Thank you all for your insights and comments! After talking with a coworker in more detail about it yesterday, he was convinced there was nothing mechanically wrong with the prop (maybe marine growth), but I was making some novice mistakes, like over throttling, and expecting power boat - esqe results.
I have a good friend with dive gear who is excited for the opportunity to help out, and I going to send him down with a paint scraper and wire brush on Sunday. I will report back with the results ... and hopefully the events of a good daysail to follow.
1976 Bristol 30, Mariah