Kenny,
If from the photo that is the final postion of the props, then as mentioned earlier, the prop wash probably like the original never hit the rudder, the rudder works only when the hull moves through the water causing a flow across the rudder. Tugs tend to operate at close quarters, so when working the master uses his props, so you need the props set to turn outwards like the original boat, that way you will get the full paddle wheel effect. I have known of older masters in the P.A.S. on old twin screw tugs take there tugs all the way down and out of the Plymouth Sound from the top of Devonport harbour just using the screws and the Helms man standing at the wheel like a lemon when they have point to make. Close quarters you use tank operation and going light speed through the water slowing one engine or stopping it to help a tight turn. Also how is the trim of your tug, it should be deep at the stern and the bow a lot shallower, a level trim will make it handle awkwardly.