Set your spread angle as mentioned above. I usually start the first at 0 and the go 2-4 degrees towards the direction of travel for each torpedo after the first. There is really no reason why all three should not hit bow, midsection and stern. Ship sunk. Also, how long are you waiting? One good hit to the engine room should shut that puppy down. Serve up the killing torp from the stern of your sub. I hit a old split freighter last night with three torps. Two exactly in the middle under the stack and one just ahead of the stack. She stopped dead and sank in about 25 minutes. Every now and then you get that on that sinks in under 5 minutes. Play with spread angle a bit and make a fan of your torpedoes. She how she goes
In fact, go to the torpedo training school. You already know what the warship is and the speed. Just dial that in and start messing with spread angles. Once you shoot hit F11 and follow your torpedoes and watch how they track. Eventually you will see a pattern that works well. Rinse and repeat until comfortable with what you have.