Yeah, that looks a lot more reasonable. Getting a hit on the engineroom or far aft to blow of a screw usually disables a ship, bringing it to a stop, although not necesarilly sinking it. Best advice I can probably give you is to fire 2 fish at each target, and hit them some distance apart. Hitting them twice in the same spot generally doesn't do much, though stock SH uses a "hitpoint" system for damage, instead of simulating flooding and having a ship sink by that. That's why I'm using NSM; in stock, ships usually go down in seconds, minutes at best. With NSM it can literally take hours, although rare. Never saw a ship capsize or lift the stern or bow right up in the air in stock.
As you probably know, ships are built up in watertight compartments. Punching a hole in just one is not enough with the bigger ships, especially warships, those are built to last! (and withstand some damage, obviously)
Had a run in with a huge european liner once; fired a spread of 4, got 3 hits. Ship was listing badly, bow low in the water, but it didn't sink. It came to a stop after a while, so I went on over to finish her of. Thing was, I pulled up on her starboard bow, while the first spread hit the port side. It took 3 more hits to get it to finally sink! Ran into another one of those sometime later; fired a spread of 2 (all I had left), and watched her go up in a big fireball at the first hit! Must have hit a fuel bunker...
And that's just it; if you hit the sweetspot, all it takes is one. But sometimes you can keep firing without any real results. If you want to be sure of a kill on the first go, hit it more than once.