Not sure what mods you use, but in my experience using TMO, convoys Zig like crazy. It seems like they only keep the same course for like 20 nm or something. This may exaggerate the truth, but compared to my experiences in the Atlantic (sh3+gwx), these convoys zig a lot more (maybe because they are so lightly protected?). I rarely get that perfect lineup on a convoy that I used to get. How many times recently have I had the perfect setup, and just when they get in firing range, the convoy shifts to a new course. That almost never happened in SH3+GWX. Also, in TMO, it seems to me that after being attacked, convoys almost certainly change course. But I'm not saying I'm unhappy about it. I _love_ the challenge. Convoy tracking in SH3+gwx was almost too easy.
Rather than count on a perfect firing position, these problems have encouraged me to adopt tactics that allow one to make good of a messy situation. If a convoy turns on me when I'm nicely set up, all is not lost. Instead I try to get a sense of their new course. This will allow me to pursue them later, but also I might still have a chance at a shot. Once their course stabilizes and they get in order, I'll use the same speed estimate I had before, and count on a decent AoB estimate (eyeball or based on their presumed new course) and try to get the best range estimate possible with the stadimeter. I've had some success this way - a botched attack can sometimes turn into a sinking and a severe damaging. First of all, any range of attack, up to about 6000(!) yards is viable. The range on your mark 14s is 9000 yards. You can't take a shot at that range, because your torp will most likely have to take an oblique shot (i.e., run along the hypotenuse), but that is that max range on slow setting. If i'm firing for long ranges > 3000 yards, I fire them slow, and make a spread in order to hedge my now imperfect firing solution. Just fire a big spread - like 6 torpedoes, and you'll probably hit one or two ships, which isn't bad efficiency overall - you might get an instant-kill. If fuel prevents you from making the required over-taking maneuver, then just take your best shot. Sometimes you don't have the option to overtake the convoy again. With a good spread (with solid speed info!), you almost _have_ to hit something. Better than going back with torps in my opinion.
Also, when you have radar, you can consistently track a convoy outside of visual range. This is wickedly useful and almost makes it too easy. On radar you can even see the convoy lanes when the blips fade, making it easy to eye-ball their course. This feels like cheating, but perhaps it is at least vaguely realistic. On the other hand, when you get good with radar, you can abuse convoys with virtual impunity when in fog and rain. Not sure if they did that in real life.
Finally, and perhaps most importantly, you have to use common sense to guess the convoy's course. If they are heading towards Japan, south of the Bungo strait, that is likely their ultimate destination, so you can intercept them at a choke point. Get a sense of whether a convoy is outgoing or incoming (to japan). This gives you a very rough, but useful indication of what kind approach course you should take.
If you are using radar, and you travel at roughly merchant speed (e.g., 10 kts), and you make contact, chances are you aren't chasing him. Instead, you are likely crossing his path on some angle. Look at the geography and make a guess about where he is going.
Hope this helps. It gets a lot easier (too easy?) with practice.
Kb
P.S. What's the biggest Jap convoy you've seen in TMO? I've been encountering 4-merchant convoys for a long time. I'm thirsty for something big. Big.
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