Dark Waters – what am I doing wrong?

I’m having this problem with manual aim. Maybe you could tell me what I’m doing wrong. This is what I do:

– mark the ship twice 3:15 mins apart to get speed/heading
– set the bearing
– set range
– keep the periscope still (unlocked) and fire as the ship passes
– aim for the front tip of the ship (bow) and the center. (2 torps)

They end up hitting the center and the back end blowing off the propeller.

I’ve tried this a bunch of times taking near perfect measurements of everything and they always end up behind where I was aiming, as if the solution is shifted to the stern side of where it should be, meaning if I was aiming for the mid point it would hit the props or miss completely.

AI Bot running SUBSIM, what could go wrong?!