yes 2 would accurate, but it all depends on the convoy composition, which ships can be hit, which can't. and when in the war it is, and what sort of attack...
from an attack from outside the convoy at medium range ( 2 to 4 km) I would consider 1 sunk one damaged a good result, but from close in, or even inside the convoy it would be 2 or 3 hit, and at least 1 definitely sunk.
with a surface attack at night, where you have time to maneuver to get it right 2 would be a minimum, and if i use the stern tubes as well, 3
I never shoot more than 2 eels per target, except for the real big ones like liners, carriers and battleships
oh and passenger/cargos because 1 hit is not enough, the 2nd eel always either misses or duds and the 3rd is the charm
