Thank you Denis for that detailed explanation. I'm no engineer but when physically building the vessel, is the ship built around the tanks (incorporated within the structure) or are they installed separately? Thanking you in advance,
Regards,

I'd guess to match the hull shape while having as much volume as possible. Also, from looking at many GA plans of such tankers, the bigger tank is most likely made out of 2 almost half tanks (they have C-like profile) placed parallel & welded together. The smaller tank is of a simple barrel-like shape.

Why is one tank larger than the other?