In our area it seems the soda blasting process stops several inches from the waterline (so as not to damage the gelcoat on the topsides?) So you will still have to do some manual work where it will show.
I am in the carbide scraper camp. Over the years, I've used carbide scrapers to strip the bottom paint from an 18' catboat and a 23' powerboat with excellent results. It wasn't necessary--even with the hard chine and strakes on the powerboat--to round the ends of the scraper. The trick is to apply pressure to fracture the brittle bottom paint, which comes off in chunks, leaving much less dust than brute force sanding. This is where the sharp, long-life edge of a two handled carbide scraper comes into play. What you don't want to do is shave or plane the bottom paint. Recycled, discarded shrink-wrap served as a drop cloth.
I then used 80 grit paper with a palm sander before applying Interlux 2000 barrier coats. Applying bottom paint over the barrier coat was a cinch.
A bit of advice: tape your waterline beforehand. If you are concerned about airborne debris, consider tenting your boat--perhaps from your rub rail to the ground with polyethylene--to keep peace with your neighbors and the yard manager. As it turned out, I didn't need to tent the boat, as the dust from scraping and sanding was minimal, but I did use a vacuum cleaner attachment to the sander.