Cleaner for fiberglass/kevlar and gel coat?

My beloved Bell Magic interior needs a cleaning. For a couple decades, I’ve been using Watco Teak finishing oil on all of the wood, and it continues to look beautiful. I used to use a spray called “303 Aerospace” gel coat cleaner on the interior kevlar/fiberglass and exterior gel coat, but apparently, 303 was either bought out, or has expanded on its own into numerous other cleaning materials, and I can’t find the original stuff now. What do you recommend?

Where do you live? 303 is readily available locally in my area as well as at Amazon:

BTW, welcome to Pcom.


I’ll take a wild guess that he (or she) lives in New Hampshire :stuck_out_tongue_winking_eye:

But yes, 303 should be readily available. I was just in West Marine this afternoon and saw some.

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Wenonah recommends this product for protecting their fiberglass and Kevlar canoes and kayaks. Can be used as an alternative to 303.

A friend who knows a lot about restoring and maintaining boats recommended the “Mr. Clean” Magic Eraser sponges for cleaning fiberglass and Kevlar. I just used one this morning on a 33 year old Kevlar Wenonah canoe that was cruddy from being stored for 15 years in a barn. Worked like a charm. The “erasers” have very low abrasion cleaner which should not harm surfaces. It took the surface corrosion off the aluminum gunwales nicely too.


Magic erasers are, well, magic! Seriously though I keep a stock of them on my sailboat at all times. They’ll clean almost anything.

I used the Maxiglide Boat Guard on my new-to-me Xtreme and it worked Xtremely well.


Best stuff I ever used for protection. Use on my Boston Whaler, kayaks, outboard motor, cars, glass. Easy on, easy off. I use to use 303 not no more.


The 303 product that’s historically been used on kayaks is not a cleaner, it’s a UV protectant that should be applied after cleaning to prevent UV damage. However, looking at their website, they’ve apparently expanded into a variety of products. They’re on the pricey side and Meguiar’s automotive detailing products will do the same job for less money.

That said, if it’s just dirt you need to remove, pretty much any cleaner will do. If you need to remove oxidation from the gelcoat, you need a polishing product. Again, there are lots of automotive products that work perfectly for the job.

Regarding 303 protectant, I’ve found that it washes off hulls and decks pretty quickly, probably because it can’t penetrate the surface. A high-quality wax would likely work better. 303 is more durable when used on hatch covers and fabrics.


Prior to using the Maxglide product I washed thoroughly with soapy water and a soft bristle brush just like I do all of my boats. Dawn dish soap works just fine.

Clean gelcoat buff with a 3M cleaner wax / compound they have 3 or 4 grades.

I use Magic Erasers or equivalent for cleaning gel coat. Sometimes I use some sort of car wax or some such as a follow up but usually not due to the slipperiness it imparts to the surface. I personally use 303 only on rubber/plastic hatches and never on the fiberglass surface. In my experience it makes the surface scary-slick for the first outing and washes off first time on the water. The ceramic finishes seem to have much longer staying power for me than car waxes and certainly exponentially longer staying power than 303.

This is only my personal opinion based on what I have experienced. YMMV. I’m just not sure that a glassy smooth finish on a kayak, though beautiful, is in anyone’s best interest. Trying to remount a glossy capsized kayak from the water feels to me like trying to climb on top of a slimy log.

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You’re grabbing deck lines not the deck no?

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Yes I am but having a higher coefficient of friction between the swimmer and the boat, in my opinion, aids to the speed of the rescue by maximizing the swimmer’s energy reserves and bolstering their confidence. I think of it sort of like an artificial climbing wall where the wall is made of glass and the only friction available is on the individual climbing holds. Though you are supposed to only need the holds any bit of additional friction helps.

Only my personal opinion and I admit that it leads to my boats not being as pretty as I would like for them to be but generally you can count on them to provide a decent grip.

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Dawn dishwashing soap and a grout sponge. To polish it up, 3M extra cut fine polishing compound.

If it is going to hang out in the sun for a while use 303 or the equivalent. If you apply those a few days before paddling, they won’t wash off at first immersion.

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Ayaah, New Hampshuh fer sure. I had been getting it at my local Ace hardware store for more than a decade. It used to be in the boating gear aisle, but now it’s in the paints section. They had five or six varieties of 303 (it used to be just the one) , but not the original that I had been using. The sales guy said, “They don’t make it anymore, or we’d have it.” Here’s a shot of the old bottle that I had in my garage.

Is it now the same stuff that’s in the large white spray bottle I saw on Amazon?

Various things that work on fiberglass and gel coat to remove difficult stains that the folks on the sailing forum suggest. I have used the magic eraser before.

Lemon juice and let it dry in the sun.
Citric Acid Powder stronger than lemon juice.
Soft soap and magic eraser.

Last resort
Muriatic Acid fortified with Dawn.
Or Oxalic acid mix lightly and increase if needed

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Thanks for that info., willowleaf. I’ll check it out.

For the hull, not the deck, I tend to use Star Brite or West Marine Instant Hull Cleaner. Easy to use and quickly removes stubborn scum lines, leave stains, and rust stains. Spray or wipe it on, let it sit for a couple of minutes, and hose it off. Contains oxalic acid. Not too acidic, but gloves recommended.

For the deck, my Kevlar boat is 22 years old and gets a lot of sun, so I use a fiberglass restorer once or twice a year. Finish up with 303 for whole boat. A good marine wax would work, but is a little more work.

I take the view that it is a boat, not a fine piece of furniture and I spend a fair amount of time on the water. So I don’t spend a lot of time cleaning and polishing it.

Yes my advice is for a white hull. Don’t know how it would work on colored gelcoat. The two acids are for what Star Bright can’t handle. This advice on that forum came after someone couldn’t get Star Bright to do the job.

After a while the water spots (calcium deposits) build up on mine, had to use vinegar to dissolve it.