Depends if you wish to follow real life tugs or modelling theory. Standard twin screw tug with no kort nozzles, twin or single rudder are always outward turning for manoeuvrability, with a kort nozzle I would not expect much paddle wheel effect. British warships with CP propeller's have inwards turning props for fuel efficiency, Ferries with cp gear have outwards props for extra manoeuvrability. Though as my mate Bob says and I have some sense in practice, that a single rudder with twin shafts and one speed controller the model does steer better with inwards turning props, as the spiral wash does veer towards the rudder. As a standard prop when turning gives two forces 1. forwards & reverse 2. Paddle wheel effect, it is a small force sideways in the direction of its rotation. That is why a single prop boat always carries about 3 degrees of wheel to counter act.