4 (C) – Friction Fender (FF) Part A and B – Wellspring Jack in Engaged Position
During Mating Operation
Figure 5 – Friction Fender (FF) Part B – Concave Friction Surfaces and Fenders
Rubber Strip
Fender (TYP)
FF – Concave Friction
Surface (TYP)
Deck Receptacle (TYP)
Semi Column Top (TYP)
Figure 8 – FF System Application to an 8-Leg Fixed Jacket Installation
(FF in Disengaged Position, Deck and Skidbeams Omitted for Clarity)
Jacket Leg (TYP)
Pneumatic Jack (TYP)
Figure 9 – FF System Application to an 8-Leg Fixed Jacket Installation
(FF in Engaged Position, Deck and Skidbeams Omitted for Clarity)
Figure 10 (A) – Wellspring Jack Application in Disengaged Position
2~Wellspring Jacks (TYP)
30 Degree Slope (TYP)
R = 3 feet to Match 72” O.D. Leg
Figure 10 (B) – Wellspring Jack Application in Engaged Position
Convex Friction Surface w/ 30% Slopes
8 feet (L) x 2 feet (H) x 4 feet (W) (TYP)
Figure 11 – Pre-Entry Configuration
Slip Sheave
(TYP)
Tug
(TYP)
Cross
Wire
(TYP)
Wire
(TYP
Deck
(TYP
Pneumatic
Jack (TYP)
(TYP
Stopper
(TYP)
Figure 12 – Mating Configuration – ISO View
Figure 13 – Mating Configuration Prior to Load Transfer (Section View)
2 Meter Gap
(TYP)
Stabbing Cone
(TYP)
Receptacle
72”O.D. (TYP)
Pneumatic Jack
(TYP)
Figure 14 – Mating Configuration during Load Transfer (Section View)
Figure 15 – Post Separation Configuration (ISO View)
Figure 16 – Post-Separation Configuration (Section View)
2 Meter Gap
(TYP)
Figure 17 – Pre-Entry Configuration in MOSES Model Loaded with the Deck
Figure 18 – Mid-Entry Configuration in MOSES Model Loaded with the Deck
Figure 19 – Mating Configuration in MOSES Model Loaded with the Deck
Figure 20 – Exit Configuration in MOSES Model for Semi and Deck
Figure 21 – Vessel Surge RAO
Figure 22 – Vessel Heave RAO
Figure 23 – Vessel Pitch RAO