Rust-looking Stains on Hull Beneath Through-hulls and Drains

[jviss]

For above the waterline outlets like holes for sea chests, scupper outlets, etc. - I have stains that are rust-colored. I don't think they are rust, though. What is it? How can it be easily cleaned?

Thanks,

jv

 

[kappykaplan]

Oxyclean might work.

 

[LloydB]

tannin ?

 

[rgranger]

Oxalic acid works well on tannin stains. Try barkeeper's friend. I use it often and it works well.

 

[Stu Jackson]

How can it be easily cleaned?

You are kidding, right? You've been here on sbo for ages and haven't heard about FSR? Or Mary Kate ON&OFF? Really?

 

[jviss]

You are kidding, right? You've been here on sbo for ages and haven't heard about FSR? Or Mary Kate ON&OFF? Really?

I have certainly heard of both, and both contain the same active ingredient, I think. But I want to know, what causes these stains, what is it? And what's the best way to not only remove it, but prevent it?

 

[PaulK]

The stains are caused by crud on deck that gets washed down the scuppers. The crud falls out of the sky as dust particles: exhaust from diesel & gasoline trucks & cars, tread wear from tires, industrial emissions... you name it. There is probably some iron compound making it look like rust, but it could be lots of things. To prevent it you can store your boat inside and filter the air that goes into the room. Too bad the Supreme Court just de-clawed the EPA.

 

[jviss]

The stains are caused by crud on deck that gets washed down the scuppers. The crud falls out of the sky as dust particles: exhaust from diesel & gasoline trucks & cars, tread wear from tires, industrial emissions... you name it. There is probably some iron compound making it look like rust, but it could be lots of things. To prevent it you can store your boat inside and filter the air that goes into the room. Too bad the Supreme Court just de-clawed the EPA.

Are you serious, or was that meant as sarcasm combined with a ding of the SCOTUS?

 

[PaulK]

What lands on your deck from air pollution gets washed off down the scuppers. People living in the Interstate 95 corridor know this. Besides this, if your varnish crew uses iron oxide sandpaper, grit that wears off the paper ends up on the deck. Swabbing the deck or rainwater takes it down the scuppers. We have dark topsides, so it doesn't show there, but there are spots visible on our deck apparently because of this. We bought our boat in Marion, MA last year. Highway pollution would be minimal there compared to what we have in CT, less than a mile from I 95. There were still rusty-looking spots on the deck along the toerail when we got her.

 

[Tally Ho]

My marina is right next to one of the biggest steel mills on the Great Lakes…stuff spews out of that plant day and night, and my boat always has some silvery dust all over it. Certainly isn’t very picturesque either.

Greg

 

[jviss]

What lands on your deck from air pollution gets washed off down the scuppers. People living in the Interstate 95 corridor know this. Besides this, if your varnish crew uses iron oxide sandpaper, grit that wears off the paper ends up on the deck. Swabbing the deck or rainwater takes it down the scuppers. We have dark topsides, so it doesn't show there, but there are spots visible on our deck apparently because of this. We bought our boat in Marion, MA last year. Highway pollution would be minimal there compared to what we have in CT, less than a mile from I 95. There were still rusty-looking spots on the deck along the toerail when we got her.

Ah, I see. I bought my boat in Marion, too! About 4 1/2 years ago. I keep it in Westport, MA. There is no industrial or highway pollution in either place, as far as I can tell. Burr Bros. Marina is just about a mile as the crow flies from I-195, but it's not a very heavily traveled road at that point. F.L. Tripp Marina in Westport is 10 miles as the crow flies from I-195. There is a danger from others' sanding dust when it's in storage, but that doesn't happen every year. I don't have a varnish crew! Wish I did. It could be tannin stains. Then, must this moment, I thought, gee, maybe it really is rust, perhaps from aging wire-reinforced scupper hoses, and similarly, exhaust hose?

 

[dLj]

For above the waterline outlets like holes for sea chests, scupper outlets, etc. - I have stains that are rust-colored. I don't think they are rust, though. What is it? How can it be easily cleaned?

Thanks,

jv

And here I thought you'd been on these forums long enough to know that photos are always mandatory....

dj

 

[jviss]

I didn't take any pics, sorry!

 

[RoyS]

In a former life I worked in public transit (subway trains). The never ending rail and wheel wear filled the subway tunnels with steel dust that glued itself (chemically) to the train bodies. We used a diluted oxalic acid solution in our automatic car washers and that effectively removed the steel dust. A chemist once explained to me the chemical bond and how the oxalic acid broke that, but it was over my head. Sometime later, as the transit agency began to decline, an idiot in the Safety Department got all worked up over the word ACID and insisted that it not be used. They stopped using it and the trains are a filthy mess to this day. When they really get bad now, they hand wash the trains with the oxalic acid solution under the supervision of the Safety Department.

 

[rgranger]

... A chemist once explained to me the chemical bond and how the oxalic acid broke that,....

I got you @RoyS

The formula of rust is Fe2O3 with a few associated water molecules. You often see the formula written as Fe2O3-xH2O. This is a neutral, water insoluble salt. The point you need to focus on is the fact that the iron atom is in a +3 ionic state (Fe+3).

Oxalyic acid is a dicarboxylic acid (structurally similar to vinegar -- yes your safety department was being ignorant) but oxyalic acid has two acidic groups per molecule. The red hydrogen atoms in this molecule are the "acidic" protons.

The two red protons can pop off in water and the resulting di-anion (oxalate) that looks like this....

... and two of these oxalate anions will bind to an iron+3 cation like this...

.....

Groupings like this are called a chelation compound. (Chelate comes from the Greek verb "to cage"). The iron atom is trapped in a negative (-1) anionic group that is now water soluble and can be rinsed away with water.

Oxalic acid is also very good at destroying tannins which is the compound that gives leaves and wood their brown color. That mechanism is a little different and I'd have to get into the organic chemistry of conjugated pi-bonds to explain it but in short, oxalic acid should be part of every boat owner's cleaning arsenal.

 

[rgranger]

BTW: Barkeeper's Friend (BKF) is oxalic acid + a mild abrasive and a little surfactant. BKF does wonders on SS appliances, bathtub drains etc but do not let BKF sit on gelcoat for very long. It WILL oxidize your gelcoat ...

 

[gettinthere]

stuff a short stub of hose into the scupper outlet. that will direct the water out away from the side of the hull...no stain. only needs to stick out about an inch. I could not find hose OD that would match scupper ID so I had to sand the hose a bit for a press fit.

 

[jviss]

stuff a short stub of hose into the scupper outlet. that will direct the water out away from the side of the hull...no stain. only needs to stick out about an inch. I could not find hose OD that would match scupper ID so I had to sand the hose a bit for a press fit.

I must say, that is fairly brilliant!

 

[Stu Jackson]

I must say, that is fairly brilliant!

The Catalina 42 skippers figured this one out 20 years ago. It works.