Hi Raymond,
I would try entering terms like:
navigation authority clyde
(or whatever river/lake you plan to sail on) in your favourite search engine. It should help you find the appropriate body and the information you need or, of course, look more closely at a relevant licence disk itself. Once you know who to contact you'll be able to find out more about the appropriate licence for you. Unlike angling licences, navigation licences are frequently for a minimum period of a month so work out far more expensive than an annual licence.
P.S. Always use a subject line that relates to your post. People are more likely to read your message if they see it will relate to something they know about.