Okay, thanks for your attention guys.
@makman94, your tool seems to do the job... more or less. But it's not exactly how I wanted it. And on longer distances it becomes quite hard to match the distance with the correct bearing. Anyway, I think I'll stick to the stock ruler. I guess I just need more practise with it.
edit: Oh, and another thing! I will not make another topic for a single question, so here it goes - how do you manually use hydrophone? Might sound noobish, but I've tried everything and I just can't figure it out.
I'm asking because when I ask sonarman to report on nearest contact he often replies that there is no contact.