targeting: what am i likely doing wrong?

[old1]

I *think* I'm up to speed on all the concepts of targeting (playing 100% realism with RFB+RSRD), and in fact, I've sunk some amount of merchant shipping, so I'm doing something *sorta* right. I've watched tutorial videos and read a lot of online stuff, so I should have a basic idea of what's up by now.

But the following happens to me with annoying frequency. The last time was like this: I tracked a large-ish (~7000 ton) merchant boat going 10 knots. I know he's going 10 knots, because (a) I paralleled him for half an hour, and (b) on getting close, I measured his distance over 3 minutes. I'm about 98% sure I've nailed his speed. I establish a track on the TDC about 4000 yards out (measure AoB, etc) and refine it a little as he gets closer. The track seems to be good: he's always right where the TDC predicts and the AoB in the TDC seems good. I launch at about 1000 yards, three torps, with a +2/0/-2 spread (I'm trying to avoid a 90deg impact angle of course). All three torps pass in front of him by about half a boat length. Ack!

By this time he's perpendicular to me on a 0deg relative bearing around 700 yards out, so I quickly reset AoB to 90deg and launch the other three tubes. He still has apparently not detected me. A bit of a stern chase now, but once again all three pass in front of him by around 1/3 or 1/2 a boat. Grrr!!

It makes sense if I'd got his speed wrong, but I'm pretty dang sure I didn't. Anyway, say I missed by 2 knots - that's only 100 feet difference or so in his position, and he's way longer than that. I'm also pretty sure he didn't detect me: he didn't manoeuvre at all, and I hardly had the scope up at all inside 2K yards - maybe 3 or 4 seconds total.

I had a similar issue earlier: I found a large modern composite, similar scenario to the above except that one managed to hit him *right* at his bow. The other two missed.

I can't figure out what I'm doing wrong. Range estimation maybe? But inside 1500 yards, the stadiometer is agreeing with the sonar range really closely - within yards. And as I said, I'm pretty sure I nailed his speed too. Which leaves AoB, but that seemed OK and anyway shouldn't be super critical once it's set inside 1500 yards as long as the TDC track is good, as it appeared to be.

I just can't figure out why I'm missing from such close range. I have enough problems hitting stuff inside 1000 yards that I can't even fathom needing the slow speed/long range setting on the torpedoes. My chance of a hit from over 2K yards is probably around zero.

*Edit* A bit of other data I forgot to post: If I recall right, the gyro angle was something like (roughy) 30 deg. I was aligned perpendicular with the target course, and he'd pass about 680 yards from me, and I'm using the fast torpedo setting.