Beauty, but they all have this problem!
The direct vented exhaust for the midship diesel engines, I believe it's similar to the APU exhaust on aircraft for internal battery start instead of having an outside source. When they start the engines, the left-over unburnt fuel creates an initial burst of black smoke & soot which stains the side of the ship just like that. It's common on all the A200 MEKOs because they have to vent the exhaust of those centerline diesel engines somehow and that's where they chose to direct the exhaust and that's what it causes.
The exact thing happens on the Eurofighter Typhoon for its APU exhaust. It's right on the portside fuselage above the center of the wing and leaves a similar nasty soot stain. It's horrible.
Same problem with the brand new Egyptian Navy A200 Mekos and it seems that it bothered them so bad that they had that section of the hull painted with black, bottom paint so as not to show up against the navy grey loool.
Before.
After.
Too bad, not sure which is uglier, with the soot stain or that stupid weird black patch paint?!?! And they angled the ends to make it look "custom" lmao. We know what that is, nice try. What was that stupidity that clown George W. Bush said? "Fool me once, shame.....me, you....fool me twice.....won't get fooled again" lolzo.
I believe those midship diesel engines are either the main, operating engines or just the long voyages engines that supposedly are smaller and more efficient which is why they're at the mid-section of the ship, separate from the main engines that operate most of the time. These are like auxiliary engines to the main ones to reduce fuel consumption on longer sea & ocean travels. It's a good concept for conserving energy and if that bit of soot stain is the only drawback, I think we can all live with it!