I borrowed this image from Tycho in another thread
, hope he doesn't mind.
So here's what we have:
- We have spotted a ship some 10000 metres away and we set a collision course (Our paths will cross somewhere in the future)
- Our intercept course is, as can be seen in the instruments, heading 130º at 6 knots
- We start the stop watch and each 5 minutes we ask the IWO for a report about nearest ship.
- The forward motion of our uboat is represented by the blue arrow, and each 5 minutes it will have moved forward as many marks as knots we are doing. Because we are moving at 6 knots, you can see each bearing line start from 0,6,12 and 18 respectively, as that is how much our uboat as moved on the map.
- On each of those moments we got a bearing (relative to our uboat) and distance report from the IWO, which we plotted accordingly
- Connecting the end of all those lines we have now the target course, as shown by the red arrow
- If you drag the transparent circular 360 degree ruler over the enemy course, you will see that it indicates a heading of 154º
But, that is the heading RELATIVE to our uboat. Because we are not heading 90º true course as shown in the plot but instead 130º as shown in the instruments, that means that the plot is wrong by exactly 130-90=40º
Hence, the enemy ship's course of 154º needs the same correction, and gives us a real course of 154+40=194º
If we could turn the map around in SH3 to make true plots that correction would not be necessary and instead our plot would look like this:
