Purchased our 1991 boat in 2002. Needed a bottom job and from the looks of it, the PO had used a blue hard bottom paint. The bottom had several coats of paint from previous years. Scraped a small amount of loose stuff off mostly around the waterline, feathered the edges of what had scrapped away, light sanded the entire bottom using the type that sheet rock installers use to level dry wall mud. What works for me is an articulating sanding pad on the end of a painter pole.
Used WM brand black ablative on sale. A 3/4" foam paint roller on the end of the painter pole works great. Applied three coats. That was in 2002. Did it again in 2004, not necessary, but did it anyway. Bottom in the same condition as 2002. Next bottom job was 2011, then in 2018. Use the same procedure in each case with the original number of paint coats still adhering to the bottom gelcoat.
Each year a hired diver inspects the bottom at the beginning of the season. Checks for rudder play, installs new zincs, clears the through hulls if needed, cleans the transducer speed wheel, shaft strut/bearing, etc. Scrapes any mussels off the keel bulb and a barnacle or two from the prop, if any. Usually the first year or so not much to clean, but over time the ablative looses its strength. He never cleans the bottom. Usually the flow of water passed the hull each time we cruise year around removes any marine fuzz.
We keep our boat in sea water year around ready to go at a moments notice. If fair weather holds during a three day weekend, I'm gone. Just finished a winter cruise rendezvous this past MLK weekend and had a great time. So far no need to take off all the old paint and start afresh. Maybe someday, but until then...
