[WernherVonTrapp]

You mention triangle so I'm guessing that you're using Auto-Targeting. Like pabbi mentioned, make sure you open the torpedo tubes a few seconds before firing (by pressing the "Q" key). Also, make sure the triangle color is green, indicating that you have a "good" firing solution. You can lock onto the target by pressing the "L" key, but I prefer to unlock just prior to firing (again by pressing "L") and leading the specific targeted section ever so slightly.
Try to close to within 1000 yds or less (if possible) before launching your attack. Also, make sure you're not firing at too extreme an angle or accidentally firing the rear tubes when you mean to fire the front (or bow) tubes.