if their like submarines, comparing them to the biggest submarine on earth, then they'd be about 170 meters long =3 so... yeah..... my *ahem* the RZE's Frigates are about 700 meters long....so e-yeah.... pretty much 7 times bigger then your black hole class ship..... 

....... how big/tall are Kerbals?, I always assumed they were short, they looked short =3