Removing dried algae of Whaler

Fly'n Family

Fly'n Family

Active Member
Sep 19, 2013
812
TX / CO
Boat Info
2008 Meridian 341
2004 Boston Whaler Sport 130 w/40 hp Merc
Engines
6.2's
Pulled our Boston Whaler out last winter with temps plummeting. Got her in the garage, and unfortunately did nothing other than park her.

She's loaded with dried algae on her fiberglass body, and I want to get it off before putting her in again. Power wash removed a little, but not much.

She's at home, so I need to be careful of anything I get on the driveway.

Suggestions?
 
Scrub as much as you can get off and then use Mary Kate on/off. Just be careful to protect anything it drips on. It will destroy the surface of painted metal, raw metal, galvanized metal.
 
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Toilet bowl cleaner works well. Zing or any other muriatic acid product works as well. All are hard on trailers so work quickly and use lots of water to rinse the trailer and concrete drive.
 
A safer alternative to muriatic (hydrochloric acid) based products is Slimy Grimy. It won't hurt grass/flowers/etch concrete/etc. Heck, you can hold it in your hand. It practically has a cult following. But, any of the items listed above can work. Mix it up with HOT water.
 
Bixlers orange off.
 
Lazy Daze said:
A safer alternative to muriatic (hydrochloric acid) based products is Slimy Grimy. It won't hurt grass/flowers/etch concrete/etc. Heck, you can hold it in your hand. It practically has a cult following. But, any of the items listed above can work. Mix it up with HOT water.
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I think Slimy Grimy is based on Oxalic acid, which is much less corrosive than muriatic acid (which I think is Mary kate on/off). It does not work as well/fast, but it works. If you can't find Slimy Grimy, I have used wood deck renewer powdered oxalic acid from Home Depot and it worked basically the same.
 
Creekwood said:
I think Slimy Grimy is based on Oxalic acid, which is much less corrosive than muriatic acid (which I think is Mary kate on/off).
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You are correct on both of those statements. You're right, it's not "as fast", but it still works really well. We use it a lot at the shop because it's much safer for the guys doing that job... which I no longer do! :) Once in a while, you might still come back and power wash some spots again - but at that point it comes right off.

It really does have an almost "strange" following. From the retail side, we sell cases and cases of it every Fall! But, again, anything previously mentioned in this thread will do the job.
 
carterchapman said:
Bar Keepers Friend is mild oxalic acid as well...we use it on our teak deck...
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I thought it was citric acid, but maybe not. Its great for mild rust stains too.
I think it has an abrasive in the powder though so not great for shiny gelcoat.
 
Creekwood said:
I thought it was citric acid, but maybe not. Its great for mild rust stains too.
I think it has an abrasive in the powder though so not great for shiny gelcoat.
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It's very gentle - used on SS sinks. Very little abrasive...works great on teak! Definitely mild oxalic acid. I would just put it on and let it sit - not rub it - let the mild oxalic acid do the work - not the mild abrasive...
 
You can buy oxalic acid on the internet and mix it your self as strong as you want, I mix it 4 oz to a quart of warm water melts the algea off the hull before a can get the pressure washer started. Do a search for oxalic acid and it comes from florida pharmacutical labs, 10lbs for like $15, been a while as it lasts me 2 or 3 years before I need to restock.Just make sure you blast the trailer off good because it will turn galvanized metal white if left on for long time.
 
So I ordered Slimy Grimy, and tried it today. Heated the water, proper mixture ratio, and applied heavily via a spray system.

I tried different wait times, allowing it to sit from a minute to 10 minutes. It did a real good job on the slime line, but had limited effect on the dried on, hard core algae. I used a pressure washer at 2400psi. The pressure washer provided the same results by itself as where the Slimy Grimy was applied on the dried algae......thus the Slimy Grimy wasn't effective on the dried algae, but it did do a great job on the slime line.

Ick1.jpg Ick2.jpg Ick3.jpg Ick4.jpg
 
So what is left is essentially hardcore algae spots that when you run your hand over it, it almost feels like 80 grit sandpaper. The bottom is worse than the sides.

I haven't scrubbed with anything on it yet - any recommendation of what to do to get this crap off and get back to a smooth hull so I can wax can get her back to being a clean boat?
 
Well, it was worthwhile to start with the Slim Grimy as it was the safer choice and may have worked. There are times when even dried on stuff can be taken off with Slimy Grimy. But in this case, you might have take it up a notch and move to On & Off. You might even have to saturate a rag with it and hold it in place for a bit to soften things up.

Working the shade always seems to help.
 
I recall now that they have a gel version of Mary Kate On/Off that does not drip as much. Still VERY nasty stuff, but it will take off just about anything. Including skin, paint, lungs, etc. Or maybe diluted muriatic acid, but it WILL mess up anything it drips on. If you go that route, be very careful. Heavy rubber gloves, open area (fumes are chlorine)
 
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