View Full Version : Stains at the waterline on fiberglass boat

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06-14-2011, 05:57 PM
I know this is not an auto detailing question per se, but does anyone have any suggestions on how to remove stains at the waterline from the gel coat of a fiberglass boat?

Old Tiger
06-14-2011, 06:10 PM
Try DG 501 first and then get more aggressive if need be!

06-14-2011, 06:13 PM
I use a wool pad, and some 1000 grit marine compound. Does the trick every time. Just be prepared to put a little muscle into it.

06-14-2011, 07:13 PM
Actually I would try Duragloss #541 Marine & RV Cleaner with mildew buster (http://www.autogeek.net/rv-cleaner-mildew-buster--541.html) first, assuming that you have washed the boat with a marine wash such as Duragloss #591 Marine & RV Wash Concentrate (http://www.autogeek.net/marine-rv-wash-concentrate-591.html). If this didn't work then I would go to DG #501 Marine/RV Polish (http://www.autogeek.net/duragloss-marine-rv-polish--501.html), finally reaching for a marine grade compound as a last resort. Duragloss has released a marine compound but it is not available at AG at this time.

06-15-2011, 01:33 PM
Did you spray the boat down with degreaser first? Usually roll off will take most of it off. Otherwise a wool pad and compound get rid of it quick.

06-15-2011, 07:02 PM
How old is the boat and how long has the stain been there? If it's years and years of staining your gonna need a marine compound, if your new to this I would recommend meg's marine line 1 step compound, works great and easy on/off with good results even by hand

06-15-2011, 07:20 PM
You do not need a marine compuond, Any will work

06-15-2011, 08:29 PM
You do not need a marine compuond, Any will work

True you don't "need" a marine compound but depending on how long that stains been there it will speed the process up, generally marine compounds have more cut then automotive, but something like menzerna pg or xmt #4, megs 105 is decent if that's all you have

06-15-2011, 09:43 PM
A little more information please!
What kind of stain? Metallic, algae or just lack of maintenance as the boat sat in the water? Salt water or fresh? Is the boat out of the water on a trailer or cradle?
If its metallic there is a product called FSR (Fiberglass Stain Remover) you can get at any marine store (I have not looked for it here) that will take it off chemically in about 20 minutes. Be carefull and wash your hands a lot. It will take the hide off. Have not tried AOL for anything drastic but it does work
If its a plant stain vs plant life I just used the Collinite #920 cleaner with decent results. Plant life takes a scraper or green pad first.
If the boat is out of the water, well and good.
If you are going to try it in the water, safety first! Things powered by electricity seem to have a natural affinity for mixing with water and producing the smell of bad BBQ, and it always takes less than you think. There are also a group of people around who frown about mixing certain chemicals with public water supplies.
Fiberglass gel coat is generally pretty resistant to deep stains unless you have other issues. Like your car, tread lightly first. You can damage the gelcoat and then it gets ugly

06-16-2011, 12:08 AM
Thank you for the product recommendations.

Yes, I sprayed the boat down with degreaser. It removed some of the staining, but not all of it.

The boat is kept in fresh water and is not bottom painted.

The boat is a 1987 Crestliner Nordic. The staining was not visible when we bought the boat 1 year ago. Since then, it was kept in the water 1 entire season. This is where the staining came from The staining has gotten progressively more obvious as we now keep the boat on a trailer.

I believe the staining to be from algae and other fresh water plant life, and contaminants.

06-16-2011, 01:50 AM
Sounds like you just have bottom growth. That is what the paint is for, to keep that to a minimum.
When it is in the water for extended periods you need to hire a diver to go under and clean it with a scotch pad. I pay a dollar a foot twice a month in saltwater.
Since it is out of the water, park it somewhere that you will not mind the stain on the ground after and start scraping (plastic bondo trowels work ok, not metal, do not gouge the gel) Just get the film off. Then pull out your machine and the cleaner. This will cost you a pad or two cause they will never be clean again.
If it is something else let us know

05-21-2020, 11:39 PM
Marykate On Off Hull Cleaner

05-22-2020, 05:58 PM
Marykate On Off Hull Cleaner

This thread was made before I even joined AGO.

But, having worked in the marine industry for over 30 years, this is the correct answer.

And without sounding like an a$$h*le, all of the suggestions offered on page one of this thread are laughable at best.

05-22-2020, 07:48 PM
I'd definitely put some anti-fouling paint on her ... West Marine and Pettit both make decent products for this.

05-22-2020, 07:57 PM
I'd definitely put some anti-fouling paint on her ... West Marine and Pettit both make decent products for this.

WM and Pettit are far inferior to Interlux products. The price reflects it. (Akin to buying NuFinish vs. Collinite).

But the OP was asking about stains right above the waterline. That browning that affects the gelcoat just above. ;)