Operational window for touchdown of jack-up barges-Werkbaarheid voor plaatsing van jack-ups

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Delft University of Technology

MATERIALS ENGINEERING

Department Maritime and Transport Technology Mekelweg 2 2628 CD Delft the Netherlands Phone +31 (0)15-2782889 Fax +31 (0)15-2781397 www.mtt.tudelft.nl

Specialization:

Transport Engineering and Logistics

Report number: 2013.TEL.7807

Title:

Operational window for

touchdown of jack-up barges

Author:

J. van Essen

Title (in Dutch): Werkbaarheid voor plaatsing van jack-ups

Assignment: literature Confidential: yes

Initiator (university): ir. W. van den Bos

Initiator (company): ir. L. van Adrichem (Temporary Works Design, Rotterdam) Supervisor: ir. W. van den Bos

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Delft University of Technology

FACULTY OF MECHANICAL, MARITIME AND MATERIALS ENGINEERING

Department of Marine and Transport Technology Mekelweg 2 2628 CD Delft the Netherlands Phone +31 (0)15-2782889 Fax +31 (0)15-2781397 www.mtt.tudelft.nl

Student: J. van Essen Assignment type: Literature

Supervisor (TUD): W. van den Bos (TU Delft)

Creditpoints (EC): 12 Supervisor (Company) L. van Adrichem

(Temporary Works Design)

Specialization: TEL

Report number: 2013.TL.7807 Confidential: Yes

Subject:

Operational window for touchdown of jack-up barges

Jack -up barges are barges equipped with legs that are able to jack themselves out of the water. When jacked, a stable work platform is available and operation is not influenced by wave motion. Jack-ups can be used as working platform for, among other utilities, installation and servicing structures such as: offshore wind turbines, long bridges, and drilling platforms.

The legs and a jacking system are used to lift the barge out of the water. Jacking up a barge is a dangerous operation, especially during the transition phase between floating and standing on the legs. During this phase there will be a repeated impact between the leg and the seabed when the barge follows the wave motions. The workability of the barge is limited by the allowable magnitude of the impact.

This literature assignment is to study and make an overview of the parameters influencing the impact magnitude and make an overview of existing measures to improve workability of jack-ups. The research in this assignment should cover the following:

• An overview of jack-up types (e.g. sizes, weights, jack-up systems); • An overview of parameters (and range) influencing the impact magnitude; • International Standards and Codes concerning leg impact for jack-up barges; • Jack-up leg impact calculation

• Patented systems reducing leg impact;

The supervisor,

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Summary

Jack-up barges are barges equipped with legs that are able to jack themselves out of the water. When jacked, a stable work platform is available and operation is not influenced by wave motion. Jack ups can be used as working platform for, among other utilities, installation and servicing structures such as offshore wind turbines, long bridges, and drilling platforms.

The legs and a jacking system are used to lift the barge out of the water. Jacking up a barge is a dangerous operation, especially during the transition phase between floating and standing on the legs. During this phase there will be a repeated impact between the leg and the seabed when the barge follows the wave motions. The workability of the barge is limited by the allowable magnitude of the impact.

The impact of the leg during touch down depends on the vessel specifications and environmental parameters. Jack-ups are present in a large variety of size and shape. Two main groups were distinguished. Flat barge type and jack-ups with the shape of a vessel. The barge type is often not self-propelled while the vessel type often is self-propelled and equipped with dynamic positioning system. The length of barge types ranges from 30 to 100 m. Ship type has range in length of 90 to 160 m. The barge type jack-ups are usually built for shallower water, up to 45 m, while the ship type is used in water to 80 m depth.

Several leg types are used with jack-ups; cylindrical legs, square tubular legs, and lattice legs. The lattice legs are often used for larger water depth. The length of the leg determines the operating depth which is important in the calculation of the impact load.

Jacking of the units can be achieved in several ways. Two types are most common: rack and pinion and pin-hole. The first is by use of hydraulic jacks and the second uses electric motors driving the pinion over racks along the legs. The jacking system has lower influence on the impact load but determines the possibility of a leg impact reducing device.

Besides dimensions of jack-ups, environmental conditions are important to determine the impact load. Maximum operating conditions are prescribed in specifications sheets for each vessel. It often concerns the maximum significant wave height. The corresponding wave period is often not provided but is important for determining the impact load. Another important parameter which is not prescribed is the seabed condition. Soft clay results in much lower reaction loads than dense sand and hard clay. Some classification societies provide calculation method for the impact load. Of all the members the International Association of Classification Societies (IACS) only three provide a method. They all provide more or less the same method. There are some difference in presentation, but the principles are the same. The three societies are: Bureau Veritas, Det Norske Veritas and Russian Maritime Register of Shipping.

The DNV calculation method was used to perform calculations to determine leg impact for the range of jack-ups concerned in this research. Impact loads were calculated and compared for three situations. The first was according to prescribed allowable operating conditions. The second was calculated to determine the effect of a shock absorber. And the third calculation was to compare higher wave conditions, which represented a larger weather window, with allowable values when a shock absorber was used. The impact loads for lattice legs were different from tubular legs. Loads were higher and the shock absorber had less effect than for tubular legs. The conclusion for all jack-ups was that adding only a small damping stroke resulted in large allowable wave conditions.

The calculation was simplified on vessel motion and leg specifications. This means that for accurate load values more detailed information should be used.

In the past several patented designs were made to reduce the leg impact load during installation of jack-ups. Designs consider shock absorbing at location of the jack house or at the bottom of a jack-up leg. Designs for the leg bottom often use compressive members, while designs for jack housing often use compressible gas or hydraulics to reduce the shock.

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List of symbols

Symbol Description Unit

θ

roll Roll angle

[º]

T

Roll period

[s]

Pv Vertical impact force [MN]

PH Horizontal impact force [MN]

EK Kinetic energy [MNm]

List of abbreviations

Abbreviation Description Unit

DNV Det Norske Veritas [-]

JUB Jack-Up Barge [-]

MODU Mobile Offshore Drilling Unit [-]

SWH Significant Wave Height [m]

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1 Introduction

1.1 General introduction

Jack-up barges are working platforms generally used at sea. They are used to perform operations like wind turbine installation or oil drilling. The platforms have retractable legs and can lift themselves out of the water. That provides a stable working platform without influence of sea motion. Different operating modes of a jack-up are presented below.

Figure 1-1, Different operating modes for a jack-up [3.1]

All of the jack-up types are designed for operation in locations with wave motion. When positioning or removing a jack-up on or from its location, the legs are lowered while the jack-ups motion is influenced by the waves. This causes impact between the legs and the seabed during touchdown. This happens between the modes ‘lowering legs’ and ‘coming out of the water’ in figure 1.1.

The possibility to install or remove a jack-up is limited by the sea state. The amount of time the weather or sea state allows safe operation is known as weather window. Of course, it is desired to have a weather window as large as possible.

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1.2 Goal of the research

Goal of this research is to survey of what determines the operational window of installing a jack-up unit. The focus is on the leg impact during touchdown. Furthermore, this research should result in an overview of what information is necessary to design a jack-up leg shock absorber, which then improves the workability.

1.3 Report structure

The report is setup in 7 main chapters. First, an introduction is made into several jack-up types. Its main components are discussed and the several types of jack-ups are distinguished. An overview is given of specifications of a set of jack-ups built in the last decade. This shows in what parameters jack-ups differ and in what range. These parameters are discussed in chapter 3. To find rules for determination of leg impact research was done on several standards and codes. The results of this search can be found chapter 4. As a result, a calculation sample was performed with use of the codes from chapter 4. The calculation and results are described in chapter 5. In the past, several designs were patented that provide leg impact reduction. Results of a patent search and description of the patents can be found in chapter 6. The last chapter contains conclusions of this report. References used for this report can be found in the section after the conclusion. Through the report references are presented as [x.x]. Calculations and detailed specifications on a selection of jack-ups can be found in the appendices.

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2 Jack-up specifications

To start this research first a survey is made of existing jack-up units. It resulted in what type and size of jack-ups are used nowadays. A selection is made of several jack-ups built in the last decade. This selection should only represent the variety in jack-ups instead of presenting a complete overview of all jack-ups. The selection is used throughout the report to determine and discuss subjects concerning the leg impact during touch-down.

Two main differences were identified. A platform can be specially made as working platform. Then it is often called a jack-up barge or rig. When the hull shape is like the shape of a regular vessel it is often called a jack-up vessel. The latter have a second important function of transport besides the function as working platform. The vessel types are often used for wind turbine transport and installation.

The following table presents the selection of jack-ups with specifications. The upper half presents the barge type jack-ups and lower half the vessel type. This distinction is used more often in this report. Table 2.1

Name Length

(m)

Width (m)

Legs Leg Type Leg length (m) Max Operating depth (m) Year built Barges: JB104 30.5 17.1 4 Cylinder 47.4 25 n/a

Pauline (SEA 900) 48 25 4 Cylinder 50 30 2002

JB114 (SEA 200) 55.5 32.2 4 Cylinder 73.15 40 2009

JB117 (SEA3250) 75.9 40 4 Cylinder 80 45 2012

Sea Jack 95 33 4 Square

Tube 50.4 30 2003

Ships:

Sea Energy 91.7 21.6 4 Square

tube 32 24 2002

Nora 105 50 4 3 Chord

lattice 130 80 2011

MPI Resolution 130 38 6 Square

lattice 71.8 35 2003

Seafox 5 151 50 4 3 Chord

lattice 106 65 2012

Pacific Orca 160 49 6 3 Chord

lattice 105 75 2012

Separate jack-up specifications with figures can be found in the appendix. For more information is referred to reference section 4.

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3 Parameters and range

This chapter discusses the parameters and range of specifications of jack-ups based on the selection in section 2.1. The parameters are selected on their influence on the jacking operation.

3.1 Hull shapes

The family of jack-up units consists of floating platforms and vessels. Both can elevate themselves out of the water by standing on their own legs. The three main groups can be considered as:

• Drilling platforms • Jack-up barges

• Vessels with jacking capabilities

The difference is noticeable by their hull shape and movability. Drilling platforms

The first group, jack-up drilling units, are often built as a triangular barge with three legs. One of the three barge corners is shaped similar to a ship’s bow. Triangular drilling units are normally not self-propelled and require tow boats to move to their destination.

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2013.TEL.7807 Barges

The second group, jack-up barges, or self-elevating platforms, are normally rectangular flat barges with legs at the corner points. Jack-up barges are often not self-propelled and therefore need to be towed. However, there do exist examples with own propulsion systems. This is an advantage, because in case of daily moves self-propulsion results in lower costs compared to the use of tugboats.

Figure 3-2, Four legged multipurpose self-elevating unit, GustoMSC type SEA-3250 [2.4] Vessels

Finally, jack-up vessels often have a bow of a cargo ship and are equipped with movable legs. Jack-up vessels are self-propelled. And in addition to that they are often equipped with dynamic positioning systems. This also saves additional tugs for the vessel to maintain its stationary position.

Sizes depend, amongst others, on their afloat and elevated load carrying capabilities [3.1].

Figure 3-3, Six legged Wind farm Installation Vessel, Pacific Orca [3.4]

This report will further on focus on the last two types of jack-ups. Reason for this is that it is expected those will have more frequent moves in their lifetime. In that case leg impact is more important because it occurs more often than for the drilling rigs, which stay for long time at one position.

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3.2 Sizes

The following figures show the difference in platform dimensions, see figure 2-1 for top view of barges and figure 2-2 for vessels.

Figure 3-4, Top view of jack-up barges (above) and jack-up vessels (below) size range

The barge type jack-ups are usually used for service operations. Oil drilling and maintenance on oil rigs used to be the main operations. In the last decade installation of wind farm has become a more important occupation for the jack-ups.

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Figure 3-5, Top view of jack-up vessels size range

The figures above show the shortest vessel types are almost as long as the largest barge type. The ship type jack-ups are often used for transport of large off shore structures like wind turbines. The extra space required for transport explains why the ship types are larger, as shown in the following figure. Besides transport they can at least fulfil the same operation as the barge types. The trend in jack-up design is increasing the size and offer larger operating depth. The latest jack-up vessels are equipped with longer legs and larger cranes.

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3.3 Operating depth

Another important specification, next to size, is the operating depth. The figures below show the different operating depths for the concerned jack-ups. The distinction between barges and vessels in the overview of the dimensions was also applied here.

Figure 3-6, Front view of jack-up barges (above) and jack-up vessels (below) range of operating depth

The figures above show that vessel type jack-up units have a maximum operating depth up to twice as large as the operating depth of barge type jack-ups. The newer ship type are built to be more versatile than the barge type jack-ups.

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3.4 Jack-up legs

The legs can differ in number and in shape. For different operation conditions a different type of jack-up leg can be used. For certain seabed types, often soft, an additional footing is necessary at the bottom of the legs to avoid too much leg penetration. The leg differences are described below.

Leg shape

A survey of jack-up specifications shows two leg shapes are commonly used for jack-up units. Long legs, for use in deep waters of more than 90 m [3.1], often used on drilling units, consist of lattice structures. lattice legs often have three chords and bracings between the chords. For shallow water or lower loads, cylindrical shaped legs can be used, which require less deck space and are less complicated than lattice legs to fabricate. Other leg shapes present are square tubes. Typical leg shape designs as shown in figure 3-4.

Figure 3-7, Different leg type sections for jack-ups, from DNV-RP-C104 [5.3]

Number of legs

During design of jack-up units the number of legs is considered. Jack-up drilling rigs, with their triangular shape, usually have three legs (see figure 4-1). Jack-up barges and vessels normally have four legs (figure 4-2) and large jack-up vessels often have six legs (figure 4-3). Special jack-up units may contain even eight legs [4.4].

More legs increase safety due to redundancy. More legs also increase the preload speed. Preloading is simulating the maximum expected load on each leg to ensure the soil has enough strength to bear the loads of the platform. Preloading is normally performed by ballasting the unit with water. With more than three legs, the preloading can be performed by fully loading two legs and slightly raising the remaining legs, without compromising stability. This requires less time than ballasting. However, increasing the number of legs also increases drag of protruding legs during transit and increases the weight of the total unit. The latter has the consequence of reducing the cargo capacity. Furthermore, with more raised legs, the center of gravity is higher and more wind area is present.

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Leg length and operating depth (m)

Leg length differs from 50 to 80 m for barges. For self-elevating vessels this is higher; 70 to 130 m. The difference between operating depth and leg length for barges has an average of 25 m while for the ships this is 40 m. Although the ships can have longer legs, the operating depth does not increase equivalently. The leg shape for barges is usually a cylinder shape, while for the ships it is a lattice. Tables 1 and 2 show that operating depth can be increased by increasing the leg length, but also requires using lattice legs instead of cylinder shape. The type of jacking system shows that cylindrical shaped legs are often driven by hydraulic pin-hole systems. Lattice legs are driven by rack and pinion. This shows that the extra length of the lattice legs is result of the space required by the rack and pinion jacking systems.

Footings

Jack-up legs are often provided with footings. When the jack-up is being installed in relatively soft soil the legs can penetrate several meters. The footings reduce this and provide a stable foundation. A footing can be one large structure, a mat, at the bottom connected to all of the legs. Another common type is a footing structure for each leg separately, known as spud cans. These provide load spreading of the leg when in contact with the soil.

Figure 3-8, Different footings for jack-ups; mat footing (left) and spud can (right). [3.1]

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3.5 Jacking systems

Jacking systems are used to lower and raise the legs and lift and lower the jack-up platform out of the water. For all present jack-ups each leg has its own jacking system. Jacking systems are present in variable configurations. Application of a certain jacking system depends on the capabilities of the jack-up where it is installed. The system determines, amongst others:

The jacking capacity and therefore the cargo capacity The jacking style

The jacking speed

The allowable jacking conditions

The following table presents the different jacking systems and specifications for the selection of jack-ups. Table 3. 1 Name Jacking system Jack Capacity (mT/leg) Jack speed (m/h) Jack stroke (m) Jacking SWH (m)/ period (s) JB104 Pin Hole 400 15 1.5 1.5**

SEA 900, Pauline Pin Hole 900 n/a n/a 1.5**

SAE 2000 JB114 Pin Hole 1250 39 1.7 1.5**

JB117 Pin Hole 2250 15 n/a 1.5**

Sea Jack Wire winch 2500 48 n/a 1.5

Sea Energy Wire winch n/a 42 n/a 1.5**

Nora Rack & Pinion 1800* 27 n/a 2.0

MPI Resolution Hydraulic brace 2850 30 n/a 3.0/18

Seafox 5 Rack & pinion 1750* 60 n/a 2.0/ 6

Pacific Orca Rack & pinion 1400* 72 n/a 2.5

* based on deck capacity. ** based on common practice.

Two common basic jacking systems are: “rack and pinion” and hydraulic “pin and hole” [3.1]. Less common are use of “hydraulic brace”, “pneumatic grippers”, and use of “wire and winch”.

The jacking system can be continuous or discontinuous. Rack and pinion and winch systems are continuous. “Pin in the hole” systems usually are discontinuous because of discrete jacking.

The selection of jack ups shows that the units with cylindrical legs are provided with the pin-hole system while the lattice legs are provided with rack and pinions. For some jack-ups with cylindrical legs the rack and pinion system is used.

The relationship between legs and jacking system depends on the leg length possibly. Longer legs are often lattice legs. The longer the legs the more time it takes to jack. As rack and pinion is usually a quicker jacking method, this will be used for the longer leg types. The jacking systems will be shortly discussed below.

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Rack and pinion

Rack and pinion consists of teeth racks along the legs. In case of lattice legs the rack is applied at one or more chords. Usually each chord is provided with two racks opposite of each other. Two opposed racks are preferable to use over one rack per chord. When one rack is used it is in radial position of the leg. This results in additional horizontal load on the leg, while two opposed racks cancel out each other’s horizontal load [3.1]. In case of cylindrical legs also two racks opposite of each other are used. The jacking system is fixed to the hull, usually fitted in housings. On the inside a set of pinion drives is located.

Figure 3-9, Schematic arrangement of rack and pinion elevating system. [3.3]

The pinion can be driven by hydraulics or by electric motor. Usually more than one set of pinion drives is used above each other.

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Pin hole jacking system

The second common used elevating system is the “pin in the hole” system. Its name literally explains its principle. The legs are provided with holes over longitudinal intervals. The jacking systems are provided with pins. Pointing the pins into the legs and activate hydraulic jacks connected to the pin results in moving the legs. The limited jack stroke is repeated until the barge is elevated to the required height. This jacking method has been transformed from discrete jacking to continuous jacking. This is developed by the company MSC-Gusto [6.4]. It results in a relatively fast and high capacity jacking system.

Figure 3-11, Schematic arrangement pinhole system. [3.3] Hydraulic brace

Less common jacking system, the hydraulic brace, works similar to the “pin hole” principle. It uses hydraulic jacks, but instead of pins through holes in the legs, a brace can be fixed on the exterior of the toothed leg.

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Hydraulic gripper

Similar to the hydraulic brace is the hydraulic gripper. It consists of inflatable rubber grippers on the circumference of a tubular leg. The grippers are connected by a set of single and double working pneumatic jacks. They work in discrete steps as with standard hydraulic jacking systems. This system is mounted on the Titan jack-ups Karlissa A and B [8.4].

Figure 3-13, Schematic arrangement hydraulic grippers. [3.3] Wire and winch

Another less common jacking system mentioned, “wire and winch”, uses wires and winched for lifting and lowering the platform. It is a relatively fast manner for continuous jacking. Disadvantage is the required wire length for large water depth. A wire and winch system is mounted on the jack-up Sea Energy [11.4] mentioned in chapter 2.

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3.6 Environmental parameters

The only environmental parameter that has influence on the impact load of the leg with the seabed is the condition of the seabed itself.

A research was performed to describe objectives and proposed approach for a joint industry study. It investigated the problems associated with jack-ups manoeuvring on and off location [2.2]. Part of the research considered seabed reactions. The considered seabed characteristics were as follows:

Figure 3-14, Soil characteristics according to [2.2].

Where φ is the angle of internal friction and c is the undrained shear strength in kN/m2. The density of both soils was taken as 1 t/m3.

For a certain jack-up barge calculations were performed by use of finite element (FE) analysis and an analytical method. Results are shown below. It shows the difference of the seabed conditions on the impact loads. C is the FE analysis and A the analytical analysis.

Figure 3-15, Axial force in legs for different sea bed, according to [2.2].

The graph shows that only soft clay seabed results in low axial force. Dense sand and hard clay result in similar results except that dense sand results in bouncing effect, as shown in the timespan between 1.5s and 2s.

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4 Standards and Codes

The previous chapters described several jack-ups and their specifications. The information can be used to determine the impact load of the leg with seabed. The next step is to determine how to calculate this. Classification societies provide rules and guidelines for designing and classifying ships. This chapter has as goal to provide rules and calculation methods concerning leg impact.

4.1 International Association of Classification Societies (IACS)

The International Association of Classification Societies (IACS) is the covering institution for the 13 most important classification bureaus worldwide. The current associates of the IACS are:

• American Bureau of Shipping • Bureau Veritas

• China Classification Society • Det Norske Veritas

• Germanischer Lloyd

• Korean Register of Shipping • Lloyd's Register of Shipping • Nippon Kaiji Kyokai

• Registro Italiano Navale

• Russian Maritime Register of Shipping • Indian Register of Shipping

• Croatian Register of Shipping • Polish Register of Shipping

This group of societies was reviewed to determine if and what rules are available for calculating the leg impact during touch down.

The following sections mention the rules of each classification bureau which were found and searched for jack-up leg impact. Behind each name of the associate a reference number is given. Reference information on the specific rules, if available, can be found in reference section 3 at the end of this report.

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4.2 American Bureau of Shipping (ABS) [1.3], [2.3]

• Liftboat Guide:

Part 4, chapter 4: no specific rules about jacking impact

• Mobile Offshore Drilling Unit MODU Guide: chapter 2, section 3. no specific rules found about jacking impact

4.3 Bureau Veritas [3.3]

• NI 534 - Guidance Note for the Classification of Self-Elevating Units: Section 6, par 4:

4.4 China Classification Society [4.3]

• Rule for classification of sea-going steel ships: Does not mention jack-ups/self-elevating platforms.

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4.5 Det Norske Veritas [5.3]

• Recommended practice: DNV-RP-C104; Self-elevating Units, November 2012: section 4.6 Global analysis for the installation and retrieval conditions:

“Normally the impact force may be assumed to be governed by rolling and pitching except for platforms with roll and pitch damping devices.”

“The rotational energy of the jack-up must then be absorbed by the leg and the porting structure at the barge. The impact force may be given as:

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4.6 Germanischer Lloyd [6.3]

Only described by:

Rules for Classification and Construction IV Industrial Services, 6 Offshore Technology, 2 Mobile Offshore Units, section 2, B, 4.3.4; Condition while lowering legs:

“The maximum design motions, water depth, bottom conditions and sea state while lowering legs are to be clearly indicated in the Operating Manual, and the legs are not to be permitted to touch bottom when the site conditions exceed the allowable.”

4.7 Korean Register of Shipping [7.3]

No specific rules on leg impact found in: GUIDANCE FOR MOBILE OFFSHORE DRILLING UNITS

4.8 Lloyd's Register of Shipping [8.3]

Rules on leg strength for installation conditions:

Rules and Regulations for the Classification of Mobile Offshore Units, June 2013. Part 4, Chapter 4, section 3.12: Legs during installation conditions:

“When lowering the legs to the sea bed, the legs are to be designed to withstand the dynamic loads which may be encountered by their unsupported length just prior to touching the sea bed and also to withstand the shock of touching bottom while the unit is afloat and subject to wave motions.”

4.9 Nippon Kaiji Kyokai [9.3]

Rules for the Survey and Construction of Steel Ships / Guidance. Part P MOBILE OFFSHORE DRILLING UNITS AND SPECIAL PURPOSE BARGES. Section 7.4.2:

“Legs are to be designed to withstand the dynamic loads which may be encountered by their unsupported length just prior to touching bottom, and also to withstand the shock of touching seabed while the unit is afloat and subject to wave motions.”

4.10 Registro Italiano Navale [10.3]

Rules for the Classification of Floating Offshore Units at Fixed Locations and Mobile Offshore Drilling Units, Effective from 1 January 2012. Part E, chapter 4, section 2, 7.3.3:

“Legs are to be designed to withstand the dynamic loads which may be encountered by their unsupported length while being lowered to the bottom, and also to withstand the shock of bottom contact due to wave action on the hull.”

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4.11 Russian Maritime Register of Shipping [11.3]

Rules for the Classification, Construction and Equipment of Mobile Offshore Drilling Units and Fixed Offshore Platforms, 2012. Part II Hull, section 3.1.10. Leg pounding against seabed during self-elevating MODU positioning at a site.

“During preloading and pulling out the leg may be subjected to pounding against seabed, caused by the unit rolling.

Pounding force caused by rolling may be determined by the simplified method based on the following: only one leg touches seabed;

the lower end of the leg comes to a stop immediately upon touching seabed; seabed is extremely hard.

The unit rotation energy is absorbed by the leg structure that gives the pounding force P:

The result will depend on wave condition intensity and waterarea depth. The maximum permissible pounding force may be determined on the basis of strength criterion. The maximum permissible amplitude of rolling and pitching during preloading and pulling out shall be as follows:

."

4.12 Indian Register of Shipping [12.3]

Rules and Regulations for the Construction and Classification of Mobile Offshore Drilling Units, January 2013. Chapter 7, section 2.2.5:

“Condition - while lowering to bottom: Legs are to be designed to withstand the dynamic loads which may be encountered by their unsupported length just prior to touching bottom, and also to withstand the shock of touching bottom while the unit is afloat and subject to wave and wind motions.”

4.13 Croatian Register of Shipping

No rules available for Jack-ups/MODU’s/Self-Elevating Vessels

4.14 Polish Register of Shipping

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4.15 Observations from codes and standards

Only three classification bureaus provide calculation methods for the leg impact. The other associates only say that the impact should be considered, but not exactly how. China, Croatia and Poland do not specify any rules considering jack-up units.

Bureau Veritas [3.3] and DNV [5.3] provide similar design recommendations of main structures for self-elevating units. For installation and retrieval of a jack-up unit they present a simplified method to determine impact force on the legs due to roll or pitch motion. Heave motion is not included in the analysis. The motion values can be determined by motion analysis software for a certain barge and its loading condition. The method is based on three conservative assumptions:

• Only one leg touches the bottom.

• The lower end of the leg is stopped immediately when the leg touches the bottom. • The bottom is infinitely rigid. (worst case).

The principle of the calculation is that the kinetic energy of the structure at impact is equal to work of the reaction force at the bottom of the leg.

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5 Load impact calculation

The previous chapters provide data and calculation methods which can be used to determine the leg impact load. The information was used to perform a simplified load impact calculation for this report. The goal was to determine what order of magnitude the loads are. The calculation can be found in Appendix A.

5.1 Method

The calculation is according to the DNV recommended practice mentioned in chapter 4. From all the rules this provided the method with most detail for calculation. First the load was calculated for a non-damped impact. This was done for the selection of jack-up barges and vessels mentioned in chapter 2. In addition, a calculation was performed to determine the influence of a shock absorber.

By combining the non-damped impact load with a certain amount of damping stroke the damping energy was found. Assumed is that this amount of energy is equal to the kinetic energy of the jack-up in roll motion. The allowable kinetic energy with use of a shock absorber was compared to kinetic energy from motion with higher roll angles. The higher roll angle was a result of increased wave height. That is the result of the calculation. It shows that increased wave height results in allowable loads when a shock absorber is used on the leg.

5.2 Assumptions

As is described in the calculation of DNV three main assumptions are made: • Only one leg touches the bottom.

• The lower end of the leg is stopped immediately when the leg touches the bottom. • The bottom is infinitely rigid. (Worst case).

Roll motion

Only roll motion was considered for this case as loads for this motion are usually governing over pitch motion. Roll angles are determined by comparing the width of a ship and its allowable significant wave height for jacking, called SHW (m). Roll periods, T(s), are based on allowable jacking conditions as specified in the spec-sheets for the jack-ups. As for most jack-ups no information was available, a simple assumption was done based on the size of the vessel.

Significant wave height

Research was performed on severity on several locations in the North-Sea [3.2]. It supplies statistics about monthly significant wave heights, SWH, between the years 1974 and 1995. This information was used to determine a mean significant wave height over several years. The chosen location was Forties oil field. This showed data covering a possible working location for the considered jack-ups in this research. The data is shown below.

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In the selection of jack-ups half of the group can only be installed with a maximum SWH of 1.5 m. That means they could only operate between May and August. To improve the possible operating period assumed is that an addition of 1 m to the SWH would be preferable.

Exact data necessary for the calculation was not available for all jack-ups. Therefore, instead of exact impact loads, the results only show the order of magnitude and the influence of adding a shock absorber.

5.3 Calculation results

The impact calculation resulted in loads at the bottom of the jack-up leg. Vertical loads as well as horizontal loads were calculated.

The first part of the calculation was based on standard conditions. No shock absorber was applied and the normal significant wave heigth was used as input.

Standard conditions

Compared to the vertical load, the horizontal load is low. This means that axial force is governing over shear force. The horizontal load diagram below shows large difference between the loads from three vessels: Nora, the Seafox 5 and the Pacific Orca and the others. The main difference between the vessels is that the ones with high horizontal load have long lattice legs. While the others have tubular legs. In the calculation the ratio between lateral and axial stiffness is much smaller than the lattice legs. This could cause the difference in horizontal loads.

Figure 5-2, Horizontal impact loads.

The vertical impact loads show expected results. The larger the ship, the larger the impact will be.

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Besides the impact load also the static load was calculated. The static load was based on the maximum ships weight divided over half the number of legs of each jack-up. Assumed is that during preloading of a jack-up all the weight of the ship is supported by half the number of legs. The ratio between the dynamic load and static load is considered as a dynamic factor. It is presented below.

Figure 5-4, Dynamic factor for vertical impact loads.

The graph shows that the smaller and barge type jack-ups have higher dynamic factors than the largers jack-ups. The vessel type jack-ups have similar factors.

Effect of shock absorber

The following results show the effect of adding a shock absorber at the bottom of the leg. The shock absorber was assumed to provide constant deceleration. The stroke of the absorber was equal for all jack-ups. Iteratively it was determined that a stroke of 0.2 m provided enough energy dissipation to reduce the load significantly.

The results show a similar course to the results of the horizontal loads without shock absorber. Again the long and lattice legs are distinct. The shock absorber has less effect on the lattice legs. Although the effect is less than for tubular legs, it stilldecreases the load to approximately 30 %.

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Increasing significant wave height

The effect of adding a shock absorber is that the allowable kinetic energy, developed by the jack-up during roll motion, can be increased. The impact load was calculated for the wave conditions according to the assumptions in section 5.2. The developed kinetic energy was compared to the allowable kinetic energy when a shock absorber is used. The results are presented in the graph below.

Figure 5-6, Ratio kinetic energy to allowable kinetic energy.

The graph shows that even with an increase of 1 m to the allowable significant wave height the shock absorber with a stroke of 0.2 m is sufficient. Loads are then at 10 to 50 % of what is allowed.

5.4 Calculation conclusion

For the barges it is clear there is an improvement possible. A shock absorber stroke of 0.2 m shows much higher allowable significant wave height. The calculation was performed for hard seabed conditions. A shock absorber for soft seabed conditions might not be necessary. That can be concluded when the assumption is made that soft sea bed acts as a similar shock absorber used in this calculation, and the jack-up legs penetrate at least 0.2 m during impact.

The results for the vessels with lattice are different from the tubular leg jack-ups. The impact loads are higher and the reduction due to shock absorber is less. Possibly the assumptions made in the calculation need to be improved. For exact values of impact loads a more detailed approach is necessary for each jack-up. Especially barge motion, leg dimensions and connection stiffness between legs and hull is required to get useful results.

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6 Patents for jack-up leg shock absorber

Jack-up leg impact has been a problem since several decades. Since the 1970s patented designs were made for a device which should reduce this impact. The following sections describe nine patented designs for jack-up leg shock absorbers. An abstract is given from each patent with figures and followed by some keywords important for that particular design. Some patents are provided with detailed designs, while others only describe the concept.

The designs have a wide range of approach of the problem. Some devices are mounted at the bottom of the leg while others absorb shocks at location of the jacking houses. Some designs use compression of fluids and others use compression of elastic material.

The designs can be distinguished in three levels:

1. The first level shows difference in location of the device. Two options are possible: at leg bottom, and at jack housing.

2. The second level differs in jacking type. For leg bottom devices no difference is made for this, as the jacking system does not affect the leg bottom. A difference is recognized for several leg types. However, all the considered designs for leg bottom can be adapted to tubular and lattice legs.

3. The third level shows difference in shock absorbing. This is often compression of gas or compression of elastic members.

Al the possibilities for each level are shown in the following diagram.

Figure 6-1, Design differences for patented impact reducers.

The diagram shows that more or less half of designs are focused on the leg bottom and the other half on jacking systems. Furthermore, for the devices at the jacking system the focus is on the rack and pinion. An explanation could be that rack and pinion was mostly used at time of the inventions. Another explanation could be that rack and pinion systems are more vulnerable than hydraulic pin hole jacking.

Although there exist several patented designs for shock absorbing devices for jack-up legs, no information was found about actual applied devices on the selection of jack-ups.

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6.1 Fast jack lift boat shock absorbing jacking system

Date of patent: June 10, 2010. Juan, Lizarraga J. [1.5]

Abstract:

A shock absorbing device and system for the jacking system of a liftboat with air or cylinder chambers and manual and pressure activated control valves connecting the shock absorbing system to the hydraulic manifold of the jacking system allowing isolation or activation of the shock absorbing system. The shock absorbing system can be retrofitted to an existing jacking system. The shock absorbing device and system cushions the vessels impact with the seabed while jacking in rough seas, reducing structural fatigue and damage to the hull and jacking system. In addition, the shock absorbing device and system can broaden the liftboat's operational envelope and allow it to operate in rougher conditions without damage to the vessel.

Keywords:

Normal limit, 4 to 5 ft. sea, wave period, 6 to 10 sec. Compressible gas

Addition of air chamber to jacking system

More complex: isolate gas from fluid in jacking system Valve

Easily retrofitted

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6.2 Load equalizing and shock absorber system for off-shore

drilling rigs

Date of patent: Oct. 19, 1976. Levingston Shipbuilding Company (Orange, TX). [2.5] Abstract:

A load equalizing system for a jack-up leg on a mobile off-shore drilling platform barge, wherein the leg has a plurality of rigidly interconnected generally parallel chords. Each of the chords is connected to the barge by a rack and pinion type jack assembly arranged for raising and lowering the leg relative to the platform and wherein lateral deflection of the leg by wave action or the like causes the chords to move vertically unequally relative to the barge. The improvement comprises a pair of hydraulic cylinder assemblies mounted between each of the jack assemblies and the barge, with the working axes thereof generally parallel with the longitudinal axis of the leg. Each cylinder assembly has a cylinder piston mounted therein and a piston rod connected to the piston and extending longitudinally therefrom. Each of the hydraulic cylinder assemblies has one end connected to the barge and the other end arranged for vertical bearing against the top of one of the jack assemblies. Conduit means are provided for interconnecting the fluid containing ends of the cylinders for permitting hydraulic fluid to be transmitted there between. Means are also provided for charging hydraulic cylinders with at least sufficient hydraulic fluid to maintain the piston rods at about mid-stroke, whereby unequal vertical loads on the chords are reduced by equalization of hydraulic pressure in the cylinders through the conduit means. In the shock absorbing mode, the system includes a plurality of accumulators, each of which is arranged for containing a quantity of gas. Second conduit means are arranged for interconnecting the cylinders with the accumulators. Means are also provided for pressurizing the accumulators with gas whereby shock force exerted on the leg, as would be caused by heaving of the barge during raising and lowering of the leg, are absorbed by displacement of hydraulic fluid from the cylinder to the accumulators and compression of the gas therein.

Keywords:

Equalizer mode Shock absorbing mode

Plurality of accumulators containing quantity of gas

Applicable to leg with at least two rigidly interconnected generally parallel chords Chords connected to the platform by jacking assembly

Equalizing vertical unequal movement due to lateral deflection of chords Shock absorbing by compression of gas upper side of jacking

Particular utility for jack assemblies of rack and pinion type Shock pads

Hydraulic cylinder

Sump tank containing adequate supply of hydraulic fluid

Piston hydraulic cylinder diameter of order 0.5 m and stroke of 0.3 m Working pressure order of 350 bar

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6.3 Offshore drilling platform with vertically movable legs

Date of patent: May 23, 1978.Verschure, Pietrus J. M. (17 Prinses Marykestraat, Amsterdam, NL). [3.5] Abstract:

An offshore drilling platform with vertically movable legs comprises a buoyant body and a plurality of legs for supporting the body on the sea floor at an elevation above the water level. To permit floating the body for transportation, the legs are selectively vertically movable relative to the body; and in the present invention, this is effected by providing vertical racks on the legs that engage with power-driven pinions carried by the body. The pinion drive has two free-wheel devices, one which free wheels in one direction, and the other which free wheels in the other direction. Each free wheel is clutch connected to the pinion drive, so that when the legs are at an intermediate stage of being raised or lowered, and the platform is at about water level and the bottoms of the legs engage the sea floor, the appropriate free wheel is utilized to let the wave action speed the movement of the legs and platform relative to each other in the same direction that they are being more slowly driven by the pinion drive. In this way, the pounding of the bottoms of the legs on the sea floor is greatly diminished. Also, a system of slides and resilient connections between the legs and the platform absorbs the shocks and reduces the stresses between these elements.

Keywords:

Two free wheel devices

System of slides and resilient connections Free wheel in the form of one way clutch Prevents platform from falling

Worms

Elastic block in housing

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6.4 Shock absorbing structure and method for off shore jack-up

rigs

Date of patent: Apr. 1, 1980. Goldman, Jerome L. (225 Baronne St., New Orleans, LA, 70130).

[4.5]

Abstract:

A new and improved shock absorbing structure and method for use on a jack-up off-shore drilling rig is disclosed. The shock absorbing structure is designed for mounting on the bottom of each existing leg of the drilling rig and comprises a novel bottom member fixedly attached to each leg with the bottom member having a piston member positioned in the central portion thereof. The piston member is associated with at least one compression member formed around the piston member with the compression member being designed to absorb shock during a shock absorbing condition on the drilling rig leg. The compression member is fixedly attached to the bottom member by retaining means thereby making the structure self-contained.

Also disclosed is a new and novel method utilizing the shock absorbing structure on a jack-up off-shore drilling rig.

Keywords:

Designed for drilling rig

Fixedly attached to bottom of each existing leg Piston member

Compression member, roughly 4 meter diameter Relatively simple shock absorbing structure Minimum of moving parts

Relatively maintenance free

Solid/partially solid/web construction bottom member Rubber bumpers

Spool like compression member, can be substituted by hydraulic shock absorbing device Horizontal retaining of upper end piston by four leg spider member with central hub

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6.5 Device for absorbing impacts during lowering or lifting

respectively of the support legs of an artificial island

Date of patent: Sep. 18, 1984. RSV-Gusto Engineering B.V. (NL). Boon, Bart (Schiedam, NL). [5.5] Abstract:

Device for absorbing impacts during lowering or lifting respectively of the support legs (1) of an artificial island comprising a pontoon and legs that are movable and lockable with respect to said pontoon further comprising the fact that the legs (1) at or near their lower end are surrounded by an apron (3) out of flexible material that is fixed to the circumference of each leg and extends beyond the lower end of said leg.

Keywords:

Designed for legs of artificial island

Lower end of legs surrounded by apron, extends beyond lower end Flexible material

Defines a water-filled room

Hydraulic absorption in both directions Sucked against the ground

Horizontal movement absorbed also Apron of cylindrical/conical shape

Weights on lower end stretch and strengthens

Apron of sieve material, promoting uniform flow in or out

When manufactured of impervious material, provided with openings To use in more unfavorable conditions

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6.6 Load transfer and monitoring system for use with jack-up

barges

Date of patent: Nov.13, 1984. Ateliers, Et Chantiers De Bretagne Acb (FR). [6.5] Abstract:

A load transfer apparatus for jack-up barges provides a barge and at least three legs movably attached to the barge with a jacking mechanism associated respectively with each of the legs for vertically moving the legs with respect to the barge. A hydraulic pad is associated with each of the jacking mechanism and is placed between the jacking mechanism and the barge, forming a load transfer and load monitoring interface between the jacking mechanism and the barge. The pad includes preferably a hollow inflatable steel reinforced rubber pad which is pressurized during operation using suitable hydraulic fluid. The apparatus reduces impact load on the platform structure when the legs first touch bottom and might also be used to pre-load the legs using the hydraulic pads instead of ballast. The apparatus can be additionally used to monitor the load carried by each leg and to balance the loads among the legs, as well as to dampen vibrations.

Keywords:

Hydraulic pad

Between jacking mechanism and barge Hollow inflatable steel reinforced rubber pad Pressurized using hydraulic fluid

Additional load monitoring, load balancing, dampen vibrations Loading configuration statically determinate

Short stroke jacking capacity

Preloading without using ballast or adding weight, reducing ballast space requirements Flexible curtain, to prevent dust entering assembly

Filled with core, to prevent side walls to be crushed. (use of glass beads) Valves

Preload force of f.e. 120 tons

Gas compression participates as shock absorber

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6.7 Shock absorber and method for offshore jack-up rigs

Date of patent: Nov.6, 1990. Goldman, Jerome L. (935 Gravier St., Ste. 2100, New Orleans, LA, 70112). [7.5] Abstract:

A new and improved shock absorber mechanism and method for use on the leg structure of a jack-up offshore drilling rig is disclosed. The shock absorbing mechanism is designed to be mounted on the bottom of each existing leg of a drilling rig and comprises a pointed piston member which is positioned on the bottom of the leg structure, wherein the piston member projects downward through the can/footing of the rig leg and is held in place by a resilient tension member which is designed to absorb shock forces during vertical/axial impact of the leg structure when contact is made with the ocean floor.

Keywords:

Made for vertical impact only Simple shock absorbing device Quick operation and maintenance Can be used in rough ocean conditions Sliding vertical manner

Designed to limit any horizontal forces

Piston cuts through ocean floor, creating soft surface

Tension member possibly made of nylon chords, which is not expensive.

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6.8 Device for the integrated suspension and manipulation of

the legs of a jack-up platform

Date of patent: April 7, 1992. Technip, Geoproduction (Paris La Defense, FR).[8.5] Abstract:

A device for the integrated suspension and manipulation of legs supporting a jack-up oil platform having a hull mounted displaceable on the legs by drive mechanisms having at least two opposite units each formed by a motor associated with at least one speed reducer driving an output gear co-operating with opposite racks mounted on at least part of the length of the legs. The opposite units of each drive mechanism are mounted in articulated fashion on a structure supporting them via at least one bearing allowing a determined angular deflection of the units and of each corresponding output gear. The motor and the speed reducer of each opposite unit are housed in a member for absorbing energy, used, in particular, at the moment of the placement of the legs on the sea bed and for limiting the stresses due to the flexure of the legs under the action of swells and the wind.

Keywords:

Housing member for absorbing energy Twisting sleeve

Intermediate collar Adjustable tie Shock damping

Flexibility between legs Compact, low bulk

Without endangering personnel

Large damping travel, torsional turns not limited Equalize torques between speed reducers

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6.9 Device for sitting on the seabed for self-raising sea vessels

Date of patent: 05.03.2010. Saipem S.p.A. (Via Martiri di Cefalonia, 67, 20097 San Donato Milanese (Milano), IT). [9.5]

Abstract:

Device for sitting on the seabed for sea vessels (1) equipped with self-raising support legs (4), wherein each leg comprises:

a vertical structural element capable of lowering and raising;

a device for absorbing collisions and for centering essentially consisting of:

i. a coaxial telescopic means (11) fixedly connected to said structural element through a hinged elastic means (13);

ii. a support foot comprising a semi-spherical joint (14) connected to the telescopic element; and iii. a coaxial centering pin (15) fixedly connected to the support foot through a hinged elastic means. Keywords:

Coaxial telescopic means fixedly connected through hinged elastic means Support foot of semispherical joint

Coaxial centering pin

Rack jacking and hydraulic jacking system

Elastic means of jacks or oil-dynamic pistons connected to accumulators by mechanical springs or rubber elements

Resting system initiates at f.e. 100 to 150 cm leg bottom to seabed distance when leg lowering is stopped

Cardan joints

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7 Conclusion

The goal of this research was to survey the operational window of installing a jack-up unit. The focus was on the leg impact during touch down. This research resulted in an overview of what information is necessary to design a device to reduce the leg impact. The impact of the leg during touch down depends on the vessel specifications and environmental parameters.

Size and shape

Jack-ups are present in a large variety of size and shape. Two main groups were distinguished: flat barge type and jack-ups with shape of a vessel. The barge type is often not self-propelled while the vessel type often is self-propelled ad equipped with dynamic positioning system.

The length of barge types ranges from 30 to 100 m. Ship type has range in length of 90 to 160 m. The mass of the ships was based on jacking capacities. It was determined in the leg impact calculation.

Legs

Several leg types are used on jack-ups; cylindrical legs, square tubular legs, and lattice legs. The lattice legs were often used for larger water depth. The barge type jack-ups are usually built for shallower water, up to 45 m, while the ship type is used in water to 80 m depth. The length of the leg determines the operating depth which is important in the calculation of the impact load.

Jacking system

Jacking of the units can be achieved in several ways. Two types are most common: rack and pinion and pin-hole. The first is by use of hydraulic jacks and pins the legs. The second uses electric motors driving the pinion over racks along the legs. The jacking system has lower influence on the impact load but determines the possibility of a leg impact reducing device.

Environmental conditions

Maximum operating conditions are prescribed in specifications sheets for each vessel. It often concerns the maximum significant wave height. The corresponding wave period is often not provided but is important for determining the impact load. Another important parameter which is not prescribed is the seabed condition. Soft clay results in much lower reaction loads than dense sand and hard clay. Calculation

Some classification societies provide calculation method for the impact load. Of all the members the International Association of Classification Societies (IACS) only three provide a method. They all provide a more or less same method. There some difference in presentation, but the principles are the same. The three societies are: Bureau Veritas, Det Norske Veritas and Russian Maritime Register of Shipping.

The DNV calculation method was used to perform calculations to determine leg impact for the range of jack-ups concerned in this research. Impact loads were calculated and compared for three situations. The first was according to prescribed allowable operating conditions. The second was calculated to determine the effect of a shock absorber. And the third calculation was to compare higher wave conditions, which represented a larger weather window, with allowable values when a shock absorber was used. The impact loads for lattice legs were different from tubular legs. Loads were higher and the shock absorber had less effect than for tubular legs. The conclusion for all jack-ups was that a small damping stroke resulted in large allowable wave conditions.

The calculation was simplified on vessel motion and leg specifications. This means that for accurate load values more detailed information should be used.

Patents for jack-up leg shock absorbers

In the past several patented designs were made to reduce the leg impact load during installation of jack-ups. Designs consider shock damping at location of the jack house or at the bottom of a jack-up leg. Design for the leg bottom often use compressive members, while designs for jack housing often

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8 References

8.1 General literature

[1.1] Swales, John M. and Christine B. Feak (1994) Academic Writing for Graduate Students: A Course for Nonnative Speakers of English. Michigan. The University of Michigan Press [ISBN 0472082639]

[2.1] Elling, R. e.a. (2005), Rapportagetechniek, schrijven voor lezers met weinig tijd. Groningen: Wolters-Noordhoff. 3e herz. dr. (boekhandel) [ISBN 9001291384]

[3.1] Dr Jose H. Vazquez (BASS) e.a. (2005), Jack up Units, A technical primer for the offshore industry professional [E-Book]

[4.1] Tetra Tech EC, Inc. (February 2010) Port and Infrastructure Analysis for Offshore Wind Energy Development

[5.1] R.C. Hibbeler (2011) Mechanics of Materials, 8th Edition [6.1] http://www.ultramarine.com/g_info/moses/moses.htm

[7.1] Kurt Thomsen (2012) Offshore Wind; A Comprehensive Guide to Successful Offshore Wind Farm Installation; Chapter Twelve – Vessels and Transport to Offshore Installations. [8.1] Pierre Le Tirant, Christian Pérol – 1993, Stability and Operation of Jack-ups.

8.2 Research papers

[1.2] X.M. Tan, J. Li, C. Lu. Structural behaviour prediction for jack-up units during jacking operations. 2003.

[2.2] I. A. A. Smith, T. C. Lewis, B. L. Miller, P. S. K. Lai, Limiting Motions for Jack-Ups Moving onto Location, 1995.

[3.2] P.J. Owrid, Notrth Sea severity assessment, 1998.

8.3 Standards and Codes

[1.3] American Bureau of Shipping, Mobile Offshore Drilling Unit (MODU) Guide.

[2.3] American Bureau of Shipping, Guide for building and classing liftboats, January 2009. [3.3] Bureau Veritas, Guidance Note for the Classification of Self-Elevating Units,

September 2010, Guidance Note NI 534 DT R00 E.

[4.3] China Classification Society, Rules for classification of sea-going steel ships, 2006. [5.3] Det Norske Veritas AS (November 2012), Recommended Practice – Self-elevating

units: DNV-RP-C104.

[6.3] Germanischer Lloyd, Rules for Classification and Construction IV Industrial Services, 6 Offshore Technology, 2 Mobile Offshore Units, Edition 2007.

[7.3] Korean Register of Shipping, Guidance for Mobile Offshore Drilling Units, 2013. [8.3] Lloyd’s Register, Rules and Regulations for the Classification of Mobile Offshore Units,

June 2013.

[9.3] Nippon Kaiji Kyokai, Rules for the survey and construction of steel ships, Part P Mobile offshore drilling ujnits and special purpose barges, July 2009.

[10.3] Registro Italiano Navale, Rules for the Classification Units at Fixed Locations Drilling Units,January 2012.

[11.3] Russian Maritime Register of Shipping, Rules for the classification, construction and equipment of mobile offshore drilling units and fixed offshore platforms, 2011.

[12.3] Indian Register of Shipping, Rules and Regulations forthe Construction and Classification of Mobile Offshore Drilling Units, January 2013.

Operational window for touchdown of jack-up barges-Werkbaarheid voor plaatsing van jack-ups

Specialization:

Transport Engineering and Logistics

Report number: 2013.TEL.7807

Title:

Operational window for

touchdown of jack-up barges

Author:

J. van Essen

Operational window for touchdown of jack-up barges

Summary

List of symbols

θ

[º]

T

[s]

List of abbreviations

Contents

1

Introduction

1.1

General introduction

1.2

Goal of the research

1.3

Report structure

2

Jack-up specifications

3

Parameters and range

3.1

Hull shapes

3.2

Sizes

3.3

Operating depth

3.4

Jack-up legs

3.5

Jacking systems

3.6

Environmental parameters

4

Standards and Codes

4.1

International Association of Classification Societies (IACS)

4.2

American Bureau of Shipping (ABS) [1.3], [2.3]

4.3

Bureau Veritas [3.3]

4.4

China Classification Society [4.3]

4.5

Det Norske Veritas [5.3]

4.6

Germanischer Lloyd [6.3]

4.7

Korean Register of Shipping [7.3]

4.8

Lloyd's Register of Shipping [8.3]

4.9

Nippon Kaiji Kyokai [9.3]

4.10

Registro Italiano Navale [10.3]

4.11

Russian Maritime Register of Shipping [11.3]

4.12

Indian Register of Shipping [12.3]

4.13

Croatian Register of Shipping

4.14

Polish Register of Shipping

4.15

Observations from codes and standards

5

Load impact calculation

5.1

Method

5.2

Assumptions