One of the benefits of the new yard location for Whimsy is that we're allowed to do our own bottom-jobs. Needless to say the red ablative anti-fouling on my boat had long expired and needed to come off. I also wanted to check everything under the waterline, to make sure there were no hidden surprises under the anti-fouling, and to take care of a couple of projects including checking the rudder shoe.
Options for removing old antifouling are: sanding, stripping with chemical stripper, or blasting (usually with something relatively soft like walnut shells, to avoid damaging the gelcoat underneath the antifouling). Since blasting was not allowed in the yard and I wasn't a sucker for punishment, I decided to try the paint stripper option.
I bought pail of Peel Away paint stripper from the local hardware store (about $50/pail), and tried a test patch on my hull. This material is basically drain opener chemicals but in cream form, which you trowel onto the hull. Cover it with the paper/plastic sheets provided, tape the sides to make sure the stuff stays moist for as long as possible.
It worked amazingly well once left overnight and then washed with a power washer. The antifouling stuck onto the now dried-up chemical stripper, and I was able to scrape it off with a handheld scraper. The remaining residue sloughed-off under a power washer, especially once the dried-up chemical stripper absorbed the water and softened-up again.
The area around my boat was an environmental disaster, flooded with several inches of orange-colored slurry. And once it all dried, the antifouling turned into dust and settled on everything including my car. Yet this is normal in the yard, and worse has been happening for several decades since the Navy owned the place. I suspect this is where I will catch cancer.
WARNING: Peel Away is highly corrosive so I suggest taking all the necessary precautions (especially eye protection and gloves.) A little bit of it was accidentally smeared on the inside of my wrist, under the glove, and now have a scab there. I'd hate to think what could happen if even the dust from the dried-up material got into anyone's eyes - so I suggest not only eye protection but also keeping a water hose nearby and handy as an emergency eyewash station.
The stuff I used was the regular hardware store version of Peel Away that comes with a plastic spreader, some pH testing strips, and the plastic/paper sheets used to cover the area being treated, and a packet of neutralizing powder (which I suspect is a mild citric acid. Vinegar also works.) Peel Away makes a "safe" version for use on boats that won't damage underlying gelcoat, which I also tried. (Since my boat had an epoxy barrier coat under the antifouling, I wasn't worried about gelcoat damage using the regular stuff.) The "safe" marine version is slightly runnier, so you need a better trowling technique especially on the upside-down surfaces of the keel to avoid plopping it all on the ground. They were both equally effective.
The spread the material, I used a notch trowel with 1/4" notches. First, I smeared a heaping of the stuff on the trowel using the provided plastic spreader. Then I smeared that on the surface of the hull using the straight edge of the trowel, much like smearing butter on toast with a butter knife, spreading it all out as smoothly as I could until a patch on the keel about the size of one of the plastic/paper sheets was covered in stripper. I scraped the notched side of the trowel across the patch, leaving 1/4" high streaks or lines of stripper running horizontally. I then knocked down the straight lines by moving the spreader lightly vertically across the lines, to even it all out. Finally, I covered the patch with a sheet of the special paper/plastic provided, gently kneaded all the air pockets out from under it, and taped the edges of the sheet to prevent air from drying out the stripper too soon. Left over night, the stripper was mostly dried especially in areas where it was applied thinly. The paper and tape was removed, and the stripper was scraped off. The rest was washed off with a power washer.
I had to buy 6 pails of Peel Away to complete the project but in the end I got a nice clean hull with no sanding. Of course, then I had to sand it all with 80 grit in preparation for the new coat of barrier paint. While sanding, I occasionally accidentally went through the old barrier coat and got to see the gelcoat underneath, which while crazed was still in decent condition. There's no sign of pox or blisters; boats as old as Whimsy generally didn't have problems with blisters. I figure, if there was going to be osmotic blistering, she would have shown it by now. However a couple of extra coats of epoxy barrier coating comes next.
Also, while the antifouling is gone, I want to check out the rudder shoe and investigate a worrying crack in the fiberglass around there.