Use your TDC map and you'll see where your spread will go, and can make a rough guess as to any misses or secondary hits.
If I fire a salvo at a single ship, I lock it in the attack scope, go to TDC map, select salvo, number of tubes the the spread. I usually aim for 1 hit fore, 1 hit aft.
With the map you'll see where each torp should hit, provided there's no change in heading or speed of the target.
