Double-Hull Tanker Legislation An Assessment of the Oil Pollution Act of 1990 (1998) / Chapter Skim
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Appendix K
Appendix K
Pages 191-242
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From page 191... ...
Four of the areas in which double-hull tankers perform differently as compared to single-hull tankers have been identified and investigated. These are: · environmental performance with regard to oil outflow from collisions and grounding · survivability characteristics after experiencing a collision or grounding · intact stability during load and discharge operations · hull girder strength and draft considerations for the ballast condition For comparative purposes, both single-hull and double-hull configurations have been investigated.
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From page 192... ...
Figure K-1 shows cross-sections of typical cargo tank arrangements for double-hull tankers. The "STA" or singletank-across arrangement has a single center cargo tank spanning between wing tanks.
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From page 193... ...
The calculation methodology and assumptions are described below. Evaluating Oil Outflow All cargo oil tanks on a double-hull tanker built to OPA 90 requirements are protectively located.
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From page 194... ...
When a tanker experiences bottom damage through the double bottom tanks and into the cargo tanks, a certain portion of the oil outflow from the cargo tanks will be entrapped by the double bottom tanks. This phenomenon was investigated through model testing at the David Taylor Research Center (DTRC, 1992)
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From page 195... ...
The Marine Environmental Protection Committee (MEPC) concluded that "if both outer and inner bottoms are breached simultaneously and the extent of rupture at both bottoms is the same, it is probable that the amount of sea water and oil flowing into the double-hull space would be the same." In its regulations, IMO assumes that double bottoms below oil tanks retain a 50:50 ratio of oil to sea water.
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From page 196... ...
The probability of zero outflow is the likelihood that such an encounter will result in no cargo oil spillage into the environment, and is an indicator of a design's tendency towards avoiding oil spills. The mean outflow is the weighted average of the cumulative oil outflow, and represents the expected or average outflow.
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From page 197... ...
The oil entrapped in the double bottom is not included in the assumed spill volume. For breached cargo tanks bounding the bottom shell, oil outflow equal to 1 percent of the tank volume is assumed as the minimum outflow.
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From page 198... ...
In addition, the double bottom raises the height of the cargo oil, which translates into a higher center of gravity for the intact condition as compared to a single-hull tanker. Free surface effects may also be higher, as single-tank-across arrangements of cargo tanks are not uncommon in double-hull tankers.
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From page 199... ...
Consumables are assumed to be 50 percent full, and all cargo tanks 98 percent full. Where breached tanks are filled or partially filled, it is assumed that 100 percent of the fluid in the tank is displaced by seawater.
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From page 200... ...
h, _~ _ _ 36.00 M _ o o N L PA~11@~S LBP 203050 M BEAM 36000 M DEPTH 18000 M DRAFT (FULL LOAD) 13050 M FIGURE K-4 IMO reference double hulls.
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From page 202... ...
The increase in the number of ballast tanks and the tendency towards wider ballast and cargo oil tanks means increased free surface effects, and a reduction in stability. This reduction in stability is exacerbated by the rise in the center of gravity of the cargo oil due to the double bottoms.
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From page 203... ...
For nonrectangular tanks, the free surface effect will vary with the level of the liquid in the tank. For instance, Figure K-7 shows a ballast U tank which is 35 percent full with the water level at one-half the double bottom height, and a tank in which the water level is increased so that the ballast extends into the wings.
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From page 204... ...
(b) With centerline bulkhead, free surface effect = 1/4.
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From page 205... ...
All ballast tanks are set to 2 percent filling, and all cargo tanks to the level which minimizes GM. Even at 2 percent filling, the free surface effects can have a significant impact on stability.
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From page 206... ...
This is in response to a number of factors: the desire to provide better access into the ballast tanks for inspection and construction purposes, owner requirements to have deeper ballast drafts than the IMO minimum values, and for structural and oil outflow considerations. Methodology for Evaluating Ballast Condition Longitudinal Strength and Drafts The fore and aft drafts and the maximum still-water bending moments and shear forces have been computed for the heavy ballast condition.
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From page 207... ...
Double-hull tankers in the 35,000 DWT to 160,000 DWT range include vessels with single-tank-across cargo tank arrangements, as well as vessels fitted with tight centerline bulkheads through the cargo block. Oil outflow, survivability, intact stability, ballast draft, and strength evaluations have been carried out for each tanker.
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From page 208... ...
Design #40-D1 has a single-tank-across arrangement for all cargo oil tanks, and a combination of U and L ballast tanks. Design #40-D2 and #40-D3 are arranged with an oil tight centerline bulkhead fitted over the entire length of the cargo block, and L type ballast tanks.
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From page 209... ...
APPENDIX K .~ _ 77~ L l ~ 509000 ~: JELE-~ULL Tin ~ BWLKHE E E E 1-~ 5019000 ~T DOUBLE-~LL TANKE Th1 cENTERL FIGURE K-9 Typical arrangements for 50,000 DWT tanker.
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From page 211... ...
211 ~ o to o He a' Em Go To of Go l E~ o o o s~ ,~o.
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From page 212... ...
212 o no o sol a' CO En Go To of To To To of so do o .5 · _4 ·_4 VO C)
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From page 213... ...
213 o o o Cq so a' Ed ca En o $ To 8 o so Jo o .~ o o Cq ¢ En Do is, o V, ~ o ¢ $ ~ o ~ ¢ V, $ ~ ~o ~ ~ ~ ~ ~ i, ~ ~ ~ ~ ~ Do ~ ~ o Do ~ o o Do Do ~ ~ lo so Do CM ~ Do ~o ~ ~ ~ o.~ ~ ~oo ~ ~ o .
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From page 214... ...
1 :::::: ::::. i" ' ., and cE ANAL FIGURE K-10 Typical arrangements for 80,000 DWT tankers.
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From page 215... ...
215 o oo ° oo ° Cq a' E~ E~ o o o o^ o o o o o oo Cq C)
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From page 216... ...
216 Cq s~ a' E~ E~ o o o o^ o o o o o^ oo s~ ,~o.
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From page 217... ...
217 o o oo ° o o Cq a' Ed En of To of of of Ed of of of of oo so Coo.
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From page 218... ...
218 o o Do ° o o Cq so a' Ct En Ed To of of of of En of or So lo oo so Jo o .s o .0 o Cq ¢ Ed o o ca · ~ ~ i V, ~ o o Do c~, ~o V, ~ 1 , o <; oo ~ o ~ ¢ V, oo ~\~ ~ ~ o.
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From page 219... ...
Design #150D5 has relatively wide wing tanks and a deep double bottom. In order for design #150-D5 to meet the IMO two compartment and raking bottom damage stability requirements, approximately 60 percent of the ballast capacity within the cargo block length is arranged in U tanks.
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From page 220... ...
220 DOUBLE-HULL TANKER LEGISLATION id= 1 = ma. T: r Dot r Y, ~ _ =~ it, _ FN @~ FIGURE K-11 Typical arrangements for 150,000 DWT tankers.
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From page 222... ...
222 Cq E~ E~ o o o o o o o s~ ~o o .s 3 o o ·_4 o ¢ E~ n o ~ In o o ~ In o o ~ In o CM 1 ~ In o 1 ~ In o oo ~ o V, o ~ n ¢ # ~i oo CM o V, o ~ n ¢ # ~i o ¢ 1 =!
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From page 223... ...
223 Cq En 3 lo To To To To To To so Jo o .5 · ~ VO ¢ Ed In 1 a)
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From page 225... ...
Design #280-D1 has all L ballast tanks, design #280-D2 has predominantly L ballast tanks with one U tank. Design #280-D3 has predominantly full-breadth double bottom ballast tanks with independent side tanks port and starboard, together with midship ballast tanks arranged inboard of the longitudinal bulkheads.
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From page 229... ...
229 o ~ ~ ho o ~ ~ ho sol o = En En ~ o o o ~ 8 -> so l ~ o 8 ~ To o o ~ -= ~ · · Vat CON ¢ o ~ ~ ~o o o o ~ ~ ~ ~ o ~ ~o o o - ° ~ ~o ~ ~ ~ c~)
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From page 230... ...
230 o do ox o Cq so a' ~ o En ~ To No of I l En Do Cal sly Jo o o = o Cq Cal ¢ En Do o V, o ~ Do ¢ ~ hi o _4 V, o ~ o ~ ~ ~ Do o ~ o.
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From page 231... ...
Single-hull barges above 5,000 DWT are generally arranged with one and sometimes two longitudinal bulkheads. The cargo tank arrangement will vary depending on the extent of cargo segregation required.
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From page 232... ...
232 o ~ ~ to 1 o ~ ~ be ~ .= _ o ~ ~ o _ o ~ ~ o A bl)
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From page 233... ...
233 o ~ ~ o 1 o bO ~ .= _ o as ~ o _ o as ~ o so bO ~ .= Cal a' be be ·_4 o be a' C)
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From page 234... ...
As shown in Figure K-14, the probability of zero outflow is four to six times higher for double-hull tankers, indicating single-hull tankers involved in a collision or grounding will be four to six times more likely to spill oil. The probability of zero outflow is a function of the double bottom and wing tank dimensions, and is not affected by the internal subdivision within the cargo tanks.
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From page 235... ...
The projected outflow is consistently lower for designs #150-D3, #150-D4, and #150-D5, all of which have an oil-tight centerline bulkhead over the length of the cargo block. Design #150-D1, with all single-tank-across cargo tanks, has the highest mean outflow.
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From page 236... ...
As shown in Figure K-17, double-hull tankers without centerline bulkheads typically have twice the expected outflow of designs with oil-tight longitudinal bulkheads in way of the cargo block. 0.03 0.025 , 0.02 ct Q Ct o ~ 0.015 0.01 ct 0.005 J X X X · Double-Hull Tankers with Single-Tank-Across Cargo Tanks - Double-Hull Tankers with Centerline Bulkhead in Some Cargo Tanks x Double-Hull Tankers with Centerline Bulkhead in All Cargo Tanks x O 0 50,000 100,000 150,000 200,000 250,000 300,000 350,000 Deadweight Tons FIGI~E K-17 Mean outflow for double-hull tankers with and without centerline bulkheads.
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From page 237... ...
Of interest is design #150-D2, which has an Index E of 0.99, roughly equivalent to the IMO reference ship. Although approximately half the cargo oil capacity of this design is contained in single-tank-across cargo tanks, the detrimental effect of these tanks is offset by the contributions from the relatively wide wing tanks and deep double bottom tanks.
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From page 238... ...
Designs #80-D1, #150-D1 and #150-D2 all had angles of loll below 8 degrees for the worst case loading situation, with no possibility of capsize. The load restrictions required to assure positive stability for these vessels are quite straightforward, requiring monitoring of any two ballast tanks.
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From page 239... ...
The load restrictions to assure positive stability for this vessel are quite complex, requiring monitoring of both ballast and cargo tanks. Observations on the Ballast Condition Analysis for Tankers The double bottom and wing tank dimensions for existing double-hull tankers generally exceed the rule requirements, providing ballast capacity in excess of that required to achieve the minimum IMO drafts.
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From page 240... ...
0.06 0.05 0.04 co Q Cow o Cut o 0.03 0.02 0.01 o . x ~ Single-Hull Barges x Double-Hull Barges 0 5,000 10,000 15,000 20,000 25,000 Deadweight Tons FIGURE K-20 Mean outflow for single-hull and double-hull barges.
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From page 241... ...
1993. Explanatory Notes to the SOLAS Regulations on Subdivision and Damage Stability of Cargo Ships of 100 Metres in Length and Over.
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From page 242... ...
1995. Application of IMO's Probabilistic Oil Outflow Methodology.
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