Mysterious Black Spots

rcwass · Posted: Wed May 31, 2006 6:05 pm Post subject: Mysterious Black Spots

My C-Dory was on a boat lift in Maryland for 6 years. I started getting these tiny pin head black spots all over the outside of the boat. These are like raised bubbles and are hard. My boat is a 1990 that has been exposed to California and Maryland sun since new so the gel coat is pretty much gone. When I scrape these spots off they leave a stain in the fiberglass. I've since moved to Maine and have noticed these same spots on my galvanized trailer. The boat was on the trailer in California and in storage in Maryland. I haven't found anything that removes these spots or stains. It was suggested I use accetone but I'm hesitant. Does anyone know what these black spots are and have any idea how to get rid of them? Right now I have about a thousand of these on the fiberglass, stainless steel and trailer.

I have photo's if needed but they don't show up that well.
Thanks for your help.
Dick

lloyds · Posted: Wed May 31, 2006 6:16 pm Post subject:

The most obvious GUESS would be liquid ashphalt kicked up from the tow vehicle tires. It would harden over a short time, and when rubbed off would leave a brownish-black stain. They can usually be rubbed out easily with rubbing compound on the boat. Probably on the trailer as well.

Patrout · Posted: Wed May 31, 2006 6:24 pm Post subject:

Those spots could also be organic residue from trees or insects. Have you tried solvents designed to get rid of that kind of stuff?
Pat

rcwass · Posted: Wed May 31, 2006 7:04 pm Post subject: Mysterious Black Spots

I've tried mild rubbing compound, waxes and marine cleaners with no results. I've tried scraping the bubbles off which can be done but the stain below is stubborn. I doubt if its asphalt related because the bubble shell is hard and when scraped in the sun there's no smudge.
Thanks for the input.
Dick

Da Nag · Posted: Wed May 31, 2006 7:13 pm Post subject:

Perform a search here for "barkeepers".

Barkeeper's Friend is the gelcoat and stainless secret weapon. I've yet to find any gelcoat stain it would not easily remove, and it takes rust off of stainless like nobody's business. Mix it thick with water so it forms a paste, rub it a bit, and presto...

Your stains may be the first it fails to remove...but I'd be surprised.

Patrout · Posted: Wed May 31, 2006 7:15 pm Post subject:

Right, Bill.
I get my Barkeeper's Friend at Walmart.
Pat

Da Nag · Posted: Wed May 31, 2006 11:07 pm Post subject:

Larry H · Posted: Thu Jun 01, 2006 4:52 am Post subject:

Dick,

Was your boat near any oil wells? An oil well near my marina in LA leaked and sprayed a fine mist of crude oil into the air. All the boats in the marina had tiny black dots!

Paint thinner or kerosene would dissolve asphalt, tar, or crude oil.

Acetone or lacquer thinner will also work and since it won't hurt galvanized (or stainless) steel I would practice removing the spots on the trailer or SS rails first!

Papillon · Posted: Thu Jun 01, 2006 11:26 am Post subject:

Dick,
Scrape off a bit of the black and take a taste....I bet you can figure out what it is without having to call 911. If it taste nasty spit it out and rinse with Jack Daniels. Heck, I might have to look for some black spots on my boat now I think about it.

Mike

Swee Pea · Posted: Thu Jun 01, 2006 1:19 pm Post subject:

I do not want to be an alarmist, but when you said "bubbles", it may be what is referred to as "osmosis". I am no where near an expert, but if you go to the bottom paint discussion refer to the aurora web site, www.auroramarine.com. Join the aurora marine "club" and search for osmosis. They have a picture posted of the bubbles. THEY ARE NOT BLACK, SO THIS MAY BE A FALSE ALARM. But it's worth the effort to eliminate this possibility.

John
Swee Pea

Papillon · Posted: Thu Jun 01, 2006 1:39 pm Post subject:

I can't remember seeing any "osmosis" on trailers or stainlass seel before, so I would pretty much rule it out in this case.

Byrdman · Posted: Thu Jun 01, 2006 1:52 pm Post subject:

Mike I think you are right on this....but I'd keep the Jack handy just in case. Ya never know when it might start hitting the metal stuff...

lloyds · Posted: Thu Jun 01, 2006 1:56 pm Post subject:

Osmosis, or blistering, is pretty easy to see and identify. Even the untrained eye will recognize it if they see it. Just go to any boatyard and look for boats with lots of spots sanded or opened on their bottoms. Then go to a boat on blocks with a dry bottom but no prep work and spot the blisters. This can and does happen in all regions, types of weather, salt or fresh water. They vary in size from the size of the lead in a pencil to a silver dollar, and are usually round. Once they get past a dime or so the chances of them going into the core material is much greater. I haven't heard of C-Dory having much of a problem, but I am sure there are a few around in this brand as well. But the problem in this thread is not osmosis. They don't take on a color, at least not much. If you drain a blister the liquid will come out about the color of light varnish, and will smell somewhat like varnish, because it has some of the same chemical makeup. But these black spots are kind of intriguing. If it isn't petroleum, it almost has to be some foreign substance landing on the hull, then possibly reacting with sunlight. Maybe some petroleum based substance or insecticide emulsified in the water the boat is in.

Sea Wolf · Posted: Thu Jun 01, 2006 2:16 pm Post subject:

Two possible explanations arise:

1. Bug poop. (or)

2. For years cosmologists have speculated about where all the material goes that is sucked into giant black holes in the Universe so large that not even light can escape their gravitational pull. Where can all those untold billions of suns masses of matter be? Is it all locked up inside the black holes? Or does it reappear in another parallel Universe at another time or dimension of space? Could it reappear as black spots on boat hulls in Maine? Inquiring astrophysists want to know!

Get the BarKeepr's Friends:

Booze

Friendly Women

Scouring cleanser

oldgrowth · Posted: Fri Jun 02, 2006 2:42 am Post subject:

rcwass – I get the same thing on my boat. If I clean it on a regular basis the spots come off easily. My boat is stored in my equipment shed and I believe the spots are caused by spider poop. The spiders are in the rafters above my boat, the spiders catch other insects, suck their juices out, then poop on my boat. I put up with it because they keep the insect population down.