Hello Michael,
Nice tug, indeed and also with flanking rudder! Thanks for the pdf... .
Also, I like the design of the Kotug with 3 Schottel azimuthing propellers, of whom I dont attach a picture, to avoid angering sam simmer who doesnt like the magic beauty of the Kotug.
But I found an short presentation of the development; from this, I can infer that a mathematical model giving realistic results is not straightforward, to say the least.
http://www.rotortug.com/downloads/its_paper_2000.pdf
And they give a bollard pull of 75t with only 6400hp.
Regards,
Luc