Various plans for RC tugs available in the
Ships and Sailboats section of Aerofred.com
This is a website with a lot of plans for RC models, mostly aircraft, but there's also a Ships and Sailboats section. Most plans are taken from 1950's and 1960's magazines, some were published more recently. The tugboats are pre and post WW2. You'll need to register to download the plans, but no costs and no spam
a sample: