Yes the torpedoes always miss aft of the second ship!
Yes I have been setting the AOB to be 90 degrees for a quick 90 type shot, yes this goes back to my old way of thinking with SH3, hard to shake it off after all this time.
The white line should be pointing in the same direction as the ships course? Why didn't I figure that out?

I haven't been adjusting the PK to the ships course as it is on a course of 90deg ...
wrong obviously, I didn't think that would make a huge difference.

The reason that I've been hitting the first one, or single ships, is probably because I haven't fired the torpedoes till it was almost at 0 degrees, then it would be 90 degrees, provided I still keep setting AOB, would this be correct? Confusing isn't it!
What I should do:Go back to setting the ships course and when switching to the second ship I should lock on it, get & set range, set AOB, then bounce between setting AOB until PK is set to the ships correct course (approximately).
Thanks again Fincuan, what would I do without your help!

(not sink ships thats for sure)
Edit: I'm going to keep trying a mod to get the AOB dial into the attack screen, would be great!