You can set the depth and speed on all torpedoes long before you fire them. That way, when you're attacking, you'll have less steps to do.
When you're on your torpedo depth screen, you can click the different torpedo tubes to select them and set them however you want. This is typically the first thing I do once I've identified my target and know its draft.
Also, remember to flood the tubes you intend to use before firing them. In real life, they would do this in the final minutes before firing because the longer they were flooded, the more likely the torpedoes would malfunction. I don't think that this is modeled in the game though, so just make sure you flood them before things get too hectic.
Also, you should be able to move the stopwatch to a different part of the screen once and it stays there. There's also a shortcut key to get rid of the stopwatch or make it re-appear: In TMO it's the "X" key... I'm not sure about stock.
For a constant bearing shot, once you get everything set up, it should be as simple as firing at the right time, then moving the crosshair and hitting the "Send data to TDC" button again (the red one), selecting the next tube, then firing again when the new target spot crosses the wire.
__________________
|