Newb in need of HELP

First off...can someone explain the spread angle to me....

I was under the impretion that it would allow me too spread my torpedos over that distant so if a ship was coming left to right across my bow, i set for 3 degrees spread right, and fire 4 torpedos, that those 4 torpedos spread out over 3 degrees, but when i put it into practice, i don't see any results, all of my torpedos will hit withing 50 feet of each other on my target.

Also, how many torpedos should it take to sink a medium size freighter I know that with a properly placed torpedo i should be able to break the keel, but whenever i fire the torpedo simply slams into the side and detonates. It does damage yes, but nothing would be more satisfying then watching my fish detonate and snap a freighter like a twig. I DO use automatic targeting and I have checked my run depth against my recognition manual, but the settings are correct. I know that the Mk14 have a rud depth variance of 1.3m or so but even on a calm day my torpedos still detonate at what appears to be 5-7 feet below the surface even when the draft may be 20.

Lastly, If someone has a link to some good tactics or rules of thumb for the ammount of torpedos needed to sink vessels I would appreciate it.

Sorry about the wall o' text. P.S. only running 360 degree bearing mod and smaller radar contacts on v1.5