Tips for intercepting ships?

Hi,

I'm 2 weeks into my fourth patrol and have seen no action and only a couple of ships so far. The contacts were greater than 25km away from my position and after setting what I thought was a reasonable intercept course, I arrived only to find nothing. Realism is set to 35% and I've burned 1/3 of my fuel already.

I've not received any contact reports from HQ and all they ever tell me is to "be more aggressive!" :-). Ha.

Any tips for intercepting more reliably? I've already completed my patrol mission and am hanging out in what I think are active shipping lanes.

I guess by February of '41 I expected a bit more action ;-).

I do use time compression a fair amount while stopping occasionally to check sonar. Could time compression be limiting my contact opportunities?