Transocean offshore operation 2

OFFSHORE OPERATIONS COURSE
SECTION 2
MOORING AND ANCHOR HANDLING
TABLE OF CONTENTS
Training to be FIRST
1
SECTION 2
TABLE OF CONTENTS MOORING
CHAPTER 1 INTRODUCTION 4
1.1 TYPES OF DRILLING RIGS 4
1.2 CRITERIA FOR THE DESIGN OF AN ANCHOR MOORING SYSTEM 5
CHAPTER 2 SOIL 9
2.1 SOIL CLASSIFICATION AND SOIL MECHANICS 9
2.1.1 SOIL TYPE 9
2.1.2 SOIL STRENGTH 10
CHAPTER 3 ANCHORS 11
3.1 NOMENCLATURE OF ANCHORS 11
3.2 TYPES OF ANCHORS 13
3.3 CRITERIA FOR A GOOD ANCHOR DESIGN 15
3.4 FLUKE ANGLE 19
3.5 PROOF LOAD AND STRENGTH OF ANCHORS 20
3.6 MOORING SYSTEM ANALYSIS WITH THE SEAMOOR SYSTEM. 20
CHAPTER 4 MOORING CHAIN AND WIRE 22
4.1 CHAIN OR WIRE 22
4.2 ADVANTAGES OF CHAIN COMPARED TO WIRE 22
4.3 CHAIN AND WIRE CONSTRUCTION 23
4.3.1 CHAIN CONSTRUCTION 23
4.3.2 CHAIN GRADES AND STANDARDS BY CLASS SOCIETIES 25
4.3.3 CHAIN SIZES 25
4.3.4 CHAIN INSPECTION 26
4.3.5 ANCHOR WIRE 27
4.3.6 MAXIMUM SAFE WORKING LOAD AND DIAMETER. 27
4.3.7 CONSTRUCTION, LAY, GRADE OF STEEL, COATING 27
CHAPTER 5 THE MOORING SYSTEM AND ATTACHMENTS 32
5.1 LAY-OUT DIAGRAM OF MOORING SYSTEM 32
5.2 ANCHOR PATTERNS 32
5.3 THE CATENARY SYSTEM 35
5.4 ATTACHMENTS AND CONNECTIONS 36

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TABLE OF CONTENTS
2
CHAPTER 6 ANCHOR RUNNING AND RETRIEVING PROCEDURES 48
6.1 SELECTION OF ANCHOR HANDLING VESSELS 48
6.2 PRE-MOVE PREPARATION AND PLANNING 51
6.3 PRE-MOVE MEETING 52
6.4 INFORMATION FOR AHT CAPTAINS 54
6.5 ANCHOR HANDLING CHECK LIST 54
6.6 POSITIONING SYSTEMS 57
6.7 NOTES ON APPROACHING AND LEAVING THE LOCATION 57
6.8 WEATHER CRITERIA 59
6.9 APPROACHING THE LOCATION AND RUNNING ANCHORS 60
6.10 RETRIEVING ANCHORS AND DEPARTING LOCATION 69
6.11 SOAKING AND PENETRATION OF THE ANCHOR 74
6.12 TEST TENSION AND OPERATION TENSION PROCEDURES 75
6.13 THE HOLDING POWER OF THE CHAIN OR WIRE. 78
6.14 STORM CONDITION 79
6.15 TEST TESNION PROCEDURES 79
6.16 ANCHOR HOLDING PROBLEMS 79
6.17 RUNNING PIGGY-BACK ANCHORS 82
6.18 FISHING AND GRAPPLING OPERATIONS 84
6.19 ANCHOR WINCHES. 86
CHAPTER 7 DEEPWATER MOORING SYSTEM DEVELOPMENTS 91
7.1 INTRODUCTION 91
7.2 THE PRELAID MOORING SYSTEM. 92
7.3 ANCHORS FOR VERTICAL LOAD SYSTEM (FIG 7.7) 97
7.4 DEAWEIGTH ANCHOR. 97
7.5 PILE ANCHOR. 98
7.6 SUCTION EMBEDDED ANCHORS (SEAS) 98
7.7 VERTICAL LOADED EMBEDDED ANCHORS (VLAS) 100
7.8 SUCTION EMBEDDED PLATE ANCHORS.(SEPLAS) 105
7.9 SYNTHETIC ROPES FOR DEEPWATER MOORING. 105
CHAPTER 8 MOORING SYSTEM CERTIFICATION AND INSPECTION 108
8.1 CERTIFICATION OF ANCHOR CHAIN 108
8.2 TYPE AND SCHEDULE OF INSPECTION 108
8.3 INSPECTION LOCATION 109
8.4 ANCHOR CHAIN INSPECTION (FIG.8.3) 111
8.5 ANCHOR WIRE INSPECTION 112
CHAPTER 9 APPENDIX SECTION II –MOORING 115
9.1 ANCHOR CHAIN PROOF AND BREAKING LOAD TABLES SI UNITS. 115

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TABLE OF CONTENTS
3
9.2 ANCHOR CHAIN PROOF AND BREAKING LOAD TABLES INCH/POUND
UNITS. 115
9.3 STEVPRIS MK5 DRAWINGS, WEIGHT, AND DIMENSION. 115
9.4 VRYHOF STEVPRIS MK5ANCHOR UHC CHART 115
9.5 VRYHOF STEVPRIS MK5 ANCHOR DRAWINGS, WEIGHT AND DIMENSIONS
115
9.6 VRYHOF STEVMANTA ANCHOR UPC 115
9.7 BRUCE FFTS MK4 ANCHOR DRAWINGS, WEIGHT, AND DIMENSIONS 115
9.8 BRUCE FFTS MK4 ANCHOR HOLDING CAPACITY CHART. 115

SECTION 2
CHAPTER 1 INRODUCTION
4
CHAPTER 1 INTRODUCTION
1.1 TYPES OF DRILLING RIGS
The development to maintain Mobile Offshore Drilling (Units MODU’s) in a fixed position
started with the use of drilling tenders, which were moored with a spread anchor mooring
system alongside a fixed drilling platform.
The need and desire to be able to drill in deeper water and to move between drilling locations
generated various designs of Mobile Offshore Drilling Units (MODU`s):
a) Submersibles.
Columns with flotation hulls support the deck with the drilling equipment and
accommodation. The submersible maintains it position by ballasting down until the lower
hulls rest on the seabed.
To maintain position these units do not need a spread anchor mooring system.
Maximum of water depth 100 Ft.
b) The Independent Leg and Mat-Supported Jack Ups.
A watertight floating barge type hull fitted with cylindrical or truss type legs with a jacking
arrangement. The legs are connected to spud cans or a mat type support. In the drilling
operation mode the hull is jacked up to a save distance above the water level. Some JU's are
self propelled or have propulsion assistance.
As for the submersibles the JU's do not need a spread anchor mooring system.
Maximum water depth: 450 Ft
c) The Semi-Submersible. (Column Stabilised Drilling Units)
These units consist of lower displacement hulls (pontoons) with columns to support the
upper deck with the drilling equipment and accommodation. The Semi-Submersible can
ballast up or down from operating draft to towing /moving draft and visa versa. A few
designs can be used as Submersibles. Some Semi-Submersibles are self-propelled with a
DP System or have propulsion assistance.
To maintain position in the floating drilling mode the Semi-Submersible needs a spread
anchor mooring or a Dynamic Positioning (DP) system.
Maximum water depth: Anchored: 8000 ft.
DP system: No limits
d) Drilling vessels
Drilling vessels are mono hull ship- or barge shaped drilling units. Drilling vessels always
operate in the floating condition. Swamp barges are not classed as drilling vessels.
Drilling vessels maintain position with a spread mooring system or with a Dynamic
Position (DP) system.
Maximum water depth: Anchored: 8000 ft
DP system: No limits

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5
Fig 1.1 shows a drawing from Aker Marine the maximum water depth for various types of
mooring systems in operation and developments for future taut leg systems.
The section Mooring and Anchor Handling discusses the concept of the anchor mooring
systems for Semi-Submersibles and Drilling Vessels
1.2 CRITERIA FOR THE DESIGN OF AN ANCHOR MOORING SYSTEM
a) Forces
Wind, wave, and current produce loads on the rig. These loads are transferred to the mooring
system.
To perform a mooring analysis it is necessary to know the maximum combined forces caused
by the environmental loads. In the mooring analysis all forces work in the same direction at the
same time. The combined total mooring force generated by wind, wave, and current depends
on:
1) The size and weight of the drilling unit.
2) The maximum wind speed
3) The maximum combined wave height and period
4) The maximum current force
5) The water depth
6) The height above the water level
The forces on the anchor system generate two types of loads:
1) The Quasi-Static Load (QSL). The combined load of wind, swell, current and the
frequency of the system. The system moves with a low frequency of 140 to 200
seconds. The analysis for the QSL is used most often to evaluate the mooring for
a specific location. This analysis assesses the capabilities of the system when
acted on upon by environmental loads.
2) The Total Dynamic Load (TDL). In addition to the QSL, a high frequency load
occurs with a period of 10 to 14 seconds caused by the individual action of the
wave and swell forces. The roll, pitch, and heave of the drilling unit and the
movement of the anchor chain through the water are responsible for the shock
loads in the mooring system. The TDL analysis contains line dynamics completed
in the frequency domain. This analysis is complicated and therefore subcontracted
To calculate the required Ultimate Holding Capacity (UHC) of an anchor the designer adds a
safety factor of 1.5 to 2 to the QSL and TDL. A major factor contributing to the UHC of an
anchor is the soil mobilised by the anchor or with other words the penetration. To design an
efficient modern anchor, the manufacturer needs to know the principles of soil mechanics (See
Fig 1.2)

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6
b) Selection of Equipment
With the results from the calculation of the forces, the designer selects the mooring equipment
for a specific rig and the operations limits such as:
1) To use anchor chain or anchor wire or a combination of both
2) The size and type of anchor
3) The amount of anchors to that will be installed or deployed
4) The type and capacity of the anchor winches
Apart from the weather criteria and the size and type of the rig, the selection of the equipment
depends too on:
1) The maximum operation water depth
2) The type of soil
c) The Efficiency and Holding Power of an Anchor
Because there are many types of anchors available, each with their own characteristics, we have
to know the efficiency and holding power of an anchor.
One way of defining the efficiency of an anchor is:
The efficiency as quoted by the manufacturer "the holding power" in good holding soil should
be at least 12. Modern designed anchors claim much higher values of 20 and more.
Holding power depends on:
1) The type and weight of the anchor
2) The type of soil
3) The friction of the soil along the fraction lines and the fluke area
4) The final penetration including the friction of the sub-soil part of the
anchor line
Because the soil can have a detrimental effect on the holding power, we should always be
cautious with the manufacturer's specification. On rock or coral the holding power of an anchor
will be close to the anchor weight.
weightAnchor
powerHolding
efficiencyAnchor ====

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7
Fig. 1.1.Maximum water depth for various type of mooring system
(With courtesy to Aker Marine)

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8
d) Rig Motions
The rig motions for floating MODU’s are the surge, sway, heave, roll, pitch, and jaw (Fig. 1.3)
The motion characteristics for each rig are different and all motions i.e. surge, sway, heave,
roll, pitch and jaw induce forces on the anchor system.
Fig. 1.2 Penetration and soil (Courtesy of Vryhof Anchors)
Fig. 1.3 Rig motions
heave
pitch
roll
sway
surge
yaw

SECTION 2
CHAPTER 2 SOIL
9
CHAPTER 2 SOIL
2.1 SOIL CLASSIFICATION AND SOIL MECHANICS
The theory on the strength and characteristics of soils discussed in the JU section applies too to
the behaviour of anchors. To predict the penetration of an anchor we need to know the type of
soil. The penetration of an anchor determines the Ultimate Holding Power.
2.1.1 Soil Type
The soil type is classified by particle size. The Table in Fig 2.1 classifies the soil by its particle
size
Grain Size Soil Classification
>2 µm Clay
2 - 6 µm Fine Silt
6 - 20 µm Medium Silt
20 - 60 µm Coarse Silt
60 - 200 µm Fine Sand
200 - 600 µm Medium Sand
0.6 - 2 mm Coarse Sand
2 - 6 mm Fine Gravel
6 - 20 mm Coarse Gravel
60 - 200 mm Cobbles
- 200 mm Boulders
Fig. 2.1 Soil Classification
The holding capacity of the seabed can be categorised in three groups:
1) Good Holding Soil. Normal clay and dense sand or silt.
2) Poor Holding Soil. Soft clay/mud, fine gravel with coarse sand.
3) Extremely Poor Holding Soil Rock, coral, boulders and cobbles
The designer of an anchor shows the maximum performance for a specific type of soil. Some
anchors perform better in soft muddy soil than in hard sand.

SECTION 2
CHAPTER 2 SOIL
10
2.1.2 Soil Strength
For soil strength we refer to section in the Jack-up seminar. It is not common practice to carry
out soil surveys for the anchor locations. However, soil condition is important to decide what
type and size of anchor is required to obtain the maximum holding effect on the mooring
system. If it is not possible to obtain a soil test for each anchor location, we should use any
information that is available from the client from the spud location or from previous operations
in the same area.
The soil test depth depends on the type of soil. The test depth for sand is twice the length of the
anchor flukes and for soft clay for 8 times the fluke length. Generally, a depth of 8 to 10 meter
will be sufficient. The most common locations soil types are sand and clay, or a combination of
both
The table in Fig. 2.2 gives a description of the density (mechanical resistance) for fine to
medium sand in relation to the angle of internal friction, the Standard Penetration test (SPT)
and Cone Penetrometer Test (CPT).
Descriptive Term Relative Angle SPT CPT
Sand Density ø N MPa
Very Loose < 0.15 < 30 0 - 0.4 0 - 5
Loose 0.15 - 0.35 30 - 32 4 - 10 5 - 10
Medium Dense 0.5 - 0.65 32 - 35 10 - 30 10 - 15
Dense 0.65 0.85 35 - 38 30 - 50 5 - 20
Very Dense > 0.85 > 38 >50 > 20
Fig. 2.2 Soil characteristics for sand
To describe clay we use the undrained shear test (SU) in relation to the STP and the CPT (Fig.
2.3)
Descriptive Term SU SPT CPT
Clay kPa N Mpa
Very Soft 0 - 13 0 - 2 0.0 - 0.2
Soft 13 - 25 2 - 4 0.2 - 0.4
Firm 25 - 50 4 - 8 0.4 - 0.7
Stiff 50 - 100 8 - 15 0.7 - 1.5
Very Stiff 100 - 200 15 - 30 1,5 - 3.0
Hard/Very Hard >200 > 30 > 3.0
Fig 2.3 Soil characteristics for clay

SECTION 2
CHAPTER 3 ANCHORS
11
CHAPTER 3 ANCHORS
3.1 NOMENCLATURE OF ANCHORS
The manufacturer fabricates the anchors from high quality cast steel or high quality steel
The anchor various parts are shown in. Fig 3.1 B and C. The flukes are hinged or fixed. On
most anchors with hinged flukes, the angle allows adjustment for sand or mud.
Fig 3.1.A Anchor systems
Anchor Systems
Dead weight anchor Pile anchor Suction anchor
2
Stevmanta VLA
Drag embedment anchors.
1) Conventional Anchors
2) Vertical Loaded Anchors
1
Bruce FFTS MK4 Anchor

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CHAPTER 3 ANCHORS
12
Fig. 3.1.B. Nomenclature conventional anchor
Fig. 3.1. C Nomenclature of Anchor (Flipper Delta)

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CHAPTER 3 ANCHORS
13
3.2 TYPES OF ANCHORS
The very first anchors dated from 2000 years BC. Primitive anchors in the form of heavy
stones, baskets filled with bags of sand and any type of weight attached to a rope held the
vessel in position. The invention of iron produced the first anchor that resembles the modern
anchor. During the last decennia only a relative small amount of anchor design- and
construction companies took the challenge to improve the traditional ship anchors to develop
anchors for the offshore industry with light weight, deep penetration and high holding power.
At present most common the anchors are the drag embedment anchors, designed to penetrate
the soil. Recent developments are Suction Anchors, Vertical Load Anchors (VLA) and
Suction Embedded Plate Anchors (SEPLA). Fig. 3.1.A For very deep-water anchors systems
these new generation mooring system deploys a taut line system instead of the catenary system
in combination with synthetic fibre ropes and vertical loaded anchors.
To identify the drag embedment types of anchor of anchor we can categorise the anchors in
seven groups. (As per Vryhof definition and figures) (See fig 3.2)
CLASS A Anchors with ultra-penetration in which holding power extends
to the third power of penetration
(Stevpris, Stevshark, Delta, Kite)
CLASS B Anchors with "elbowed" shank, allowing deep penetration.
(Bruce SS, Bruce T.S. Hook, AC12)
CLASS C Anchors with open crown hinge near the centre of gravity and relative
short shank and stabilisers.
(Stevin, Stevfix, Stevmud, Flipper Delta)
CLASS D Anchors with hinge and relative long stabilisers at the rear and
relative long shanks .
(Danforth, LWT, Moorfast-Stato-Offdril, Boss)
CLASS E Anchors with extremely short, thick stabilizers, hinge at the rear and a
relative short square shaped shank
(AC-14, Stokes, Snugstow, Weldhold)
CLASS F Anchors with square shank, no stock stabilizers, but built in stabilizing
effect in the fluke design.
(US Navy Stockless, Beyers, Union, Spek)
CLASS G Stock anchors with small fluke area and stabilizers at the front of the
shank.
(Single Fluke Stock, Stock, Dredger, Mooring Anchor)
The anchors listed by Vryhof Anchors shows the mixture of conventional and modern anchors.

SECTION 2
CHAPTER 3 ANCHORS
14
Fig. 3.2.Classes of Anchors (Courtesy Vryhof Anchors)
Fig. 3.3 A. Comparison of anchors with equal scale and weight

SECTION 2
CHAPTER 3 ANCHORS
15
3.3 CRITERIA FOR A GOOD ANCHOR DESIGN
Soil conditions differentiate from very soft or very loose to very hard or very dense. Until now,
it has been impossible to design and fabricate a single type of anchor for the offshore industry
that will perform with maximum holding power in all types of soil.
The anchor for the offshore industry should meet the following qualification:
1) Fast Engagement and Penetration
To commence penetration the anchor should orientate itself in the correct position
when the tension is applied. This will minimise the amount of drag. The shank
design cuts through the soil. Tripping-palms force the flukes into the angled
position. Cutting edges on the flukes and a minimum of obstructions enable free
movement through the soil.
2) Stability
Throughout the penetration process and until the maximum embedment, the
anchor should maintain good stability. Only well designed stabilizers guarantee
stability of an anchor during penetration
3) High Holding power (HHP)
The fluke area determines the holding power. Any increase in fluke area improves
the holding power. The fluke area and the size of the anchor determine the
structural strength of the anchor. The size of the anchor should be must be
manageable for running, retrieving and decking of the anchor. Fig. 3.3.A and Fig
3.3.B shows clearly the amount of difference in fluke area for various types of
anchors with equal weight at the same scale, including the comparison the
modern design anchors with like Stevpris MK5 ,Bruce FFTS MK4 and the older
conventional type of anchor.
4) Variable Fluke Angle.
The anchor should be capable to give HHP in a range of soils from loose sand to
stiff clay as per tables in Fig. 2.2 and Fig.2.3. For this purpose anchors are
equipped with hinged flukes and a system to change the fluke angle.
5) Approved by Class Society
The construction and strength of the anchor must be in accordance with the Class
Societies such as ABS, Bureau Veritas. It is obvious important not to buy an
anchor without the proper certification.
6) Easy to handle and to retrieve
A good designed anchor penetrates deep. The design of the anchor should give
minimum resistance to pull the anchor free. The new designs have a minimum
area at the back and cutting edges on the flukes..
An explanation from Flipper Delta anchors shows the effect of well designed tripping palms in
Fig. 3.4.
Independent studies and tests with conventional anchors and modern anchors confirm the
difference of the holding power in sand and clay as shown in Fig 3.5 A and 3.5 B.

SECTION 2
CHAPTER 3 ANCHORS
16
Fig. 3.3.B. Fluke area difference between Stevpris MK5 anchor and Moorfast anchor
compared to fluke areas of modern design anchors like Stevpris MK5 and Bruce FFTS
MK4.
Fig. 3.5 The effect of tripping palms

SECTION 2
CHAPTER 3 ANCHORS
17
Fig. 3.5.A. Test results anchor holding capacity for various anchors in sand.

SECTION 2
CHAPTER 3 ANCHORS
18
Fig. 3.5.B. Test results anchor holding capacity for various anchors in soft clay

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CHAPTER 3 ANCHORS
19
3.4 FLUKE ANGLE
The fluke angle is a significant factor to determine the final penetration depth of the anchor.
From extensive tests and experience from operations, the best fluke angle for hard and stiff soil
is 32 º and for soft soil 50º. Only anchors equipped with hinged flukes have the possibility to
change the angle. The fluke angle should be set before running the anchor. An incorrect angle
may cause the anchor to fall over and drag without penetration or restrict penetration as
clarified by Fig. 3.6 and Fig.3.7.
Fig. 3.6 Fluke angles for sand and mud as per Vryhof Anchors Stevpris anchors.
Fig. 3.7 Correct and wrong angles. Courtesy Vryhof and Bruce anchors.
Correct angle. Good penetration
Angle for sand
35°
Angle for mud
50°
Wrong angle. No penetration

SECTION 2
CHAPTER 3 ANCHORS
20
3.5 PROOF LOAD AND STRENGTH OF ANCHORS
After the completion of the fabrication, all anchors are subject to a proof load test in
accordance with the Class Societies Rules. Special rules are applicable for the Mobile Offshore
Units and Permanently Moored Units. Depending on area and Classification Society for Mobile
Offshore Units the rules may require an anchor proof load of 50% of the breaking load of the
chain. For the older type of anchors like Danforth, this causes a problem. The reinforcements
required to comply with the rules decrease the holding power of the anchors. The construction
of modern anchors like Stevpris and Bruce anchors is in accordance with the latest rules and no
additional reinforcements are required. As an indication, for an anchor of 12 ton with 84 mm
chain (breaking load 720 ton) the proof load will be 360 ton. Compared to the old rules the
proof load is only 133 tons.
In operations, numerous loads work on the anchor such as:
1) Loads caused by the soil during penetration, tensioning and retrieving. In
sand and soft soils, the loads are less than in hard soil. In hard soil point
loads on the flukes tips may damage the anchor.
2) In soft sticky soil and deep penetration, the anchor handling vessel may
need to apply excessive load to break out the anchor. These forces are
transferred to the anchor shaft and can cause damage
3) An anchor that is embedded with deep penetration and orientated under an
angle may be subject to excessive side loads on the shank under high
tension or when in the process of retrieving the anchor.
4) While running and retrieving anchors, damage may occur because the
anchor is wedged or jammed behind an obstacle. Racking an anchor with
high-powered winches and/or using a chain chaser requires careful
attention to prevent excessive loads on the anchor or the anchor rack. The
wrong type of chain chaser will damage the anchor.
3.6 MOORING SYSTEM ANALYSIS WITH THE SEAMOOR SYSTEM.
The SEAMOOR system is a mooring simulation system developed by Noble Denton. The
simulation program meets the needs of those involved in operational management of spread
moorings. It enables all aspects to assess the mooring and station keeping performances.
SEAMOOR uses well-proven algorithms from the Noble Denton MECA program, which has
NMD approval. All regulatory authorities, classification societies, and mooring system
designers accept and use the quasi static analysis method.

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CHAPTER 3 ANCHORS
21
There are two ways to input user data to SEAMOOR:
1. Pre-prepared data files
2. Interactive data input
Data files are plain text (ASCII) files, which must be prepared prior to running the program.
Any text editor or word processor with a text file mode accepts the system to prepare the files.
Interactive data input can be made directly to the program whilst it is running, either in
response to prompts or by editing accessible fields on the displays.
All SEAMOOR input data can be specified using the 4 separate data files listed below:
1. SEAMOOR control file
2. Vessel data file
3. System data file
4. Field data file
Vessel data file are in accordance to the data from MOM by R & E therefore it is a constant for
every type of rig. Once it is developed, the program uses it all the time
System data file is where the mooring parameter likes water depth, length of pre-laid mooring
line for each system. It is different for every location, therefore the parameter change according
to the particular location
Field data file is necessary with the existence of pipeline or obstacle within the location of
mooring. It is useful for simulating the clearance of the mooring lines from the obstacles.
Important criteria and information to perform a anchor mooring analysis are:
1) Water depth
2) Rig draft.
3) If not already available at R & E, the general description of the rig
4) Type, size, weight, and amount of anchors and anchor chain.
5) Prevailing weather conditions.
6) Survival weather conditions.
7) Any Government Regulations and Requirements concerning mooring systems.
8) Maximum allowable offset limits for operations.
9) Type of soil
10) Required anchor pattern and heading.
11) Operations-, Stand By- and Survival Conditions if different from company policy
and MOM.
12) Thruster assistance for special conditions.
13) Any other information that may effect the mooring system and is not common
knowledge for the Engineering Department.

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CHAPTER 4 MOORING CHAIN AND WIRE
22
4.1 CHAIN OR WIRE
Most mooring systems for the Mobile Offshore Drilling Units (MODU's) are equipped with
chain for water depth from 1000 to 2000 ft. For deeper water depth a combination chain-wire is
used. Some of the latest generation of Semi-Submersibles are equipped with a combination
chain-wire system with the capacity to drill in water depth of 3000 ft.
The decision to use chain or wire or a combination depends on:
1) The maximum water depth.
2) The size and shape of the rig.
3) The maximum winch capacity of the AHT.
4) The winch capacity of the anchor winch on the rig.
5) The capacity of the storage area on board of the rig and on the AHT.
6) The type of operation
7) The maximum weather criteria for the operations area.
4.2 ADVANTAGES OF CHAIN COMPARED TO WIRE
The advantages of anchor chain compared to the same diameter of wire are:
1) Higher breaking load strength
2) Up to a certain water depth the additional weight provides a better catenary
system
3) Less shock loads and more spring effect
4) Less wear an tear and therefore longer life
5) Additional friction and holding power in soil (See the Appendix for the anchor
chain coefficients).
6) Storage in the bottom of the columns will give more stability than wire stored on
the anchor winch on deck
The advantage of anchor wire is:
1) Faster deployment and retrieval
2) Cheaper per unit of length
Offshore units, which move a lot such as pipe lay barges, work barges, support vessels and
crane barges prefer to use wire.

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23
4.3 CHAIN AND WIRE CONSTRUCTION
4.3.1 Chain Construction
Most offshore mooring systems use stud-link chain, but in deep water operations the offshore
industry started to deploy studless chain.
The advantages of studless chain are
• Lower weight with same safety factor
• Higher safety fatigue failure
• More corrosion allowance
Studless chain is preferable for long-term mooring systems. Any mentioning of chain in the
discussion of this chapter means stud-link chain
The studs add strength to the chain and prevent fouling in the chain locker or twisting on the
seabed.
Anchor chain qualifications is expressed by grade of steel and by type of construction
The construction depends on the manufacturer’s procedure. The Baldt-DiLOk chain link is
composed of two members. A forged and heat treated serrated member and a forged upset
member with a stud that is impossible to dislodge. The stem member mates at ambient
temperature with the socket member at forging temperature. (Fig 4.1)
The chain factory manufactures the flash weld chain from heated rolled steel bars formed into a
link shape. A flash welding machine welds the ends together. A hydraulic press presses the hot
drop forged studs in the open link (Fig.4.1). Because of the rugged use of offshore chain, the
studs need to be welded.(Fig. 4.3) Some Classification Societies do not accept welding of the
studlinks. Long-term anchor systems often use the studless chain. Fig 4.2 shows with some
photographs of the manufacturer’s process.
Fig 4.1. Baldt DiLOk Chain- Studded link and Studless link

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24
Fig. 4.2.Manufacturer process anchor chain. (Photos courtesy of Zhengmao Group)
After the six processes the chain undergoes heat treatment and tensile testing.
1) Cutting
3) Bending
2) Heating
6) Stud
setting
5) Trimming
4) Welding

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25
Fig. 4.3. Example of stud welding.
4.3.2 Chain Grades and Standards by Class Societies
The chain manufacturers offer chains in standard classifications from grade 1 through grade
4.and the Oil Rig Quality (ORQ)
A higher grade means higher steel quality and higher breaking load strength.
The offshore industry mainly uses ORQ chain. Grade 4 is specifically for areas with extreme
cold weather such as drilling near the arctic area. The graphs of Fig.4.4 show the various
grades and breaking load/size
To obtain certification, proof and breaking loads of anchor chain has to be in accordance with
The Class Societies specifications. More information with tables of Proof Load and Breaking
Load Tables are in the Appendix.
4.3.3 Chain sizes
Most MODU’s use 3" or 76-mm. chain but other sizes from 2½" (64 mm) up to 4" (102 mm)
are utilised. Chain sizes are in inches or mm. When ordering new chain it is important to verify
with the manufacturer that the size will fit the wildcat. In case you order the size in inches and
the manufacturer’s process is in mm. The manufacturer will round off the mm size to the higher
decimal. This may cause problems if the original chain already had a tight fit on the wildcat.

SECTION 2
26
4.3.4 Chain Inspection
The anchor chains are subject to the Class Societies periodic inspection schedules.
In addition the barge engineer should visual inspect at regular intervals the anchor chain on any
deformation and loose or missing studs. Details on inspection will follow in another section.
Fig 4.4 Example with comparison of chain grades (From Ramnäs)

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27
4.3.5 Anchor wire
To select a wire we have to specify:
1) The type of utilisation
2) The maximum safe working load
3) Diameter
4) Characteristics of the construction.
5) Lay
6) Grade of steel and coating
7) Length
8) Certification
MODU’s use anchor wire mainly in combination with chain for deep-water operations. Once
moored the anchor wire on MODU's will remain in almost the same position for prolonged
periods. Construction units run and retrieve anchors at a much higher interval.
For wires with the same diameter, the wire with the largest amount of wires will be the more
flexible, but the diameter of the individual wires will be smaller. This means that with
excessive use individual small wires will wear faster. In addition, the breaking load and safe
working load will be less than a wire construction with thicker wires
For anchor wire on drilling-rigs, we need a strong wire with good resistance to abrasion and
wear and tear. The flexibility is less important than for example the use of anchor wire on
construction units.
4.3.6 Maximum Safe Working Load and Diameter.
There is a direct relation between the diameter and the safe working load. The safe working
load for the anchor chain or wire will be the maximum calculated tension for storm conditions.
4.3.7 Construction, Lay, Grade of Steel, Coating
This section explains briefly the wire rope construction of steel wires used for slings, pennant
wires, and anchor wire. ((Fig 4.5, 4.6, and 4.7)
• Strands and Wires. Wire rope consists of strands. Each strand consists of wires.
(Fig. 4.5)
• Ordinary Lay and Lang’s Lay. The wire rope construction is designed in ordinary
lay or Lang’s lay. In ordinary lay the strand and wire run in opposite direction, in
Lang’s lay the strands and ropes run in the same direction. For general purpose only
use ordinary lay
• Right Hand or Left Hand. This indicates the direction the wire spirals. The lay
runs left-handed or right-handed In general, only order right hand ordinary lay wire.
Always install the wire on the drum in the same direction as the lay.(Fig. 4.8)

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28
• Core. The strands lay around a central core. The core is made of steel wire or soft
rope. Except for special purpose always use steel core wires.
• Construction. Most wire ropes have six strands with a steel core. Specify wire by
the amount of strands, the amount of wires and the type of core. The steel grade
(steel tensile) is Improved Plow Steel (IPS) equivalent to 180 kgf/mm³ or Extra
Improved Plow Steel (EIPS) equivalent to 190 kgf/mm³. Because of the higher
breaking strength, the EIPS wire is the better choice. Typical anchor wire
construction is 6 x 19 IWRC or 6 x 37 IWRC. (Fig. 4.6.and 4.7))
• Coating. Wire rope comes with a corrosion protecting lubricant that will wear off
in operation. The maximum effective coating is a permanent galvanised coating.
• Pre-forming. In a pre-formed wire rope, the strand and the wires have been given
the twist they take up in the completed wire
• Length. The correct length of wire is important because it is not possible to make a
splice on location to connect one of more length with a shackle like done with
anchor chain. The storage and transport require special care. Use lifting beams.
• Certification. Like anchor chain, wire needs proper certification in accordance
with the local and Class Society regulations.
When ordering wire specify:
a) The number of strands in the rope
b) The number and arrangements of wires in the strand
c) The tensile strength
d) The type of core
e) Any special processing, pre-formed etc
f) Zinc coating and lubrication
Fig. 4.5. Regular and Lang’s lay

SECTION 2
29
Fig. 4.6 Wire rope construction
Centre wire
Strand
Wire
rope

SECTION 2
30
Fig. 4.7. Various types of wire rope.

SECTION 2
31
Fig.4.8Thumb rule to reel wire in same direction as lay.

SECTION 2
CHAPTER 5 MOORING ATTACHMENTS
32
CHAPTER 5 THE MOORING SYSTEM AND
ATTACHMENTS
5.1 LAY-OUT DIAGRAM OF MOORING SYSTEM
Fig. 5.1 shows the various sections and components of the mooring system configuration with
an anchor buoy, piggyback anchor, and main anchor with a permanent chain chaser.
5.2 ANCHOR PATTERNS
The purpose of a spread mooring system is:
1) In the Operating Condition:
To maintain the drilling unit position within certain offset limits
under normal environmental conditions.
2) In Maximum Operating Condition:
Not to exceed the maximum allowable offset from the centre of
the drilling hole, which depends on the maximum allowable angle
between the riser and BOP before disconnection is required, which
is between 8°and 10°. The radius of the circle for the Maximum
Operating Condition is expressed in percentage of water depth.
3) In the Survival Condition:
To maintain a safe position in severe weather and current
condition. The mooring pattern should give protection for severe
weather/current conditions from any direction. In the Survival
Condition the riser system is disconnected which allows much
larger offset values than during operating conditions.
4) For all conditions
To give enough reserve and strength to prevent the mooring
system to break or to go beyond the holding power of the
anchor(s).
The mooring analysis calculates the optimum tension to incorporate the corresponding various
conditions as mentioned above. The standard mooring assessment determines the following:
An anchor pattern defined for the existing bathymetric and geological layout of the
location.
Pretension and initial line tension.
Chain and/or wire payout.
The rig heading.
Ranges and bearing of the anchor positions.
Mooring line configuration such as chain and wire size..

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33
Pennant
200ft to 600ft
2.5 pennant
wires (2.5” or
75t to 85t
Piggyback
anchor
Pigtail
chain
Chain-wire
pigtail
Primary
anchor
600ft
pennant
wires (3”)
Chain chaser
Rig anchor
chain (3”)
Fig 5.1. Mooring components of buoyed and piggyback configuration.
If we expect the most severe weather and current condition from a certain direction, a mooring
analysis also calculates the best heading and anchor pattern. To moor the rig with the bow
pointing into the most severe weather has some advantages and disadvantages:
1) The control room in most cases is located on the bow. When the rig arrives on
location the view from the control room looks into the direction of the location,
which it easier for the barge engineer to monitor the progress.
2) In case of a blowout or H2S situation the wind will blow the gasses away from the
accommodation.
3) For most Semi-Submersibles the forces from wind, current and seas are less in the
fore ward-aft direction than in the port-starboard direction
4) For the helicopter pilots the bow heading into the wind makes landing more
difficult because with the landing approach into the wind the helicopter has to
pass by the derrick.
5) With seas and wind from straight-ahead, no real lee-side is available for the crane
to load/discharge cargo to the supply vessel. With item 4 and 5 in mind often the
rigs heading is offset 15 ° from the prevailing wind and weather direction.
Most drilling rigs are fitted with 8 anchors but there are rigs with 9 or 10 anchors.
The ideal anchor pattern is a symmetric configuration with all anchors at the same water depth,
deployed with the same length, in the same type of soil and same depth of anchor penetration,
which is a hypothetical case.

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34
Fig 5.2 shows a few examples of anchor patterns of which the 45º/45º and 30º/60º patterns are
the most common. Asymmetric patterns are sometimes necessary to avoid contact with
obstructions or pipelines. When alongside platforms work-over rigs, construction- and
accommodation units often have to use asymmetric patterns.
Fig.5.1 Examples of anchor patterns
Vessel Excursion
Mean Offset : 73.0m
Motion : 0.9 m
Max Offset : 73.7 m
Wind : 15.1 m/s
Wave : 2.7m & 6.2 Tz
Current Dir : 45 deg
Wind Dir : 90 deg
Current : 1.25 m/s
Fairlead : C1
Payout : 1436.6 m
WD : 1524.0 m
A Ten : 115.2 MT
F Ten : 155.7 MT
Current
Wind
Environmental
Fairlead : C8
Payout : 1436.7 m
WD : 1524.0 m
A Ten : 79.5 MT
F Ten : 129.4 MT
Fairlead : C2
Payout : 1314.6 m
WD : 1828.0 m
A Ten : 51.1 MT
F Ten : 117.4 MT
Fairlead : C3
Payout : 1314.4 m
WD : 1828.0 m
A Ten : 14.2 MT
F Ten : 91.5 MT
Fairlead : C4
Payout : 1314.6 m
WD : 1828.0 m
A Ten : 0.0 MT
F Ten : 77.5 MT
Fairlead : C7
Payout : 1436.5 m
WD : 1524.0 m
A Ten : 27.3 MT
F Ten : 91.7 MT
Fairlead : C6
Payout : 1436.7 m
WD : 1524.0 m
A Ten : 2.2 MT
F Ten : 74.2 MT
Fairlead : C5
Payout : 1436.6 m
WD : 1524.0 m
A Ten : 0.0 MT
F Ten : 69.7 MT
Well
Location
6.5% of 5000’ WD
Case 1 : Worst Weather Scenario without Line Adjustment
Line Breaking Strength
: 333.71 MT
Anchor Holding Power
: 360 MT

SECTION 2
35
5.3 THE CATENARY SYSTEM
a) Definition and Configuration
By definition, a catenary is the curve formed by a perfectly flexible chain or cord hanging
freely between two fixed points at the same level. To discuss the catenary we use anchor chain.
The configuration of the catenary curve depends on:
1) The horizontal distance between the two points
2) The length of the line
3) The weight of the line
In respect of the anchor chain catenary, we always discuss the half catenary, i.e. the distance
from the fairleader to the touch down point on the seabed. If we leave the anchor chain without
tension, the anchor chain will hang straight up and down. By heaving on the anchor chain we
start to apply tension and the anchor chain will follow an increasingly shallow curve until it
approaches a straight line. In operation, the half catenary will be a gentle curve, which will
partly straighten as the drilling unit oscillates by the environmental forces. The catenary
functions as a dampening spring. This flexibility is the strength of an anchor system since the
rig can return to its original position and does not move beyond a certain distance away from
point zero because of the restraining forces.
Less tension on the system means more movement; a high tension restricts the movement but
reduces the flexibility (spring effect). Fig. 5.3 (Detailed calculations of the catenary system are
discussed in Stability II course.)
Fig. 5.3. The catenary system. High tensions restrict movement – reduces spring effect.

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36
5.4 ATTACHMENTS AND CONNECTIONS
Each length of chain needs a connection link or shackle to attach the next length of chain. Often
these connections are patented and named after the manufacturer.
5.4.a. The Open-End Link (Fig. 5.4. E)
For easy transport and installation, chain comes in lengths as ordered. To give room for the
installation of connecting links or shackles a chain length has at each end an open-end link. To
maintain the same strength as the stud link the end link is larger in diameter. To select the size
of connecting link or shackle, use the larger diameter.
5.4.b. Connecting Links.
Connecting links are designed to inter connect the anchor chain and to give smooth passage
over the anchor winch. These links are patented and named after the manufacturer such as:
1) The Kenter and Ramfor Links (Fig 5.A.)
These connection links come in three asymmetric parts, which make them more
difficult to assemble. Fix the assembly with a tapered pin. Hammer the lead plug
in the larger hole size. On the other side the hole is left open to punch the pin
out if we have to replace the link. One punch is used to place the tapered pin and
a smaller punch is used to remove the pin. The link has to pass horizontal over
the wildcat. The links have tight fit. Damage to the rims may cause problems
with assembly and disassembly
2) The Baldt Connection Links (Fig 5.4.B)
These links are easy to put together. Use the Baldt Pear Shaped to connect
different diameters such as the anchor shackle to the chain or chain to wire.
3) The “D” Type Anchor Shackle (Fig. 5.4.C and 5.4.D)
This shackle connects the chain to the anchor shank. Do not confuse this shackle
with the D -Type joining shackle, which is an alternative for a chain connection
link.
4) Swivels, Links and various possible combinations of Couplings to the
Anchor.(Fig 5.4.D and 5.4.E)
Many operators do not favour the use of swivels at or close to the anchors
because they have the tendency to break on side loads and do not work under
load. Swivels used in anchor wires may cause damage in case of a quick load.
One theory is that the outer layers will open and the wire core carries the load
for a very short moment. This can cause a “bird cage” or break the wire rope
core. In some cases, the extra length of the swivel may cause a problem with the
available distance between the anchor shackle and the fairleader. The swivel can
be a bow and eye type or a jaw and swivel type. The latter one fits direct to the
anchor shackle.

SECTION 2
37
Fig. 5.4.A .Pictures of Kenter and Ramfor Links (courtesy Rämnas)
Fig. 5.4 B. Baldt Connecting links for chain and anchor connection.

SECTION 2
38
Fig 5.4.C. D Type anchor- and joining shackle
Fig. 5.4.D. Swivels and links

SECTION 2
39
Fig.5.4.E.Various possible coupling combinations to the anchor
Fig.5.4.F.Bow or ‘D “type Safety shackle. Safety shackle with large bow.
D type safety shackles as connection between pennant wires may cause damage to the pennants
stored on the drums because of the obstacles on this type of shackles. Always check the safety
pins before transferring the pennant to the anchor handling vessel. D shackles with a larger and
faired bow facilitate the eyes better and reduces the wear and tear. (Fig. 5.4.F)

SECTION 2
40
5.4.c. Crown Chain
The crown chain is a short piece of stud link chain (30-60 m) between the anchor crown and the
first pennant wire. The crown chain purpose is:
1) To provide a strong protection against wear-and-tear at the seabed.
Without he crown chain the circular and up and down movement of the
buoy will wear the bottom part of a pennant wire within a short period.
2) In case of replacement of the first pennant wire the anchor-handling vessel
does not have pull the anchor on deck to disconnect the pennant wire.
3) When the anchor is decked, the greatest strain on the pennant or crown
chain will be just behind the crown when the anchor passes the stern
roller. Fig 5.5 See Fig. 5.6.B for a typical pennant wire damage
4) If the anchor needs double securing on deck of the AHT, the crown chain
provides easy securing points.
It is good practice to have an open link at each end of the crown chain because it makes it
easier to pass the connecting links or shackles.
5.4.d. Pennant wires
If the anchor system is not equipped with a permanent-chain chaser-system we need to deploy
the anchors with a pennant-and-buoy-system.
The pennant wire function is:
1) To run and lower the anchor to the sea bed
2) To pull the anchors free and to retrieve the anchors
3) To be able to reposition the anchors if they drag
4) To be used as the connection between the first and second anchor if we
piggyback anchors.
Generally shackles connect the ends between the pennant wires, Baldt hinged links (Fig. 5.6
A.) or similar types of connections between pennant wires are a better way of connection but
more expensive. Normal shackles or D type safety shackles may damage the pennant wire
when reeled on the storage winch on the AHT. See shackle in Fig. 5.4 F.
On each end of the pennant wires, the recommended termination is an eye with a high quality
heavy-duty thimble with gusset and tapered pressed ferrule or with an aluminium alloy ferrule.
For heavy-duty work sometimes closed spelter sockets are used. Fig. 5.7 shows various wire
terminations. Only use heavy-duty thimbles with gusset plates or the closed spelter sockets.

SECTION 2
41
Fig 5.5. Pig tail chain prevents damage when anchor passes over the stern roller
Fig.5.6 A. Hinged links
High bending forces on
the pennant wire and eye
High bending forces
on the chain.
Wire
Chain

SECTION 2
42
The pennant wire construction is usually of the Warrington-Seale 6 x 19 or 6 x 37 EIPS-IWRC
Classification.. Pennant wires can be ordered in any length form 50 ft, 100 ft, 150 ft. etc.
The length of pigtails varies from 30ft to 120 ft.
Store pennant wires in coils and mark the ferule with a colour code to identify the length.
To hang off the pennant wires use a funnel shaped design of catcher or other safe designs.
Never use pieces of rope to hang off the pennant wire, this is not a safe procedure. Fig 5.7.A
shows two systems to hang off pennant wires.
Fig.5.6.B. Damage to pennant wire thimble by high bending forces.
Fig. 5.7Pennant wire terminations and pennant wire hang off system

SECTION 2
43
5.4.e Pigtail Pennant wires
The function of the pigtail pennant wire is:
1) To have a short and easy way to handle the connection between the
anchor buoy and the rest of the pennant wires.
2) The section under the buoy sustains more wear and tear. It saves time and
money to replace a short section.
3) Short pigtails from 50 ft to 100 ft are useful to complement the last section
to reach the total required length. It may prevent to install another long
length.
5.4.f. Inspections
Each time the anchor hangs under the stern roller or comes on deck of the AHT, ask the crew to
inspect the anchor and attachments.
After retrieving the barge engineer should inspect the pennant wires on "kinks"", "birdcages",
wear patterns and broken wires and loose or damaged thimbles.
5.4.g. The Permanent Chain Chaser System (PCC)
The PCC system enables to run and set the anchors without the use of a buoy/pennant system
The PCC system is faster to run but the strain on the equipment is much higher. To operate the
system heavier PCC pennants and connections are required. Various type and shapes of chain
chaser are available. Fig. 5.8 A and 5.8.B
• The J Chaser
The AHT deploys the J chaser from the stern. Hanging at approximately 1/3 of the
water depth the AHT tows the chaser across the mooring line until it catches the
chain. The AHT tows the chaser until contact with the anchor shank/fluke for
anchor break out and retrieval.
• The Permanent Chaser
The permanent chaser is the alternative to the buoy-and pennant system.
• The Detachable Chain Chaser.
The detachable chaser makes it possible to install or replace the chaser without
removing the anchor.
• The Permanent Wire Chaser.
The permanent wire chaser came into operation when the rigs moved to deeper
waters and a composite wire/chain mooring system became necessary. The chaser
incorporates a “rocker”, which is centrally mounted on a hinged bolt. The rocker
has two opposing wire grooves, which enables the wire to slide through with
minimum friction. The material of the groove is less hard than the wire. This means
the rocker takes the wear. The rocker is easy removable. The permanent wire chaser
is easily detachable by withdrawal and re-assembly of the hinged bolt and rocker.

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44
• The Permanent and J Chain Lock Chasers.
Increased rig dimensions and anchor forces lead to higher requirements to break out
the anchors. The chain lock chasers provide a design to break out an anchor without
having to contend the force in the mooring and the break out force. By locking on
the chain ahead of the anchor shackle, the AHT only deals with the weight of the
anchor and its resistance to break out.
The Bruce permanent chain chaser and roller chasers serve the same purpose as the chasers
described above. Apart from the right chaser for Bruce anchors, Bruce chain chaser mate with
other anchor types.
Regardless of the system used to retrieve the anchor, large forces are required to breakout a
heavy anchor with deep penetration. If not done with skill and patience the AHT tug easily
exceeds the breaking strength of the recovery system
Fig. 5.8 A. Various types of chain chasers

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45
Fig. 5.8.B Pictures of a grapnel, chain chasers and fishing hook.
It is important to install the proper type and shape of the chain chasers on the anchor system. If
in doubt, contact the anchor manufacturer. Damage and serious running problems will occur
with the wrong type of chain chaser.
To reduce the amount of connections on the winch drum of the AHT use the longest available
length of pennants as work wire. Long lengths of pennant wires reduce the possibility to have a
connection at the stern roller when setting or pulling the anchor.
Always use a short length of chain connected to the chain chaser for the same reason as we use
a crown chain on the anchor.

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46
5.4.h. Anchor Buoys
The function of the anchor buoy is:
1) To uphold the weight of the pennant wire
2) To be able to retrieve the anchor
3) To mark off the anchor pattern and the position of the anchor
Anchor buoys come in various sizes, shapes, and material of construction. In the early days of
the offshore drilling and construction industry only used steel buoys. In many cases the buoys
disappeared to the seabed because of damage during handling or due to corrosion. The design
of the buoys improved with the construction of watertight compartments and with the use of
foam filled buoys.
Because steel buoys are a hazard to smaller vessels, resilient buoys were developed. A core of
Expanded Polyurethane surrounded by solid Polyethylene Foam covered with an elastic skin
assembles around a core of steel fitting. The steel fitting includes a cross bar to snatch the buoy.
These buoys are unsinkable. Some manufacturers use inter-changeable sections, which in case
of damage are easy to replace. When the drilling unit moves to deeper water, additional
sections increase the buoyancy. Compared with steel buoys the resilient type of buoy is more
expensive .In certain areas local regulations only allow the use of resilient type of buoys. Fig.
5.9.. One type is a sliding or suitcase buoy. The buoy slides through the pennant wire. The
advantage is that the buoy remains attached to the system.
Fig. 5.9 Resilient polyurethane pennant wire buoys

SECTION 2
CHAPTER 6 RUNNING AND RETRIEVING
47
Summarising the modern buoy design should have the following features:
1) Unsinkable. Use of foam filled compartments or built from unsinkable
material
2) Hull and shape should be collision safe. Preferable constructed from
resilient material
3) Easy to handle for the anchor handling vessel with a cross bar at the top
and an easy accessible eye on the bottom
4) Strong to withstand rough handling
5) Easy to repair on board or made out of replaceable sections
6) Painted in highly visible colour like orange or yellow with reflecting
strips.
7) Buoys should be painted with number and rig name
8) Provided with a radar reflector and automatic activated light
In deep water, it takes a very large buoy to support the pennant wires. The use of a spring buoy
system limits the size of the surface buoy and reduces the wear and tear on the crown chain and
bottom section of the pennant wire system. The spring buoy should be strong enough to
withstand the compression of the water depth.

SECTION 2
48
CHAPTER 6 ANCHOR RUNNING AND
RETRIEVING PROCEDURES
6.1 SELECTION OF ANCHOR HANDLING VESSELS
Depending on the contract, the Company or the Drilling Contractor selects the anchor handling
vessels. In most cases, the Company has the AHTS and Supply Vessels under contract and the
Drilling Contractor can only advise the Drilling Contractor what type of AHT is required to
perform a good and safe mooring operation.
Important factors to select the right type of anchor handling vessel are:
1) The availability on the market. In a tight market the required vessel may
not be available.
2) The area. As an example, the type and design of anchor handling vessels
used in the North Sea is different from the vessels used in West Africa.
The average weather, wave height and current conditions are important
factors to decide on the type of anchor handling vessel
3) The type and size of the rig
4) The manoeuvrability. For confined areas a vessel with high
manoeuvrability is required
5) The water depth.(see also item 7)
6) The size type and weight of the anchor. The size of the stern gate and
stern roller should accommodate the size of the anchor.
7) The amount and size of chain to be deployed. The vessel must have
enough power and bollard pull to deploy the length of chain for the water
depth on the location. The capacity of the winch and other deck
equipment must be adequate to handle the weight of the chain and
attachments
8) The deployment of the system with buoys or with a permanent chaser.
Modern deck equipment with the right size of pins and stoppers are
necessary to work fast and safe. Check the storage capacity of the pennant
storage winches on the anchor handling vessel
9) The deck space and chain locker space. If we need to store chain and/or
have to run piggyback anchors the vessel should have enough deck space
and chain lockers.
The Towing Section explains in detail the selection of Anchor Handling Vessels and Ocean
Going Tugs. To tow and mooring a large Semi Submersible the choice will be between an
Anchor Handling Tug (AHT) or an Anchor Handling Tug Supply Vessel (AHTS) all with a
bollard pull of at least 125 Tonnes. Although the difference between AHT and AHTS is
disappearing, there are still vessels in the filed from both classes. In general, the anchor
handling tug is easier to handle as it is build for the job and the AHTS has the advantage of
more storage capacity. Both types of vessels are suitable for the job.

SECTION 2
49
To determine which AHT(S) is the best equipped to operate with the drilling unit check the
following details:
1) The required minimum power:
2) Brake horse power
3) Bollard pull
4) The capacity and details of the deck equipment
5) Amount and capacity of the storage reels
6) Towing winch specification, size and length of the wire
7) Spare towing wire
8) Specification of the work wire winch, wire size and length
9) Size and capacity of the hydraulic operated wire/chain stopper
10) Hydraulic operated guide pins
11) Availability of a towing bar
12) Deck space and storage capacity for bulk, fuel, and water.
13) Chain locker capacity
14) Stern roller and stern gate size
15) Jewellery, such as shackles and grapnels
16) Manoeuvrability.
Below is a list, as a guidance to compare the characteristics of AHT or AHTS.
Limited = L
Good = G
Excellent = E
Characteristics AHT AHTS
1 Effective Bollard Pull in rough seas L G
2 Effective Bollard Pull in normal conditions G E
3 Manoeuvrability and sea keeping ability in rough seas E E
4 Towing facilities, double drum and anchor handling winches E E
5 Chain locker capacity L G/E
6 Deck space for storage of buoys and anchors L E
7 Pennant wire storage reels capacity L/G G/E
8 Barite, Cement and Bentonite storage capacity G G/E
9 Fuel and water storage capacity G E
10 Ability for anchor handling, fishing, buoy retrieval E G
11 Deep water anchor handling capacity L E
12 Salvage capabilities G E
13 Work in confined areas E L/G

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50
It is important too know how well the AHT is equipped with modern navigation and
manoeuvring equipment. Radar, Global Position System (GPS), computer steered positioning
systems (Joystick-Poscon and DP systems), three or four thrusters Check the power of the
thrusters. DP assisted manoeuvring systems are now common for an AHT.
For tows, it may be necessary to use a towing gog and stern gate. Modern equipment on deck
such as remote controlled guide pins and wire/chain stoppers are common standards.(Fig. 6.1).
Fig. 6.1. Pictures with guide pins and chain/pennant wire stoppers.
Note: Dual set retracted position flush with deck and combined use of wire and chain
stopper

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51
6.2 PRE-MOVE PREPARATION AND PLANNING
The discussion on the preparation and procedures for moving is for guidance only. There may
be different procedures depending on the area, operator, local regulations and even from rig to
rig. Always consult the M.O.M. for rig-specific operations procedures.
The staff onshore and the OIM on board should start preparations well ahead before the
intended date of the move. It will make some difference if the rig will move within the field or
embarks on a long ocean tow.
Pre-move actions are:
1) Prepare the site survey in time. This is normally the responsibility of the
operator. The divers should perform the survey only a few days before the
date of arrival. The survey includes confirmation of the existence of any
sub-sea pipelines, templates or other major obstructions. Request an
accurate large-scale survey chart of the area for the barge engineer and
AHT to plot positions while running the anchors.
2) If applicable, advise the Warranty Surveyor about the estimated date of
the move. If a Warranty Surveyors is required to attend the move (JU),
needs to schedule his arrival in time to survey the rig and to prepare the
move approval certificate. If no surveyor is required to be on board a
move approval certificate is prepared ashore. The Certificate of Approval
gives detailed guidelines and instructions concerning the stability,
securing, weather limits and AHT vessel requirements.
3) Advise the local authorities. The Government Authorities have to approve
any movements within the territorial waters or Continental Shelf. This can
be the Mining Agent, the Department of Energy, Marine Directorate,
Coast Guard, or Port Authorities.
4) Establish the chain of command. With the drilling superintendent, barge
engineer or captain, the company man, the warranty surveyor and other
supervisors on board only one can be the O.I.M. Confirm with the
operator if any additional company persons need to attend the move.
5) Confirm with the client that on the estimated move date the area will be
free to arrive or depart. If possible, avoid any move to coincide with other
rig move operations near the rig location.
6) Establish what position system will be used and where the system will be
installed

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7) Confirm with the operator what maximum allowable offset limits are
acceptable for the drilling unit in respect of heading and distance from the
hole position.
8) For prolonged moves, arrange adequate storage of additional water, fuel
and other supplies. Sometimes the crew-change dates need to be changed.
9) Set up a long- and short-term professional weather forecast service.
Normally the weather forecast service company is arranged by the
Company
10) Obtain soil information for the jack up leg position and for the anchors. It
may be necessary to find additional piggy-back anchors what will take
time.
11) Decide if placement of a marker buoy system on the new location is
required
12) Confirm pretension procedures and tension values.
13) Establish anchor pattern and heading. Contact the Engineering
Department to carry out a Mooring Analysis with the SEAMOOR
program for non-conventional anchor patterns.
14) Start the selecting procedure for the AHT’s. If the client provides the
AHT’s verify if the bollard pull and winch capacities are in accordance
with the move approval requirement.
6.3 PRE-MOVE MEETING
6.3.a. Persons to attend
Arrange a pre-move meeting on board of the drilling unit. In addition to the rig manager the
following persons should attend the meeting:
1) Rig or Drilling Superintendent
2) Master or Barge Engineer
3) Company Representative
4) Warranty Surveyor (If required to be on board)
5) Positioning Surveyor
6) Safety |Supervisor
7) Chief Mechanic
8) Chief Electrician
9) Night Pusher

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6.3.b. Pre-move Meeting Topics
Subjects and information to discuss in the pre-move meeting are:
1) General sequence of operations and the time schedule to complete the
well
2) The sequence of operations and time schedule to prepare the rig for the
move.
3) The ballast and de-ballast procedure and corresponding draft for the
mooring operation.
4) The responsibilities and tasks for each supervisor.
5) The chain of command.
6) The role of the Warranty Surveyor and move approval requirements.
7) Communication system and channels to be used on VHF/UHF
8) The water depth and anchor pattern on the new location
9) The soil condition and fluke angle.
10) Availability of piggy-back anchors, additional pennant wires and
connections.
11) The exact position, heading and maximum offset limits for the new
location
12) The type of positioning system. Requirements for the installation on
board.
13) The weather criteria. Determine the prevailing weather and current
condition. Agree on the best possible heading.
14) The information on the amount and type of anchor handling AHT's.
15) Any special operations that may be required because of pipelines and
obstruction.
16) Authorities that need to be informed. Assign the person(s) to advise the
authorities. (Department of Energy, Port Authorities, Navigational
Warning Notification, Coast Guard).
17) The marker buoys system.
18) Last but not least the safety on job. Initiate Safety Meetings before each
rig move to discuss and explain the specific dangers related to the anchor
handling procedures.

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6.4 INFORMATION FOR AHT CAPTAINS
After the pre-move meeting the barge engineer writes up a move procedure and planning. Each
AHT captain receives a copy of the move procedure. This information plays an important role
while running anchors because if there are questions the persons involved can refer to the
information without going into a long discussion. Essential information is:
1) The name and position of the man in charge (OIM) on board of the rig.
2) The geographic and grid co-ordinates of the new location.
3) A drawing of the rig with the indication Forward/Aft and SB/Port. The
American system sometimes uses Left/Right. The horizontal and vertical
plan should indicate the anchor rack , the location of the thrusters and any
under water hazards of the rig.
4) The draft of the rig during anchor handling and under tow.
5) The type, weight and numbering system, of the anchors.
6) The proposed routing between locations
7) Drawing and details of the towing bridle arrangement and attachments
8) Crown chain size and connection
9) The type and pay-out speed of the anchor winches
10) The anchor pattern chart including water depth, the heading and
maximum allowed offset
11) Communication and channels on VHF and SSB
12) The survey chart of the area with the position of pipelines and
obstructions
13) Weather limitations
14) Soil information
15) The make up of the pennant and connection for a buoy/pennant system
and colour code system.
16) If a chain chaser system is installed give details of the make up of the
system including size/length of the pennant to be used to lower the anchor
17) The maximum crane reach and position of the cranes
18) If applicable special running procedures for passing over pipe lines
19) Procedures to lower and to set the anchors on the seabed.
20) Approaching plan, the marker buoy system and designation of the lead tug
21) Any other special procedures discussed in the pre-move meeting.
22) Discuss and if appropriate add the comments from the AHT captains.
It is a good practice, if time allows, for the barge engineer to pay a short visit to the AHT's to
discuss the plan. It is for both parties a good opportunity to check each other’s experience,
which is a very important factor in the entire operation.
6.5 ANCHOR HANDLING CHECK LIST
The Barge Engineer and/or OIM use their own checklists to prepare and follow up on the
moving procedure. The contents of the checklists are based on the experience. Alternations are
added as required because of changes in conditions or circumstances.

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55
The use of a checklist may be expressly prescribed as a company policy or serves as a reminder
for an individual. Whatever the reason, the use of a check list is a good practice The following
list serves as a guideline line to create a model for a check list for running or retrieving anchors.
List of Items to create a planning check list for Anchor
Running and Anchor Retrieving
Anchor
Retrieving
Anchor
Running
1. Completed pre-move meeting X X
2. Confirmed Longitude and Latitude of the new position X
3. Verified water depth with tide tables X
4. Heading and anchor pattern, for prevailing weather-and
current condition
X
5. Passed written information on anchor handling procedure
and rig plan to AHT’s captains
X X
6. Obtained approval from local authorities to move X X
7. Inspected and install tow wire and emergency tow wire X X
8. AHT’s. Captain names, HP, bollard pull, storage capacity,
winches, tow wire, equipment etc.
X X
9. Confirmed anchor running/retrieving sequence with AHT’s
captains
X X
10. Confirmed minimum required amount of AHT’s and bollard
pull is in accordance with move approval.
X X
11. Obtained information of soil condition X
12. Set fluke angle for soil condition X
13. Plotting charts, navigating charts and grid charts on board X X
14. Carry out a safety meeting for each shift X X
15. Arranged weather forecast service X X
16. Established maximum weather acceptable weather condition
for mooring operations
X X
17. Confirmed weather forecast for next 24- 12 – and 6 hours
before move date
X X
18. Installation of positioning system completed. Equipment
operational
X
19. Established communication channels X X

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56
20. Verified position of sub-sea pipelines and obstructions X X
21. Prepared materials (slings, shackles, buoys, pennant wires,
split pins. lead shots etc.)
X X
22. Checked availability of piggy-back anchors, additional
pennant wires and enough connections
X
23. Advised the Warranty Surveyor. Confirm date to be on board X X
24. Ballast and de-ballast procedure. Complete ballasting/de-
ballasting
X X
25. Note draft at departure and arrival X X
26. Checked condition of pennant wires and shackles. X
27. Checked buoys. No leaks. Pigtail pennant condition and
shackles
X
28. Function tested anchor winches X X
29. Loaded AHT’s with anchor handling equipment, buoys
pennants, slings, shackles, piggy-back anchor(s) etc.
X
30. Confirmed pre-tension and operation tension values X
31. Completed stability calculation. Check results with actual
draft.
X X
32. Loaded enough fuel, water and supplies X X
33. Discharged equipment and cargo not required to remain on
board
X X
34. Received warranty surveyor’s move approval X X
35. Secured all loose equipment and deck cargo. X X
36. Function tested all cranes. Snatch slings and safety slings
ready
X X
37. Verified watertight integrity, all doors and hatches closed. X X
38. Confirmed allowable offset for final position X
39. J Chaser and/or grapnel ready for use X X
40. Submitted anchor break out procedure X
41. Submitted chain chaser procedure for running and retrieving X X

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6.6 POSITIONING SYSTEMS
To position the drilling rig within a few meters of the spud location requires a high accuracy
positioning system. A service company installs the equipment on board of the rig.
The most used positioning systems are:
1) Short range systems. These systems use laser beams and microwaves. The
accuracy is within two meters. The installation of the equipment must be within a
few kilometres of the drilling rig location
2) Medium range systems. These systems (Pulse 8) use three radio wave stations on
the principle of Decca Systems but with a higher accuracy between 5 and 10
meters.
3) Long range satellite positioning systems. The most popular system nowadays is
the Global Position System (GPS). This system makes use of a Geostationary
Satellite Network. The accuracy is 5 meters or less
4) Transponder systems. Sometimes Hydrophones are placed on the sea bed or a
well head template When the rig arrives on location the hydrophone is switched
on and the location is calculated and displayed the same way as on a DP drilling
vessel
To locate the position of the anchors AHT plots his position with radar and the GPS system.
There are some limitations to each system:
1) Satellite systems can loose accuracy because of loss of differential correction data
2) Laser systems and micro wave system do not like heavy rain, dense fog and may
loose the signal by obstructions.
3) Hydrophones signals can be masked by disturbed and aerated water
4) Radio waves from the Pulse 8 system are sensitive to atmospheric conditions
All over the GPS system is now the most accurate and easy to use system.
6.7 NOTES ON APPROACHING AND LEAVING THE LOCATION
Each approach to a location or leaving a location requires a specific procedure. The following
section explains some basic principles without going into details of a specific move.
Some important factors effecting the approaching and leaving procedures are.
1) If the location is free or if we approach a congested area with other rigs or
platforms close by
2) The existing weather/current condition
3) The amount and type of AHT’s
4) The existence of sub sea obstructions within the anchor pattern area
The final decision to start to run or retrieve the anchors depends very much on the weather
condition. Ensure that the weather window is long enough to deploy at least four anchors.

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With four anchors deployed, the rig will maintain position even in a storm condition. Of course,
the best situation is to have a weather window that allows enough time to run all anchors.
If any doubt about the weather window i.e. marginal conditions it is better to wait than to
suffer. Always calculate the risk that the anchor(s) may not hold. As a guide, do not continue
anchor handling in worsening weather conditions once four anchors are set on the seabed.
Only retrieve anchors when there is enough time to retrieve all anchors and safely leave the
area before the weather deteriorates. The average time to run or retrieve one anchor is between
1½ and 2 hours. When using the PCC system, the average time may be less.
The margin to start or continue depends for a great deal too on the experience of the barge
engineer and the AHT captains.
Another significant factor is the capacity of the AHT’s. If the AHT are under powered the
weather margin is much lower.
In good weather and water depth up to 120 ft at least two AHT’s are required to arrive or depart
from the location and to be able to complete a safe anchor handling operation. For the large
Semi- Submersibles and/or deep water mooring operations it is advisable to use three AHT’s.
The ideal situation is to approach the location with the bow (heading) into the wind and current.
The wind and current act as a break. For the lead-tug it is easier to maintain the rig position into
the wind/current direction.
Assign the most powerful AHT to the windward corner of the rig.
If the first anchor is a “drop” anchor from the AHT do not worry about the exact position.
Reset the anchor after completion of deployment of the other anchors.
Run and retrieve the anchors in de-ballast condition with the anchor racks just in or above the
water level. This has the advantage that it is possible:
To see if the pennant wire is fouled around the anchor
To see fair leaders are lined up and function properly
If within crane reach to grease the fairleader before starting the operation
To see the anchor to engage the anchor rack in the correct position
To see direction of the anchor chain
When running anchors first deploy the anchors without additional work (Piggy-back., special
procedure, running over pipe lines). Run four anchors, one at each corner and follow up with
the anchors that need special procedures.
Complete fishing and grappling work before retrieving the other anchors. With four anchor still
deployed the rig will maintain position even in bad weather.

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With other rigs or platforms in the vicinity, the last anchors to retrieve should move the rig
away from the danger zone.
Again, these guidelines are not hard rules. Judge each situation together with the captains of the
AHT. Use common sense and experience.
6.8 Weather Criteria
As mentioned before it is extremely important to have a good weather forecast service set up in
time. Do not wait until the last moment. In parts of the world with very constant and
predictable weather such as tropical areas, the weather forecast service may not be available or
will not be necessary. For harsh environment areas and locations with unpredictable weather,
the weather forecast from the radio or TV is not accurate enough to predict the weather on the
mooring location. Information over the internet is nowadays another source.
From the operators economic point of view, towing- and anchor handling is a non-productive
operation. The drilling contractor may be on reduced day rate or receive no day rate at all
during the move. The OIM/Barge engineer is therefore always under pressure to finish the
anchor handling work within the shortest possible time. To take the decision to abandon the
move is sometimes difficult. These are some basic suggestions to use to make the decision
easier:
To abandon or not to start the anchor handling work is not a one-man decision.
Although the OIM is the responsible man on board he takes advice from other
experts to make a decision:
In the pre-move meeting the participants agreed on the weather limitations. Do not
change the limits except if there is a change in circumstances or conditions
Do not start the operations if the weather is marginal and deteriorates
In marginal conditions, consult the AHT’s captains. If there is doubt, call the
weather forecast service direct and discuss the situation. A good indicator is to look
at the deck of the AHT’s. If the deck takes a lot of water do not risk the life of the
AHT’s crew. With a chain chaser system the limits of operations are higher
The experience of the barge engineer and the captains of the AHT’s are very
important. The limits are lower for anchor handling work with crews without
experience. Be more patient and do not question time and again the captains about
their progress. If there are problems let the captains of the AHT sort them out and
discuss any dissatisfaction about the anchor work after the job is done.
If the AHT’s can not hold their position against the weather and/or current, it is
time to stop or not start the operation. In this respect consider too that the vessels
coming to the windward side of the rig to pick up pennants and anchors, run high
risks to collide with the rig
If different types of vessels are used the shorter AHT may be able to continue
anchor handling while the longer AHTS has to stop operations because of heavy
pitching. If two out of three AHT have higher HP the operation may continue with
only two vessel.
Allow for an eight-hour weather window to run 4 anchors.
In a congested area with other rigs, platforms or construction barges in the vicinity
do not take any risk.

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It is not possible to give exact figures for work limitations of each AHT. As an indication, the
work limit for anchor handling with the AHT or AHTS in the range between 9000 BHP to
14000 BHP is cross winds of 30 knots and about 15 ft significant wave height. With 2 knots
crosscurrents these vessels start to have problems to maintain position. A combination of wind
current and waves requires judgement on a case by case situation.
6.9 APPROACHING THE LOCATION AND RUNNING ANCHORS
The example we use in this discussion is just one of the many possible scenarios. But in general
running and retrieving anchors follow the same procedures. We assume to run eight anchors
with three AHT on a location without sub-sea obstructions and no other platforms or rigs in the
vicinity. The procedure to run or retrieve anchors with only two AHT's is not very much
different.
This easiest scenario is to approach the location into the weather and current. To approach a
location in a congested area and in the same direction of the weather and current requires
different procedures and more skill in boat handling and teamwork.
6.9.a Towing arrangement at arrival
The towing arrangement at arrival can be:
1) One Ocean Going Tug on towing the bridle. Three AHT standing by to
connect. This is typical for the arrival after a long ocean tow. The towing vessel
is not equipped for anchor handling. At a safe distance from the anchor location,
the AHT’s make the connection to the primary pennants. Release the ocean going
tug. In most cases, two AHT’s take the forward inside anchor pennants and one
AHT connects to an aft inside anchor.
2) One high powered AHT on the towing bridle. The modern high-powered AHT
have 16000 HP and 160 ton bollard pull. Although the towing characteristics may
not be as good as an ocean going tug the modern AHT are capable to perform
field tows and ocean tows. The advantage is that at arrival the towing vessel can
take part in the mooring operation. At a safe distance from the anchor location,
one AHT connects to the forward inside anchor and the second AHT connects to
one aft inside anchor. The towing vessel releases the towing bridle and connects
to the other inside forward anchor. Fig 6.2.A.
3) Two AHT’s connected to the bow (forward) anchors. The AHT’s tow from the
anchor chain or pennant wire. This is more typical for a short tow or field move.
At a safe distance from the anchor location, the third AHT connects to the aft
inside anchor and the two forward AHT’s re-arrange the towing set up. When
towing from the anchor chain the AHT needs to reconnect the anchor and pennant
wire system.
The section Towing explains and shows the various towing arrangements.

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Fig. 6.2.A. Initial set up to run anchors with three anchor handling vessels.

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Fig. 6.2.B Sequence of running anchors with three anchor handling vessels
6.9.b Moving in and Running anchors
Fig. 6.2.B Shows the sequence after the initial set up with three AHT’s at about 3 miles away
from the anchor location, followed by the approach and final position to run eight anchors. One
AHT towed the rig from the towing bridle. Two AHT are waiting for orders area. During the
approach with the three AHT’s the line distance to the vessels is approximately 400 ft.
Arrange the AHT’s to run anchors at a distance between 3 to 5 nautical miles
away from the anchor location. (1) and (2)
In this case, the two AHT’s connect to the forward SB inside anchor and the aft
Port inside anchor. The AHT at the stern assists to maintain the heading while
moving in. Her function is to stop the rig moving forward as requested. The
towing AHT releases the bridle after the two other AHT’s are safely connected.
(3) It is possible to leave the towing AHT attached to the bridle until arrival at the
anchor location. The procedure will be slightly different.
Proceed slowly toward the anchor location.(4)

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Prepare the Port aft anchor. (5). Lower Port aft anchor on the seabed and set the
anchor as close as possible to the required position. (6) If necessary, reposition
the anchor the anchor at the final stage of the mooring procedure. After the first
anchor is set on the seabed, the AHT aft moves to the other stern inside anchor
and makes the connection. (7). Continue to move into the direction of the anchor
location. Slack the stern anchor chain but maintain a low tension while moving
towards the anchor location.
At arrival on the anchor location, apply the brake to the stern anchor winch.
Watch the anchor tension and slack off if needed. Turn the rig heading into the
correct direction, with the windward anchor fairleader pointing into the direction
of the anchor position. (8) Run the windward forward anchor. Lower the anchor
to the seabed. (9)
While the two AHT’s maintain the rig in position the third vessel moves to the
next outside bow anchor. First run the inside anchors and then the breast anchors.
Normally run anchors in opposite pairs.
If necessary, reset the drop stern anchor.
Reconfirm that all parties agree on the final position.
Start the pretension procedure.
Self propelled drilling units with four or more thrusters may not use a drop anchor but proceed
to the anchor location. The rig maintains position with assistance of the thrusters. The AHT
tugs start running the four inside bow and stern anchors followed by the breast anchors. The
MOM explains the procedure to follow.
For a work-over location alongside a platform the rig will move in and run the anchors at a safe
distance from the platform. Complete the anchor tension procedure and move to the final
position alongside the platform.
6.9.c Running and Setting the Anchors with the Permanent Chain Chaser System (PCC
System)
As mentioned before it is important to verify that the chain chaser of the PCC system fits the
anchor. Bruce Anchor Limited and other manufacturers designed the ring chaser and a roller
chaser. The roller chaser reduces the friction and gives a smoother chasing process. Both
chasers accommodate chain and wire and allow easy passing of over the anchor.
When ready the AHT moves within crane reach. The example is the course of action from one
the MOM as per Fig. 6.3, 6.4. Generally, this procedure applies to running anchors with minor
differences specific for each anchor design. The pictures in Fig. 6.5 show three different
anchors and chaser arrangements.

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Lower the pennant wire and ensure that the chaser engages over the anchor shaft.
To transfer the pennant wire to the AHT use two slings. One sling (double or
single) is the connection between the pennant wire and the crane hook. This so
called the messenger of safety sling has a s purpose:
In event of fouling, it functions as a weak link that will break, prior to damaging
the crane.
It keeps the crane hook and ball at a safe distance from the crew on the AHT. The
other sling is a loose hanging sling (Lazy sling)
The other sling is a loose hanging sling (lazy sling) which enables the
crew on deck on the AHT to make a safe connection to the work wire.
(Fig. 6. 6)
When AHT captain confirms he is ready to go, start to slack off on the anchor
winch while the AHT starts to move slowly ahead. Maintain enough tension on
the system to prevent that the anchor slips through the chaser. (Fig 6.7) Do not
use thrusters at the corner when working with pennant wires or running anchors.
After securing the anchor against the stern roller of the AHT, slack off just
enough chain to touch the seabed. The crew on the AHT will check if the correct
engagement of the chaser and verify all connections are in good shape. The rig
confirms with the AHT captain when they are ready.
The AHT slowly increases to medium or full power and haul out the chain. The
rig maintains tension on the system to ensure to stretch out the chain and that the
anchor will not slip through the chaser during the running procedure. For a winch
with a dynamic pay out system, ensure that the spline clutch is engaged. Do not
exceed the maximum allowable pay out speed. If the chain catenary starts to drag
over the seabed reduce slowly the tension on the anchor winch, enough to keep
the chain stretched.
Pay out chain to the required distance. Verify distance with the positioning
system. With reduced power, the AHT continues to go ahead to stretch the chain.
The AHT lowers the anchor by slacking off the work wire. To orientate the
anchor in the correct position on the seabed the AHT continues to move ahead
with a work wire length of about 1.5 to 2 times the water depth. At this stage, the
anchor hangs still about 30 feet above the seabed.
After confirmation from the AHT captain that the anchor touches bottom the rig
starts to haul in the anchor chain and the AHT releases the tension on the work
wire/pennant. The AHT should not pull on the pennant wire. (Fig 6.8)
The rig continues to heave on the anchor winch until the tension meter shows
about 150 Kips. This figure is arguable and may be different. The purpose is to let
the anchor flukes set firmly in the soil.
The AHT must come astern and heave on the work wire. The AHT continues to
move astern in the direction of the chain and the rig to pull the chaser back over
the anchor without lifting the anchor. Experience of the captain of the AHT plays
an important role. Only after the chaser has cleared the anchor the AHT starts to
turn around with the bow in the direction of the rig
The AHT returns with the bow or stern in the direction of the rig with a work wire
length between 1.5 to 2 times the water depth The AHT knows that the chaser is
running free over each chain link because of the low tension and the jumping
action of the wire

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65
On approaching the rig, the AHT shortens the work wire to negotiate the catenary
of the system close to the rig. The AHT turn around to a safe position for the
crane to pick up the pennant chaser system. (Fig 6.9)
Avoid a bight in the chain because the heavy weight of the chain bight may cause
shock loads on the crane wire
Fig. 6.3 Example running anchor from a MOM.

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Fig. 6.4. Example from MOM showing the importance to maintain the proper tension on
the anchor line to prevent chaser slipping from the anchor.
Fig. 6.5 Chain chaser arrangements for three different anchors. Courtesy Vryhof and Bruce anchors

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Fig. 6.6. Transfer of chain chaser pennant
Fig. 6.7 Pictures from Bruce and Vryhof anchors anchor manuals showing the
importance to maintain tension when passing or returning anchors.

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Fig. 6.8 Wrong and right procedures to set an anchor. As per Vryhof’s anchor manual.
(Courtesy Vryhof anchors)
Fig 6.9 Returning the chain chaser. (Courtesy Bruce Anchors)
Wrong procedures setting an anchor
Right procedures setting an anchor

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6.9.d Running Anchors with Buoy – Pennant System
For the components of the pennant wire system see Fig 5.1
The course of action for running the buoy and pennant wire system:
Before starting the mooring operation, the barge engineer organises distribution
and loading of pennant wires, buoys, shackles, and split pins to the AHT’s. The
AHT crew spools the pennant wires on the storage wire drums. To gain time use
the maximum storage capacity of the drums and long pennant wires.
On the AHT the crew prepares the deck with one or more buoys.
When ready the AHT is called to take position within crane reach
The rig transfers the primary pennant (attached to the anchor) similar as the
procedure for the PCC system.
The running and anchor setting procedure is identical as for the PCC system. The
only difference is that there is no chaser that can slip back from the anchor
After the anchor is set on bottom, the rig applies a tension of about150 kips. The
AHT attaches the buoy to the top pennant wire and launches the buoy.
6.10 RETRIEVING ANCHORS AND DEPARTING LOCATION
6.10 a Sequence of Action to Retrieve Anchors and to Leave the Location
To retrieve the anchors and leave the location the course of action is (Fig. 6.11):
Start to retrieve all four breast anchors. Keep the AHT’s as far apart as possible.
Avoid using thrusters during retrieving operations.
The recovery sequence depends on the weather and current condition. The
upwind anchor is normally the last anchor to recover of the four inside anchors
Transfer the towing bridle to the towing vessel or AHT assigned for the tow.
Lengthen tow wire to about 500 ft.
Retrieve the last four anchors with the two remaining AHT. In case of a rig field
tow with two AHT’s towing from the bow anchor pennant wires, retrieve the
forward anchors first. The two AHT’s keep the rig heading into the wind while
the third AHT retrieves both stern anchors.(Fig. 6.11)
Turn the rig into the heading required to leave the area. Start the tow.

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Fig. 6.10. Example of anchor retrieving sequence.
1
2
3
4
4) Retrieve last fwd sb
anchor
3) Retrieve aft inside
anchors
Wind direction
1) Retrieve
breast anchors
2) Attach one AHT to
bridle. Retrieve fwd
port anchor
FWD

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71
6.9 b. Retrieving Anchors with PCC System (Fig 6.11 Step 1 to 9 as per Bruce Anchor
Handling Manual for MK4 Anchor))
The following procedure from Bruce Anchor handling manual generally applies to other drag
embedment anchors. Always verify the on board anchor procedures based on the specific
anchor design in use.
Start up and function test the anchor winch.
Call the AHT to take position within crane reach. Transfer the primary pennant as
per PCC procedure
Secure pennant wire in shark jaw or pelican hook. Disconnect crane hook.
Connect the pennant wire to the work wire. The AHT lines up into the direction
of the anchor bearing. As the vessel moves away, maintain an anchor tension of
about 50% of the test tension (approximate 150.000 lbs.). The AHT moves ahead
and slacks the work wire 1.5 to 2 times the water depth. Without enough tension
on the anchor chain, the chaser may pick up a bight and not engage over the
anchor shaft.
The twitching action of the work wire indicates that the chain chaser is moving
free along the chain. The disturbed soil around the chain on the seabed reduces
the friction when retrieving the anchor.
Monitor the AHT position between rig and AHT captain.
The chasing load increases when the chaser arrives at the part of the deep buried
chain and anchor. The captain of the AHT takes every effort to seat the chaser
onto the anchor shank to avoid damage to the anchor connection and anchor
Reduce the tension on the anchor chain. The AHT increases the power to about
50% with a heading lined up with the chain direction away from the rig. When the
chaser engages over the shaft of the anchor the tension on the chaser pennant
increases rapidly. This moment is critical because with rough weather and heavy
movement of the AHT the pennant wire can break. Avoid a vertical pull.
The normal break out procedure is to move ahead with the AHT lined up in the
direction of the chain away from the rig, to pull the anchor out along its original
penetration path. The AHT maintains a work wire length of 1.5 to 2 times the
water depth (Fig. 6.12). Another method is to almost stop the AHT but with some
tension on the work wire. The rig hauls in on the anchor winch. Once the anchor
drags the AHT starts to heave on the work wire.

Transocean offshore operation 2

Transocean offshore operation 2

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