6. About 80 percent of deaths and injuries resulted from fire and/or explosions, many of which followed collisions. There were no deaths following rammings or groundings during this period. DESIGN DESCRIPTIONS Twelve design alternatives for segregated ballast tankers built in accordance with the standards of the 1973 IMCO Pollution Convention were considered. The study group analyzed and evaluated each design in comparison with the others and a conventional nonsegregated ballast tanker. Figure 1 provides schematic SYMP IV/1 outlines for each of the thirteen design concepts. A brief description of each design is outlined below. With the exception of Case 1-Conventional all other designs comply with the 1973 IMCO Convention requirements for segregated ballast capacity. Case 1-Conventional.-Segregated ballast capacity, if any, carried in small wing tanks. Case 2-Staggered wing tanks.-This design configuration with all ballast capacity in alternate wing tanks provides maximum protection if groundings or collisions occur at a point involving the ballast wing tanks. Case 3-Double sides.-This design provides a continuous but thinner ballast protection area along the entire side of the cargo length. Case 4-"J" Wing tanks.-This design concept provides continuous but narrow protection for the entire side walls of the cargo area plus shallow bottom protection throughout the wing tanks. Case 5-"L" Wing tanks. This design, like the "J" design, provides full bottom protection through the wing tanks but with deeper protection of that area and partial side shell protection. Case 6-Center line double bottom.-This design provides maximum protection against grounding damage in the center tank portion of the bottom. Case 7-Full double bottom.-This design provides protection against grounding across the entire bottom but with protection to a lesser depth than case 6. Case 8-8/15 Double bottom plus wing tanks.-This double bottom is of lesser depth than in case 7, but some protective capacity results for a portion of the side shell. Case 9-Forward double bottom and wing tanks.--This design concentrates protection afforded by segregated ballast capacity in the forward half of the tanker with a measure of protection of the side shell. Case 10-Double bottom wing tanks.-This design provides maximum protection against grounding throughout the wing tanks only. Case 11-8/15 Double bottom plus center line tank. This design provides protection against groundings only. Case 12-Double hull-This design provides protection across the entire bottom and along the entire side wall of the cargo area. However, the resulting ballast tanks are relatively narrow and do not afford protection against deep penetrations as side shell or bottom. Case 13-Center tanks only. This design offers minimum protection due to the interior positioning of segregated ballast tanks and was dropped from further consideration. IV. METHOD OF ANALYSIS AND EVALUATION The U.S. Coast Guard studies on damage location (appendix A) were analyzed to determine if strategic placement of segregated ballast capacity could substantially improve the degree of protection afforded against accidental pollution. The U.S. Coast Guard 5-year analysis on tanker accidents (reference 1) was reviewed to ascertain the frequency and resultant pollution outflow of the various types of accidents. The study group then made a technical assessment of each of the thirteen tanker designs to determine: 1. Initial stability. 2. Damage stability. 3. Hypothetical oil outflow: Collision-Two degrees of severity. Grounding Two degrees of severity. 4. Salvage considerations after grounding (ability to recover ship and cargo). 5. Susceptibility to fire and explosion considerations. 6. Impact on personnel safety. These analyses drew upon data from several sources and were agreed upon by the group as a whole. The analyses of items 1 and 2 were based on International Conventions or the appropriate IMCO formulas. The analysis of item 3 included both the accident assumptions specified in IMCO's hypothetical oil outflow regulation and a lesser degree of damage. The analyses of items 4-6 was necessarily of a more subjective nature but were reached as a group conclusion. The study group concluded that initial stability and damage stability considerations, as well as strength and capacity problems, could be resolved on each design with varying economic and operational penalties. These items (1 and 2) were dropped from further evaluation as they do not have a direct bearing on accident resistance despite the very real operational, design, and economic considerations involved. Eight of the study group participants then proceeded to complete an individual evaluation of each of the twelve designs relative to the conventional design which was arbitrarily assigned midscale values. Each individual participant was asked to rank each of the twelve designs on a 1 to 10 basis (poor to best) in each of the five following categories: 1. Impact on reducing pollution outflow due to collision-major and minor. 2. Impact on reducing pollution outflow due to grounding. 3. Impact on salvage considerations after grounding. 4. Fires and explosion considerations. 5. Impact on personnel safety. These rankings were based on the technical analyses done by the group. Each participant was then directed to assign his own weighting (relative importance) factor to each of the five categories on which each design had been ranked. Each participant then established an overall ranking or evaluation of each design. All of the ranking and evaluation work was done independently by each participant. These evaluations were compiled by the U.S. Coast Guard personnel and the results were reviewed and evaluated by the study group. Based on the overall evaluation, the recommendations for appropriate regulations on defensive placement of segregated ballast capacity were prepared. Evaluation of the twelve tanker designs showed that all versions of the segregated ballast tankers should have advantages over the nonsegregated ballast design in reducing pollution outflow. These advantages stem from: 1. Excess cubic capacity and the resultant ability to transfer cargo in an emergency situation. 2. Reduction of human error in handling cargo and ballast. 3. Some added degree of protection to the cargo spaces in and accident situation. 4. Fewer cargo tank cleaning operations. The independent evaluations of the eight study group members are summarized in Table I resulting in a ranking for the twelve designs within three categories which all participants could generally agree upon. The three categories are outlined below: 1. Better Accident Protection: Case 2-Staggered Wing Tanks. Case 4-"J" Wing Tanks. Case 5-"L" Wing Tanks. 2. Some Improvement in Accident Protection: Case 8-B/15 Double Bottom and Wing Tanks. Case 11-B/15 Double Bottom and Center Line Tank. 3. Minimal Improvement in Accident Protection: Case 6-Center Line Double Bottom. Case 9-Forward Double Bottom and Wing Tanks. The study group was unable to establish meaningful differences between the value of the design concepts within the top category. V. SENSITIVITY OF ANALYSIS The ranking of each design on several categories was largely quantitative with such rankings based on calculations carried out under International Conventions or IMCO formulas. These rankings were largely a group effort. The weighting factor (relative importance) placed by each participant on the five categories is highly subjective. The task of weighting the relative value of protecting the environment from gounding accidents as compared to collision accidents is difficult enough. Weighting environmental values against considerations of personnel safety is even more difficult. As might be expected, there was a wide range of values assigned to the weighting factors by the various participants. A summary of the weighting factors used is shown in Table II. Table II shows the lowest, highest and average weighting factor (percentage importance) used by the participants. The sum of each participant's factors totals 100 percent. A review of Table II shows that one participant placed a value on the importance of protecting against grounding of 54.5 percent; almost twice the group average. That some participant placed a much lower value on categories 3-5 which relate to salvage, fire and explosion, and safety. A review of that participant's overall evaluations provides a good insight into the sensitivity of this analysis. The participant who placed the high value on protection against groundings came up with six preferred (best) designs. These were: Case 2-Staggered Wing Tanks. Case 4-"J" Wing Tanks. Case 5-"L" Wing Tanks. Case 7-Full Double Bottom. Case 8-B/15 Double Bottom and Wing Tanks. Four of these six designs (Cases 2, 4, 5 and 12) match the overall group evaluation. The remaining two (Cases 7 and 8) fell in the middle category. Several of the participants requested various members of their organization to assign relative importance factors. They found a wide divergence of opinion on an internal basis as to the relative importance of various categories, but determined that they always came up with the same general group of best designs no matter what scale of relative importance they used. In summary, it appears that the evaluation systems established by the study group is valid in that it yields consistent results over a wide range of input values. VI. CONCLUSIONS AND RECOMMENDATIONS The study group concluded that some general guidelines on the placement of segregated ballast for defensive purposes in preventing accidental oil outflow would be appropriate. Several designs were found superior to others in this regard, but no overwhelming choice existed between those superior designs. The study group concluded that there is no design basis which would prevent the catastrophic accident except as it minimizes the possibility of explosion and fire after a collision. The study group also concluded that several locations of ballast placement may reduce hypothetical outflow from collision. Some such designs increases the probability of some outflow as compared to the double hull concept (Case 12), but can sustain greater damages while yielding lower outflow. Inspection of the available accident data, together with the results of the design analysis, suggests that segregated ballast capacity should be placed adjacent to the shell and that at the bottom it should preferably be outboard. The study group expected to find some preference for forward placement as compared to aft placement, but this preference does not seem to be supported by experience or analysis. The study group concluded that it could accept a regulatory proposal for new segregated ballast tankers of over 70,000 tons DWT encompassing only the fundamental guideline above which would encourage designs meeting its intent and exclude designs which would not The group further concluded that because of the several design approaches which appear to offer significant benefit in accident circumstances, it could not recommend a regulatory approach which would specify one type of design concept only and thoroughly rule out positive further development of promising new concepts. At the request of the Coast Guard the group attempted to develop a more precise approach to possible regulations which would specify the general guidelines. This resulted in the following formula: 98-834-77-23 |