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Using Bottom Paint on Brass Propeller

12K views 35 replies 21 participants last post by  73Morgan 
#1 · (Edited)
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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#9 ·
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.
 
#10 ·
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
 
#12 ·
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.
 
#13 ·
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
 
#17 · (Edited)
Sheesh MaineSail, thanks for adding one more thing to my spring to-do list. :rolleyes:

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
 
#19 ·
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.
 
#21 ·
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.
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? :confused:
 
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#23 ·
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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#28 ·
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.
 
#31 ·
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?
 
#33 ·
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
 
#36 · (Edited)
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
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.
 
#35 · (Edited)
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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