Which states are you referring to? Locally you need a certificate for motorized craft and it seems like almost every other state is in this situation.

You can get the certificate after taking training but I imagine there is some way to test out of it.

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The training doesn't need to be months long though. Try renting a jet-ski; they'll give you a very quick training but it's still present. Although jet-skis are probably not long enough to qualify as motorized boats in a lot of states.

https://www.americasboatingcourse.com/lawsbystate.cfm?lid=50

Sweden and New Zealand doesn't require any licence to operate a boat which is great. But try leaving marina without any experience and your boat neighbour will stop ya or at least help you get your feet wet.

Thanks for the correction. My own state of Washington mandated boater education only about ten years ago, I assumed it was an early mover given how much navigable water we have.