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Old 22-11-2006, 17:56   #16
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I just got the quote from the plating shop. On my 18x14 three bladed prop they will plate it first with copper then follow with tin for a 10 mill thickness for $125.

First, I asked not for both, but a quote on one OR the other. I think with both you would be asking for trouble since a nick in the edge gives exposure to both pure metals. It is true however that both are very close to the same on the Galvanic Table so it might not be a problem.

Second, the guys are idiots since they could not figure out why I was worried about electrolysis. Apparently being 200 miles inland removes certain knowledge from the brain.

Third, at that price I will be looking at other alternatives before pursuing the plating technique. Yesterday we splashed "Isabella" with her new 18x13 prop with one coat of silver epoxy followed by two coats of EP-ZO. EP-ZO is good for up to 30 MPH so we shall see how it goes.

I will be testing several other alternatives in the canal over the next several months.
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Old 23-11-2006, 21:34   #17
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After reading this thread, I just know this is going to be a stupid question, but I really have to ask.

What about the frying pan coating? Teflon? it sticks on pretty good, water doesn't like to stick to it and I would imagen things having a difficult time getting a foot hold on it.

Oviously there is some reason but I don't have enough know how in boats to know why.
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Old 23-11-2006, 22:34   #18
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Thats a great idea. Now,....how do you coat a metal object with Teflon? Is there a process that can be done at home or is there a place where you could take a prop to get it done?

I suspect it is a difficult process that would not be easy on a one time basis??? I hope I am wrong because I think this idea might also be good for efficiency.
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Old 24-11-2006, 04:15   #19
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Quote:
What about the frying pan coating? Teflon?
If you put a Teflon frying pan in sea water and left it there a while marine growth would occur on both sides of the pan equally. It's not that the application of Teflon would be hard but it wouldn't really work. Marine growth is far tougher than the food you cook.

The search for a marine application that would not allow growth to stick seems to be another "Holy Grail". No one has found one and any company could make many many billions of dollars if they could come up with such a product. I believe Teflon based products have been promoted in recent times.
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Old 24-11-2006, 04:29   #20
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Teflon PTFE (polytetrafluoroethylene) coatings require high curing temperatures, of between 1750 C (350F) and 370 C (700F). These application temperatures wouldn’t be wise on FRG substrates.
See DuPont’s Fact Sheet: http://www.dupont.com.br/adm/port/up...20Coatings.pdf
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Old 24-11-2006, 22:55   #21
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OMC used to market a Stainless outboard prop with a teflon coating. They called it SST. I don't know whether it was in any way effective or even if antifouling was the objective since outboard props don't have to live underwater. Perhaps somebody here has some experience of these?
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Old 25-11-2006, 01:31   #22
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Every "SST" propeller I saw had the black coating worn off at the tips.
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Old 02-12-2008, 00:46   #23
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The technical reason why barncles love growing on a bronze propeller or shaft, even when painted with strong cupper based antifouling paint, is like follows:

Stainless and marine quality bronze are cloe in nobility and does not fight each other galvanically. So, as long as the shaft and the propeller is electrically isolated from all other underwater metal parts, they need no protection zinc mounted. Shurley you have seen many old sailboats having rudder hinges with bronze bearings and stainless shaft. No zinc, no corrosion problem, yet 30+ years of use.

When a zinc anode is installed on a propeller / shaft, it starts a fairly strong galvanic process to prevent any and all metal ions to leave the propeller and the shaft.
That may seem OK, but since bothe the cupper in the bronze and the cupper in the antifouling paint is then completely prevented from getting loose. Since the cupper ions is what stops the barnacles, the protection from the antifouling is lost.

This problem has come up when the tin based antifouling (luckily for the environment) was stopped. That paint was not dependent on ion release, but other mechanisms. Now we try to rely on Cupper for protection, and that gets ruined by the zinc anodes.

If contemplating to take teh zinc away ONLY do this when:
1) The propeller is made of proven marine quality bronze
2) there i absolutely NO electrical connection (ground) between the shaft/propeller and ANY other metal object under water. (Isolated shaft coupling, engine not connected to the bonding system, if any, or two-pole main engine cutoff switch, off during harbour stay) This can be checked with a multimeter for ohms, on land, it shall exceed 10000 ohm between propeller and any ather underwater item.

Basically, the commonly practized bonding system used in USA boats cretes more problems than it solves. Lightning protection to sea should be installed by sparc-gap isolaters.


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