Hi All
This might be slightly off topic, or stating the obvious but if you're using a conventional tug ie. propulsion units right aft, make sure the towing point is well ahead of the screws. If you tow from a point just above the screws, attaching to bollards for instance, you will find that it is almost impossible to turn the tug when there is any load on the tow wire. The load on the towline will negate any effect that the rudder might have. If the towing point is ahead of the screws, the tug will manage to pivot around the towing point. Obviously the less tension on the line, the more successful this will be.
This only applies to conventional tugs, without bowthrusters. ASD tugs, Voiths, SDMs etc, with units ahead of the towing point, don't suffer from this difficulty.
Cheers - Pierre