I bought a bare hull a couple ago, rigged it, and used it last year. Parts of the bottom have a brown petrified growth that feels like 40 grit sandpaper. The boat came out of Virginia and was probably used in salt/brackish water. I started to sand it off in spots, but really don't want to refinish the bottom of the boat. Open to ideas to remove it with chemicals if that is and option. I have it off the trailer.
Thanks,
Jason


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HYdroblast, put it in the water and run full throttle. if bottom doesnt come out clean, install larger motor and repeat.

Slimey Grimey. Thats what we all use to clean our boats that stay in the water full time or get a brown stain just from use. Mix up a batch and use a weed sprayer to spray it on your hull, then wait several minutes. Then hose it off.

Lol, tried that. Adding more power as we speak.
Also, after sitting in the water for 3 days it is still it doesn't change or come off.

Muratic acid or Sno Bowl toilet bowl cleaner or the Works toilet bowl cleaner. Those two toilet bowl cleaners are acid based as well. The acid will not hurt gel coat or paint. It will discolor bare metal or concrete.
Muratic acid fumes are pretty bad, so I'd say go with one of the toilet bowl cleaners. Easiest way is get a $10 1 gallon plastic garden sprayer. Spray it on, maybe agitate slightly with brush and rinse it off. Rinse it very well. A gallon should be enough to clean the entire bottom.

Next time scrub the bottom while the boat is in the water, stuff is harder to remove once it drys.

On off boat bottom cleaner in the cheap pump sprayer. I used the muriatic acid and toilet bowl cleaner before but I think the on off works better. It uses less scrubbing then I use the pressure washer to wash it off. My boat gets a discoloration from being in the rivers in PGH for even a day. The one I keep in the water gets all that growth yearly.

Mary Kate On-Off. Good for staining.

+1. Many of the hull cleaners are diluted acid, many times with a sudsing additive so it stays on the surface a bit better, and a pretty high price tag for what you get. A gallon of muriatic acid is cheap. You can mix it 50/50 with water, add a little dawn dish detergent, and you have a better product than most bottom cleaners on the market. Make sure your sprayer has all plastic parts, the acid will eat any metal. As Griff said, rinse it very well.

I've also used Power 1 Fountain_of_Youth_Home.html , for the slight yellowing I get after a season at LOTO. It works great, just spray on and rinse off. I've never had to scrub it. But I know people who boat on other waterways, who get more staining, and it doesn't work well. I doubt it will do the job for your job. The biggest reason I use Power 1 is it is not acid based, and my boat sits on a galvanized metal lift.