That is a tough nut to crack ~AND~ survive. The main problem being of course, that you are at PD of about 11-12m, but sitting in only 22-24m waters... that is what the convoy's route will be almost the entire journey. To cheat just a pinch, here is the scenario as seen in the SH3 ME:
Note what the K-Ship does there. It's routing is where you see the big circles around the waypoints, which gives the game quite a bit of leeway to place the K-Ship anywhere in that area. You might notice though, that the grouping seems to follow a string of slightly deeper water most of the journey, so if you go to the south of where the K-Ship peels off to the north east and takes that 'odd' routing, that there is the possibility of attacking down there off Atlantic City, New Jersey. It would be a good place for a night surface attack, except for those Clemson DDs in the grouping - and SH3 doesn't always do very well at night attacks... Maybe take the seaward side Clemson out first, and then attack a merchant, preferably a tanker, giving a tail fish as you retreat toward deeper water?? Do a run around and try again? The several times I have run that, I have always been 'killed'...