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  #11  
Old 04-23-2013
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Re: Using Bottom Paint on Brass Propeller

Quote:
Originally Posted by Faster View Post
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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  #12  
Old 04-23-2013
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Re: Using Bottom Paint on Brass Propeller

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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Old 04-23-2013
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Re: Using Bottom Paint on Brass Propeller

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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Old 04-23-2013
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Re: Using Bottom Paint on Brass Propeller

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Originally Posted by 73Morgan View Post
Why is it too late?
A brass prop would have disintegrated by now. Bronze, not so much.
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Old 04-23-2013
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Re: Using Bottom Paint on Brass Propeller

I second Pettit Zinc Barnacle Barrier Coat Spray.

Pettit Zinc Coat Barnacle Barrier
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Old 04-24-2013
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Re: Using Bottom Paint on Brass Propeller

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I second Pettit Zinc Barnacle Barrier Coat Spray.

Pettit Zinc Coat Barnacle Barrier

Me, too!

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Old 04-24-2013
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Re: Using Bottom Paint on Brass Propeller

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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Old 04-24-2013
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Re: Using Bottom Paint on Brass Propeller

Quote:
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..

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??

Last edited by 73Morgan; 04-24-2013 at 11:08 AM.
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Old 04-24-2013
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Re: Using Bottom Paint on Brass Propeller

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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Old 04-26-2013
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Re: Using Bottom Paint on Brass Propeller

Quote:
Originally Posted by JimMcGee View Post

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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