110(49) Revised interim guidelines for the approval of alternative methods of design and construction of oil tankers under Regulation 13F(5) of Annex I of MARPOL 73/78

THE MARINE ENVIRONMENT PROTECTION COMMITTEE,

RECALLING Article 38(a) of the Convention on the International Maritime Organization concerning the functions of the Marine Environment Protection Committee (the Committee) conferred upon it by international conventions for the prevention and control of marine pollution,

NOTING resolution MEPC.52(32) by which the Committee adopted regulations 13F and 13G and related amendments to Annex I of MARPOL 73/78,

NOTING ALSO resolution MEPC.66(37) by which the Committee adopted the Interim Guidelines for the approval of alternative methods of design and construction of oil tankers under regulation 13F(5) of annex I of MARPOL 73/78,

NOTING FURTHER that by resolution MEPC.66(37), the Committee resolved to keep the Interim Guidelines under review and to develop final guidelines in the light of experience,

HAVING CONSIDERED, at its forty-ninth session, the recommendation made by the Sub-Committee on Bulk Liquids and Gases,

1. ADOPTS the Revised Interim Guidelines for the approval of alternative methods of design and construction of oil tankers under regulation 13F(5) of Annex I of MARPOL 73/78, the text of which is set out in the Annex to the present resolution;

2. INVITES Member Governments to give due consideration to the Revised Interim Guidelines when evaluating other methods of design and construction of oil tankers as alternatives to the requirements prescribed in regulation 13F(5) of Annex I of MARPOL 73/78 for submission of such designs to the Committee for approval;

3. AGREES to keep the Revised Interim Guidelines under review in the light of experience gained;

4. INVITES the Maritime Safety Committee to note the Revised Interim Guidelines;

5. URGES Member Governments to bring the aforementioned Revised Interim Guidelines to the attention of shipbuilders, shipowners, ship operators and other parties concerned with the design, construction and operation of oil tankers with a view to encouraging their use for oil tankers constructed on or after 1 April 2005;

6. REVOKES resolution MEPC.66(37).

Annex Revised interim guidelines for the approval of alternative methods of design and construction of oil tankers under regulation 13F(5) of Annex I of Marpol 73/78

Preamble

1 The purpose of these Revised Interim Guidelines, hereunder referred to as "the Guidelines’’, is to provide an international standard for the evaluation and approval of alternative methods of design and construction of oil tankers under regulation 13F(5) of Annex I of MARPOL 73/78.

2 The basic philosophy of the Guidelines is to compare the oil outflow performance in case of collision or stranding of an alternative tanker design to that of reference double-hull designs complying with regulation 13F(3) on the basis of a calculated pollution-prevention index.

3 The oil outflow performance of double-hull tankers which comply with regulation 13F(3) may be different. The longitudinal subdivision of the cargo tanks has a major influence on the oil outflow in case of inner hull penetration. The selected reference double-hull designs exhibit a favourable oil outflow performance.

4 The calculation of oil outflow is based on the probabilistic methodology and best available tanker accident damage statistics. Reappraisal of the Guidelines may be appropriate when more information on tanker accident damage has become available and more experience with the application of these Guidelines has been gained.

5 Falling tides will have an adverse effect on oil outflow from a stranded tanker and the Guidelines take account of this. The tide values specified in section 5 represent realistic average tidal changes which have been chosen to identify the influence of tidal changes on the oil outflow in case of stranding.

1 General

1.1 Regulation 13F of Annex I of MARPOL 73/78 specifies structural requirements for new tankers of 600 dwt and above, contracted on or after 6 July 1993. Paragraph (3) of the regulation requires tankers of 5,000 dwt and above to be equipped with double hulls. Various detailed requirements and permissible exceptions are given in the regulation. Paragraph (5) of the regulation specifies that other designs may be accepted as alternatives to double hull, provided they give at least the same level of protection against oil pollution in the event of collision or stranding and are approved in principle by the Marine Environment Protection Committee (MEPC) based on Guidelines developed by the Organization.

1.2 These Guidelines should be used to assess the acceptability of alternative oil tanker designs of 5,000 dwt and above with regard to the prevention of oil outflow in the event of collision or stranding as specified in paragraph (5) of regulation 13F.

1.3 For any alternative design of an oil tanker not satisfying regulation 13F(3) or (4), a study of the cargo oil outflow performance should be carried out as specified in sections 4 through 6 of these Guidelines.

1.4 This study should cover the full range of ship sizes with a minimum of four different ship sizes, unless the approval is requested for only a limited range of vessel sizes. Data for four reference double-hull designs are given in section 7.

1.5 Evaluation of the cargo oil outflow performance of the proposed alternative design should be made by calculating the pollution-prevention index E, as outlined in section 4 of these Guidelines.

1.6 The probabilistic methodology for the calculation of oil outflow according to these Guidelines is based on available tanker casualty statistics. With the collection of additional statistical material, the damage density distribution functions specified in paragraph 5.2 should be periodically reviewed.

1.7 In principle, and as far as applicable, the requirements of paragraphs (3)(d)-(f), (6) and (8) of regulation 13F apply also to alternative designs. The requirements of paragraph (9) of regulation 13F also applies to alternative designs. In addition, it should be demonstrated by means of a risk analysis that the new design under consideration provides an adequate safety level. Such analysis should address any specific risks associated with the alternative design and, if there are any, it should be demonstrated that safe solutions exist to cope with them.

2 Applicability

2.1 These Guidelines apply to the assessment of alternative designs of oil tankers to be constructed of steel or other equivalent material, as required by SOLAS regulation II-2/11. Designs for tankers intended to be constructed of other materials or incorporating novel features (e.g. non-metallic materials) or designs which use impact-absorbing devices should be specially considered.

2.2 The approval procedure of these Guidelines applies to oil tankers of sizes up to 350,000 dwt. For larger sizes the approval procedure should be specially considered.

3 Approval procedure for alternative tanker designs

3.1 An Administration which receives a request for approval of an alternative tanker design for the purpose of complying with regulation 13F, should first evaluate the proposed design and satisfy itself that the design complies with these Guidelines and other applicable regulations of MARPOL Annex I. That Administration should then submit the proposal and the supporting documentation, together with its own evaluation report, to the Organization for evaluation and approval of the design concept by the MEPC as an alternative to the requirements of regulation 13F(3). Only design concepts which have been approved in principle by the MEPC are allowed for the construction of tankers to which regulation 13F(5) applies.

3.2 The submission to the Administration and the Organization should at least include the following items:

.1 detailed specification of the alternative design concept;

.2 drawings showing the basic design of the tank system and, where necessary, of the entire ship;

.3 study of the oil outflow performance as outlined in paragraphs 1.3 to 1.5;

.4 risk analysis as outlined in paragraph 1.7;

.5 details of the calculation procedure or computer program used for the probabilistic oil outflow analysis to satisfy the Administration that the calculation procedure used gives satisfactory results. For verification of the computer program see paragraph 6.2. Any additional information may be required to be submitted if deemed necessary. 3.3 In addition to the approval procedure for the design concept specified in paragraphs 3.1 and 3.2 above, the final shipyard design should be approved by the Flag State Administration for compliance with these Guidelines and all other applicable regulations MARPOL Annex I. This should include survivability considerations as referred to in paragraph 5.1.5.10.

3.4 Any approved design concept will require reconsideration if the Guidelines have been amended.

4 Oil outflow analysis

4.1 General

4.1.1 The oil pollution prevention performance of a tanker design is expressed by a non-dimensional oil pollution prevention index E which is a function of the three oil outflow parameters: .probability of zero oil outflow., .mean oil outflow. and .extreme oil outflow.. The oil outflow parameters should be calculated for all conceivable damage cases within the entire envelope of damage conditions as detailed in section 5.

4.1.2 The three oil outflow parameters are defined as follows:

.1 Probability of zero oil outflow. This parameter represents the probability that no cargo oil will escape from the tanker in case of collision or stranding. If, e.g., the parameter equals 0.6, in 60% of all collision or stranding accidents no oil outflow is expected to occur.

.2 Mean oil outflow parameter. The mean oil outflow represents the sum of all outflow volumes multiplied by their respective probabilities. The mean oil outflow parameter is expressed as a fraction of the total cargo oil capacity at 98% tank filling.

.3 Extreme oil outflow parameter. The extreme oil outflow is calculated - after the volumes of all outflow cases have been arranged in ascending order - as the sum of the outflow volumes between 0.9 and 1.0 cumulative probability, multiplied by their respective probabilities. The value so derived is multiplied by 10. The extreme oil outflow parameter is expressed as a fraction of the total cargo oil capacity at 98% tank filling.

4.1.3 In general, consideration of ship’s survivability will not be required for the conceptual approval of an alternative design. This may, however, be required in special cases, depending on special features of the design.

4.2 Pollution-prevention index

The level of protection against oil pollution in the event of collision or stranding as compared to the reference double-hull designs should be determined by calculation of the pollution-prevention index E as follows:

4.3 Calculation of oil outflow parameters

The oil outflow parameters PO, OM and OE should be calculated as follows:





where the index "ie" represents the extreme outflow cases, which are the damage cases falling within the cumulative probability range between 0.9 and 1.0 after they have been arranged as specified in paragraph 6.1.

5 Assumptions for calculating oil outflow parameters

5.1 General

5.1.1 The assumptions specified in this section should be used when calculating the oil outflow parameters.

5.1.2 Outflow parameters should be calculated independently for collisions and strandings and then combined as follows:

.1 0.4 of the computed value for collisions; and

.2 0.6 of the computed value for strandings. 5.1.3 For strandings, independent calculations should be done for 0 m and 2.5 m fall in tide. Outflow parameters for the stranded conditions should be a weighted average, calculated as follows:

.1 .7 for 0 m tide condition; and

.2 0.3 for 2.5 m fall in tide condition. 5.1.4 The damage cases and the associated probability factor Pi for each damage case should be determined based on the damage density distribution functions as specified in paragraph 5.2.

5.1.5 The following general assumptions apply for the calculation of outflow parameters:

.1 The ship should be assumed loaded to the load line draught ds with zero trim and heel. All cargo tanks should be assumed loaded to 98% of their volumetric capacity. The nominal density of the cargo oil should be calculated as follows:

.2 For the purposes of these outflow calculations, the permeability of each space within the cargo block, including cargo tanks, ballast tanks and other non-oil spaces should be taken as 0.99, unless proven otherwise. .3 For all cases of collision damage, the entire contents of all damaged cargo oil tanks should be assumed to be spilled into the sea, unless proven otherwise. .4 For all stranded conditions, the ship should be assumed aground on a shelf. Assumed stranded draughts prior to tidal change should be equal to the initial intact draughts. Should the ship trim or float free due to the outflow of oil, this should be accounted for in the calculations for the final shipyard design. .5 In general, an inert gas overpressure of 0.05 bar gauge should be assumed if an inert gas system is fitted, otherwise the inert gas overpressure should be taken as zero. .6 For the calculation of oil outflow in case of stranding, the principles of hydrostatic balance should apply, and the location of damage used for calculations of hydrostatic pressure balance and related oil outflow calculations should be the lowest point in the cargo tank. .7 For cargo tanks bounded by the bottom shell, unless proven otherwise, oil outflow equal to 1% of the volume of the damaged tank should be assumed to account for initial exchange losses and dynamic effects due to current and waves. .8 For breached non-cargo spaces located wholly or in part below breached cargo oil tanks, the flooded volume of these spaces at equilibrium should be assumed to contain 50% oil and 50% seawater by volume, unless proven otherwise. .9 If deemed necessary, model tests may be required to determine the influence of tidal, current and swell effects on the oil outflow performance. .10 For ship designs which incorporate cargo transfer systems for reducing oil outflow, calculations should be provided illustrating the effectiveness of such devices. For these calculations, damage openings consistent with the damage density distribution functions defined in paragraph 5.2 should be assumed. .11 Where, for the final shipyard design referred to in 3.3 and in the special cases referred to in paragraph 4.1.3, damage stability calculations are required, the following should apply: A damage stability calculation should be performed for each damage case. The stability in the final stage of flooding should be regarded as sufficient if the requirements of MARPOL regulation I/25(3) are complied with. Should the ship fail to meet the survivability criteria as defined in MARPOL regulation I/25(3), 100% oil outflow from all cargo tanks should be assumed for that damage case.

5.2 Damage assumptions

5.2.1 General, definitions

The damage assumptions for the probabilistic oil outflow analysis are given in terms of the damage density distribution functions specified in paragraphs 5.2.2 and 5.2.3. These functions are so scaled that the total probability for each damage parameter equals 100% (i.e. the area under each curve equals 1.0).

The location of a damage refers always to the centre of a damage. Damage location and extent to an inner horizontal bottom or vertical bulkhead should be assumed to be the same as the statistically derived damage to the outer hull.

The location and extent of damage to compartment boundaries should be assumed to be of rectangular shape, following the hull surface in the extents defined in paragraphs 5.2.2 and 5.2.3.

The following definitions apply for the purpose of paragraphs 5.2.2 and 5.2.3.



5.2.2 Side damage due to collision





5.2.3 Bottom damage due to stranding

6 Probabilistic methodology for calculating oil outflow

6.1 Damage cases

6.1.1 Using the damage probability distribution functions specified in paragraph 5.2, all damage cases n as per paragraph 4.3 should be evaluated and placed in ascending order of oil outflow. The cumulative probability for all damage cases should be computed, being the running sum of probabilities beginning at the minimum outflow damage case and proceeding to the maximum outflow damage case. The cumulative probability for all damage cases should be 1.0.

6.1.2 For each damage case the damage consequences in terms of penetrations (breaching) of cargo tank boundaries should be evaluated and the related oil outflow calculated. A cargo tank should be considered as being breached in a damage case under consideration if the applied damage envelope reaches any part of the cargo tank boundaries.

6.1.3 When determining the damage cases, it should be assumed for the purpose of these calculations that the location, extent and penetration of damages are independent of each other.

6.2 Oil outflow calculations

6.2.1 The probabilistic oil outflow calculations may be done as outlined by the .Example for the Application of the Revised Interim Guidelines. given in the appendix to these Guidelines. Other calculation procedures may be accepted, provided they show acceptable accuracy.

6.2.2 The computer program used for the oil outflow analysis should be verified against the data for oil outflow parameters for the reference double-hull designs given in section 7.

6.2.3 After the final waterline has been determined, the oil outflow from each damaged cargo tank should be computed for each damage case under the assumptions specified in paragraph 5.1.5.

7 Reference double-hull designs

7.1 Data for four reference double-hull designs of 5,000 dwt, 60,000 dwt, 150,000 dwt and 283,000 dwt are summarized in tables 7.1 and 7.2 and are illustrated in figures 5 to 8. Table 7.1 also contains the data for the oil outflow parameters POR, OMR and OER to be used for the concept approval (ship survivability not considered).

7.2 Table 7.2 contains the corresponding data to be used for the shipyard design approval (ship survivability considered).

Appendix Example for the application of the revised interim guidelines

1 General

1.1 The application of the Revised Interim Guidelines, hereunder referred to as "the Guidelines", is shown in the following worked example illustrating the calculation procedure of the oil outflow parameters for a tank barge. For presentation purposes, a simplified hull form and level of compartmentation have been assumed. The procedures described herein are readily adaptable as a computer application, which will be necessary as more complicated arrangements are evaluated. This example is evaluated in accordance with the requirements for .concept approval.. Additional requirements for a shipyard design approval are noted where applicable.

1.2 An application of the Guidelines will typically follow these seven basic steps:

.1 Vessel design: In accordance with paragraph 3.1 of the Guidelines, the vessel is designed to meet all applicable regulations of MARPOL Annex I.

.2 Establishing of the full load condition: In accordance with paragraph 5.1.5 of the Guidelines, a full load condition is developed.

.3 Assembling of the damage cases: By applying the damage density distribution functions provided in the Guidelines, determine each unique grouping of damaged compartments and the probability associated with that damage condition. Independent sets of damage cases are derived for side (collision) and bottom (stranding) damage.

.4 Computation of the equilibrium condition for each damage case: Compute the final equilibrium condition for all side and bottom damage conditions. This step is only required for the final shipyard design, in accordance with paragraph 5.1.5.10 of the Guidelines.

.5 Computation of the oil outflow for each damage case: Calculate the oil outflow for each damage case. Separate calculations are done for side damage and for bottom damage at 0.0 m and 2.5 m fall in tide conditions. For side damage, all oil is assumed to escape from damaged tanks. For bottom damage, a hydrostatic balance method is applied. For the final shipyard design, survivability is evaluated in accordance with the requirements of MARPOL regulation I/25(3).

.6 Computation of the oil outflow parameters: The cumulative probability of occurrence of each level of oil outflow is developed. This is done for the side damage and for each bottom damage tide condition. The associated oil outflow parameters are then computed. The bottom damage tidal parameters are combined in accordance with paragraph 5.1.3 and the side and bottom damage parameters are then combined in accordance with paragraph 5.1.2 of the Guidelines.

.7 Computation of the Pollution Prevention Index E: The new design has satisfactory characteristics if index E, as defined in paragraph 4.2 of the Guidelines, is greater than or equal to 1.0.

2 Analysis procedure

The basic steps 1 through 6 below are described in this section.

2.1 Step 1: Vessel design

The arrangement and dimensions of the example barge are as shown in figure A1 (Barge arrangement). For clarity purposes, a simple arrangement has been selected which does not meet all MARPOL 73/78 requirements. However, for actual designs submitted for approval as an alternative to double hull, the vessel must meet all applicable regulations of Annex I of MARPOL 73/78.

2.2 Step 2: Establishing of the full load condition

An intact load condition shall be developed with the vessel at its maximum assigned load line with zero trim and heel. Departure quantities of constants and consumables (fuel oil, diesel oil, fresh water, lube oil, etc.) should be assumed. Capacities of cargo oil tanks should be based on actual permeabilities for these compartments. All cargo oil tanks shall be assumed to be filled to 98% of their capacities. All cargo oil shall be taken at a homogeneous density.

For this example, it is assumed that the permeability of the cargo oil tanks is 0.99 and 0.95 for the double bottom/wing tank ballast spaces. The 100% capacity of the cargo oil tanks CO1 and CO2 is:

CO1: 9,623 m3
CO2: 28,868 m3
Total: 38,491 m3

Cargo tank capacity at 98% filling: C = 0.98 x 38,491 = 37,721 m3. For this barge, for simplicity reasons, zero weight for the constants and consumables has been assumed. At the 9.0 m assigned load line the following values for the cargo oil mass (W) and density (ρ C) are obtained:

W = displacement - light barge weight = 33,949 t

ρC = 33,949 t/C = 0.90 t/m3 2.3 Step 3: Assembling of the damage casesIn this step the damage cases have to be developed. This involves applying the probability density distribution functions for side damage (figures 1 and 2) and the probability density distribution functions for bottom damage (figures 3 and 4). Each unique grouping of damaged compartments is determined together with its associated probability. The sum of the probabilities should equal 1.0 for both the side and the bottom damage evaluations. There are different methods available for developing the compartment groupings and probabilities, each of which should converge on the same results. In this example, the compartment groupings and the use of the probability density functions is shown by a .step-wise. evaluation method. This method involves stepping through each damage location and extent at a sufficiently fine increment. For instance, it is assumed (for the side damage) to step through the functions as follows: longitudinal location = 100 steps, longitudinal extent = 100 steps, transverse penetration = 100 steps, vertical location = 10 steps, and vertical extent = 100 steps. You will then be developing 109 damage incidents. The probability of each step is equal to the area under the probability density distribution curve over that increment. The probability for each damage incident is the product of the probabilities of th e five functions. There are many redundant incidents which damage identical compartments. These are combined by summing their probabilities. For a typical double-hull tanker, the 109 damage incidents reduce down to 100 to 400 unique groupings of compartments. 2.3.1 Side damage evaluation The damage density distribution functions provide independent statistics for location, length, and penetration. For side damage, the probability of a given damage longitudinal location, longitudinal extent, transverse penetration, vertical location and vertical extent is the product of the probabilities of these five damage characteristics. To maintain the example at a manageable size, fairly coarse increments have been assumed:

Longitudinal location at 10 steps = L/10 = 0.10L per step

Longitudinal extent at 3 steps = 0.3L/3 = 0.10L per step

Transverse penetration at 6 steps = 0.3B/6 = 0.05B per step. To further simplify the evaluation, each damage is assumed to extend vertically without limit. Therefore, the probabilities of vertical location and vertical extent are taken as 1.0 for each damage case. This is a reasonable assumption as the double bottom height is only 10% of the depth. Taking the area under the density distribution function for vertical location up to 0.1D (see figure 2, function fS5) yields a value of 0.005. This means that the probability of the centre of damage location falling within the double bottom region is 1/200. Figure A2 (Side damage definition) shows the steps for longitudinal location, longitudinal extent and transverse penetration in relation to the barge. Table A1 (Increments for step-wise side damage evaluation) gives the range for each step, the mean or average value over the step, and the probability of occurrence of that particular step. For instance, Z1 covers the range of transverse penetration beginning at the side shell and extending inboard 5% of the breadth. The average penetration is 0.025B or 2.5% of the breadth. The probability of occurrence is the likelihood that the penetration will fall within the range of 0% to 5% of the breadth. The probability equals 0.749, which is the area under the density distribution function for transverse penetration (figure 1, function fS3) between 0.0B and 0.05B. The area under each probability density function is 1.0, and therefore the sum of the probabilities for all increments for each function is 1.0. A total of ten longitudinal locations, three longitudinal extents and six transverse penetrations will be evaluated. All combinations of damages must be considered for a total of (10)\times(3)\times(6) = 180 separate incidents. The damaged compartments are found by overlaying each combination of location/extent/penetration onto the barge. These damage boundaries define a rectangular box. Any compartment which extends into this damage zone is considered damaged. Each of the 180 incidents results in damage to one or more compartments. Incidents with identical damaged compartments are collected into a single damage case by summing the probabilities of the individual damage incidents. Let us begin at the aft end of the barge and proceed forward. The first damage location X1 is centred 0.05L forward of the transom. The first damage extent Y1 has an average length of 0.05L. The average value for the first transverse penetration Z1 is 0.025B. The resulting damage box lies entirely within the WB1 compartment and therefore damages that compartment only. The probability of this incident is:

P111(X1Y1Z1) = (0.1000) x (0.7725) x (0.7490) = 0.05786 If we step through the transverse penetrations Z2 through Z6, we find that only the WB1 compartment is damaged for each of these cases. The probabilities for these cases are 0.01074, 0.00216, 0.00216, 0.00216, 0.00216, and 0.00216 respectively. The combined probability for the six cases at longitudinal damage location X1 is:

P111-6(X1Y1Z1-6) = 0.05786 + 0.01074 + 0.00216 + 0.00216 + 0.00216 + 0.00216 = 0.07725 Next, we move to damage extent Y2. The damage box X1Y2 Z1 once again falls within the WB1 compartment. Likewise, transverse penetrations Z2 through Z6 fall within this compartment. We compute the probability for these cases and find that: P121-6 (X1Y2 Z1-6) = 0.01925. Similarly, the damage boxes defined by X1Y3 Z1-6 lie within the WB1 compartment and have a combined probability

P131-6(X1Y3 Z1-6) = 0.00350. We now move to the next longitudinal location, X2. With longitudinal extent Y1, the damage stays within the WB1 compartment. The combined probability is P211-6(X2Y1 Z1-6) = 0.07725. The forward bound of the damage box X2Y2 Z1 extends forward of the transverse bulkhead located 20.0 m from the transom, damaging compartments both fore and aft of this bulkhead. Transverse penetration Z1 extends to a point just outboard of the longitudinal bulkhead. Therefore, this combination damages both the WB1 and WB2S compartments. The probability is P221(X2Y2 Z1) = 0.01442. We find that the damage box X2Y2 Z2 extends inboard of the longitudinal bulkhead, damaging compartments WB1, WB2S and CO1. A cargo oil tank has been damaged and oil outflow will occur. Similarly, damage penetrations Z3 through Z6 result in breaching of the three compartments. The combined probability for these five incidents is:

P222-6(X2Y2 Z2-6) = 0.00268 + 0.00054 + 0.00054 + 0.00054 + 0.00054 = 0.00483 By stepping through the barge for all 180 incidents and combining unique damage compartment groupings, we obtain the compartment grouping and probability values shown in table A2 (Probability values for side damage). Each compartment group represents a unique set of compartments. The associated probability is the probability that each particular group of compartments will be damaged in a collision which breaches the hull. For instance, the probability of damaging the WB1 compartment is 0.17725. This means there is approximately a 17.7% likelihood that only this compartment will be damaged. Likewise, the probability of concurrently damaging the WB1 and WB2S compartments is 0.03408 or about 3.4%. Note that the cumulative probability of occurrence for all groups equals 1.0. 2.3.2 Bottom damage evaluationFor bottom damage, the probability of a given damage longitudinal location, longitudinal extent, vertical penetration, transverse location and transverse extent is, analogously to the side damage evaluation, the product of the probabilities of these five damage characteristics. The following increments are assumed for the bottom damage evaluation: Longitudinal location at 10 steps = L/10 = 0.10L per step Longitudinal extent at 8 steps = 0.8L/8 = 0.10L per step Vertical penetration at 6 steps = 0.3D/6 = 0.05D per step. To further simplify the evaluation, all damage is assumed to extend transversely without limit. Therefore, the probabilities of transverse extent and transverse location are taken as 1.0 for each damage case. Compartment groupings are developed using the same process as previously described for side damage. Analogously, a total of ten longitudinal locations, eight longitudinal extents and six vertical penetrations need to be evaluated. The damage incidents to be taken into account for groundings sum up to a total of (10) x (8) x (6) = 480 separate incidents. Figure A3 (Bottom damage definition) shows the steps for longitudinal location, longitudinal extent and vertical penetration in relation to the barge. Table A3 (Increments for step-wise bottom damage definition) gives the range for each step, the mean or average value over the step, and the probability of occurrence of that particular step. Again, putting the aftmost compartment WB1 together in terms of damage increments, the following probabilities have to be summed up:

P111-6 X1Y1 Z1-6) = (0.0240) x (0.38333) x (1.0) = 0.00920

P121-6(X1Y2 Z1-6) = (0.0240) x (0.2500) x (1.0) = 0.00600

P131-6(X1Y3 Z1-6) = (0.0240) x (0.11677) x (1.0) = 0.00280

P211-6(X2Y1 Z1-6) = (0.0320) x (0.38333) x (1.0) = 0.01227. Therefore the likelihood of damaging the WB1 compartment sums up to:

PWB1 = P11 + P12 + P13 + P21 = 0.03027.

By addressing each of the 480 incidents to the relevant compartment (or groups of compartments) the likelihood of a damage to these resulting from a grounding is obtained. This is shown in table A4 (Probability values for bottom damage). 2.4 Step 4: Computation of the equilibrium condition for each damage caseThis example describes the concept analysis only. Damage stability analyses to determine the equilibrium conditions are only required for the final shipyard design, in accordance with paragraph 5.1.5.10 of the Guidelines. 2.5 Step 5: Computation of the oil outflow for each damage caseIn this step the oil outflow associated with each of the compartment groupings is calculated for side and bottom damage as outlined below. 2.5.1 Side damage evaluationFor side damage, 100% of the oil in a damaged cargo oil tank is assumed to outflow into the sea. If we review the eleven compartment groupings for side damage, we find that oil tank damage occurs in three combinations: CO1 only, CO2 only, and concurrent damage to CO1 and CO2. The oil outflow for these tanks is as follows:

CO1 (98% full volume) = 9,430 m3

CO2 (98% full volume) = 28,291 m3

CO1 + CO2 (98% full volume) = 37,721 m3. 2.5.2 Bottom damage evaluationFor bottom damage, a pressure balance calculation must be carried out. The vessel is assumed to remain stranded on a shelf at its original intact draught. For the concept analysis, zero trim and zero heel are assumed. An inert gas overpressure of 5 kPa gauge is assumed in accordance with paragraph 5.1.5.5 of the Guidelines. The double bottom spaces located below the cargo oil tanks "capture" some portion of the oil outflow. In accordance with paragraph 5.1.5.8 of the Guidelines, the flooded volume of such spaces should be assumed to contain 50% oil and 50% seawater by volume at equilibrium. When calculating the oil volume captured in these spaces, no assumptions are made on how the oil and seawater is distributed in these spaces. The calculations are generally carried out for two tidal conditions: 0.0 and 2.5 m fall in tide. The actual oil volume lost from a cargo tank is calculated for each of the two tidal conditions, assuming hydrostatic balance as follows: Step-wise application of the damage extents and assumed increments results in fourteen compartment groupings for bottom damage. Oil tank and double bottom damage occurs in three combinations. The oil outflows for these tanks at 0.0 m and 2.5 m fall in tide are summarized in the table below: 2.6 Step 6: Computation of the oil outflow parametersIn this step the oil outflow parameters are computed in accordance with paragraph 4.3 of the Guidelines. To facilitate calculation of these parameters, place the damage groupings in a table in ascending order as a function of oil outflow. A running sum of probabilities is computed, beginning at the minimum outflow damage case and proceeding to the maximum outflow damage case. Tables A5 and A6 (Cumulative probability and oil outflow values) contain the outflow values for the side damage and bottom damage for the two tide conditions. Probability of zero oil outflow, PO: This parameter equals the cumulative probability for all damage cases for which there is no oil outflow. From table A5, we see that the probability of zero outflow for the side damage condition is 0.83798, and the probability of zero outflow for the bottom damage (0.0 m tide) condition is 0.84313. Mean oil outflow parameter, OM: This is the weighted average of all cases, and is obtained by summing the products of each damage case probability and the computed outflow for that damage case. Extreme oil outflow parameter, OE: This represents the weighted average of the damage cases falling within the cumulative probability range between 0.9 and 1.0. It equals the sum of the products of each damage case probability with a cumulative probability between 0.90 and 1.0 and its corresponding oil outflow, with the result multiplied by 10. For this example, the computed outflow values are as shown in tables A5 and A6. In accordance with paragraph 5.1.3 of the Guidelines, the bottom damage outflow parameters for the 0.0 m and 2.5 m fall in tides are combined in a ratio of 0.7: 0.3, respectively. In accordance with paragraph 5.1.2, the collision (side damage) and stranding (bottom damage) parameters are then combined in a ratio of 0.4: 0.6, respectively. In table A7 (Summary of oil outflow parameters) the oil outflow parameters PO, OM and OE for the example tank barge are listed.

• Informatietype: Internationaal
• Documentsoort: Resolutie
• Toegangsrechten: Extern
• Identificatie: PUC_2111_14
• Versie: 1
• Datum beschikbaarheid: 26-06-2009
• Geldigheid van: 01-04-2005
• Wijzigingsdatum: 24-11-2016
• Titel: 110(49) Revised interim guidelines for the approval of alternative methods of design and construction of oil tankers under Regulation 13F(5) of Annex I of MARPOL 73/78
• Organisatie: International Maritime Organization (IMO)
• Taal: Nederlands
• Onderwerp: Veiligheid / Safety
• Hoofdtaak: Koopvaardij / Merchant Shipping
• Thema: Zeevaart / Seagoing ships / Policy Rules / IMO Instruments (Policy Rules) / Resolutions (Policy Rules) / MEPC Resolutions (Policy Rules) / MEPC/Res. 100 until 199