1、 Guidance Notes on In-service Hull Stability Verification GUIDANCE NOTES ON IN-SERVICE HULL STABILITY VERIFICATION OCTOBER 2017 American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 2017 American Bureau of Shipping. All rights reserved. ABS Plaza 16855 Northcha
2、se Drive Houston, TX 77060 USA Foreword Foreword 7-2-5/5 of the ABS Rules for Building and Classing Mobile Offshore Drilling Units (MODU Rules) requires ABS verification of an effective weight control program throughout the operational life of all column-stabilized units. Similar requirements apply
3、to any other column-stabilized units, such as a tender unit, or an accommodation unit. These Guidance Notes provide technical recommendations and guidance for monitoring lightship weight and vertical center of gravity while a column-stabilized unit is in service. Having a satisfactory in-service hul
4、l stability verification program may avoid the excess time and cost spent for preparation and completion of an inclining test. The in-service hull stability verification program determines the location of vertical center of gravity of a column-stabilized unit at the operating location. This is achie
5、ved by performing frequent inclining tests at regular intervals at sea. Allowances can be made for the mooring and other external forces. By applying the in-service hull stability verification program, trends are developed from multiple tests, and these trends can be used to help identify any unacco
6、unted weight onboard. This results in the improvement of the accuracy of the weight log. These Guidance Notes become effective on the first day of the month of publication. Users are advised to check periodically on the ABS website www.eagle.org to verify that this version of these Guidance Notes is
7、 the most current. We welcome your feedback. Comments or suggestions can be sent electronically by email to rsdeagle.org. Terms of Use The information presented herein is intended solely to assist the reader in the methodologies and/or techniques discussed. These Guidance Notes do not and cannot rep
8、lace the analysis and/or advice of a qualified professional. It is the responsibility of the reader to perform their own assessment and obtain professional advice. Information contained herein is considered to be pertinent at the time of publication, but may be invalidated as a result of subsequent
9、legislations, regulations, standards, methods, and/or more updated information and the reader assumes full responsibility for compliance. This publication may not be copied or redistributed in part or in whole without prior written consent from ABS. ii ABSGUIDANCE NOTES ON IN-SERVICE HULL STABILITY
10、VERIFICATION .2017 Table of Contents GUIDANCE NOTES ON IN-SERVICE HULL STABILITY VERIFICATION CONTENTS SECTION 1 Introduction 5 1 General . 5 3 Objective . 5 5 Scope and Application 5 7 Definitions . 5 9 Abbreviations 6 SECTION 2 In-Service Hull Stability Verification Procedure 7 1 General . 7 3 Typ
11、ical System Components 7 3.1 Inclinometer . 7 3.3 Hydrometer 7 3.5 Draft Gauge . 7 3.7 Tank Sounding Device 7 3.9 Mooring Tension Sensor . 8 3.11 Onboard Software . 8 3.13 On Shore Analysis . 8 5 Environmental Conditions . 8 7 Preparation and Procedure for In Service Hull Stability Verification 8 7.
12、1 Unit Condition 8 7.3 Tank Conditions and Free Surface Effects 8 7.5 Mooring Arrangements . 9 7.7 List and Trim 9 7.9 Test Weights 9 7.11 Communication . 10 7.13 Dynamic Positioning Systems . 10 9 Reporting In-service Hull Stability Verification Results . 10 SECTION 3 Installation, Operation and Ma
13、intenance . 12 1 Location of Measurement Devices . 12 3 Installation Report and Operations Manual 12 5 Verification of Operability 12 ABSGUIDANCE NOTES ON IN-SERVICE HULL STABILITY VERIFICATION .2017 iii 7 Verification of Equipment Performance In-Service . 13 7.1 Access to Instruments . 13 7.3 Calib
14、ration . 13 7.5 Performance 13 SECTION 4 Monitoring and Record Keeping . 14 1 New Construction 14 3 Existing Units in Operation 14 3.1 Weight Management 14 3.3 Lightweight Survey 14 3.5 In-Service Lightship Displacement Verification 14 3.7 Discrepancy in Lightship Alteration Log and In-service Light
15、ship Displacement . 14 3.9 Recommendation for Conservative Positions 15 5 Modifications . 15 APPENDIX 1 References 16 iv ABSGUIDANCE NOTES ON IN-SERVICE HULL STABILITY VERIFICATION .2017 Section 1: Introduction SECTION 1 Introduction 1 General The in-service hull stability verification program allow
16、s the location of vertical center of gravity of a Column-Stabilized Unit (CSU), hereafter referred as “unit”, to be determined throughout its operation life at any point in time. This is achieved by performing frequent inclining tests at regular intervals at sea. Allowances can be made for the moori
17、ng and other external forces. By applying the in-service hull stability verification program, trends developed from multiple in-service hull stability verification tests can be used to help identify unaccounted weight onboard and update the weight log accordingly. This results in a reduction in weig
18、ht log discrepancies, and helps meet regulatory requirements. In comparison, a conventional inclining test requires the unit to be transported to a sheltered location in order to determine the vertical center of gravity (VCG), which is only known when the inclining test is complete. 7-2-5/5 of the A
19、BS MODU Rules and 3.1.5 of the IMO Code for the Construction and Equipment of Mobile Offshore Drilling, 2009 (MODU Code) requires a lightweight survey or an inclining test to be conducted during a CSUs first Special Survey of Hull. If the survey or test during first Special Survey demonstrated that
20、the owner was maintaining an effective weight-control program, and onboard records/log of all weight changes throughout the CSU was well maintained in support of daily operations, lightship displacement may be verified by an in-service hull stability verification program described in these Guidance
21、Notes. 3 Objective These Guidance Notes provide recommendations and technical guidance on verifying the lightship weight and vertical center of gravity while the unit is in service. They supplement the following Rules for satisfying the classification requirements relevant to weight control: ABS Rul
22、es for Building and Classing Mobile Offshore Drilling Units (MODU Rules) ABS Guide for Building and Classing Mobile Offshore Units (MOU Guide) IMO Code for the Construction and Equipment of Mobile Offshore Drilling, 2009 (MODU Code) 5 Scope and Application These Guidance Notes are primarily applicab
23、le to in-service hull stability verification of Column-Stabilized Units (CSU) at the operating location under favorable environmental conditions. Production installations may require special consideration. Prior to acceptance for statutory purposes, flag State approval is required. 7 Definitions ABS
24、 Recognized External Specialist. Service suppliers, not employed by ABS, who at the request of an equipment manufacturer, shipyard, units owner or other clients provide services for a ship or a MODU such as inspection, measurements, test or maintenance of safety systems and equipment, the results of
25、 which are used by surveyors in making decisions affecting classification or statutory certification and services. For more information, please refer to: http:/ww2.eagle.org/en/rules-and-resources/recognized-specialists.html, or contact Corporate ABS Programs at externalspecialisteagle.org. Deadweig
26、ht. The weight of the unit excluding light weight. Thus, Displacement = Lightweight + Deadweight. ABSGUIDANCE NOTES ON IN-SERVICE HULL STABILITY VERIFICATION .2017 5 Section 1 Introduction Displacement. Total weight of the unit. For a freely floating body, this is equal to the weight of the displace
27、d water. Displacement Verification. The lightship displacement is verified in operation by comparing the calculated and observed draft. This provision was introduced in IMO MODU Code 2009 to facilitate renewal survey of structures with adequate weight control programs. Draft. The molded draft is the
28、 vertical distance from the molded base line to the assigned load waterline. Inclining Test. A series of measurements taken by moving a weight in transverse and longitudinal direction and measuring corresponding heel and trim angles. From this information, the units vertical center of gravity is det
29、ermined. The inclining procedure is submitted to ABS for review prior to the test and the inclining test is carried out in the presence of an attending ABS Surveyor. The inclining test is referred to as “conventional inclining test” in this document for clarity. In-service. The unit located at its o
30、perating site, and thus subject to environmental loads. Lightweight. Lightweight is the displacement of the complete unit with all of its machinery, equipment and outfit, including permanent ballast, required spare parts and liquids in machinery and piping to their working levels but without liquids
31、 in storage or reserve supply tanks, items of consumable or variable loads, stores or crews and their effects. Lightweight Survey. A survey carried out at the time of the stability test to audit all items which must be added, deducted, or relocated on the unit so that the unit can be adjusted to the
32、 lightship condition. The weight and location of each item are accurately determined. Using this information, the unit draft levels and hydrostatic properties, the lightship displacement and longitudinal and transverse center of gravity may be obtained. Relative Density (Specific Gravity). The ratio
33、 of the mass of a material at a given temperature to the mass of gas-free distilled water of the same volume at the same or a different temperature. The reference temperature of the material and water should be explicitly stated. 9 Abbreviations ASTM: American Society for Testing and Materials, curr
34、ently referred as ASTM International CSU: Column-Stabilized Unit GM: Distance from center of gravity to the metacenter IMO: International Maritime Organization MODU: Mobile Offshore Drilling Unit VCG: Vertical Center of Gravity 6 ABSGUIDANCE NOTES ON IN-SERVICE HULL STABILITY VERIFICATION .2017 Sect
35、ion 2: In- Service Hull Stability Verification Procedure SECTION 2 In-Service Hull Stability Verification Procedure 1 General The in-service hull stability verification uses a number of sensors to obtain the inclination angle, mooring and riser tensions, relative density and temperature of the seawa
36、ter, unit draft and tank contents. The equipment used should be checked for operability conditions and accuracy. The unit should be prepared prior to performing the onsite test. The test schedule and the unit particular information should be communicated to the involved parties. Best practices for d
37、ata acquisition and test result reporting specific to the system used for the in-service hull stability verification should be followed. The external specialist providing this service should be evaluated based on organizational and technical capabilities to carry out the required services. Further d
38、etail could be found in the ABS Recognized External Specialist program. 3 Typical System Components 3.1 Inclinometer An inclinometer can be used to measure the change in the unit heel or trim instead of a pendulum or water tube which is used in conventional inclining tests. Calibrated inclinometers
39、with at least 0.05 degree accuracy and recording capability of 0.01 degrees should be used as a system component for in-service hull stability (ASTM F1321 14/6.8.1). Devices other than inclinometers should be agreed prior to usage. Inclinometers should not be used without correction for inertial eff
40、ects when there is substantial transverse or longitudinal asymmetry in the hull for the angles of heel to be used. 3.3 Hydrometer Hydrometers are used to obtain the relative density (specific gravity) of the sea water which is then used to convert displaced volume into mass of the floating structure
41、. As the sea water density varies with temperature, it is recommended to use a thermohydrometer, which is a hydrometer integrated with a thermometer. See ASTM standard E100-17 for hydrometer specifications. 3.5 Draft Gauge Draft gauges are used to measure the draft at each column of the column-stabi
42、lized unit. This measurement is then used to obtain the displaced volume. In calm environment, draft measurements could be taken by visual observation of draft marks on the columns or plastic tubes installed internally for draft measurement. However, in the case of in-service hull stability measurem
43、ent, environmental effects could prohibit accurate visual inspection of draft markers or water tubes. Pressure gage based draft measurement devices are preferred in such cases. The measuring device used should be calibrated and certified for use in the in-service environmental condition. Some form o
44、f averaging over time should be applied either as part of the gauging or by sampling of results. 3.7 Tank Sounding Device Tank sounding devices should be used to verify the liquid levels. The measuring device used should be calibrated and certified for use in the in-service environmental condition.
45、Some form of averaging over time should be applied either as part of the gauging or by sampling of results. ABSGUIDANCE NOTES ON IN-SERVICE HULL STABILITY VERIFICATION .2017 7 Section 2 In-Service Hull Stability Verification Procedure 3.9 Mooring Tension Sensor The mooring line tension sensors are u
46、sed to obtain the tension time-history throughout the in-service hull stability verification. These values are critical to consider as they affect the total vertical load on the unit and thus the unit displacement. The measuring sensor should be calibrated and certified for use in the environmental
47、condition under which the in-service inclination test is performed. Further information regarding calibration of force measurement devices are provided in ASTM E74-13a. 3.11 Onboard Software The data acquisition system includes software that needs to be available onboard the unit. This software is e
48、xpected to be the command center that controls all peripheral equipment and sensors. It is essential that there is no lag of data acquisition between different sensors, as the synchronized time history data is the key for obtaining the final verification result. A report containing the complete resu
49、lt of the inclining test along with other peripheral sensor readings such as draft gauge, mooring load cell, hydrometer, and tank fluid levels should be prepared for record keeping and review. The in-service hull stability verification test system should have error detection/obstruction of the measurement process and be capable of detecting failure or breakdown of individual components. The system should stop the measurement and release a relevant warning or ask for new data once an error is detected. 3.13 On Shore Analysis The data obtained from the in-service inclining te
