Sharkbit, very good. The comment about the crew makes sense, in an immersion sense; but to play devils advocate, what would they think if I went in and wasted a handful of torps when I could save them for more favourable conditions?
PRiley, the conditions you mention were the plan I was considering, but I'm just not cofident with torpedoes in that position. From behind you'd need to use magnetics, not an easy thing to do with ships bouncing meteres up and down. And in low visibility, by the time you spot a target, and turn to get a reasonable gyroangle, you're under the torps minimum range
In the end I left it and turned away. Luckily I ran into slightly better weather the next day - so it worked out OK.