No need really, most of it is speculation as to different effects of rudders shapes, wings etc, thing to remember is when water rushes past a rudder either wing shaped, wedge or flat (commonly on fast electrics for the last two rudder types) the water rushing past the rear edge of the blade can cause a vacuum of air leading to loss of rudder or very reduced rudder function, not from lack of servo or movement, but that the rudder is moving in an air void rather then moving in water which is where you get your steering from. this only explained lack of rudder movement or steering within some types of vessels that move at speed, tugs are in this group due to there power not there speed. ( the ability to move large quantity's of water with less rpm)
You ever tried steering a model with one prop in reverse and it only turns one way? yup that's the props direction pulling it one way, there is a trick to steer in the opposite direction, which is when you reverse set the rudder hard over and get the boat going, it will pull the opposite way, let off the power for a few moment and let the boat under its own force drift, it will start to turn in the direction you want to go providing you keeping the rudder hard over, once the turn start in-cress the power and bingo you have steering in the direction you wanted to go. ( dunno why i typed that though it was relevant some how)
Normally all boats with submerged drives will sink the back slightly when going forwards this is the thrust created from the props to push the boat forward with a combination of bows shape. I say normally i have seen boats weighted down in the bow to counter this effect to they run 'flat' under way, and stationary they drop the bow (great braking for large vessels, not so good for fast boats aka submarine!)
Most tugs & other vessels have upward sweeps on the bow in some form which aids then 'lift the front while the rear 'digs' in, Springers for example and flat fronted vessels tend to push against the water making one hell of a bow wave, which in turn usually makes then dig in at the front bring the rear upwards, and dropping the nose under, simply as they are pushing large volumes of water rather then getting over the top of it, this does explain the bow shapes of many oil tankers and war ships with the 'egg or cone' shape on the tip of the bows keel, to aid then cut through the water, that's efficiency coming into play as the vessels are so huge pushing water is not practical nor efficiently (unlikely to actually move the ship in some cases)
Back on subject i tend to wander at time (mostly) if you want maximum pull from a tug, the rudder plays a tiny role which is tracking the vessel straight, to achieve maximum thrust running off a twin prop (korts or not) then its best to have both prop rotating inwards (to the centre) so looking from the rear the right hand prop rotating counter clock wise, and the left turning clock wise, (usually fitting the lh prop on the rh side and fitting the rh prop on the lh side) this maximises thrust as the water is being forced centrally rather then outwards if the props were rotating outwards, A type of ''jet effect'' which you already get with korts which is increased when the flow is then centralised.
So max thrust is obtained via prop rotating inwards, maximum maneuverability is props rotating outwards. This works for both fixed and rotating korts (not the full 360 ones)
Make sense no? me either anything after midnight i get confused too... j/k