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Deepwater Mooring Lines 2007
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Experience in Depth
Vryhof Anchors has been active in the offshore mooring system market for 35 years
giving it an unrivalled level of experience and knowledge in the requirements of
its selected clients and markets. An ISO 9001-2000 certified company; Vryhof is
committed to the development of cutting edge, market leading products and
works with its partners to ensure this philosophy is replicated across the
whole product range. Vryhofs partner, Bexco Ropes, was one of the pioneering
companies in the development of deep water polyester mooring lines introducing
the DeepRope product in the early 1990s.
Innovation, Research & Development
Vryhof Anchors has grown into a world
leader in state of the art engineering and
manufacturing of total mooring systems.
Fully understanding its clients needs are
not to be met with standard products alone
Vryhof focuses on specialisation and a
dedication to customer needs ensuringthe client reaps the benefit of innovative
product developments and the competitive
advantage it affords. The research teams are
constantly investing time and effort into the
continuous improvement of the established
product lines.
Quality, Health & Safety
ISO 9001-2000 certified the constant need forthe highest quality products and services is
fully recognised. Quality Assurance is a key
business driver and quality controls are in
place for all processes and procedures of
polyester rope manufacturing, splicing and
testing. The industry focus on constantly
improving health and safety performance is
also recognised with QHSE policies, procedures
and practices implemented and maintained.
DEEP ROPE MOORING LINES
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DEEPWATER MOORING LINES
Polyester Tether Manufacturing
Base Yarns
The fundamental building block of any
polyester tether is the high tenacity yarn
obtained from the premier manufacturing
companies in the world. The yarn is made up
of a large number of fine filaments twisted
together. Each is individually treated with a
specialist marine finish during the extrusion
process to provide improved performance.
Yarn material is specially selected according
to specific performance requirements such
as yarn on yarn abrasion and tenacity.
Subropes
Polyester tethers are manufactured from
a defined number of high efficiency sub
ropes. The subropes consist of a number of
assembled yarns twisted together in either
a right or left hand direction.
During manufacturing the yarn position and lay length is carefully
managed to ensure equal tension between yarns within the subrope.
Each subrope also has a unique marker ribbon enclosed within the
construction which will be later used to aid splicing operations.
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Full Rope Assembly
A defined number of subropes in a
combination of right and left hand lay to
meet the required project torque
considerations are laid parallel together
and overbraided with a high efficiency
polyester jacket. The diameter and strength
of the rope is determined by the number of
subropes used whereas the torque
properties, whether torque balanced or
torque matched to a wire rope, will be
determined by the lay directions of the
assembled subropes. Between the subropes
and the braided jacket a multiple layer sand
filter is installed to prevent the migration
of particles into the rope; the filter has a
capability to filter out particles of down
to 2m.
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DEEPWATER MOORING LINES
Termination Techniques
Polyester tethers are terminated with
a specialist splice which maintains the
efficiency of the rope construction.
Each subrope is identified by its unique
marker ribbon and spliced back into itself
to minimise performance loss in the event of
a damaged subrope and thereby making the
rope more damage tolerant. The completed
splice is further protected with the use of
DeltaWeb plus a two component
polyurethane. The standard connection
device to adjoining mooring components
is the steel thimble spool with a hole
dimensioned to suit a round pin shackle
however alternate more complex designs
may be considered.
Thimble spool and shackle dimensions areto a great degree project specific being
calculated from the minimum dimension
requirement from a rope design perspective
then adapted to suit project specific
requirements such as design life and
corrosion allowance. The table shows
typical dimensions considering a
10 year design life assuming a 0.4mm
per annum corrosion allowance.
Termination Hardware Dimensions
Diameter Minimum Thimble Dimensions Shackle Dimensions
Breaking Load
(mm) (tf) (kN) Flange Barrel Overall Internal Overall Internal Internal
Diameter Diameter Width Width Width Width Height
mm Dtot mm Dinw mm Wtot mm Winw mm Wtot mm Winw mm Hinw
151 700 6867 430 270 255 190 544 265 530
160 800 7848 460 290 265 200 570 275 560
175 1000 9810 510 320 285 220 620 295 610
190 1200 11772 550 350 305 240 670 315 650
219 1400 13734 625 395 335 270 735 345 725
233 1600 15696 670 420 360 295 805 370 770
246 1800 17658 705 445 385 315 850 395 805
258 2000 19620 735 465 405 335 870 415 835
WinwHinw
Dinw Winw
R
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Performance Characteristics
Diameter, Weight & MBL
Polyester tethers may be designed within
reason to any diameter or minimum breaking
load requirement as required by a given
project. For information purposes a range of
standard designs are presented in the table.
Diameter Minimum Breaking Load
Extension
Polyester tethers display a combination of
permanent and visco-elastic extension when
loaded. The various elements of extension
may be detailed as follows:
Constructional Elongation is the extension
exhibited due to the bedding down of the
rope when first loaded. This extension ispermanent and is fully accounted for after
5-10 loading cycles. Constructional extension
is load dependent with extensions between
1.6% and 3.6% of rope length expected at
load ranges between 20% and 50% of MBL.
Creep is the elongation of the polyester
material at a constant tension over time.
Creep is caused by molecular realignment
within the yarn structure plus physicaldamage to the rope structure which allows
further yarn realignment. Creep is for all
practical purposes permanent but is
relatively minor with creep elongation over
a typical project design life expected to be in
the region of 1% to 2% of the rope length.
Elastic elongation is the extension of the
rope when a load is applied which will
fully recover immediately once the load is
removed. Elastic elongation is highly load
dependent with extension of 2.5% to 7.5%
of the rope length expected at load ranges
between 20% and 50% of MBL.
Thus the elongation characteristic of the
polyester tether needs to be carefully
considered in conjunction with the predicted
load cycle range to establish the required
installed length of the tether.
Stiffness
An important consideration in the design
of a mooring system is the stiffness of thepolyester mooring line itself. The visco-elastic
behaviour exhibited by polyester tethers must
be understood to establish tether performance
with regard to stiffness. The offshore industry
looks at a number of load cases and the
associated polyester stiffness when determining
mooring line behaviour.
The graph (right above) depicts the stiffness
performance of a polyester tether in a scenariosimilar to that expected of a drift stiffness
condition. The graph demonstrates that
stiffness is predictable and stabilises between
Diameter Minimum Total Weight Submerged Weight Stiffness EA
Breaking Load (kg/m) (kg/m) (kN)
(mm) (tf) (kN) @2% @20% @2% @20% Cycling Cycling Cycling
MBL MBL MBL MBL 10-30% 20-30% 40-50%
MBL MBL MBL
151 700 6867 15.5 15.2 3.7 3.6 1.37E+05 1.61E+05 2.10E+05
160 800 7848 17.5 17.2 4.2 4.1 1.57E+05 1.84E+05 2.40E+05
175 1000 9810 20.8 20.4 5.0 4.9 1.89E+05 2.22E+05 2.89E+05
190 1200 11772 24.7 24.2 5.9 5.8 2.29E+05 2.68E+05 3.49E+05
219 1400 13734 30.6 29.9 7.3 7.2 2.74E+05 3.22E+05 4.19E+05
233 1600 15696 34.5 33.8 8.1 7.9 3.14E+05 3.68E+05 4.79E+05
246 1800 17658 38.4 35.7 8.6 8.4 3.53E+05 4.14E+05 5.39E+05
258 2000 19620 42.3 41.4 10.0 9.8 3.92E+05 4.60E+05 5.99E+05
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DEEPWATER MOORING LINES
80 and 100 cycles. In this load case the stiffness
approximates to 22xMBL, however stiffness
will increase with load to nominally 30xMBL
for loadings between 30-50% MBL.
Handling & Packing
Reels
An important aspect of the polyester rope is
its delivery package to ensure it arrives on sitein sound condition. The main rope carrier is a
specially designed steel transport reel
engineered to accommodate the package
weight and any loadings imposed during
shipment and respooling. Storage reels may
be painted with long life paint coating systems
designed to last the project lifetime. Each reel
will be subject to multi layer packaging to
protect the rope from the elements during
transit and storage as depicted in the diagram.
Spreader Beams
Lifting beams may be provided with any project with reels specifically
designed for each project reel package. The reels may be lifted from
either a flange arrangement at the reel barrel or by adding lifting
pad-eyes at the outer rim of the reel flange. Both onshore and offshorerated lifting beam in accordance with VMO Maritime Regulations can
be provided.
Installation Aids
Installation aids such as buoyancy lashings of tie-off lashings may be
applied to the polyester tether. Buoyancy lashings with a significant
holding capacity have been successfully supplied to projects such as
Shell Bonga.
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DeepRope is exclusively
marketed worldwide by Vryhof,
the worlds leading anchor manufacturer.
Vryhof Anchors BVP.O. Box 109
2900 AC Capelle a/d Yssel
The Netherlands
Phone: +31 10 266 8900
Fax: +31 10 266 8999
e-mail: [email protected]
www.vryhof.com
Copyright Vryhof Anchors 2007. DeepRope is a registered trademark
of Le Lis, a Bexco subsidiary. All information in this brochure is subject
to change without prior notice. Vryhof Anchors, Bexco or one of its
subsidiaries is not liable and/or responsible in any way for the information
provided in this brochure.
D e e p w a t e r M o o r i n g L i n e s