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post #21 of Old 03-02-2009
Maine Sail
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Originally Posted by Idiens View Post
When I first had my boat, I was told it was no use painting antifouling onto the shaft and propeller as is would simply be spun off. I heard tales of lanolin and all sorts of solutions. After the first season with my new expensive MaxProp coming out covered in barnacles, I had it cleaned and burnished and tried lanolin. The next year, I just cleaned off the barnacles and antifouled it. Antifouling paint may not stick on a new burnished propeller blade but it sure sticks on the residue left by barnacles. Since then the antifouling sticks and the barnacles don't.

I read somewhere that scientists are trying to isolate and manufacture barnacle glue, apparently its the strongest known adhesive. It sets underwater too.

Please, please, please do not use a copper base anti-fouling on a prop. While the Max-Prop is made of Nibral, PYI does not recommend the use of a copper based anti-fouling paint as it can cause galvanic issues!! NiBrAl is Nickel, Bronze, Aluminum.

Many props are made of Manganese Bronze, though some like the Max-Prop are NiBrAl. Manganse Bronze has a considerable amount of zinc in it depending upon the composition used to make the prop. Most marine grade Manganse Bronze is comprised of roughly 58% Copper, 39% zinc, 1% iron, 1% tin. Though different alloy compositions of Manganese Bronze can see zinc content as low as 25% and as high as 39%. The copper in bottom paint can lead to de-zincification of a Manganese Bronze prop which is not good for it.

Thru-hulls & seacocks are generally, and I use generally carefully as who knows what's coming out of China these days, made from a very low zinc content bronze. This Bronze for valves and thru-hulls is usually referred to as Silicon Bronze and is comprised of roughly 96% copper 3% silicon 1% Manganese. Again, who knows what is what these days so a call to a manufacturer is sometimes a good idea. Silicon Bronze has virtually no zinc so should not suffer from de-zincification like Manganses Bronze or Tobin Bronze. Painting thru-hulls should pose minimal threat if they are in-fact made from silicon bronze..

Prop shafts made of bronze were mostly made from Tobin Bronze which also has a higher zinc content and also does not like copper anti-fouling paints. If you paint a Bronze prop shaft or prop you should really keep up with your zincs so the zinc in the shaft or prop does not become the sacrificial material. better yet it may be wise to use a paint that is safe for underwater metals..

Bronzes are not all the same and there are many different grades of bronze that really should almost be called a brass due to the zinc content but because of the added tin or other alloys they are referred to as bronze instead of brass. I've personally never understood why most props have such a high zinc content and are made from Manganse Bronze and not something with more corrosion resistance...?

I paint my thru-hulls but not my prop, shaft or strut..

-Maine Sail / CS-36T

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Last edited by Maine Sail; 03-02-2009 at 02:50 PM.
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