3. CHECK THE DESIGN LIGHTWEIGHT CURVE AGAINST THE BLOCK WEIGHTS

An important determinate of longitudinal forces is the lightweight distribution. Class takes the Sergeant Schultz approach toward the lightweight curve: it knows nothing. Not surprisingly, the yards have learned how to take advantage of this to build a weaker ship. On our ULCC, the yard modeled all the steel weight with just five trapezoids -- standard practice we were told. The inclining experiment revealed that the actual lightweight was 1,200 tons (about 2%) higher and a remarkable 0.7 m further forward than the design lightweight curve said it should be. The yard made an arbitrary adjustment to this clearly erroneous lightweight curve which added the weight and moved the LCG without affecting the all-important hogging moment. This was accepted by both ABS and LR without any check.

In fact, the yards know exactly where all the lightweight is. They carefully calculate the weight and centroid of each of the 250 or so blocks that make up a big tanker. They must do this in order to lift and handle the blocks safely. But these calculations have no impact on the lightweight curve that is used by Class. When we used the block weights and centers to generate the lightweight curve on our ULCC, we found that it increased the critical hogging moment by 4%. The yards take advantage of the lack of Class oversight to fraudulently move the lightweight toward midships since they have figured out that the decrease in hogging moment saves them more steel than the increase in sagging moment adds.

When I asked one ABS executive why Class allowed the yards to do this, he said "We don't allow it, but we don't check it." If you can understand this distinction, then you've gone a long way toward understanding the Classification Society approach to tanker newbuilding standards.

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