I also read that the steamers had loaded British coal for the trip. Wondering about the significance of this? Anyone know?
I gather that British coal, which was mostly bituminous coal I think, would make a different color smoke that the then available American coal. I imagine it was all part of an effort by the North to lull Southerners into thinking that they were not American ships. Obi Wan voice: "These are not the American ships you are looking for."
Similarly, the Powhatan, the ship that Lincoln secretly diverted from the Fort Sumter fleet to instead aid the effort to reinforce Fort Pickens, had been intending to sail into Pensacola Bay flying "English colors" until Meigs stopped them.
I'm guessing that it is the difference between lignite and anthracite. One burns cleanly and emits little smoke, the other burns very sooty.
I don't know which we used and which the British used, but I would imagine you could tell a ship's origin from it's smoke stacks by the difference in the smoke produced by the coal.
If you were attempting a deception, the difference in the smoke would add to the illusion you were attempting to create.