How to pass a target at a specified range from it

[LemonA]

Originally Posted by sublynx

The example situation: you have stalked a convoy and plotted its course and speed as 295 true bearing, 7 knots. The convoy is now at a relative bearing of 87 degrees, range 10 kilometers. The fastest speed you can make in the prevailing winds and not wanting to risk engine failure is 15 knots. You want to pass the convoy keeping a range of 8 kilometers, thinking that at that kind of range they will not see you, but you can see them.
...

I got about 27,5.

That's wrong.
Your helmsman must change the course to 006.5° true (exactly 006.41°).

Dont mix up miles and km in a scetch. 7nm are not 7km etc.

Blue: you, red: enemy. M, eG = initial position. M_1, g = position after 1 hour. Dotted red = 8km safety distance.