No smoking you said?

This is the chemical/oil tanker Theresa Tiga (ex Shintoku if you magnify the picture). She was built in 1996, so for a vessel that is pretty old, but not too old.
It is strange that you see an emission like this after she had started up her main engine. The rules on maximum (NoX)emissions are pretty strict for new vessels, but apparently this vessel does not have to comply with any rule at all.