Generally, a sales tax is due on a purchase
in the state where you purchase
it, but some states allow an exemption if you move the boat out of the state shortly after purchase--like within 30 days. Each state is different. Here is one link to some information on NJ sales tax on boats
A lot of states have a use tax, usually equivalent to the sales tax, that becomes due if you begin keeping a boat in that state for some certain period of time, usually 60 or 90 days. I know that Maryland
has such a tax, and they will grant credit for a sales or use tax paid elsewhere. Maryland
is fairly aggressive at collecting this tax if you do something like rent a boat slip for the season. I don't believe Delaware has either a sales or use tax on boats bought and kept in the state.
All of these states have various rules on registering the boat in the state, even if it is Coast Guard documented. There will be a registration
It can get complicated. Here is one company that has articles
on how this all works.