Peter.....I have read back to your original post on 01/02/2014.....
"I can't find much on the internet regarding whether or not this is a model of an actual tug, so I think it's more representative of a type of the early 20th century ocean going steam tugs"So from this you have a few choices......
1. use the 40 diameter x 3 blade RH [plastic?] prop.....[
RED plastic kit props are usually JUNK value]
2. change the polarity on your motor to reverse rotation
3. spend $ on 3 or 4 blade brass propeller's of differing diameters & blade geometry or pitch
Why not spend a few hours researching prototypical tug vessels of similar displacement & design
.........you may from there be able to understand the as installed propulsion & scale it down to suit your model........
Keep us posted ....but don't rush in & order something that you may be unhappy with
later on......... Derek