From pics the large areas with sharp step to adjacent areas just look like very heavy bottom paint. I hadcanprevious boat with withnthis condition. Previous owner apparently painted bottom every year regardless of need and did little sand, scrape prep.
I scraped areas that came loose easily and feathered edges before repainting bare spots. Waterline tends to be a problem area as owners want it to look good and repaint every year whether it needs it or not. A thinned coat will give good appearance without the heavy build up.
I redid spots for 20+ years without ever doing the complete bottom prep all at once. If you are anal about it being perfect you can spend $$$ to have it prepped & painted but you likely will see little/ no performance difference vs simply doing spots as needed.
I scraped areas that came loose easily and feathered edges before repainting bare spots. Waterline tends to be a problem area as owners want it to look good and repaint every year whether it needs it or not. A thinned coat will give good appearance without the heavy build up.
I redid spots for 20+ years without ever doing the complete bottom prep all at once. If you are anal about it being perfect you can spend $$$ to have it prepped & painted but you likely will see little/ no performance difference vs simply doing spots as needed.