Torpedoing moving ships

[Woke Up Dead]

The SM-79 and I think also one of the Ju-88s have a special torpedo sight for hitting moving ships. I recall seeing instructions on how to use these before, but can't find them now. It has something to do with estimating the ship's speed by the angle of the smoke coming out of its stacks, and then referencing a chart with the ship's speed on one axis and the angle on the torpedo sight on the other.

Does anyone have that chart and does anyone know how to approximate ship speed by smoke angle?

Thanks.

WokeUp