SlideShare ist ein Scribd-Unternehmen logo
1 von 7
Downloaden Sie, um offline zu lesen
Twelfth International Conference
                                         The Jack-Up Platform
                                     Design, Construction & Operation

                                   Stability of Jack-ups
                          Top Ten Questions From Industry to Class
                                           J. Andrew Breuer, ABS
                                          Joseph H. Rousseau, ABS

Abstract

Even with the advanced design capabilities evident among designers and builders of jack-up rigs,
there is a number of questions on matters of stability that return with notable frequency. This
paper will ask and answer the ten most frequent questions submitted to one Class Society on the
matter of stability of jack-ups.

Keywords: Offshore, Stability

Introduction

The current worldwide fleet of mobile offshore drilling units (MODUs) consists of 49 drillships
and barges, 220 submersibles and semisubmersibles, and 435 jack-ups. Given that many rigs
have been built to one of a few standard designs, one might infer that a small number of stability
analyses resolve this matter for the entire population of MODUs. The reality is very different:
most rigs have their stability evaluated several times in their service life and the number of
stability approvals by class societies is on the order of several thousand, each with its unique
features. The first set of MODU Rules were published by ABS in 1968 and unlike Rules for
conventional vessels, they included stability requirements. The record of stability calculations is
documented in the formal files of the classing society, but the ongoing dialog with industry is
mostly held in the form of “experience” in the minds of the Naval Architects.

TOP TEN

After decades of the cooperative work
between class and industry, the questions of
why, when, who, and why on matters
related to afloat stability have enriched our
experience. Below, the authors ask and
answer the ten most recurring questions.

1. Why are the approved allowable
   vertical center of gravity (AVCG)
   values lower than those submitted for
   approval?

    Stability analyses require extensive



*   The views expressed in this paper are those of the authors and do not necessarily reflect those ABS
Twelfth International Conference
The Jack-Up Platform
Design, Construction & Operation

   computer calculations. Regardless of how detailed is the documentation submitted for
   approval, it remains necessary to verify the results through independent analysis. If the
   independent calculations by the class society results are more conservative than those
   submitted, the lower AVCG will be approved. In most cases, the reason for discrepancy is
   identified.

   In the case of jack-ups, the height of the center of gravity varies within a narrow range for a
   given position of the legs. This often allows for the selection of a reasonably conservative
   AVCG that is below the allowable that would be obtained through strict application of the
   Rules. Such a conservative approach simplifies the work by the designer and class society
   and, in most instances, such values are approved.

2. Why are the submitted wind overturning moments calculated for stability not
   acceptable to class?

   Frequently, designer calculations are in conflict with the applicable class Rules for one or
   more of the following reasons:
   • Methodology used to determine the center of lateral resistance of the below the waterline
      hull, spud cans and legs (including disregard for the effect of legs below the hull
      baseline).
   • Combining standards for the determination of the shape coefficient of legs; for example,
      SNAME 5-5A combined with Cs=0.5 from the Rules.
   • Failure to take account of piping and fittings on legs such as ladders, raw water piping,
      anodes, etc.
   • Failure to take account of racks, spoilers, and other attachments that disrupt the air flow.
   • Assuming the overturning moment to be constant regardless of heel and/or direction, or
      as decaying with the cosine of the heel as is the general assumption for ship shaped
      structures.

3. Why are the submitted damage stability calculations not approved?

   The critical direction of stability for a given set of conditions (extent of damage, draft, etc) is
   the one that results in the lowest allowable VCG. To reduce the need for a lengthy set of
   calculations, some software will select the wind direction based on speculative criteria; this
   may not always be the governing azimuth. Because the critical direction is a function of
   exposure to wind, stability characteristics of the hull, position and height of the
   downflooding points and performance criteria, the only way to identify the critical condition
   is to test multiple directions of wind and identify the true critical direction. Even when all
   cautions are taken, the angles tested by the class society and the designer may be different.
   In such cases, the results may be different and the most conservative will normally prevail.

   The allowable VCG determined for the range of stability criteria, is a special case as the
   approach to this evaluation is different for each software, developer and user.




                                                -2-
Twelfth International Conference
The Jack-Up Platform
Design, Construction & Operation

   This same answer applies to intact stability calculations.

4. Why is there often disagreements regarding buoyant and non buoyant spud cans?

   The simple answer is that buoyant cans are those where the water level in the can does not
   match the sea level. These cans are likely to be permanently full of water and this amount
   must be accounted as ballast in the loading condition.

   Non buoyant cans have the water level change as the can changes “draft” or immersion, due
   to communication with the sea. In such cases, the buoyancy of the can is disregarded and the
   water inside the cans is also ignored in the loading calculation.

   The difference between these approaches is minimal and, if comparing the payload at a given
   draft, both methods should yield close results. The non-buoyant can has the benefit of an
   AVCG that is independent from the position of the legs. Buoyant cans allow a rig to attain a
   reduced draft if the ballast is removed so the cans are empty. This is only practical during the
   increasingly unusual practice of ocean tow.

5. What is the difference between Watertight and Weathertight closures above and below
   deck?

   Doors on watertight bulkheads must be of the same or higher strength as the structure around
   them. They must also be tested for that pressure to demonstrate the strength and sealing
   capability. If they are not tested onboard, they must be certified for that service. The Class
   Rules and typical regulations mention three types of doors:
   a. Remotely operated doors
   b. Manually closed doors fitted with open/closed indicators (local and centralized in a
      permanent manned room) which may be open while the unit is afloat.
   c. Doors which are to remain closed while the unit is afloat.

   The most common practice is the fitting of manually operated doors but the need to install
   signals is often missed by many designers so that builders have to be reminded of this during
   construction.

   External doors are required to be weathertight. This means that they are capable of
   preventing passage of water. They are normally tested under a 30 psi hose test and visually
   checked for leakage. When this is not possible, the surveyor can accept a “chalk” test.

   Regardless of doors, the watertight characteristic of these doors is not unidirectional. They
   must be effective with the water pressure on either side of the door.

   The Rules have no specific expectation on the type and number of closing devices. However,
   it is generally accepted that the single action (aka quick acting) door is the preferred choice
   since it only requires a turn of the hand wheel to engage all of the dogs. This is important
   since doors with a single dog engaged are not fully effective against water ingress.


                                               -3-
Twelfth International Conference
The Jack-Up Platform
Design, Construction & Operation

6. Why is Load Line assignment so complicated?

   The assignment of Load Line, or freeboard, is both required by the Class Rules and the
   country of registry. The Convention on Load Lines does not provide much room for
   alternatives. Additionally, the organizations that assign freeboard tend to be subject to close
   auditing to verify that the applicable standards are properly applied.

   The Load Line certificate is an essential document that allows a unit to operate in waters
   away from its country of registry. Thus, regardless of the extenuating conditions, jack-up
   rigs are not allowed to proceed to sea unless the necessary certificate has been issued. This
   requires the following steps to be completed:
   a. Minimum freeboard assigned on the basis of the hull geometry (so-called “tabular”
      method from the Convention)
   b. Approved stability analysis (intact and damage) to set the allowable VCG
   c. Approved Operations Manual to provide guidance on loading the unit within the AVCG
   d. Approved Lightship characteristics (usually by way of a stability test)
   e. Completed onboard survey of the conditions of assignment and the corresponding survey
      report.

   The onboard survey report is carefully reviewed to verify that vents, air pipes, ventilators,
   hatches and door sills are of an acceptable height. Drainage, hull penetrations, doors,
   portholes, railings, scuppers must also meet the Load Line regulations. This represents a
   long list of construction details that is not always clear to the many engineering disciplines
   that participate in the design of a jack-up rig.

7. Why is it necessary to redo the stability analysis when the “as-built” ventilators and air
   pipes are different from the design?

   A downflooding point is any opening that, if submerged, will lead to the flooding of any
   space in the hull. Once this occurs, the stability calculations for that condition are terminated
   and all the relevant criteria must be satisfied. Calculations are made to minimize the
   possibility of these points being submerged; if the location of an opening changes, the angle
   of inclination at which that point is submerged changes too.

   Ventilation inlet and exhaust openings, chain pipes or hawsers, open hatches, or any other
   opening that remains unprotected, are a main concern during the intact stability assessment.

   External closures that are protected by check valves or weathertight (WeT) closures are a
   similar concern in the context of damage stability analysis, as they are not effective against a
   static immersion: they are designed only to withstand an intermittent exposure to water.
   Changes to tank vents, hatches, WeT doors, etc have a similar effect on damage stability as
   the unprotected openings have on intact stability.




                                               -4-
Twelfth International Conference
The Jack-Up Platform
Design, Construction & Operation

   If the designer defines the “boundaries of weather tight and watertight protection”, these
   boundaries may be used by all engineering disciplines to place any opening at or above the
   level at which stability was evaluated. This provides flexibility to move openings as
   necessitated by construction issues, as long as the opening remains within the boundaries.

8. Why do we have so many conflicts with the execution and results of a Stability Test?

   The short answer to this question is that “If something can go wrong; it will.” The stability
   test or inclining experiment is a very important verification of the weight and center of
   gravity, and sources of error must be minimized so they do not compound with each other
   and render the results unreliable. The most frequent conflicts are associated with:
   a) Cantilever weighing. Cantilever weighing is most important when used as the inclining
      weight. The expectation is that the accuracy of this measurement is made with a 1
      percent tolerance. Most experienced yards have learned that this task requires special
      expertise. The best work is the one carried out from professionals that work on the basis
      of “trust but verify.” It is not uncommon for some yards and owners to feel that they can
      emulate the most experienced teams, and subsequently realize that this is a sensitive task.
   b) Leg weight takeoff. This issue is a problem only when the stability test is done without
      using a full complement of legs. When this is the case, weight takeoff is the most
      frequent method of determining the weight of the remaining rounds of leg to be added.
      The weight takeoff is accurate in determining the weight of the elements known to the
      designer. However, pipes, anodes, hoses, steel ladders, aerials, wiring, lights and
      protective coating are some of the items that may be overlooked.
   c) Molded or full hydrostatics. The full hydrostatics should be used as an accurate
      representation of the hull form and the appendages, and be included in the Operations
      Manual. This will improve the prediction of draft, and the determination of weight of the
      rig. This yields an accurate determination of elevated weight, and provides for the
      reversibility of predicting draft from the calculated weight (and the reverse operation or
      determining displacement on the basis of draft).
   d) “Acceptable” lightship characteristics. The ABS procedure of reviewing stability tests
      and lightship survey reports includes an independent analysis of the data obtained. The
      detail and depth of this review is often a function of the confidence built through the
      starting verification and the criticality of the results. If the submitted results are more
      conservative than the conclusions of the reviewing process, the ABS review letter will
      quote the submitted values. While the number may have been deemed conservative, it
      may be found “acceptable”. If the cause for the discrepancy is identified, and the
      conservatism could affect the capabilities of the unit (often the case on semisubmersibles),
      the submitter will be alerted to the source of the discrepancy.
   e) Inclining with water. Inclining with water is an acceptable practice but very difficult to
      execute with a high degree of accuracy. Often problems are identified after the
      completion of the test and repeating the exercise may be required.




                                              -5-
Twelfth International Conference
The Jack-Up Platform
Design, Construction & Operation

9. What equipment and controls need to be installed above the deepest damage waterline?

   Any equipment that is needed in case of an emergency, and the access to the locations where
   this equipment will be operated, must be above the final damage waterline. For jack-ups, this
   means the main deck level or above. While the following list is not exhaustive, these are the
   most frequent cases:
   • Emergency generator and switchboard
   • Batteries and other sources of emergency power
   • Remote operation of WT Closures
   • Muster stations, and embarkation stations
   • Ballast control room (semisubmersibles)
   • GA and PA
   • Radio room
   • Main navigation equipment room, bridge
   • Centralized fire monitoring equipment
   • Centralized fire control equipment
   • Dynamic positioning system controls
   • Fire extinguishing system serving various (multiple) locations

10. Are there any requirements regarding the increase in draft on an existing unit?

   Compliance with the applicable Rules and Regulations is the short answer. In practice, the
   list of regulatory expectations depends on the existing and planned equipment on board:
   a) The new draft should correspond to a freeboard that meets the geometrical requirements
        of the International Convention on Load Lines 1966.
   b) The scantlings of the unit are suitable for the new draft. On jack-up rigs, this is not a
        common issue.
   c) The jack-up must be capable of elevating in a manner such that the jacking capacity on
        the heavier loaded leg is not exceeded. For a unit classed under the 1980 (or more recent)
        ABS MODU Rules, the rig must be able to meet this expectation after the loss of one
        single component. On conventional rack-and-pinion systems, this means the loss of a
        pinion (or possibly two pinions, in the case of opposed pinion systems).
   d) The unit can be loaded to the maximum afloat variable deck load (VDL), in a realistic
        way, with minimal trim, to a VCG equal to or lower than the allowable VCG at the new
        Load Line draft.
   e) When jacking from full draft, the resulting elevated condition can meet the storm survival
        condition without jettisoning equipment or material and without laborious or complicated
        re-distribution of weights.
   f) The load distribution on the legs in the operating condition (with the cantilever loaded to
        its capacity) and storm survival condition are compatible with the approved leg and spud-
        can strength.


                                              -6-
Twelfth International Conference
The Jack-Up Platform
Design, Construction & Operation

   g) The Operations Manual is updated to reflect the new full draft load.
   h) Depending on conditions, a deadweight survey or a stability test may be required.

Conclusions
The Rules, and statutes, that apply to jack-ups are very similar for all Class Societies, Coastal
Administrations, and Flag Administrations. The fundamental concepts are well understood by
designers and builders. Most of the questions on stability find the answers in the details that are
imbedded in the body of the applicable standards. Because such details are not in the main body
of the stability standards, their correct application often escapes the attention of the designers.
The solution to this matter is in an improved communication between designer, builder, and the
Class Societies. This communication should go beyond the small group that do the stability
related work and apply to all disciplines, from the initial design through the construction of the
jack-up


References

ABS Rules for Classing and Building Offshore Mobile Drilling Units, 1968

ABS Rules for Classing and Building Mobile Offshore Drilling Units, 2008




                                               -7-

Weitere ähnliche Inhalte

Andere mochten auch

Andere mochten auch (20)

Download
DownloadDownload
Download
 
Download
DownloadDownload
Download
 
Download
DownloadDownload
Download
 
Download
DownloadDownload
Download
 
Phân tích hạ thủy khối chân đế
Phân tích hạ thủy khối chân đế Phân tích hạ thủy khối chân đế
Phân tích hạ thủy khối chân đế
 
Download
DownloadDownload
Download
 
Download
DownloadDownload
Download
 
Download
DownloadDownload
Download
 
Download
DownloadDownload
Download
 
Ly thuyet do tin cay
Ly thuyet do tin cayLy thuyet do tin cay
Ly thuyet do tin cay
 
Download
DownloadDownload
Download
 
Download
DownloadDownload
Download
 
Bao cao thuc tap tot ngiep
Bao cao thuc tap tot ngiepBao cao thuc tap tot ngiep
Bao cao thuc tap tot ngiep
 
Download here
Download hereDownload here
Download here
 
Download
DownloadDownload
Download
 
Construction of marine and offshore structures b. gerwick (second edition)
Construction of marine and offshore structures   b. gerwick (second edition)Construction of marine and offshore structures   b. gerwick (second edition)
Construction of marine and offshore structures b. gerwick (second edition)
 
P.TK - PVMS
P.TK - PVMSP.TK - PVMS
P.TK - PVMS
 
Download
DownloadDownload
Download
 
Download
DownloadDownload
Download
 
Download here
Download hereDownload here
Download here
 

Ähnlich wie Download

Safety inspection of gates
Safety inspection of gates Safety inspection of gates
Safety inspection of gates IEI GSC
 
Cswip 11-01 - plant inspection- Week 2 cours
Cswip 11-01 - plant inspection- Week 2 coursCswip 11-01 - plant inspection- Week 2 cours
Cswip 11-01 - plant inspection- Week 2 coursRafik Guerbous
 
Determination of Range of Splash of Testing Fluid during Hydro Testing of Kni...
Determination of Range of Splash of Testing Fluid during Hydro Testing of Kni...Determination of Range of Splash of Testing Fluid during Hydro Testing of Kni...
Determination of Range of Splash of Testing Fluid during Hydro Testing of Kni...ijtsrd
 
ISOPE-2010-TCP-0462 Lessons Learnt from deepwater Riser Projects
ISOPE-2010-TCP-0462 Lessons Learnt from deepwater Riser ProjectsISOPE-2010-TCP-0462 Lessons Learnt from deepwater Riser Projects
ISOPE-2010-TCP-0462 Lessons Learnt from deepwater Riser ProjectsJean-Francois Saint-Marcoux
 
Snw ht-sea-trial-paper-rev2
Snw ht-sea-trial-paper-rev2Snw ht-sea-trial-paper-rev2
Snw ht-sea-trial-paper-rev2Jerry Brown
 
Personal Dock Bbuilding 101
Personal Dock Bbuilding 101Personal Dock Bbuilding 101
Personal Dock Bbuilding 101Clean1Waterfront
 
casing and cementing _ ADCO drilling manual
casing and cementing _ ADCO drilling manualcasing and cementing _ ADCO drilling manual
casing and cementing _ ADCO drilling manualEnriqueFigueroa42
 
Crawford Tracey AIA Course: Glazing Design
Crawford Tracey AIA Course: Glazing DesignCrawford Tracey AIA Course: Glazing Design
Crawford Tracey AIA Course: Glazing DesignDonovan and Associates
 
IRJET- Preliminary Design of Floating Dry Dock
IRJET- Preliminary Design of Floating Dry DockIRJET- Preliminary Design of Floating Dry Dock
IRJET- Preliminary Design of Floating Dry DockIRJET Journal
 
"Factors Affecting the Design and Construction of High Capacity Minipiles"
"Factors Affecting the Design and Construction of High Capacity Minipiles""Factors Affecting the Design and Construction of High Capacity Minipiles"
"Factors Affecting the Design and Construction of High Capacity Minipiles"Remedy Geotechnics Ltd
 
Flow analysis of butterfly valve using cfd
Flow analysis of butterfly valve using cfdFlow analysis of butterfly valve using cfd
Flow analysis of butterfly valve using cfdeSAT Journals
 
A life cycle approach to corrosion management and asset integrity
A life cycle approach to corrosion management and asset integrityA life cycle approach to corrosion management and asset integrity
A life cycle approach to corrosion management and asset integrityOkeme Esegine PMP
 
mh_saad_resume (2) - Copy
mh_saad_resume (2) - Copymh_saad_resume (2) - Copy
mh_saad_resume (2) - Copymohamed saad
 

Ähnlich wie Download (20)

Safety inspection of gates
Safety inspection of gates Safety inspection of gates
Safety inspection of gates
 
Cswip 11-01 - plant inspection- Week 2 cours
Cswip 11-01 - plant inspection- Week 2 coursCswip 11-01 - plant inspection- Week 2 cours
Cswip 11-01 - plant inspection- Week 2 cours
 
Determination of Range of Splash of Testing Fluid during Hydro Testing of Kni...
Determination of Range of Splash of Testing Fluid during Hydro Testing of Kni...Determination of Range of Splash of Testing Fluid during Hydro Testing of Kni...
Determination of Range of Splash of Testing Fluid during Hydro Testing of Kni...
 
ISOPE-2010-TCP-0462 Lessons Learnt from deepwater Riser Projects
ISOPE-2010-TCP-0462 Lessons Learnt from deepwater Riser ProjectsISOPE-2010-TCP-0462 Lessons Learnt from deepwater Riser Projects
ISOPE-2010-TCP-0462 Lessons Learnt from deepwater Riser Projects
 
Navtec rigging service guidelines
Navtec rigging service guidelinesNavtec rigging service guidelines
Navtec rigging service guidelines
 
[IJET-V1I2P10] Authors :L. O. Osuman, A. Dosunmu , B .S. Odagme
[IJET-V1I2P10] Authors :L. O. Osuman, A. Dosunmu , B .S. Odagme [IJET-V1I2P10] Authors :L. O. Osuman, A. Dosunmu , B .S. Odagme
[IJET-V1I2P10] Authors :L. O. Osuman, A. Dosunmu , B .S. Odagme
 
Download
DownloadDownload
Download
 
Snw ht-sea-trial-paper-rev2
Snw ht-sea-trial-paper-rev2Snw ht-sea-trial-paper-rev2
Snw ht-sea-trial-paper-rev2
 
Personal Dock Bbuilding 101
Personal Dock Bbuilding 101Personal Dock Bbuilding 101
Personal Dock Bbuilding 101
 
casing and cementing _ ADCO drilling manual
casing and cementing _ ADCO drilling manualcasing and cementing _ ADCO drilling manual
casing and cementing _ ADCO drilling manual
 
Crawford Tracey AIA Course: Glazing Design
Crawford Tracey AIA Course: Glazing DesignCrawford Tracey AIA Course: Glazing Design
Crawford Tracey AIA Course: Glazing Design
 
IRJET- Preliminary Design of Floating Dry Dock
IRJET- Preliminary Design of Floating Dry DockIRJET- Preliminary Design of Floating Dry Dock
IRJET- Preliminary Design of Floating Dry Dock
 
"Factors Affecting the Design and Construction of High Capacity Minipiles"
"Factors Affecting the Design and Construction of High Capacity Minipiles""Factors Affecting the Design and Construction of High Capacity Minipiles"
"Factors Affecting the Design and Construction of High Capacity Minipiles"
 
343312365 mt-ppt
343312365 mt-ppt343312365 mt-ppt
343312365 mt-ppt
 
Chinmoy Pathak Choudhury_LTV Internship report
Chinmoy Pathak Choudhury_LTV Internship reportChinmoy Pathak Choudhury_LTV Internship report
Chinmoy Pathak Choudhury_LTV Internship report
 
COMPL OF WORKS1
COMPL OF WORKS1COMPL OF WORKS1
COMPL OF WORKS1
 
Flow analysis of butterfly valve using cfd
Flow analysis of butterfly valve using cfdFlow analysis of butterfly valve using cfd
Flow analysis of butterfly valve using cfd
 
A life cycle approach to corrosion management and asset integrity
A life cycle approach to corrosion management and asset integrityA life cycle approach to corrosion management and asset integrity
A life cycle approach to corrosion management and asset integrity
 
mh_saad_resume (2) - Copy
mh_saad_resume (2) - Copymh_saad_resume (2) - Copy
mh_saad_resume (2) - Copy
 
CFD_salesmaterial_261215
CFD_salesmaterial_261215CFD_salesmaterial_261215
CFD_salesmaterial_261215
 

Kürzlich hochgeladen

Machine Learning Model Validation (Aijun Zhang 2024).pdf
Machine Learning Model Validation (Aijun Zhang 2024).pdfMachine Learning Model Validation (Aijun Zhang 2024).pdf
Machine Learning Model Validation (Aijun Zhang 2024).pdfAijun Zhang
 
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...Will Schroeder
 
Linked Data in Production: Moving Beyond Ontologies
Linked Data in Production: Moving Beyond OntologiesLinked Data in Production: Moving Beyond Ontologies
Linked Data in Production: Moving Beyond OntologiesDavid Newbury
 
Designing A Time bound resource download URL
Designing A Time bound resource download URLDesigning A Time bound resource download URL
Designing A Time bound resource download URLRuncy Oommen
 
KubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCost
KubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCostKubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCost
KubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCostMatt Ray
 
UiPath Platform: The Backend Engine Powering Your Automation - Session 1
UiPath Platform: The Backend Engine Powering Your Automation - Session 1UiPath Platform: The Backend Engine Powering Your Automation - Session 1
UiPath Platform: The Backend Engine Powering Your Automation - Session 1DianaGray10
 
Videogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdfVideogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdfinfogdgmi
 
Artificial Intelligence & SEO Trends for 2024
Artificial Intelligence & SEO Trends for 2024Artificial Intelligence & SEO Trends for 2024
Artificial Intelligence & SEO Trends for 2024D Cloud Solutions
 
VoIP Service and Marketing using Odoo and Asterisk PBX
VoIP Service and Marketing using Odoo and Asterisk PBXVoIP Service and Marketing using Odoo and Asterisk PBX
VoIP Service and Marketing using Odoo and Asterisk PBXTarek Kalaji
 
NIST Cybersecurity Framework (CSF) 2.0 Workshop
NIST Cybersecurity Framework (CSF) 2.0 WorkshopNIST Cybersecurity Framework (CSF) 2.0 Workshop
NIST Cybersecurity Framework (CSF) 2.0 WorkshopBachir Benyammi
 
UiPath Solutions Management Preview - Northern CA Chapter - March 22.pdf
UiPath Solutions Management Preview - Northern CA Chapter - March 22.pdfUiPath Solutions Management Preview - Northern CA Chapter - March 22.pdf
UiPath Solutions Management Preview - Northern CA Chapter - March 22.pdfDianaGray10
 
UiPath Studio Web workshop series - Day 8
UiPath Studio Web workshop series - Day 8UiPath Studio Web workshop series - Day 8
UiPath Studio Web workshop series - Day 8DianaGray10
 
COMPUTER 10: Lesson 7 - File Storage and Online Collaboration
COMPUTER 10: Lesson 7 - File Storage and Online CollaborationCOMPUTER 10: Lesson 7 - File Storage and Online Collaboration
COMPUTER 10: Lesson 7 - File Storage and Online Collaborationbruanjhuli
 
Bird eye's view on Camunda open source ecosystem
Bird eye's view on Camunda open source ecosystemBird eye's view on Camunda open source ecosystem
Bird eye's view on Camunda open source ecosystemAsko Soukka
 
9 Steps For Building Winning Founding Team
9 Steps For Building Winning Founding Team9 Steps For Building Winning Founding Team
9 Steps For Building Winning Founding TeamAdam Moalla
 
UiPath Studio Web workshop series - Day 6
UiPath Studio Web workshop series - Day 6UiPath Studio Web workshop series - Day 6
UiPath Studio Web workshop series - Day 6DianaGray10
 
Igniting Next Level Productivity with AI-Infused Data Integration Workflows
Igniting Next Level Productivity with AI-Infused Data Integration WorkflowsIgniting Next Level Productivity with AI-Infused Data Integration Workflows
Igniting Next Level Productivity with AI-Infused Data Integration WorkflowsSafe Software
 
Empowering Africa's Next Generation: The AI Leadership Blueprint
Empowering Africa's Next Generation: The AI Leadership BlueprintEmpowering Africa's Next Generation: The AI Leadership Blueprint
Empowering Africa's Next Generation: The AI Leadership BlueprintMahmoud Rabie
 

Kürzlich hochgeladen (20)

Machine Learning Model Validation (Aijun Zhang 2024).pdf
Machine Learning Model Validation (Aijun Zhang 2024).pdfMachine Learning Model Validation (Aijun Zhang 2024).pdf
Machine Learning Model Validation (Aijun Zhang 2024).pdf
 
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
Apres-Cyber - The Data Dilemma: Bridging Offensive Operations and Machine Lea...
 
Linked Data in Production: Moving Beyond Ontologies
Linked Data in Production: Moving Beyond OntologiesLinked Data in Production: Moving Beyond Ontologies
Linked Data in Production: Moving Beyond Ontologies
 
Designing A Time bound resource download URL
Designing A Time bound resource download URLDesigning A Time bound resource download URL
Designing A Time bound resource download URL
 
KubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCost
KubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCostKubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCost
KubeConEU24-Monitoring Kubernetes and Cloud Spend with OpenCost
 
20230104 - machine vision
20230104 - machine vision20230104 - machine vision
20230104 - machine vision
 
UiPath Platform: The Backend Engine Powering Your Automation - Session 1
UiPath Platform: The Backend Engine Powering Your Automation - Session 1UiPath Platform: The Backend Engine Powering Your Automation - Session 1
UiPath Platform: The Backend Engine Powering Your Automation - Session 1
 
Videogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdfVideogame localization & technology_ how to enhance the power of translation.pdf
Videogame localization & technology_ how to enhance the power of translation.pdf
 
Artificial Intelligence & SEO Trends for 2024
Artificial Intelligence & SEO Trends for 2024Artificial Intelligence & SEO Trends for 2024
Artificial Intelligence & SEO Trends for 2024
 
VoIP Service and Marketing using Odoo and Asterisk PBX
VoIP Service and Marketing using Odoo and Asterisk PBXVoIP Service and Marketing using Odoo and Asterisk PBX
VoIP Service and Marketing using Odoo and Asterisk PBX
 
20150722 - AGV
20150722 - AGV20150722 - AGV
20150722 - AGV
 
NIST Cybersecurity Framework (CSF) 2.0 Workshop
NIST Cybersecurity Framework (CSF) 2.0 WorkshopNIST Cybersecurity Framework (CSF) 2.0 Workshop
NIST Cybersecurity Framework (CSF) 2.0 Workshop
 
UiPath Solutions Management Preview - Northern CA Chapter - March 22.pdf
UiPath Solutions Management Preview - Northern CA Chapter - March 22.pdfUiPath Solutions Management Preview - Northern CA Chapter - March 22.pdf
UiPath Solutions Management Preview - Northern CA Chapter - March 22.pdf
 
UiPath Studio Web workshop series - Day 8
UiPath Studio Web workshop series - Day 8UiPath Studio Web workshop series - Day 8
UiPath Studio Web workshop series - Day 8
 
COMPUTER 10: Lesson 7 - File Storage and Online Collaboration
COMPUTER 10: Lesson 7 - File Storage and Online CollaborationCOMPUTER 10: Lesson 7 - File Storage and Online Collaboration
COMPUTER 10: Lesson 7 - File Storage and Online Collaboration
 
Bird eye's view on Camunda open source ecosystem
Bird eye's view on Camunda open source ecosystemBird eye's view on Camunda open source ecosystem
Bird eye's view on Camunda open source ecosystem
 
9 Steps For Building Winning Founding Team
9 Steps For Building Winning Founding Team9 Steps For Building Winning Founding Team
9 Steps For Building Winning Founding Team
 
UiPath Studio Web workshop series - Day 6
UiPath Studio Web workshop series - Day 6UiPath Studio Web workshop series - Day 6
UiPath Studio Web workshop series - Day 6
 
Igniting Next Level Productivity with AI-Infused Data Integration Workflows
Igniting Next Level Productivity with AI-Infused Data Integration WorkflowsIgniting Next Level Productivity with AI-Infused Data Integration Workflows
Igniting Next Level Productivity with AI-Infused Data Integration Workflows
 
Empowering Africa's Next Generation: The AI Leadership Blueprint
Empowering Africa's Next Generation: The AI Leadership BlueprintEmpowering Africa's Next Generation: The AI Leadership Blueprint
Empowering Africa's Next Generation: The AI Leadership Blueprint
 

Download

  • 1. Twelfth International Conference The Jack-Up Platform Design, Construction & Operation Stability of Jack-ups Top Ten Questions From Industry to Class J. Andrew Breuer, ABS Joseph H. Rousseau, ABS Abstract Even with the advanced design capabilities evident among designers and builders of jack-up rigs, there is a number of questions on matters of stability that return with notable frequency. This paper will ask and answer the ten most frequent questions submitted to one Class Society on the matter of stability of jack-ups. Keywords: Offshore, Stability Introduction The current worldwide fleet of mobile offshore drilling units (MODUs) consists of 49 drillships and barges, 220 submersibles and semisubmersibles, and 435 jack-ups. Given that many rigs have been built to one of a few standard designs, one might infer that a small number of stability analyses resolve this matter for the entire population of MODUs. The reality is very different: most rigs have their stability evaluated several times in their service life and the number of stability approvals by class societies is on the order of several thousand, each with its unique features. The first set of MODU Rules were published by ABS in 1968 and unlike Rules for conventional vessels, they included stability requirements. The record of stability calculations is documented in the formal files of the classing society, but the ongoing dialog with industry is mostly held in the form of “experience” in the minds of the Naval Architects. TOP TEN After decades of the cooperative work between class and industry, the questions of why, when, who, and why on matters related to afloat stability have enriched our experience. Below, the authors ask and answer the ten most recurring questions. 1. Why are the approved allowable vertical center of gravity (AVCG) values lower than those submitted for approval? Stability analyses require extensive * The views expressed in this paper are those of the authors and do not necessarily reflect those ABS
  • 2. Twelfth International Conference The Jack-Up Platform Design, Construction & Operation computer calculations. Regardless of how detailed is the documentation submitted for approval, it remains necessary to verify the results through independent analysis. If the independent calculations by the class society results are more conservative than those submitted, the lower AVCG will be approved. In most cases, the reason for discrepancy is identified. In the case of jack-ups, the height of the center of gravity varies within a narrow range for a given position of the legs. This often allows for the selection of a reasonably conservative AVCG that is below the allowable that would be obtained through strict application of the Rules. Such a conservative approach simplifies the work by the designer and class society and, in most instances, such values are approved. 2. Why are the submitted wind overturning moments calculated for stability not acceptable to class? Frequently, designer calculations are in conflict with the applicable class Rules for one or more of the following reasons: • Methodology used to determine the center of lateral resistance of the below the waterline hull, spud cans and legs (including disregard for the effect of legs below the hull baseline). • Combining standards for the determination of the shape coefficient of legs; for example, SNAME 5-5A combined with Cs=0.5 from the Rules. • Failure to take account of piping and fittings on legs such as ladders, raw water piping, anodes, etc. • Failure to take account of racks, spoilers, and other attachments that disrupt the air flow. • Assuming the overturning moment to be constant regardless of heel and/or direction, or as decaying with the cosine of the heel as is the general assumption for ship shaped structures. 3. Why are the submitted damage stability calculations not approved? The critical direction of stability for a given set of conditions (extent of damage, draft, etc) is the one that results in the lowest allowable VCG. To reduce the need for a lengthy set of calculations, some software will select the wind direction based on speculative criteria; this may not always be the governing azimuth. Because the critical direction is a function of exposure to wind, stability characteristics of the hull, position and height of the downflooding points and performance criteria, the only way to identify the critical condition is to test multiple directions of wind and identify the true critical direction. Even when all cautions are taken, the angles tested by the class society and the designer may be different. In such cases, the results may be different and the most conservative will normally prevail. The allowable VCG determined for the range of stability criteria, is a special case as the approach to this evaluation is different for each software, developer and user. -2-
  • 3. Twelfth International Conference The Jack-Up Platform Design, Construction & Operation This same answer applies to intact stability calculations. 4. Why is there often disagreements regarding buoyant and non buoyant spud cans? The simple answer is that buoyant cans are those where the water level in the can does not match the sea level. These cans are likely to be permanently full of water and this amount must be accounted as ballast in the loading condition. Non buoyant cans have the water level change as the can changes “draft” or immersion, due to communication with the sea. In such cases, the buoyancy of the can is disregarded and the water inside the cans is also ignored in the loading calculation. The difference between these approaches is minimal and, if comparing the payload at a given draft, both methods should yield close results. The non-buoyant can has the benefit of an AVCG that is independent from the position of the legs. Buoyant cans allow a rig to attain a reduced draft if the ballast is removed so the cans are empty. This is only practical during the increasingly unusual practice of ocean tow. 5. What is the difference between Watertight and Weathertight closures above and below deck? Doors on watertight bulkheads must be of the same or higher strength as the structure around them. They must also be tested for that pressure to demonstrate the strength and sealing capability. If they are not tested onboard, they must be certified for that service. The Class Rules and typical regulations mention three types of doors: a. Remotely operated doors b. Manually closed doors fitted with open/closed indicators (local and centralized in a permanent manned room) which may be open while the unit is afloat. c. Doors which are to remain closed while the unit is afloat. The most common practice is the fitting of manually operated doors but the need to install signals is often missed by many designers so that builders have to be reminded of this during construction. External doors are required to be weathertight. This means that they are capable of preventing passage of water. They are normally tested under a 30 psi hose test and visually checked for leakage. When this is not possible, the surveyor can accept a “chalk” test. Regardless of doors, the watertight characteristic of these doors is not unidirectional. They must be effective with the water pressure on either side of the door. The Rules have no specific expectation on the type and number of closing devices. However, it is generally accepted that the single action (aka quick acting) door is the preferred choice since it only requires a turn of the hand wheel to engage all of the dogs. This is important since doors with a single dog engaged are not fully effective against water ingress. -3-
  • 4. Twelfth International Conference The Jack-Up Platform Design, Construction & Operation 6. Why is Load Line assignment so complicated? The assignment of Load Line, or freeboard, is both required by the Class Rules and the country of registry. The Convention on Load Lines does not provide much room for alternatives. Additionally, the organizations that assign freeboard tend to be subject to close auditing to verify that the applicable standards are properly applied. The Load Line certificate is an essential document that allows a unit to operate in waters away from its country of registry. Thus, regardless of the extenuating conditions, jack-up rigs are not allowed to proceed to sea unless the necessary certificate has been issued. This requires the following steps to be completed: a. Minimum freeboard assigned on the basis of the hull geometry (so-called “tabular” method from the Convention) b. Approved stability analysis (intact and damage) to set the allowable VCG c. Approved Operations Manual to provide guidance on loading the unit within the AVCG d. Approved Lightship characteristics (usually by way of a stability test) e. Completed onboard survey of the conditions of assignment and the corresponding survey report. The onboard survey report is carefully reviewed to verify that vents, air pipes, ventilators, hatches and door sills are of an acceptable height. Drainage, hull penetrations, doors, portholes, railings, scuppers must also meet the Load Line regulations. This represents a long list of construction details that is not always clear to the many engineering disciplines that participate in the design of a jack-up rig. 7. Why is it necessary to redo the stability analysis when the “as-built” ventilators and air pipes are different from the design? A downflooding point is any opening that, if submerged, will lead to the flooding of any space in the hull. Once this occurs, the stability calculations for that condition are terminated and all the relevant criteria must be satisfied. Calculations are made to minimize the possibility of these points being submerged; if the location of an opening changes, the angle of inclination at which that point is submerged changes too. Ventilation inlet and exhaust openings, chain pipes or hawsers, open hatches, or any other opening that remains unprotected, are a main concern during the intact stability assessment. External closures that are protected by check valves or weathertight (WeT) closures are a similar concern in the context of damage stability analysis, as they are not effective against a static immersion: they are designed only to withstand an intermittent exposure to water. Changes to tank vents, hatches, WeT doors, etc have a similar effect on damage stability as the unprotected openings have on intact stability. -4-
  • 5. Twelfth International Conference The Jack-Up Platform Design, Construction & Operation If the designer defines the “boundaries of weather tight and watertight protection”, these boundaries may be used by all engineering disciplines to place any opening at or above the level at which stability was evaluated. This provides flexibility to move openings as necessitated by construction issues, as long as the opening remains within the boundaries. 8. Why do we have so many conflicts with the execution and results of a Stability Test? The short answer to this question is that “If something can go wrong; it will.” The stability test or inclining experiment is a very important verification of the weight and center of gravity, and sources of error must be minimized so they do not compound with each other and render the results unreliable. The most frequent conflicts are associated with: a) Cantilever weighing. Cantilever weighing is most important when used as the inclining weight. The expectation is that the accuracy of this measurement is made with a 1 percent tolerance. Most experienced yards have learned that this task requires special expertise. The best work is the one carried out from professionals that work on the basis of “trust but verify.” It is not uncommon for some yards and owners to feel that they can emulate the most experienced teams, and subsequently realize that this is a sensitive task. b) Leg weight takeoff. This issue is a problem only when the stability test is done without using a full complement of legs. When this is the case, weight takeoff is the most frequent method of determining the weight of the remaining rounds of leg to be added. The weight takeoff is accurate in determining the weight of the elements known to the designer. However, pipes, anodes, hoses, steel ladders, aerials, wiring, lights and protective coating are some of the items that may be overlooked. c) Molded or full hydrostatics. The full hydrostatics should be used as an accurate representation of the hull form and the appendages, and be included in the Operations Manual. This will improve the prediction of draft, and the determination of weight of the rig. This yields an accurate determination of elevated weight, and provides for the reversibility of predicting draft from the calculated weight (and the reverse operation or determining displacement on the basis of draft). d) “Acceptable” lightship characteristics. The ABS procedure of reviewing stability tests and lightship survey reports includes an independent analysis of the data obtained. The detail and depth of this review is often a function of the confidence built through the starting verification and the criticality of the results. If the submitted results are more conservative than the conclusions of the reviewing process, the ABS review letter will quote the submitted values. While the number may have been deemed conservative, it may be found “acceptable”. If the cause for the discrepancy is identified, and the conservatism could affect the capabilities of the unit (often the case on semisubmersibles), the submitter will be alerted to the source of the discrepancy. e) Inclining with water. Inclining with water is an acceptable practice but very difficult to execute with a high degree of accuracy. Often problems are identified after the completion of the test and repeating the exercise may be required. -5-
  • 6. Twelfth International Conference The Jack-Up Platform Design, Construction & Operation 9. What equipment and controls need to be installed above the deepest damage waterline? Any equipment that is needed in case of an emergency, and the access to the locations where this equipment will be operated, must be above the final damage waterline. For jack-ups, this means the main deck level or above. While the following list is not exhaustive, these are the most frequent cases: • Emergency generator and switchboard • Batteries and other sources of emergency power • Remote operation of WT Closures • Muster stations, and embarkation stations • Ballast control room (semisubmersibles) • GA and PA • Radio room • Main navigation equipment room, bridge • Centralized fire monitoring equipment • Centralized fire control equipment • Dynamic positioning system controls • Fire extinguishing system serving various (multiple) locations 10. Are there any requirements regarding the increase in draft on an existing unit? Compliance with the applicable Rules and Regulations is the short answer. In practice, the list of regulatory expectations depends on the existing and planned equipment on board: a) The new draft should correspond to a freeboard that meets the geometrical requirements of the International Convention on Load Lines 1966. b) The scantlings of the unit are suitable for the new draft. On jack-up rigs, this is not a common issue. c) The jack-up must be capable of elevating in a manner such that the jacking capacity on the heavier loaded leg is not exceeded. For a unit classed under the 1980 (or more recent) ABS MODU Rules, the rig must be able to meet this expectation after the loss of one single component. On conventional rack-and-pinion systems, this means the loss of a pinion (or possibly two pinions, in the case of opposed pinion systems). d) The unit can be loaded to the maximum afloat variable deck load (VDL), in a realistic way, with minimal trim, to a VCG equal to or lower than the allowable VCG at the new Load Line draft. e) When jacking from full draft, the resulting elevated condition can meet the storm survival condition without jettisoning equipment or material and without laborious or complicated re-distribution of weights. f) The load distribution on the legs in the operating condition (with the cantilever loaded to its capacity) and storm survival condition are compatible with the approved leg and spud- can strength. -6-
  • 7. Twelfth International Conference The Jack-Up Platform Design, Construction & Operation g) The Operations Manual is updated to reflect the new full draft load. h) Depending on conditions, a deadweight survey or a stability test may be required. Conclusions The Rules, and statutes, that apply to jack-ups are very similar for all Class Societies, Coastal Administrations, and Flag Administrations. The fundamental concepts are well understood by designers and builders. Most of the questions on stability find the answers in the details that are imbedded in the body of the applicable standards. Because such details are not in the main body of the stability standards, their correct application often escapes the attention of the designers. The solution to this matter is in an improved communication between designer, builder, and the Class Societies. This communication should go beyond the small group that do the stability related work and apply to all disciplines, from the initial design through the construction of the jack-up References ABS Rules for Classing and Building Offshore Mobile Drilling Units, 1968 ABS Rules for Classing and Building Mobile Offshore Drilling Units, 2008 -7-