# Using Bottom Paint on Brass Propeller



## 73Morgan (Dec 2, 2012)

Just polished up my brass propeller after 15 years of using ablative bottom paint on it. It polished up real nice, no corrosion damage. I was told I should use some fancy stuff ranging in price. It seemed like a lot of money, I had to understand what it was going to do for me. Found an old post on here which had some good alternatives (link below). Not giving up yet, I looked up galvanic reaction of various metals (second link below). A difference of hundreds of mill volts is likely to result in galvanic corrosion, but only a few tens of mill volts is unlikely to be a problem. Note that the numbers at the top are in Volts. The chart shows copper and brass in the same range. Plumbers have been mixing brass and copper for over 100 years with no problems. The paint I've been using is the cheapest I can find, it has Copper and Cuprous Oxide (principal oxides of copper), which I believe to be very common ingredients for bottom paint. I am not a scientist but it seems that this is just a bunch of nonsense with the brass props.

Interested in knowing what you guys think, or maybe shed some more light on the subject.

http://www.sailnet.com/forums/gear-maintenance/53302-brass-prop-anti-fouling-coatings.html

Galvanic Corrosion Chart*


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## Faster (Sep 13, 2005)

The prop will be bronze, not brass....


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## SimonV (Jul 6, 2006)

If its brass its too late.


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## sww914 (Oct 25, 2008)

Slightly off topic, but my friends were stuck in one spot at anchor for 3 months with a dead engine. She put pieces of nylon stockings on the blades to protect them. After all that time, the nylon slid right off covered in barnacles and slime and cleaning the prop was a 30 second job.


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## 73Morgan (Dec 2, 2012)

Faster said:


> The prop will be bronze, not brass....


Color is brassy, I thought bronze has a bronze hue. Are all props bronze?


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## 73Morgan (Dec 2, 2012)

SimonV said:


> If its brass its too late.


Why is it to late?


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## Faster (Sep 13, 2005)

73Morgan said:


> Color is brassy, I thought bronze has a bronze hue. Are all props bronze?


Not all props are bronze, but I'm pretty sure there are no brass props.

SS, Aluminum, Plastic etc... but not brass.


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## DrB (Mar 29, 2007)

sww914 said:


> Slightly off topic, but my friends were stuck in one spot at anchor for 3 months with a dead engine. She put pieces of nylon stockings on the blades to protect them. After all that time, the nylon slid right off covered in barnacles and slime and cleaning the prop was a 30 second job.


Clever idea.


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## 73Morgan (Dec 2, 2012)

Faster, Thanks

I appreciate the correction it's a bronze prop. If I am reading the chart correctly copper is on the Anodic side of the two bronzes shown. Copper would then be the sacrificial metal to the bronze. So, it still makes sense to me that there is no problem with using bottom paint with copper in it on bronze props.


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## tommays (Sep 9, 2008)

WELL

There is bottom paint that is made for underwater metal 


Not everything happens to things 100% of the time they are just general recommendations of what is considered good and bad practice 

I can snap a picture next time I am inside a SS vessel from the 1970s were the SS blade locking pins got in a fight with the blade they were locking and as a result the pins SS pins LOST 

I can go in its twin same age same place nothing happened


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## Maine Sail (Jan 6, 2003)

Faster said:


> The prop will be bronze, not brass....


While some props are NiBrAl (nibral) most are manganese bronze. The bronze part of manganese bronze is a little misleading because most props contain upwards of 35-40% zinc.. Applying copper bottom paint can destroy them..

This prop was fine for 25 years unpainted. It was painted with a copper bottom paint and in less than one year was dezincified and destroyed.









This manganese bronze prop had also been painted:









This one took the owner over an hour to get all the paint off and only to find out it was totally un-safe for continued use:









Here's another totaled prop due to copper bottom paint:









This one was so dezincified the color was almost uniform. The owner stripped the paint off and a few months later threw a blade:


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## lancelot9898 (Dec 30, 2008)

What Maine says is right. For that reason I make sure that I prep the prop with underwater metal primer prior to any coating of Cu bottom paint. I've used such a system for over 20 years on my expensive max prop and it stays effective for the 2 or sometimes 3 years between haul outs here on the Chesapeake.


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## CalebD (Jan 11, 2008)

I've been using the Petit Zinc Barnacle Barrier spray paint on my bronze 2 blade prop (a $20 can will last you a number of years). It is not the best protection like MaxProp but works ok; still need to clean barnacles off prop mid-season.
At least with a zinc spray coating the zinc in the bronze seems to be protected from electrolysis.
de-zincafication is a real word and is what MaineSail's photos show.
YMMV


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## CalebD (Jan 11, 2008)

73Morgan said:


> Why is it too late?


A brass prop would have disintegrated by now. Bronze, not so much.


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## dvuyxx (Jun 23, 2009)

I second Pettit Zinc Barnacle Barrier Coat Spray.

Pettit Zinc Coat Barnacle Barrier


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## downeast450 (Jan 16, 2008)

dvuyxx said:


> I second Pettit Zinc Barnacle Barrier Coat Spray.
> 
> Pettit Zinc Coat Barnacle Barrier


Me, too!

Down


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## JimMcGee (Jun 23, 2005)

Sheesh MaineSail, thanks for adding one more thing to my spring to-do list. 

I've got the prop off right now to do the cutlass bearing. It was painted with Micron after the application of a primer coat, though I'm not sure what primer the yard used.

I'll take the paint off using a brass wire wheel as the old paint is knicked up and check the condition of the prop. 

Is it OK to re-coat with a primer-paint combo as Lancelot is doing or better to just use the Petit barrier coat?

Thanks,
Jim


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## 73Morgan (Dec 2, 2012)

Maine Sail said:


> While some props are NiBrAl (nibral) most are manganese bronze. The bronze part of manganese bronze is a little misleading because most props contain upwards of 35-40% zinc.. Applying copper bottom paint can destroy them..
> 
> This prop was fine for 25 years unpainted. It was painted with a copper bottom paint and in less than one year was dezincified and destroyed.


Main Sail, thanks, great post.
Bronze has zinc in it, wow, that explains the electrolysis concerns.
Scary bunch of pictures, internal damage. I will change my ways, hope it is not to late.
You just indirectly explained why it is a good idea to have a zinc on the prop shaft. Been changing the zinc on the prop shaft every year. That probably helped a little??


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## casey1999 (Oct 18, 2010)

Why are props not made from silicon bronze?

Price looks to be about the same and then there would not be the concern of getting dezincified and destroyed.

Silicon Bronze C65500 is comprised of 95% Copper, with 4% Silicon and 1% Manganese to combine high strength and good hot and cold formability with excellent welding characteristics. Additionally, 65500 exhibits good resistance to corrosion by brine and sulfite solutions, non-oxidizing inorganic acids, alkalis, and other mixtures. The mechanical and chemical properties of Silicon Bronze 65500 are similar to those of stainless steels. 

Silicon Bronzes are commonly used in the pump & valve component, fastener, piston ring, and marine hardware industries.


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## dvuyxx (Jun 23, 2009)

JimMcGee said:


> Is it OK to re-coat with a primer-paint combo as Lancelot is doing or better to just use the Petit barrier coat?


I believe the Pettit instructions are to apply it to clean bare metal (rub down with MEK before).


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## SloopJonB (Jun 6, 2011)

casey1999 said:


> Why are props not made from silicon bronze?
> 
> Price looks to be about the same and then there would not be the concern of getting dezincified and destroyed.
> 
> ...


Where's the tin? I thought the combination of copper and tin (along with minor other additives) was the basic definition of bronze.

Copper & zinc = brass

Copper & tin = bronze

Not so?


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## 73Morgan (Dec 2, 2012)

SloopJonB said:


> Where's the tin? I thought the combination of copper and tin (along with minor other additives) was the basic definition of bronze.
> 
> Copper & zinc = brass
> 
> ...


Wikipedia says you are correct.


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## 73Morgan (Dec 2, 2012)

I was talking to an old timer at my local Marine Supply house, he said a lot of people use bottom paint on their bronze props, and he added that he hasn't seen very many and certainly not enough ruined props to warrant concerns about using bottom paint on the prop. He believes that improper grounding or some other factor would be the cause of deterioration of the prop.
I am bay no means endorsing anything. My experience after 15 years of being a low budget sailor, and just slapping some bottom paint on the prop supports what he said. My prop polished up real nice. Also, important to mention that my prop shaft zinc is half gone each year. This year since I am just about finished with the install of a new motor, I did spring for a can of Petit. Wanted the prop to be in top condition in order to see how the pitch on the prop does with the increase of HP. Also, It will be interesting to see how the zinc does this year.


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## Fstbttms (Feb 25, 2003)

I have seen my fair share of painted props and can't recall ever coming across one that had any dezincification issue that could be attributed to the paint. Of course, maybe that's because the paint doesn't usually stay on long enough to cause a problem.


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## tempest (Feb 12, 2007)

My prop has come out of the water free of barnacles after using petit zinc coat. The little circles are paint erosion not pitting of the prop. This is november after 7 months in the water. One can has lasted me at least 3 seasons.


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## FirstCandC (Mar 26, 2013)

While we are on this similar subject- I just pressure washed a layer of bottom paint off my prop. Prop looks ok. There was also bottom paint on the stainless shaft. Do you paint this with bottom paint, use a special paint, or leave it bare??
Thanks.


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## Maine Sail (Jan 6, 2003)

SloopJonB said:


> Where's the tin? I thought the combination of copper and tin (along with minor other additives) was the basic definition of bronze.
> 
> Copper & zinc = brass
> 
> ...


Michigan Wheel, the largest prop maker in the US, uses C86500 Manganese Bronze for its manganese bronze props.. It has only trace amounts of tin but about 36-42% zinc... As I eluded to in post 11 be sure you have a NiBrAl prop if you want to paint it with a copper paint. Most props on sailboats are manganese bronze. If you've got a nibral one you are lucky..

In a perfect world the shaft zinc would protect the prop but when you directly apply the paint to the prop we tend to often lose our perfect world... This is not even account for the many poorly installed zincs out there doing nothing because they are making very poor contact due to the surface of the zinc and shaft or prop not being properly prepped.


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## tempest (Feb 12, 2007)

FirstCandC said:


> While we are on this similar subject- I just pressure washed a layer of bottom paint off my prop. Prop looks ok. There was also bottom paint on the stainless shaft. Do you paint this with bottom paint, use a special paint, or leave it bare??
> Thanks.


I don't paint the stainless. I just clean it, touch it with an emery cloth and attach my zincs. I've resorted to starting the season with 2 zincs on the shaft and the one on the propeller. For some reason Sabres seem to eat zincs for breakfast. At first I thought it could be stray current in the water, or something in my wiring. But it seems to be a common complaint on my boat..even from owners who keep their boats on a mooring away from stray current.


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## MedSailor (Mar 30, 2008)

Maine Sail said:


> While some props are NiBrAl (nibral) most are manganese bronze. The bronze part of manganese bronze is a little misleading because most props contain upwards of 35-40% zinc.. Applying copper bottom paint can destroy them..


Ummm...... My boat yard just slathered bottom paint all over my bronze rudder hinges and my bronze prop shaft stern tube.

Is that a problem?

MedSailor


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## T37Chef (Oct 9, 2006)

Not just your prop, but the strut as well! 

I use Pettit Zinc Coat on the SS Prop & Strut, even thought to use it on thru hulls?


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## CalypsoP35 (Jul 24, 2006)

I've been using Trilux prop and drive spray, with limited success. By the end of the season it is pretty much all worn off. But now that I look at the label, it says for "aluminum" props. "Copper as metalic 4.48%."

Am I being an idiot by continuing to use this product on my bronze prop?


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## Fstbttms (Feb 25, 2003)

CalypsoP35 said:


> Am I being an idiot by continuing to use this product on my bronze prop?


Do so at your own risk.


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## dave6330 (Aug 16, 2006)

OK - Galvonic corrosion...so I'm a little slow on the uptake....let me get this stright...

1. No paint on the exposed SS prop shaft (just clean it and install a new zinc). 

2. Special zinc based paint for the bronze prop? Is this really better than simply cleaning the bronze prop and leaving it bare? 

3. And bronze thruhulls - do they need special paint too??? I'm a little cornfused. 

Currently "Between Boats" but wanting to stay current (no pun intended).

Dave


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## FirstCandC (Mar 26, 2013)

Bumping to find out the answers to what Dave asked.


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## T37Chef (Oct 9, 2006)

Zinc Coat Barnacle Barrier

"Zinc Coat Barnacle Barrier 1792 provides easy to use aerosol spray protection for bare metals including steel, stainless steel, cast iron, copper, bronze, galvanized steel, and lead. It forms an excellent bond to underwater metals and running gear, and inhibits corrosion on these surfaces. Zinc Coat Barnacle Barrier's smooth, hard surface will self-clean in service, and can be used above or below the waterline. The dried film of Zinc Coat contains 93% pure zinc."

I have been using the above on my prop (SS), shaft (SS), and strut (bronze) for several years now with very good results except one season when the water temp were well above the average plus we didnt use the boat much during the month of August. The above is self cleaning when the boat is in service, I doubt anything will work well if you dont use the boat often, often meaning at least once a week.

I have used vaseline on my spped paddle wheel with great result, using a Q tip to apply. Some have mentioned using a sharpie also works well? Dunno


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## 73Morgan (Dec 2, 2012)

dave6330 said:


> OK - Galvonic corrosion...so I'm a little slow on the uptake....let me get this stright...
> 
> 1. No paint on the exposed SS prop shaft (just clean it and install a new zinc).
> 
> ...


Item 1&2, that is the consensus.
Item 3, bronze through halls, you need to strip all paint off the through hall and the area 6 to 12 inches around it, paint that with epoxy paint. The epoxy isolates the area around from electrolysis between the bronze and bottom paint. Then bottom paint over the epoxy.
This has worked well for me, hope to see how other people handle that.


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