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TANKER DAMAGE STABILITY Paul Coley & Nick Quarmby Maritime & Coastguard Agency Background The UK first became concerned over the issue of damage stability verification on tank vessels in 2005 as a result of problems highlighted during flag in of tank vessels, port state control inspection and a survey of UK tank ship operators Issues identified at Flag in • Low or zero margins on stability in worst case of damage • Damage cases missing from the damage stability evaluation, particularly lesser cases • Insufficient consideration given to slack or partially filled tanks • Insufficient consideration given to use of deck tanks • Approvals based upon unrealistic conditions of loading Of eleven LPG and chemical tanker stability approvals considered for endorsement by the UK at this time, seven were found to be incorrectly based and to omit critical elements to the verification. This is a rejection rate of 63%. Port State Control Observations • Vessels loading alternate conditions from those in the approved stability book • Vessels appraising loading conditions using longitudinal strength computer with additional intact stability assessment • Masters endorsing loading conditions clearly marked “not valid for damage” Survey of UK tanker operators • How many vessels operated – including foreign flag vessels in their fleets • Do they load alternate conditions from the SIB • Do they operate with empty or slack tanks • Do they verify stability prior to departure • Do they verify using intact or damage stability assessment Survey Results • Total of 76 ships operated • 59 vessels (77%) load alternate conditions • 43 vessels (56%) regularly operate with slack or empty tanks • 69 vessels (90%) are fitted with stability assessment programs • 30 vessels (39%) only assess intact stability Conclusions • Insufficient pre-departure checks are being made on tank vessels to ensure compliance with statutory damage stability requirements. • Existing stability approvals for these vessels may not always ensure that these requirements are met • There is a compelling need for enforcement action to be undertaken to ensure that existing international instruments are being complied with UK Response • To publicise the issue amongst UK operators, IACS and international tanker operators associations • To consult other flag states on the issue and to consider proposals for co-ordinated enforcement of existing international instruments • With others, to draw attention of this issue to IMO through MSC 83/25/14, proposing development of a common interpretation for these instruments to enable consistent enforcement action to be taken • To propose that guidelines be developed for tank ship stability approval in the expectation these will be taken up by IACS under the umbrella of URL5. IACS Unified Requirement URL5 IACS has introduced a new requirement relating to stability computation under URL5 This makes it mandatory for loading computers fitted to any IACS class vessel contracted after 1 July 2005, which incorporate a stability element, to be approved to verify all aspects of stability which apply to that vessel, including damage requirements. Enforcement • Guidelines for a common interpretation of the international instruments are necessary to ensure consistent enforcement action • However, the need for enforcement action is clear and is not dependent upon such guidelines being developed • As a flag and port state administration the UK will seek to pursue co-ordinated enforcement action if guidelines cannot be agreed within an acceptable timescale Enforcement • Enforcement action shall apply only to those vessels which do not operate according to their existing stability approval • Vessels which adhere closely to their approved loading conditions will not be required to provide direct means of verification • A definition of what constitutes “closely loaded” is required to verify loading is in accordance with the approved conditions Enforcement • Where alternate conditions of loading are employed, verification by means of critical KG or GM data is acceptable subject to any parameters fixed to determine the critical data being verified as met • It is the opinion of the UK that such verifications should be made using a URL5 type 2 stability program to provide an auditable record for PSC inspection Enforcement • It is the opinion of the UK and its co- sponsors that where vessels load alternate conditions significantly different from those in the approved stability book, these should be verified on board using a URL5 type 3 stability program Enforcement - Proposal • Inspection campaign to identify where vessels are loading to alternate conditions without acceptable damage verification • In such cases an operational (ISM) defect to be raised against the ship and letter of warning to be issued • Should further cases of loading alternate conditions become apparent at subsequent inspections, detention or banning to be considered Enforcement - Conclusion • During any forthcoming inspection and enforcement campaign, operators must ensure that crews can produce records on board to demonstrate that damage stability has been verified. • UK strongly recommends the provision of damage stability programs for this purpose on any existing vessel where adherence to the approved conditions is not practicable. Operational Considerations Basic Pre-Departure Checks • Longitudinal Strength - Load Line • Intact Stability - Load Line • Damage Stability • Oil Tankers - Marpol Annex 1, reg 25 • Gas Tankers - IGC Code, Chapter 2 • Chemical Tankers - IBC Code, Chapter 2 Documentation on Board • Approved Stability Information • Intact loading Conditions • Damage Calculations • Certification • Oil Tankers – IOPP Certificate and Form B • Gas Tankers – Certificate of Fitness • Chemical Tankers – Certificate of Fitness IOPP Form B 5.7 Subdivision and Stability (regulation 25) 5.7.1 The ship is required to be constructed according to, and complies with, the requirements of regulation 25 5.7.2 Information and data required under regulation 25(5) have been supplied to the ship in an approved form IGC and IBC Certificates of Fitness 5 That the ship must be loaded: .1 in accordance with the loading conditions provided in the approved loading manual, stamped and dated ............................................................. and signed by a responsible officer of the Administration, or of an organization recognized by the Administration; or .2 in accordance with the loading limitations appended to this Certificate. Where it is required to load the ship other than in accordance with the above instruction, then the necessary calculations to justify the proposed loading conditions should be communicated to the certifying Administration who may authorize in writing the adoption of the proposed loading condition. Masters and Owners Responsibilities International Safety Management (ISM) • Paragraph 126.96.36.199 – The company should establish a safety and environmental policy which ensures compliance with mandatory rules and regulations • Paragraph 7 - The Company should establish procedures for the preparation of plans and instructions, including checklists as appropriate, for key shipboard operations concerning the safety of the ship and the prevention of pollution. The various tasks involved should be defined and assigned to qualified personnel. Stability Considerations Typical Stability Approval at Build • Intact stability information booklet – Contains sample intact loading conditions. – On approval, these intact loading conditions are themselves deemed to be “approved” for use. • Damage stability appraisal – Usually a separate submission – Demonstrates only that the approved intact loading conditions will survive the extent of damage required by the applicable Convention or Code, and achieve the minimum residual stability standard. In this approach damage is applied directly to the approved loading conditions on a case by case basis. The results, and the approval, is therefore conditional upon the assumption that the following parameters remain unchanged in the loaded vessel, otherwise damage results may be adversely affected : •Cargo SG •Draught and or Trim •Empty/Part Filled Cargo Tanks •Cargo or Ballast Distribution •Use of Deck Tanks Variation in Loading The ability to load a vessel is restricted where approval is granted on the basis of damage appraisal of approved intact loading conditions. This may be of little consequence on a large deep sea vessel fulfilling a long term charter. But it is likely to prove problematic for a small coastal parcel tanker. It is often considered that alternate loading conditions are acceptable, particularly where these do not deviate “significantly” from the approved intact loading conditions, but there is no safe basis for this conclusion. Significant Variation It is the opinion of the UK and its co-sponsors that the concept of a significant deviation from an approved loading condition requires to be defined. We are presently proposing that a loading condition should be considered to deviate significantly from an approved condition if the following limits are exceeded • Content of cargo and ballast tanks : 1% by weight • Overall condition KG or GM (corrected for FS) : ± 2cm Critical KG data Typical tanker cross section Loaded with low SG cargo Heels toward damage Loaded with high SG cargo Heels away from damage Vessel at deep draught Heels toward damage Vessel at light draught Heels away from damage Full tanks Heels away after damage Slack tanks Heels toward damage Empty tanks Severe heel toward damage Typical tanker layout Typical single SG loading pattern Typical alternate SG loading pattern Significant variation ? Significant variation ? Typical Condition ? Consider variation in cargo SG Cargo and condition KG both rise Typical Cargo Distributions (Departure) SG #1 #2 #3 #4 #5 #6 #7 #8 #9 Slop Dk GM Margin Damaged 0.630 100 100 100 100 100 100 100 100 100 100 100 1.479 0.078 0.740 100 100 100 100 100 100 100 100 100 100 - 1.326 0.016 0.835 100 100 100 100 100 100 100 100 100 100 - 1.359 0.030 0.850 87 100 100 100 100 100 100 100 100 100 - 1.367 0.042 1.180 88 100 25 100 10 100 10 100 100 100 - 1.299 0.053 1.400 66 100 44 - 100 - 100 24 100 100 - 1.423 0.259 1.530 50 100 37 - 100 - 100 - 100 100 - 1.439 0.284 1.830 50 50 50 30 50 31 50 50 50 - - 1.713 0.171 1.830 70 50 50 - 50 - 100 - 92 - - 1.488 0.162 1.900 50 50 50 15 50 30 50 50 50 - - 1.365 0.005 1.900 83 - 80 - 67 - 80 - 85 - - 1.348 0.006 Vessel is not at its marks at SG 0.63 or SG 0.74 Questions ?
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