Transcript DAMAGE STABILITY ON TANKERS

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
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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
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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
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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
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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
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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
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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
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Contains sample intact loading conditions.
On approval, these intact loading conditions are
themselves deemed to be “approved” for use.
• Damage stability appraisal
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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
0.630
0.740
0.835
0.850
1.180
1.400
1.530
1.830
1.830
1.900
1.900
100
100
100
87
88
66
50
50
70
50
83
100
100
100
100
100
100
100
50
50
50
-
100
100
100
100
25
44
37
50
50
50
80
100
100
100
100
100
30
15
-
100
100
100
100
10
100
100
50
50
50
67
100
100
100
100
100
31
30
-
100
100
100
100
10
100
100
50
100
50
80
100 100
100 100
100 100
100 100
100 100
24 100
100
50
50
92
50
50
85
100
100
100
100
100
100
100
-
100
-
1.479
1.326
1.359
1.367
1.299
1.423
1.439
1.713
1.488
1.365
1.348
Margin
Damaged
0.078
0.016
0.030
0.042
0.053
0.259
0.284
0.171
0.162
0.005
0.006
Vessel is not at its marks at SG 0.63 or SG 0.74
Questions ?