You can buy the boat in Florida, move it withing 30 days and register in in Delaware. You may have to form a Delaware corporation to register it there if you don't live there. However, if you use it anywhere but Delaware for more than 3 months (or so), the state where the principle use is will come after you for sales tax (or use tax). Maryland is well known for going after boats with out of state hail ports that stay in MD for more than 90 days. Most states will expect to see proof that you have paid sales tax somewhere if you move the boat into those states for more than their grace periods. In most cases they will asses a use tax which can be reduced by sales tax paid elsewhere