In most states, a privately-owned recreational boat must be registered in the state where it is principally used, and any sales and use taxes paid to that state. A problem arises when the boat leaves this principal-use state and enters a new one for a long visit, extended cruise, or lengthy repairs. This could include snowbirds and seasonal cruisers.
BoatUS says boaters may be subject to various sales, use, excise, or property taxes when they remain in one location for a consecutive number of days, or over-stay their visit for a certain number of aggregate days per year. This grace period is often 60 to 90 days but as little as 30 days in two states (CO, NH). Also, if the principal state's sales and use tax is not comparable to the tax in the state the boat is visiting, the second state can levy their own tax making the boat owner liable for the difference.