Near Cape Verdi Islands, course south-east at 14 knots

At night showers of sparks erupted from the funnel illuminating the convoy, by day the funnel emitted a thick blue-grey smoke, visible from tens of miles away. The convoy was not amused. Obviously something was wrong with our engines.
Ass. Engineer Adriaan Kik

The most difficult task for the U-boats is finding allied ships. The ocean is vast and with the ships concentrated in convoys, chance of random meetings are much smaller. The curvature of the earth causes the mastheads to be invisible to the U-boats up to 10 miles. On a clear day. But U-boats have more ways than one to find ships. They can detect the noise the ship’s propellers make in the water and sometimes even smell the engines because the smoke remains present on the surface of the water. But the most used method is the observing of smoke from the ships funnels. Especially the old steamships which run on coals cannot do much to avoid detection – and the detection of the whole convoy- because of the black smoke making them visible from a large distance.

Smoke gives away convoy WS.8a. Taken from Abbekerk by F.J.C. Schimmel on her previous voyage. Ship on the right is RMS Empress of Asia that is in convoy WS.12z now as well (http://www.maritiemdigitaal.nl)

But the two modern diesel engines on Abbekerk should produce almost no smoke. The commodore signals Abbekerk and orders to reduce all emissions to nothing. And to do it quickly!

With the engines running slower than they were designed for, a lot of dirt is created and this settled in a thick film of oil on the exhausts and the noise dampers. When hot enough this would burn in the funnel, so during the day we emitted a thick blue-grey smoke and at night a nice rain of sparks . The Master and chief engineer had a meeting and they concluded that the engines had to run for a while on full speed to burn off the oil. This was signalled to the Commodore, who allowed us one hour before sunset to leave our station and run around the convoy at full speed.
Ass Engineer Adriaan Kik

We were allowed to circle the convoy at full speed until the funnel was burned clean. After that we returned to our station in the convoy. This ritual was repeated every day at sea.
Third Mate Jacob Visser