The most attacks I've made with a Type VII on one perticular convoy is 3. And that was because the third attack was going for one Large Cargo. I fired all forward torpedos each time, and on one occasion, I was able to use my stern torpedo for a finishing shot. Then I let the convoy slip by, surfaced, the did the end-around.
The best advice on an end-around is stay way abreast the escort sceen, way off so you can only see their masts.(I still use 6km visibility)
There really is no set outline for attack, for me. It evolves as more data is collected. But basically, I like to attack abeam, firing at furthest ships first(Range almost 2000m), then the closest(Range about 800-1000m). Get the best solution for the furthest ship, the second one is closer and has a better chance to hit than the furthest one. You'll be surprised at escort behavior when the furthest torpedo hits. They seem to be attracted to that one hit and forget about the rest, unless youre making all kinds of noise or you are counter-detected.
Concerning tail-bubbles: The above attack tactics worked in early morning hours with the steam powered torpedo. I was never pinged and no DD's came my way, even though I was running at ahead 1/3. However, once I shot at a DD that was listening for me and was going at about 6 kts. It was a perfect set-up, an almost 90degree angle, maybe 1200m. But it was in broad daylight with about sea level 2. He saw the bubbles and evaded my torpedo. This should be a lesson: Never fire at the midships of a DD in good sea states. Always use the fastest torpedo speed and aim well ahead, perhaps even at the anchor. Anyway, when the DD evaded, he came my direction but was off about a 45 degree track. Luckily, I was able to slink away, counting my blessings. Lesson learned!
edit: this is worth reading
http://www.subsim.com/radioroom/showthread.php?t=115981