Tanker Spills Prevention by Design (1991) / Chapter Skim
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Appendix F: Comparative Study on Potential Oil Spill in Collision and/or Grounding--Different Tanker Designs
Appendix F: Comparative Study on Potential Oil Spill in Collision and/or Grounding--Different Tanker Designs
Pages 238-302
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From page 238... ...
APPENDIX F Comparative Study on Potential Oil Spill in Collision and/or GroundingDifferent Tanker Designs DET NORSKE VERITAS The appendixes to this study are not included. Committee comments on assumptions and conclusions can be found at the end of the Det norske Veritas report on page 299 and follow~ng.
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From page 239... ...
A double bottom provides a relatively better protection against overall oil spill than a double side. A passive vacuum system reduces oil outflow much in grounding.
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From page 240... ...
The objective of the study has been to investigate how double sides, double bottom, tank size and tank location influence the amount of oil escaping from a damaged VLCC. The study is based on available statistical information on damage location and extent.
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From page 241... ...
4. PROBABILISTIC RANKING OF 40,000 DWT TANKERS 4.1 The 40,000 dwt Designs Analysed 4.1.1 General Features 4.1.2 Particulars of 40,000 dwt Tankers 4.2 Probabilistic Ranking of 40,000 dwt Tankers 4.2.1 Ranking in Collision 4.2.2 Ranking in Grounding 4.2.3 Combined Ranking 4.3 Conclusions and Recommendations 5.
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From page 242... ...
As the fuel tank location is assumed similar in all designs studied, pollution potential from fuel tanks is equal and hence not included in the study. In this study the potential oil outflow from 11 different VLCC designs with double sides and/or double bottom have been compared with the potential oil outflow from a modern conventional VLCC of 280,000 dwt having segregated ballast tanks.
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From page 243... ...
SEE COMMITTEE INTERPRETATIONS OF DNV COLLISION ASSUMPTIONS ON PAGE 299. 2.1.2 Damage Analysis Procedure The procedure for calculating the potential oil outflow in collision is shown in the flow chart below(Fig.2.1)
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From page 244... ...
the damage lengths and penetrations might be short. The effect of a double side structure on damage penetration has been considered by introducing an equivalent penetration depth.
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From page 245... ...
direction , 1 , Cargo tanks punctured in trans. I direction Total cargo volume punctured l _ ~ , 1 , Oil outflow at location | More locations | .
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From page 246... ...
246 ,.o 0.8 0.7 0.5 0.4 0.3 0.2 0.1 o APPENDIX F z damage penetration ship breadtt, ! rT I Mattel i I .
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From page 247... ...
In the analysis statistical information on maximum vertical extent of damage has been used for the whole damage length. This conservative assumption has been made due to lack of detailed information on the vertical damage extent, or penetration, as a function of damage length.
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From page 248... ...
m = mS(l+aS) mS= mass of the laden ship aS= added mass coefficient for surge v = ship's speed at grounding Assuming all kinetic is transformed into deformation energy, the extent of grounding damage may be expressed for a single bottom ship as follows: Ek = Ws = L~(352B~tp e +126tp a )
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From page 249... ...
Damage length~->j Damage breadth! Cargo tanks| punctured I in long.
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From page 250... ...
The potential oil outflow in grounding is calculated at 51 locations along the ship hull(as in the collision analysis)
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From page 251... ...
Vertical Extent of Grounding Damage 25 3.0 The estimated oil outflow is given in ma, and may be converted to tons using the specific gravity of oil.
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From page 252... ...
The oil outflow is expected to be reduced by introducing either double side or double bottom or both, and possibly in addition, utilizing the vacuum method for reducing oil outflow in grounding. The influence of an intermediate oil tight deck on the potential oil spill has also been studied.
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From page 253... ...
2. Double bottom in whole cargo area Assuming all ballast in the cargo area is carried in the double bottom only, a double bottom of appr.
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From page 254... ...
There is a centreline bulkhead in tanks 1 and 2. Please observe the rather low double bottom height and that the side tanks are narrower than in 3B.
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From page 255... ...
by ballasting in order to increase the cargo capacity when filling the cargo tanks to hydrostatic balance. The VLCC with hydrostatically balanced loading can take 262,500 t of crude oil, or about 96% of the cargo in the original VLCC.
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From page 256... ...
ARRANGEMENT: 1A >~ 5995 1 j F7777~77 59 95 59 95 | IMO | REQUI RE D I 5917 AC T UA L 2 9 583 Fig.3.2. Double side/double bottom (1A)
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From page 257... ...
41.76 41.76 ~ 4176 _ Fig.3.4. Double bottom (2)
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From page 258... ...
4 ACTUAL 19761 Fig.3.6. Double bottom, single side (4)
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From page 259... ...
,_ 2 1 49.05 1 49.05 ~ 49 05 49 05 ~ 3815 116.35 , i_ Fig.3.7. Double bottom, single side (4A)
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From page 260... ...
1°91 L 103| 1 59 95 ~ 59 95 ~ 59.95 ~ 59 95 1 09 IMO 1 PP1 | PP2 | REQUIRED 1 8875 1 13312 1 20708| ACTUAL 1 14186 1 1438~7 1 14387 1 Fig.3.10. Double bottom side tanks, single bottom centre tank (6)
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From page 261... ...
PP1 PP 2 REQUIR£D 5917 11833 19229 O O ACTUAL O Fig.3.12. Intermediate Oil Tight Deck(8)
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From page 262... ...
Fig.3.13. Hydrostatically Balanced Loading(9)
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From page 263... ...
Considering the Intermediate Oil Tight Deck VLCC, this design performs similar to design 2 in about 70% of collisions, but clearly poorer for the rest of collisions. The reason for the difference is that at higher probability level the centre tanks are likely to be punctured, and as these contain only crude, then the potential oil outflow will increase much compared to design 2.
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From page 264... ...
Conventional VLCC ORIGINAL 2 ~ S iA ~ ~B ~6 7 ~ 9
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From page 265... ...
gives the damage height mean used in the PROBAN runs VLCCs as 2.308 with a standard deviation of 1.452. As no supporting values on the damage height for grounded vLCCs have been available, the extrapolated damage height used in this analysis might be too high reducing the positive influence of double bottom height on the amount of oil escaping.
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From page 266... ...
For design 2, with a double bottom height of 6.6 m, this figure is not less than 99.8% ! The intermediate oil tight deck does not completely stop oil outflow in grounding; - groundings damaging the ship bilge and side will always result in oil outflow.
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From page 267... ...
Double Bottom Height, 5 kn .
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From page 268... ...
3.20. Single Bottom, 5 kn 30000 40000 Torts of o~L ouLf tow
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From page 269... ...
3.21. Double Bottom, 10 kn 25000 31~00 Tons of out ouLf Low 0 10000 20000 30000 Fig.
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From page 270... ...
Again, the double bottom designs lA, 1B, 2, 4 and 4A show their good overall resistance against oil outflow in grounding. The intermediate oil tight deck design and the hydrostatically loaded tanker perform almost as sell.
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From page 271... ...
Camp.
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From page 272... ...
272 Comp. of cliff.
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From page 273... ...
274 100 90 80 70 0 60W 50I 40N 30 D ~ 201 0 o APPENDIX F Comp. of cliff.
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From page 274... ...
The wide side tank, single bottom design 3B performs worse than the conventional VLCC at high grounding speeds as does the partial double bottom design 5. At low grounding speeds, the performance of the partial double bottom design is much improved.
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From page 275... ...
A vacuum system reduces significantly the amount of oil escapeing in grounding for the single bottom designs analysed. However, the total amount of oil escaping from the modern conventional VLCC with a vacuum system is still about twice the amount escaping from the double side/double bottom design in case of collision and grounding.
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From page 276... ...
FOR NO I NNE R/OUT ER 5 R I N L EARAG E 2.0 M 12.1 % 3.0 M 20.4 % 5.8 M 39.4 6.3 M 42.0 CONCLUDING FROM THE ABOVE ANALYSIS ON VLCC DESIGNS : * narrow and long cargo tanks, and increased double bottom height clearly reduces the oil outflow as does reduced tank volumes.
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From page 277... ...
* intermediate oil tight decks may be effective against oil pollution if adequate collision protection is provided.
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From page 278... ...
4.1.2 Particulars of 40,000 dwt Tankers The numbers below refer to the designs shown in Fig.4.1-4.8, and to graphs showing the potential oil outflow which has been calculated for different designs. A fold out page showing the designs has been enclosed at the end of the report.
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From page 279... ...
The ballast capacity in the cargo area is ~16, 300 m3 7. Wide double sides and double bottom, short tanks This design features the same double side width and double bottom height as design 6.
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From page 280... ...
The poor collision behaviour of the double bottom tanker is expected.
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From page 281... ...
~////////// BALLAST 18500 TOTAL REQUIRED m2 BALLAST 15500 WITHIN CARGOAREA ACTUAL m2 Fig. 4.2 Double sides and single bottom( 2 )
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From page 282... ...
ARRANGEMENT 4 1,,,,,,,,,,,~,,~,,,,,,,,J,,,,,,,,,,,,1,,,,,,,,,,,1,,,,,,,,,...1 ~ 1_ 143m -1 ~ i 1 ~ 9 l , ,,,., ~ d. , , ·.,,,, 7~',~ t4_28 l.-._28 ._-1 28 , 1_ 28 ~ pa BALLAST 17000 TOTAL |REQUIREO m2 BALLAST 14000 WITHIN CARGOAREA |ACTUAL ma 28 .1 IMO PP1 PP2 | PP3 , 4666 4857 7110 1 8923 Fig.4.4 Narrow double sides and double bottom(4)
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From page 283... ...
28 BALLAS] 1K7cOo WO'~H'N tARmAREA |REQUIRED m2| 1~10 PP1 PP2 3906 4857 7110 Fig.4.6 Wide double sides and double bottom(6)
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From page 284... ...
20 1 20 ~ BALLAST 19? 00 TOTAL REQUIRED m2 BALLAST 16700 WITI1IN CARGOAREA ACTUAL m2 Fig.4.7 Wide double sides and double bottom, short tanks(7)
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From page 285... ...
Cumulative Probability for Oil Outflow in Collision - Single Side 40,000 dwt Tankers
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From page 286... ...
Integrating the outflow curves in Fig.4.9-4.10, and comparing with the original design shows(Fig.4.11) that the only design that can match the original design is design 6 - the wide double side and double bottom design with long tanks and centreline bulkhead(outflow index 98)
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From page 287... ...
Due to lack of time, the influence of double bottom height and ship speed on damage length in grounding has not been established for 40,000 dwt tankers. As expected the intermediate oil tight deck tanker performs quite well in grounding.
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From page 288... ...
4.12. Double Bottom, 5 kn or o to to 1 o o ,.
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From page 289... ...
4.14. Double Bottom, 10 kn a, ~3 ~5 ~6 7 5000 4000 Torts of out ouLf tow o o o 1000 2000 3000 Fig.
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From page 290... ...
290 APPENDIX F Comp. of cliff arrang.
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From page 291... ...
4.3 Conclusions and Recommendations The above analysis for 40,000 dwt tankers shows the importance of double bottom on the potential oil outflow. In Table 4.3.1, the effect of increasing the double bottom height and width of double side on the probability for leaking no oil is given respectively.
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From page 292... ...
292 Comp. of cliff.
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From page 293... ...
double bottoms reduce oil outflow in groundings causing bilge and side damage single bottom designs should be fitted with a vacuum system, alternatively loaded only to a hydrostatic balance level to reduce oil outflow in grounding.
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From page 294... ...
Comparing the potential oil spill volume to total cargo volume ratio, the difference is only ~ 1.3% in ratios for the VLCC and the 40,000 dwt tanker. In grounding, the overall performance is rather poor for both the VLCC and the 40,000 dwt tanker.
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From page 295... ...
The same reduction in overall oil outflow may be expected for a 80,000 dwt tanker provided the ship meets with the B/20 double side and B/15 double bottom recommendations. Double sides and single bottom designs: In the VLCC and the 40,000 dwt tanker with double sides and single bottom, the double side width is appr.
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From page 296... ...
A centreline girder should be fitted to reduce oil outflow in collisions a double bottom of B/15 should be fitted, an alternative may be a vacuum system with high capacity or hydrostatic loading of cargo tanks a double side should be considered to restricted pollution in low energy collisions; preferred width B/20 * high L/D reduces oil outflow in grounding SEE COMMITTEE COMMENTS ON DNV CONCLUSIONS FOR THE 80,000 DWT TANKER ON PAGE 3020
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From page 297... ...
double bottom protects against bilge and side damage in grounding the double bottom should tentatively be B/15 ~ vacuum systems reduce oil outflow in grounding * hydrostatic loading of cargo tanks reduces oil outflow in collision and grounding A intermediate oil tight deck reduces oil outflow in grounding oil outflow in low energy
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From page 298... ...
et.al.: Damage Estimates Grounding of Ships, MIT, June 27, l99O in High Energy /8/ K0hler, P.E.et.al.: Potential Oil Spill from Tankers in Case of Collision and/or Grounding - A Comparative Study of Different VLCC Designs, DNVC Report 90-0074, May l99O IMO International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk, London 1986
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From page 299... ...
To obtain more accurate estimates on oil outflow during the collision, it would be necessary to conduct detailed modeling of bow crushing behavior and ship side structural response during the collision process, taking into account the changes in ship speeds and headings, and added mass effects. This is beyond the scope of the present study.
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From page 300... ...
This conservative assumption was made due to lack of detailed information on vertical damage extent, or penetration, as a function of damage length. Consequently, the damage lengths calculated may be too short, due to overstatement of the energy absorbed vertically.
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From page 301... ...
VLCCs should have a double bottom height approaching Bl15 in order to be effective against pollution in grounding. The committee agrees, as one approach.
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From page 302... ...
The committee agrees that double bottoms, as well as double sides, would reduce outflow. Single bottom designs should be fitted with a vacuum system, alternatively loaded only to a hydrostatic balance level to reduce oil outflow in grounding.
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