This Thread was covered last year. I'm bringing it back because Spring is when Artillery Fungus is active and few are know of this. Please refer to: http://plantclinic.cornell.edu/FactSheets/artfungus/artilleryfungus.htm

My boat is covered with these tiny, hard shelled, pinhead sized, black spots. When the shell is scraped off, inside is a black tarry substance that stains the fiberglass. So far nothing removes these stains easy. I have a stockpile of failed products like: MEK, accetone, paint thinner, bleach, Magic Eraser, rubbing compounds, On/Off Bottom Cleaner and a variety of stain removers and cleaners. I've had a Marine Surveyor and a Marine Finisher look at it and both say use 1000 grit wet/dry sandpaper sanding wet, followed by rubbing compound, polishing compound and wax. My boat is a 1990 that has seen several years of California and Maryland sunshine so the gelcoat is pretty much gone which dosen't help matters.
When they built my house in 2003, they cleared the lot of trees, hauled off the logs and chipped the branches into a huge pile in the woods. When I moved in, I backed my boat up on a flat area next to the woods near this pile. The decaying wood chips, oak and pine, and the spours from that decay is what Artillery Fungus is. It travels about 20 feet in the air and is attracted to the sunshine or a nice white boat. My 22 foot boat is covered from the roof to the keel, on everything, even the trailer.
Please keep your toys away from wood chips.

I would spray it with bleach and keep it wet for an hour then pressure wash rinse with as high a PSI as the gel coat could take before damage. Wet sanding and polishng will take you all season.

That stuff is a nightmare. good luck

I had that crap all over my house, i had to use bleach, and dish soap, lots of elbow grease to get it off. I had it on the boat, and the power washer did a great job.

You can soak it in bleach, power wash it, acetone it and nothing will work, believe me. Get yourself a plastic putty knife (to scape off the excess) and some 3M polishing compound and have at it. Then get rid of any wood mulch you have near your boat or move your boat. The fungus is directed towards bright objects so a nice white boat is a perfect target. The longer it sits on the surface the harder it is to get it off.

You can soak it in bleach, power wash it, acetone it and nothing will work, believe me. Get yourself a plastic putty knife (to scape off the excess) and some 3M polishing compound and have at it. Then get rid of any wood mulch you have near your boat or move your boat. The fungus is directed towards bright objects so a nice white boat is a perfect target. The longer it sits on the surface the harder it is to get it off.

When the Marine Finisher came he brought his scraper, buffer and 3M Rubbing Compound. Didn't remove the spots/stains. He then used the 1000 grit Wet/Dry Sandpaper sanding wet. That did the job after a lot of work. He then used the 3M Rubbing Compound to finish that area. I'm on my own now with the rest of my 22 foot boat to do. This is bad news stuff that's why I'm posting it again to alert others so nobody has to deal with this like me.

I had success with putty knife and 3M compound and the better part of two full weekends. I have splatter coat finish on the inside of the boat so I didn't bother to remove it there.

I'll agree it is nasty stuff.

I hope you don't have what I had: overspray from bottom painting/prepping for a boat nearby at the marina at which it was winterized two seasons ago. I still have the little dark spots but I get rid of a few more every year.

I hope you don't have what I had: overspray from bottom painting/prepping for a boat nearby at the marina at which it was winterized two seasons ago. I still have the little dark spots but I get rid of a few more every year.

I had a few spots of bottom paint on my boat when I got there yesterday from the boat that had been next to me. They compounded off very easily.