Stock Prop Questions

[Mike Denest]

I removed my prop (15 x 10 three blader) to clean and apply a fresh coating.  I used a scotch brite pad to remove the old paint and see that someone in the dim and distant past used a very coarse grade os sandpaper that cut into the coating.  In the process of cleaning, I see that the prop is bronze with a copper coating?  I want to get it all down to clean metal to apply a fresh coat of protection. 

I found a product from Petit, a zinc coat barnacle barrier 1792, which is a modified epoxy.  It is available in a spray can which contains 93% zinc.  Petit suggests that at least three light coats be applied to protect any underwater metal except aluminum.  http://www.petitprod.com/catalog_browse.asp?ictNbr=120

[Stu Jackson]

Mike, you may be interested in this thread at co.com:  http://forums.catalina.sailboatowners.com/showthread.php?t=106058

[Mike Denest]

Thanks Stu.  I bought a can of the transducer paint - seems that WM will only order the other stuff special.  I sprayed on two coats and will apply the third when the prop is mounted.  I loved the picture of the hauled boat, It looks like a small version of the Flying Dutchman from Prirates of the Caribbean.

[Michael Shaner]

I know this stuff reads to be used an aluminum. CAN it be used on our props?

https://secure.international-coatings.com/pds/yacht/GB_ISO_I_5000394.htm

[Mike Denest]

No, that stuff is for aluminum.  As me how I know.

[Mike Denest]

I like this one:
(It ain't mine!  )

[Michael Shaner]

YIKES!!  Tell me that ain't your boat...

Thanks Mike...

[Bill Asbury]

Mike, Thought I'd give the Petit transducer paint a try and put three coats on my bronze Max-Prop and shaft before launch earlier this week, so will see how that holds up this season.  That Interlux prop and drive paint is strictly for power boats, of which I also have one.
Cheers,
Bill

[Ron Hill]

Mike : I think I'll try to use that Petit Zn paint this year and see how it works.  The problem is to get the anti fouling paint to STICK - that's the key.  Transducer paint will never hold up on the running gear.

The stock C34 3 bladed prop is a 15X9 so your's has been pitched up by 1" - which is good.

The prop is a (slippery) silicone bronze prop.  I've heard that if you see copper it's because of electrolysis and the other properties are leaching out and leaving the copper.  You might want to check on your grounding and that of your slip mates!!  I have a flexable coupling so my prop and shaft are electrically isolated.

If you see scratches on the prop blades from sanding do not dispare.  Most people use 60 or 80 grit sand paper to rough up the metal so some anti-fouling paint/primer will stick!! 

[Steve Hansen]

Mike

I had both the Pettit Zinc Coat barnicle and the Pettit Transducer paint sitting side by side on my shelf. I intended to use the Zinc Coat on the prop but accidently grabbed the Transducer paint and painted it on the prop. Discovered the mistake after splash. Found it worked very well, maybe 1-2 barnicles at end of season haulout, paint adhered well, did make it a point not to let boat sit too long without spinning the prop with the idea being the mechanical action of the prop spinning off any new growth. Comparing the two, not sure if there is any difference between the two products but I will use the Zinc Coat next time with hopes of similar results. Also used the Trilux Prop with the primecon primer the year before, poor results, could have not used anything and gotten same results. BTW 15x9 standard prop.

Steve

[mainesail]

  In the process of cleaning, I see that the prop is bronze with a copper coating?  I want to get it all down to clean metal to apply a fresh coat of protection. 

I found a product from Petit, a zinc coat barnacle barrier 1792, which is a modified epoxy.  It is available in a spray can which contains 93% zinc.  Petit suggests that at least three light coats be applied to protect any underwater metal except aluminum.  http://www.petitprod.com/catalog_browse.asp?ictNbr=120

I would be very careful with that prop and would seriously consider removing it and taking it to a prop shop for closer examination. Bronze props, including the Michigan wheels supplied by Catalina, are Manganese Bronze which is really more like brass than Bronze. It contains upwards of 39% zinc. What you describe, the copper coating, is classic dezincification of the zinc content in the Manganese Bronze.

When we bought our current 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 39% 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 down 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..