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post #21 of 36 Old 04-27-2013
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Re: Using Bottom Paint on Brass Propeller

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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?
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post #22 of 36 Old 04-28-2013 Thread Starter
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Re: Using Bottom Paint on Brass Propeller

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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?
Wikipedia says you are correct.
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post #23 of 36 Old 04-28-2013 Thread Starter
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Re: Using Bottom Paint on Brass Propeller

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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post #24 of 36 Old 04-28-2013
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Re: Using Bottom Paint on Brass Propeller

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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post #25 of 36 Old 04-28-2013
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Re: Using Bottom Paint on Brass Propeller




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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post #26 of 36 Old 04-29-2013
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Re: Using Bottom Paint on Brass Propeller

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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post #27 of 36 Old 04-29-2013
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Re: Using Bottom Paint on Brass Propeller

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Originally Posted by SloopJonB View Post
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?
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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post #28 of 36 Old 04-29-2013
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Re: Using Bottom Paint on Brass Propeller

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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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post #29 of 36 Old 04-30-2013
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Re: Using Bottom Paint on Brass Propeller

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Originally Posted by Maine Sail View Post
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?

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post #30 of 36 Old 04-30-2013
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Re: Using Bottom Paint on Brass Propeller

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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