Welcome to the wonderful world of sales tax. Anything you bring or buy in the state of washington is subject to sales tax except for food at a grocery store. So If you can prove what your boat and trailer is worth you will most likely not need an appraisal. The sales tax up here does what Oregons state tax does down there. There really is no getting around it. People from washington used to try to go buy a car/truck/boat down in oregon to get away from the sales tax but as soon as you try to liscense it here they nail you. You will also need tabs for it (like a car) but they're called boat tabs. Good luck!!