Er.. Convoy Approach.

[Salvadoreno]

Okay guys i know this has been asked before, but i just cant find it. My latest convoy attacked resulted in 3 ships sunk, a coastal merchant, and 2 troop transports. But the problem was this. It had about 7 escorts. And at first i was going to try and approach submerged, but scrapped that when i came to close to a DD. So i backed off, and followed the convoy due north about 5000m away starboard (left). But i noticed my bridge watch took a kneel, and usually that means ive been spotted right? Well though nothing happened i continued to approach and wait.... But no matter wut it seems like if i am on the surfrace for a while, regardless of the monstrous waves that are suppose to be hiding me, the escorts eventually catch on. Even if i am very far away. Seems like a bug, like after a certain amount of time you will get spotted. Well after a game of cat and mouse and diving and surfacing i got into good firing positio. but because of my poor skills as a submarine captain only managed to sink 3 ships. With 3 torps hitting 1 coastal merchant on accident. (the troop transport was beside it)
What was the problem with those escorts?? When i submerge i start to lose the convoy, and even if i am 5000m away with 7 knots underwater i eventually get detected as well. kinda lame.