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Old 27-09-2021, 14:21   #1
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Smile How to remove stubborn harbor scum from my boat’s waterline?

Does anyone have suggestions for how to remove harbor scum from the waterline of my boat while my boat is still at its mooring? I tried a couple scrubbing pads and it did nothing.

Thanks😀
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Old 27-09-2021, 17:16   #2
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Re: How to remove stubborn harbor scum from my boats waterline?

Marykate , On and off gel
It took our icw moustache off easily.
Put it on with a brush or small roller. Don't get it on your skin. Wait 5 min and rinse off wellClick image for larger version

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Old 27-09-2021, 17:46   #3
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Re: How to remove stubborn harbor scum from my boats waterline?

Other similar oxalic acid based products include:
FSR (Fiberglas Stain Remover) gel
Total Boat Stain Remover
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Old 27-09-2021, 17:52   #4
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Re: How to remove stubborn harbor scum from my boats waterline?

Or you can save a bunch, and buy oxalic acid in raw form, and make a 10% solution in water….
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Old 28-09-2021, 08:42   #5
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Re: How to remove stubborn harbor scum from my boats waterline?

On & Off and other acidic cleaners can soften paint, suggest a test area before getting it on your boot stripe.
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Old 28-09-2021, 08:43   #6
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Re: How to remove stubborn harbor scum from my boats waterline?

Deck cleaner from home depot. Cheap and the brown scum comes off with easy with a brush
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Old 28-09-2021, 09:02   #7
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Re: How to remove stubborn harbor scum from my boats waterline?

Lemon juice or lime juice in a spray bottle. Spray on, let set, rinse off. Repeat if necessary.
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Old 28-09-2021, 09:04   #8
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Re: How to remove stubborn harbor scum from my boats waterline?

Hull cleaner will remove the scum. Also try mixing ˝ cup of baking soda and 1/3 to ˝ cup of water to form a paste, apply and scrub.
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Old 28-09-2021, 09:11   #9
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Re: How to remove stubborn harbor scum from my boats waterline?

I use Spray 9. It is supposed to be environmentally friendly and worked for me with scrubbing brush.
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Old 28-09-2021, 09:17   #10
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Re: How to remove stubborn harbor scum from my boats waterline?

Any Oxalic acid product will work. I buy wood bleach crystals from the hardware store and mix my own - far less expensive than products with a "Marine" label on them.

Be aware that it will take the wax off as well so part two of the job is to re-wax.
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Old 28-09-2021, 09:25   #11
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Re: How to remove stubborn harbor scum from my boats waterline?

Not exactly environmentally friendly. But I watched some professionals clean a very scummy waterline with great ease on a boat that was in the water and I asked them what they were using, they replied "Toilet bowl cleaner".
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Old 28-09-2021, 09:45   #12
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Re: How to remove stubborn harbor scum from my boats waterline?

It might be good to heel first - tie main and spin halyards after launching dinghy...


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Old 28-09-2021, 09:47   #13
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Re: How to remove stubborn harbor scum from my boats waterline?

Quote:
Originally Posted by magentawave View Post
Does anyone have suggestions for how to remove harbor scum from the waterline of my boat while my boat is still at its mooring? I tried a couple scrubbing pads and it did nothing.

Thanks😀
Hit 'm on the head with the spi pole
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Old 28-09-2021, 09:50   #14
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Re: How to remove stubborn harbor scum from my boats waterline?

Oxalic acid also has the benefit of being poisonous to many algae, fishes and plants.
It will help improve the clearness of the water.
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Old 28-09-2021, 10:01   #15
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Re: How to remove stubborn harbor scum from my boats waterline?

Quote:
Originally Posted by chris mac View Post
Marykate , On and off gel
It took our icw moustache off easily.
Put it on with a brush or small roller. Don't get it on your skin. Wait 5 min and rinse off wellAttachment 246030
Quote:
Originally Posted by BillKny View Post
Or you can save a bunch, and buy oxalic acid in raw form, and make a 10% solution in water….
Quote:
Originally Posted by SIDEBYSIDE View Post
Lemon juice or lime juice in a spray bottle. Spray on, let set, rinse off. Repeat if necessary.
Quote:
Originally Posted by stormalong View Post
Any Oxalic acid product will work. I buy wood bleach crystals from the hardware store and mix my own - far less expensive than products with a "Marine" label on them.
Be aware that it will take the wax off as well so part two of the job is to re-wax.
Quote:
Originally Posted by guyrj33 View Post
On & Off and other acidic cleaners can soften paint, suggest a test area before getting it on your boot stripe.

Wait, the boat is in the water, not hauled out. and OP says stain is at the waterline. Scum probably extends from above boot stripe, all the way over the boot stripe down to the waterline and a little below. As soon as you start scrubbing on the boot stripe you will bring up water and anything you add will be washed away immediately.

This is a tough problem - we get a black coating of something very hard and durable, covering parts of our boot stripe. It may help to heel the boat over, but how do that, to any extent with a large boat, while at anchor or mooring?



I spent hours on our waterline, at anchor, with a Scotchbright pad or two. Hard work.
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