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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.