Did that last December. I used hand scrapers and finished off with 80 grit on my orbital sander. I've applied the barrier coats and the first coat of ablative. I'm waiting for a couple nice days this week to finish up.
Did ours - 58 feet - with a 4-foot long floor scraper. Keep the blade razor sharp with a belt sander - 600 grit. After scraping, hired a sand-blaster to bust off the remainder & open up the gel-blisters. A 7" diameter 4 grit diamond wheel used for terrazzo floors faired the entire boat in about 7 hours. Follow this with 6 coats of Interprotect 2000E.