Riverliver knows of what he speaks. Yes the annual permit is a scant 8 bucks per year. It comes with all the pertinent info and what is "required" when running under permit.
What a lot of folks don't know is that it is by rule illegal to tote an over width load on holidays and summer holiday weekends, and after noon on Saturday and all day Sunday during daylight hours during the summer months in Oregon. This is the short story rather than getting into more technical aspects of the rules. It has been that way for many years. I'm not justifying it, just saying that is how it is written. The problem here of course is that if you follow the rules, and display the required signs, you should not be on the road during these times. Then you say what good is having a boat if I can't drag it around when I want to. Indeed.
Enforcement is a different story. Motor Carrier Enforcement focuses on trucks. Trucks are required to pull into an open scale if over a certain weight, and must deal with officials who know and understand the rules that apply to trucking. Private vehicles are not under the same requirements for stopping at a scale, and OSP and most county mounties are not going to be that familiar with general over size rules and regulations. They are not likely to be carrying a tape measure to measure your boat width and probably won't look twice at you as long as you are not drawing attention to yourself by doing something else un-road-worthy. Therefore you are apt to be able to skate by this without any problem, especially if you are only 9 feet wide. I would think your biggest worry would be in the event you caused an accident, or a sharp lawyer at least could make it seem that way, and that you either, one, did not have a permit, and two, if you did have a permit, you were not following the terms and requirements of the permit.
As for the legal width load on an over width trailer, under most circumstances this is a no-no, but there are exceptions to almost every rule, and it is sometimes open to some interpretation too. The rules are many and often complex. They have been developed over time, to changing conditions and economic and technical circumstances in an effort to provide some degree of safety and regulation on Oregon's highways. Don't kill the messenger. The Over Dimension Permit Unit issues about 300 single trip truck permits daily, and this does not include the cookie-cutter annual permits. These are over size loads only, that are either heavy, wide, high, long or generally a combination of all of these.
Thanks for bringing it up.