Suggestions on Convoy attack!

[TomcatMVD]

Ok... I know there have been a couple of guys asking about convoy attack hints and tips, and I've read'em all.
I just want to hear a couple of thoughts about my current situation and what would an experienced Kaleun do in my position.
It's July 1940, and after reports from Bdu I've gained contact with this large convoy.
http://img352.imageshack.us/img352/6...tconvoyjm6.jpg
As you may see, there's not a single warship screw to be heard so far, though I'm not that dumb as to believe there's not any escort around.
Since this is the first convoy I see when on patrol, I went to free camera to take a look at it... but just when I started to see the smoke on the horizon, I decided it was not a good idea, since I might have spotted a threat that was not on my hydro, and that just wasn't fair.
So... suggestions and comments are welcome.
BTW, you can read range on the ruler I'm drawing, and you can see the time as well. FYI: Weather is good with a little wind.