This is probably going to be different depending on which state you're in. For my state, Texas, here is what the comptroller has to say:
"Boat and Boat Motor Sales and Use Tax
The boat and boat motor sales and use tax applies to the purchase of a boat that is 65 feet or less in length measured from the tip of the bow in a straight line to the stern.
jet skis and other motorized personal watercraft
Boat motors subject to boat and boat motor sales and use tax include:
outboard motors (gasoline or diesel)
electric motors attached to a boat subject to boat tax and sold with the boat for one price, such as trolling motors
The boat and boat motor sales and use tax rate is 6.25 percent. The tax is based on the sale price less any allowance for the trade-in of another boat or boat motor.
Permitted dealers collect the tax at the time of sale and remit it to the Texas Parks and Wildlife Department. If the seller does not collect the tax, the buyer must pay the tax when obtaining the boat’s title and registration from the Texas Parks and Wildlife Department or participating County Tax Assessor-Collector’s Office."https://comptroller.texa...Collector's%20Office