[U-96]

One way I do it, it works very often for me. But the downside is that you might be too close to the fat valuble ships. Is that I go right in the path of the convoy dive to 25 meters, and order silent running and just wait. Usually they'll pass right over you without even knowing you're there. Once you're amoung the columns, you can move pretty freely as Escorts will have a hard time picking you up with all the propeller noise from the convoy itself. And it takes a while for an escort to wade through the columns when you're detected. Though like I said you risk being too close to use your fish with this method.