Building speed boat from STYROFOAM

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As far as I know, speed boats are expensive even JetSki. The prices some times from $20,000 and above. But recently I watched speed boat making from STYROFOAM on YouTube. Yes, from styrofoam. The more I watch it the more I think I can do it myself. I think the only expensive part of a speed boat is the engine. Does anybody here live near a river or seashore? or speed boat is one of your hobbies? Here is a video, speed boat making using styrofoam.