; DAMAGE STABILITY ON TANKERS
Documents
Resources
Learning Center
Upload
Plans & pricing Sign in
Sign Out
Your Federal Quarterly Tax Payments are due April 15th Get Help Now >>

DAMAGE STABILITY ON TANKERS

VIEWS: 153 PAGES: 59

  • pg 1
									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 1.2.3.1 – 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 ?

								
To top