In all seriousness, what is the escort and weather conditions? Assuming you're in a typ VIII or IX boat:
Shadow the convoy till dusk and then track ahead of it and set up an attack that comes from an angle close to 90 Deg. AoB for best chance detonation, but at the same time furthest from the escort.
If the convoy has DD and ASW escort, then pick the latter as the lesser of two evils. If you can get a crew on the gun and sit hove too in an ambush position, so much the better in the dark (Better calculation option with the option of immediate defence.)
I always find in these scenarios that a range of not more than 2700m will have better than 90% hit-ratio (premmies do my head in!
) and seems far enough away from search lights that you can stay on the surface for better speed. Once the eels are in the water head parrallel to the convoy at silent speed and once hits register then blast it and reset.