Offshore Deck Mating onto a Pre-Installed Semi-submersible

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



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


Trim = -1.0 Deg NO Yes NO 10/45/90

Semi and HTV Relative Motions: Surge, Sway, Heave, Roll, Pitch and Yaw


Trim = 0.0 Deg

Pre-Moored


Trim = -1.0 Deg NO Yes NO 15/45/90


A1 Mid-Stage PositionDraft = 32.8 m

Trim = 0.0 Deg

Pre-Moored


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




strip fenders


Trim = 0.0 Deg

Pre-Moored




strip fenders


Trim = 0.0 Deg

Pre-Moored




strip fenders

B7

Mating Position

No Load TransferDraft = 32.6 m

Trim = 0.0 Deg

Disengaged




B8

Mating Position


Trim = 0.0 Deg

Disengaged




A3

Mating Position


Trim = 0.0 Deg

Disengaged




A4

Mating Position


Trim = 0.0 Deg

Disengaged




B9

Mating Position Deck

Load TransferDraft = 32.6 m

Trim = 0.0 Deg

Disengaged


Trim = 0.0 Deg Yes Yes NO 10/45/90

Determine required lock-in froces in surge and

heave directions

B10



Trim = 0.0 Deg

Engaged




heave directions

A5



Trim = 0.0 Deg

Engaged




heave directions

A6



Trim = 0.0 Deg

Engaged




heave directions

B11

Separation Position


Trim = 0.0 Deg

Pre-Moored




B12

Separation Position


Trim = 0.0 Deg

Pre-Moored




A7

Separation Position


Trim = 0.0 Deg

Pre-Moored


Trim = 0.0 Deg NO NO Yes 10/45/90


strip fenders

A8

Separation Position


Trim = 0.0 Deg

Pre-Moored




strip fenders

B13

Separation Position


Trim = 0.0 Deg

Pre-Moored




strip fenders

B14

Separation Position


Trim = 0.0 Deg

Pre-Moored


Trim = 0.0 Deg NO No Yes 15/45/90


strip fenders

A9 Final Exit PositionDraft = 30.0 m

Trim = 0.0 Deg

Pre-Moored




strip fenders

A10 Final Exit PositionDraft = 30.0 m

Trim = 0.0 Deg

Pre-Moored




strip fenders

B15 Final Exit PositionDraft = 30.0 m

Trim = 0.0 Deg

Pre-Moored




strip fenders

B16 Final Exit PositionDraft = 30.0 m

Trim = 0.0 Deg

Pre-Moored


Trim = 0.0 Deg NO No Yes 15/45/90


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







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

Documents

Offshore Deck Mating onto a Pre-Installed Semi-submersible