The word you're looking for is boater ... this is what the RYA would call you. It's the best generic word for a boat user. The only caveat is that it includes all vessels, including rowing boats, kayaks, canal barges, pedalos, etc. If you cross oceans in a superyacht, you might find boater slightly beneath your dignity!
It's also fine to describe a motorboat user as a sailor (yes, I disagree with the premise of your question). Certainly so if you go on lengthy voyages.
sailor: 2) a traveller by water https://www.merriam-webster.com/dictionary/sailor
... most people understand that wind power does not a sailor make, in my experience. (I do sailboats. My motor-cruising friends all describe themselves as sailors without fear of reproach or confusion.)
Similarly, anybody who uses a boat for pleasure, rather than commerce or transport is a yachtsman (although that word is also slightly more associated with puff power)
I'd suggest that you can safely describe yourself as a yachtsman or sailor around anyone who knows boats, but keep "I sail a powerboat" in reserve for lubbers.