Torpedos are battleship sized weapons and apply poorly on smaller targets.
You have different torpedos, but if you’re going for maximum damage you either choose Rage torpedos (big damage, big slow explosion) or Faction torpedos (less damage, smaller faster explosion). For small targets like destroyers and cruisers you want to use the faction torpedos, while for bigger targets like battleships (and capitals, structures) you want the rage torpedos. Battlecruisers are somewhere on the edge between the two: if you have a couple of mods and rigs to increase application (or paints and webs on the target) you probably want to use Rage.
In my experience from when I did a couple of Havens in a polarised bomber with good application: battlecruisers died in two hits. Battleships in 4-5. Cruisers required swapping to faction torpedos and die in about 3-4. And frigates either die really fast when you manage to shoot them while they’re not moving yet, or they’re the toughest targets around.
None of them will die to an ‘alpha strike’ unless you have a critical amount of torpedo ships on your side.
A T1 frigate should be too small and too quick to die to a single torpedo strike, unless you have turned your MWD on and are sitting at 0 velocity. Keep moving!