MOst of the tugs that you are talking about are scratch made by the modelers that build them. Many of them including myself have made contact with the companies that own these tugs and tried to get the drawings that are needed inorder to build these types of tugs being AHT's and PSV's. Some companies will help you, but many will not. I have found that those who already have made contact and received plans are not allowed to share them with any one, this is the way that the companies control as to who get these drawings. I have good luck with Far Stad and Maersk and a couple of other companies so far. In the future I will try again with the companies that I have done good so far with to try to get some of the other designs that are out there. At this time I have 5 different designs. Try contacting these companies and see what you can do. Also if you live in an area were these tugs come into port and you can get to them talk to the captain if possible and maybe show him or her what you do and maybe they can help you out.
Good Luck
Duane