This is bad and dubious advice, unless the boat is located in Delaware.
States with sales/use tax laws, which are most of them, want to collect that sales or use tax for every and any vessel for which it is due. If you live in one of those states, or keep you boat there, you need to deal with the sales or use tax. If you do not, and the boat is in CA eventually a harbormaster or sheriff or city or county agent will come across your boat and you will get a demand tax bill, for the sales/use tax, plus a penalty and interest from the date of original sale. Unless you can conclusively prove that you did not and don't owe that tax, you will end up paying it, the alternative being perhaps to leave the country and not return.
The taxing agencies are very aware of the desires of the boating public to not pay these taxes, and have organized their efforts to seek out, identify and tax every and any vessel subject to the tax.
In some of the other threads on sales/use tax, you may find my story of paying a MA use tax demand, even though I then lived in MN and had sold the boat several years before.r