Why Not To Paint Your Prop (with copper based paint)

Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
When we bought this boat the PO had been very upset with the bottom paint job they had done in Florida.

The boat was hauled and was bottom painted in a "no self service" yard on Florida's East coast. When the yard monkey painted the bottom he also painted the Aquamet prop shaft and the Manganese Bronze prop despite the PO asking them specifically not to do this.

The PO was furious when they painted it with regular copper ablative paint but they would not allow any DIY, and insisted on charging him to remove the paint, so he launched and figured he'd keep up with the zincs.

The boat also has a galvanic isolator but from the time the prop was painted until they hauled out in October they stayed in four or five marinas max between Florida & Maine. The rest of the time was on the hook cruising. The boat was in the water like this from May through October and the Zinc was changed once and still in good condition when I bought the boat. Norm claims the prop was in perfect condition before they applied the bottom paint. He is and was a meticulous PO so I can only trust his judgment and he knows what dezincification looks like.

Many, if not most, in board sailboat boat props are made of Manganese Bronze. Some are also made from NiBrAl a nickel/bronze/aluminum alloy. Manganse bronze contains upwards of 40% zinc content and zinc contents over about 15% are very susceptible to dezincification. Painting it with copper bottom paint can lead to dezincification of the alloy and eventually make the prop worthless as there is no way to fix it other then to melt it back donw and recycle it.

H&H Prop, one of the prop shops I use up here, recommended I retire it to the scrap heap when I asked if it was repairable or safe.

Please for your own good use a proper underwater prop paint or none at all and what ever you do please avoid copper based bottom paints on Manganse Bronze props. This wheel is a Michigan MP which is the same prop that comes standard on Catalina, Hunter and many other boats..

The pinkish, coppery colored areas are where the zinc content has been eaten away leaving behind only the copper in the Bronze alloy..
 
Sep 25, 2008
2,288
C30 Event Horizon Port Aransas
Another example

I'm not sure if this is from the bottom paint that was on it, or the fact that is sat for so long with no zincs.
Can ni-bral still get damaged somehow even though it has a lower zinc value? By copper bottom paint or no zincz?
 

Attachments

Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
There is nothing in this discription that would cause me to choose it for a propellor material.

http://www.anchorbronze.com/c86300.htm
What else do you choose? Nibral has aluminum and the bronze component differs based on the alloy. I have seen Max-Props, which are made from Nibral, show what looks exactly like dezincification. The folks at PYI specifically say, if you ask them, DO NOT paint a Max-Prop with copper based bottom paint...
 

Ross

.
Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Aluminum Bronze 9D, CDA 955 Nickel Aluminum Bronze , Grade D
ASTM B 505 , ASTM B 271
Chemical Composition % by weight
Element...........Nominal................Minimum...........Maximum
Aluminum...........11...........................10........................11.5
Copper................81.............................78
-Iron..................4................................3...............................5
Manganese--....3.5
Nickel................4..................................3................................5.5
Applications

Valve guides and seats in aircraft engines, corrosion resistant parts, bearings, bushings, gears, worm gears, pickling hooks and baskets, agitators.
NO ZINC!
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
I would

Aluminum Bronze 9D, CDA 955 Nickel Aluminum Bronze , Grade D
ASTM B 505 , ASTM B 271
Chemical Composition % by weight
Element...........Nominal................Minimum...........Maximum
Aluminum...........11...........................10........................11.5
Copper................81.............................78
-Iron..................4................................3...............................5
Manganese--....3.5
Nickel................4..................................3................................5.5
Applications

Valve guides and seats in aircraft engines, corrosion resistant parts, bearings, bushings, gears, worm gears, pickling hooks and baskets, agitators.
NO ZINC!

I would not be so sure that is the same alloy they use in NiBrAl props. There are a number of variations of NiBrAl out there. (see below)

I have seen what looks exactly like dezincification of known NiBrAl props before up close and in real life. How does a NiBrAl prop get all coppery colored when it does not have any zinc?

Also the alloy you quoted for Manganese bronze above is not the same one generally used on props. The Mangansese Bronze used by Michigan wheel has close to 40% zinc according to my local dealer who was looking at his spec sheet when he told me..

I do suppose that the aluminum in NiBrAl may be getting eaten and leaving behind the copper too and I suppose it could mimic dezincification. Geerally NiBrAl is not supposed to contain zinc. Either way I would head the advice by the folks at Max-Prop, who make it out of NiBrAl and not paint a prop with copper bottom paint if it is made with sacrificial metals below copper in the galvanic scale..

Here's yet another version of NiBrAl this one with no much less manganese and trace amounts of zinc..
Copper Alloy No. C63000
Nickel Aluminum Bronze
ASTM B 150 CDA 630 , ASTM B171
Chemical Composition % by weight
Element Nominal Minimum Maximum Copper 82 Rem. Rem. Iron 3 2 4 Tin - - .20 Zinc - - .30 Aluminum 10 9 11 Manganese - - 1.5 Silicon - - .25 Nickel (incl. Co) 5 4 5.5
 
Sep 25, 2008
2,288
C30 Event Horizon Port Aransas
It may not be the loss of zinc that causes the color change, but the loss of aluminum.
Nevermind someone already said that. Any way, whatever the case it can't be good whatever is happening. So, keep zincs on it and not copper bottom paint.
I was wondering why it's bad to have too much zinc on a prop shaft?
 

Ross

.
Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Stray electricity will distroy a prop without regard to the alloy and I suspect that is more often the cause than the alloy or the paint.
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
If

Stray electricity will distroy a prop without regard to the alloy and I suspect that is more often the cause than the alloy or the paint.
If that were the case then my boat would have continued this progression even after I removed the paint, which it did not.

I am going to take stab and guess that Ross has a copper based painted prop??;)
 
Sep 25, 2008
2,288
C30 Event Horizon Port Aransas
Hey Ross, thanks for pointing me toward those printable noaa charts. I checked out your sailing grounds, then I checked out mine. I will print those out and use them for back up.
I am going to a marina that has been recently updated to 'state of the art technology'
http://www.youtube.com/watch?v=AOXTwsZOSIw
I may be able to launch my boat in the next couple of weeks, and that's where I will go.
 
Jan 10, 2009
590
PDQ 32 Deale, MD
That the yard did not know to stay away from the prop

is completely indefensible. What knucklehead would put copper on copper, and what sort of businessman would defend it? Oh yeah; one that knows his customer is a transient. Too bad the PO didn't know to try stronger threats, and then follow-up as needed. I'm sure he just wanted to go, and I understand that well enough.

Many, many years ago I carelessly let some Cu paint stray onto Al rudder pintles, and in one season 1/3 of a heavy casting vanished. I cleaned the fitting energetically, and no further damage occurred. I am a chemical engineer and absolutely knew better. I'll blame it ont he hot sun.

If nothing else, I hope this thread amplifies the importance of watching what you paint. Electrolisis, in all of its guises, is a sneaky devil.
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
The same..

That the yard did not know to stay away from the prop is completely indefensible. What knucklehead would put copper on copper, and what sort of businessman would defend it?
The same $8.00 per hour yard monkey that was flipping burgers just the week before.:D Unfortunately many yards don't hire bottom painters & scrapers by their intelligence level.
 

Ross

.
Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Re: If

Maine Sail, I always figured that painting a copper alloy prop with copper based paint was redundant. So I don't paint my prop. On the other hand I dock in fresh water.
 
Feb 6, 1998
11,667
Canadian Sailcraft 36T Casco Bay, ME
Growth

Maine Sail, I always figured that painting a copper alloy prop with copper based paint was redundant. So I don't paint my prop. On the other hand I dock in fresh water.
Growth an still attaches to Bronze/copper based props I'm guessing because they are not 100% copper. A simple dive with a Scotch-Brite sponge once or twice per season wipes it right off though just like it would with active use of your boat. I hardly ever see a lobster boat come out of the water with any prop growth but boats that get used three to four times per season are a different story.

Up here in the colder waters I rarely if ever get any growth on my prop. Oh and yes I did buy a new prop and no it will not be painted..;);)
 
Oct 22, 2008
3,502
- Telstar 28 Buzzards Bay
The aluminum is likely as vulnerable to loss from the alloy as the zinc is... aluminum is actually a more reactive metal underwater than is zinc IIRC... which is why the "zincs", or sacrificial anodes, for brackish water are made from it rather than zinc.

I'm not sure if this is from the bottom paint that was on it, or the fact that is sat for so long with no zincs.
Can ni-bral still get damaged somehow even though it has a lower zinc value? By copper bottom paint or no zincz?
 
Jun 14, 2010
2,081
Robertson & Caine 2017 Leopard 40 CT
When we bought this boat the PO had been very upset with the bottom paint job they had done in Florida.

The boat was hauled and was bottom painted in a "no self service" yard on Florida's East coast. When the yard monkey painted the bottom he also painted the Aquamet prop shaft and the Manganese Bronze prop despite the PO asking them specifically not to do this.

The PO was furious when they painted it with regular copper ablative paint but they would not allow any DIY, and insisted on charging him to remove the paint, so he launched and figured he'd keep up with the zincs.

The boat also has a galvanic isolator but from the time the prop was painted until they hauled out in October they stayed in four or five marinas max between Florida & Maine. The rest of the time was on the hook cruising. The boat was in the water like this from May through October and the Zinc was changed once and still in good condition when I bought the boat. Norm claims the prop was in perfect condition before they applied the bottom paint. He is and was a meticulous PO so I can only trust his judgment and he knows what dezincification looks like.

Many, if not most, in board sailboat boat props are made of Manganese Bronze. Some are also made from NiBrAl a nickel/bronze/aluminum alloy. Manganse bronze contains upwards of 40% zinc content and zinc contents over about 15% are very susceptible to dezincification. Painting it with copper bottom paint can lead to dezincification of the alloy and eventually make the prop worthless as there is no way to fix it other then to melt it back donw and recycle it.

H&H Prop, one of the prop shops I use up here, recommended I retire it to the scrap heap when I asked if it was repairable or safe.

Please for your own good use a proper underwater prop paint or none at all and what ever you do please avoid copper based bottom paints on Manganse Bronze props. This wheel is a Michigan MP which is the same prop that comes standard on Catalina, Hunter and many other boats..

The pinkish, coppery colored areas are where the zinc content has been eaten away leaving behind only the copper in the Bronze alloy..
I agree that this can be caused by bottom paint, but I don’t agree with trashing that prop in the condition shown. It can be used many more years and with no noticeable performance loss if the condition doesn’t progress. I know — I have done it. ;)