I normally submerge a few times until I can get a good idea of his course. Once I've got it I will get ahead of him and submerge about 200m away from where he should pass by. As he gets closer I can fine-tune my location a bit and get the distance to 310-350m.
It would be easier just to wait ahead of him (at his 0 bearing) and just use a magnetic torp, but heavy winds usualy accompany heavy fog and will make a mag shot hard.
Alternately, if its not too windy and you have some of those fancy homing torps you don't need to work out where it is
