Cees,,that could very well be , will not dispute that. But nevertheless the black on the stern of the Discovery is from smoke from the exhaust and that is almost normal on such vessels, unless they are regular cleaned, which is seldom the case in those areas where they trading as you might know too :-)

Ted,
I don't like into discussions, but I think you are wrong.
The exhausts of those Australian made Mono hulls are not at the top of the Vessel, but at the bottom between the hulls. Look at my just uploaded photo's of the LILIAN CONCEPCION.

(lat. fusus = soot)

The proper word for this 'exhaust smoke' is soot !
What a fuzz about it....

She is currently laid up in Curacao.

An example of the stern water-jet mixed with exhaust SMOKE!

http://www.shipspotting.com/gallery/photo.php?lid=814512

At the end of her yearly service season, this craft also has her stern "blacked" by smoke ..... know it, seen it !!

Denis,,you ever been on a ship ?
The top of the funnel is never dirty or the front,(if the engines working normal),,almost always the backside of the funnel,,the backdraft from the fwd movement pulls the smoke back in,,that,s clearly visible here what happened over time and no cleaning. I passed x-times the hogh speed ferries bewtween T&T, the T&T Spirit and her sister, and both have the same and both
when passing you at high speed drag a SMOKE-cloud behind them

Ted, the exhausts are on top of those 2 red funnels.

That,s normal, Every ship has that in the funnel(exhaust) area, just a matter of cleaning it or not and here it is not

Cees
the Discovery, was she also clling the port East of Willemstad, I don,t know the name, but there was a vessel like this and an old small ferry/passenger vessel last time when I was in Willemstad and could see it on approach but the distance was to far and hazy weather,,as usual in that area off coast

Along with inadequate maintenance work...

Nothing!!!! Just exhaust smoke.

What happened?