I noticed that not only for beginners but also veterans the torpedoes in FHSW are still a mystery. I hope this tutorial can help you to understand the game mechanics behind it a bit better. If used correctly it’s possible to sink capital ships very fast, a lot faster than with regular bombs.
Let's start easy: First and foremost it’s important to always hit the side of the ship and not try to bomb the deck which causes little to no damage. To do this release the torpedo in a certain distance from the enemy ship, if it moves it’s also a good idea to lead the target a bit (practice).
Torpedoes have inertia so don’t drop them from too high or at a steep angle which can cause the torpedo to go too deep beneath the water surface and miss the target.
Against capital ships this is not that much of a problem but the hull of destroyers doesn’t expand very far under the water which often causes misses. Similarly it’s also important to not release torpedoes too close to destroyers.
Fighting capital ships
Capital ships (cruisers, battleships, aircraft carriers, transport ships) in FHSW are divided into four compartments which are called floaters. They are distributed like this:
Each floater has its own hitpoints and can only be damaged by torpedoes. If a floater is destroyed a water effect plays and the ship starts to list in this direction (picture below depicts the destruction of floater 3). The number of torpedoes required depends on the torpedo and ship, it’s usually somewhere between two and six. I haven't tested yet if they can be repaired.
This itself doesn't do much damage to the ship, it's more of an annoyance but now it gets interesting. While further torpedoes fired into this now destroyed floater still deal some damage it’s not really effective, you should concentrate your fire on the undestroyed ones. I noticed that destroying the floater opposite of the already destroyed one is enough to sink a ship (in this case floater 1 and 3). Destroying both floaters of one side only seems to make it list more.