Is NSM4 too easy?

After SH4 sat on my shelf for several months, I reinstalled it in the weekend and then downloaded all the "must have" mods. My installation order is now the following:

Silent Hunter 4 1.4 (without U-Boat addon)

Warships retextured
Trigger maru 1.5.2
RSRD for TMO
RSRD_patch
NSM4 classic
PE3_Install
PE3 Zones.cfg for NSM4 classic
Other parts of PE3
PE3 Patch for TMO

After sailing four patrols on 61% realism (unlimited fuel, automatic targeting, external cam) I am again getting bored. Every single time I shoot a ship, I get really close (1000yds), take good aim for the keel and then fire a torp. Sometimes (less than 20%), the torpedo somehow malfunctions, but 80% of the time I hit the ship and the very first torpedo sinks it (even the huge 8000 ton oiler).
Now I start to wonder: Is it realistic that every keel hit is an instant kill? Because if it were realistic, being crew of a surface ship in WWII would have been suicide.

I have one other grief about NSM4 (classic): Once I hit a ship with a keel shot, for example two thirds of the way from bow to stern, the torpedo explodes, the fountain rises and starts to fall down, and after that the ship suddenly breaks right in the middle as if its keel was made of TNT with a timed fuze.

Is this behavior normal or just limited to my computer (Apple MBP, 2.16GHz Core 2 Duo, Radeon X1600 128MB, 2GB RAM, Windows XP SP3)

P.S. I don't want to offend the makers of NSM4 in any way, it is much better than the "roulette" stock damage model.