# Cleaning/polishing Prop



## jimgo (Sep 12, 2011)

When I visited my boat yesterday, the prop still basically looked like this:









Someone had suggested that cleaning the prop might help with performance. I'll admit that it is isn't mirror-smooth, but it's not like I have 3" wide/long barnicles growing on it or anything. Is it really worth trying to clean the prop more than it already is? If so, what's an appropriate approach?


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## svHyLyte (Nov 13, 2008)

jimgo said:


> When I visited my boat yesterday, the prop still basically looked like this:
> 
> 
> 
> ...


Jim--

Any growth on the prop effects performance and only a few barnacles can quickly grow into a colony. Use a scraper to remove the barnacles and then a cloth soaked in "Lyme Away" to get rid of the craters left behind. Than take some fine bronze wool and polish the blade somewhat. You might also try using a product known as "Prop Glop" to slow down the development of growth in the future (although it will need periodic reapplications).

FWIW


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## copacabana (Oct 1, 2007)

Scraper and a plastic scouring pad works for me. I do mine underwater though.


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## outbound (Dec 3, 2012)

Have found once you get the gunk off using a polishing wheel with rouge to get a high polished finish is a help in keeping growth off.


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## copacabana (Oct 1, 2007)

BTW, you might want to put a zinc on that shaft while it's out of the water.


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## Faster (Sep 13, 2005)

copacabana said:


> BTW, you might want to put a zinc on that shaft while it's out of the water.


Wouldn't expect to see a zinc right there, Mark.. probably/hopefully something on the other side of the strut (assuming it is a strut)..


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## krisscross (Feb 22, 2013)

Is there a difference in the rate of growth depending on the prop material? Like aluminum vs. bronze?


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## capta (Jun 27, 2011)

You might want to remove that prop and get it into a prop shop. It needs to be balanced and they need to check the blades. There appears to be some old corrosion as well. They'll return it nicely polished. If you want to just clean it in place, muriatic acid is the right tool for that job. It's extremely DANGEROUS to work with, blah, blah, blah.... You'll probably want to polish the shaft with emery cloth before you replace the zinc, too. 
As for degrees of fouling, even a few barnacles can mess with the balance of a prop and that can seriously shorten the life of your cutlass bearing.
During our haul out last month in Trinidad, Alan sprayed a grey paint on the running gear and it's supposed to inhibit growth; if it even helps a little, I'll be surprised. I've even tried chroming props to reduce fouling and had absolutely no joy. I figured nothing could grow on slippery, high quality chrome; wrong.


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## jimgo (Sep 12, 2011)

Faster said:


> Wouldn't expect to see a zinc right there, Mark.. probably/hopefully something on the other side of the strut (assuming it is a strut)..


Correct. There's one on the other side of the strut. You can see it in this picture:


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## jimgo (Sep 12, 2011)

Any idea what a prop shop would charge to clean and balance it? Any suggestions for one in/near NJ or Philly? I have toyed with getting a 3-bladed prop (the Campbell Sailor), so just trying to see if it's worth putting the money into this one or if I would be better off just getting a new one.


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## GeorgeB (Dec 30, 2004)

Jimgo, do you haul every year? Do you clean your boat's bottom and prop/strut during the year? You have a lot of growth there (strut) and the growth on the prop does impact performance. Other than growth, your blade tips look in pretty good condition. The prop nut however... You wouldn't want to see my prop & strut as I use a polishing wheel and compound for my last step. Before you think about a three blade, you will need to do some basic engineering work like calaculating pitch and diameter to match the HP of your engine and that extra blade is like dragging a bucket when you are sailing.


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## jimgo (Sep 12, 2011)

George,
The boat is "new" to us. We bought her in March, and were focused on other aspects of the power system for a few months (my blog has details, if you're interested). Now that things have calmed down and we're out for the season, I'm starting to put together the list of projects that I can take home with me and work on over the winter. I have some experience polishing metals, but I just wasn't sure how much ROI I'd get for the work of polishing the prop. I'm told that our marina doesn't get a lot of barnacles (unlike the Chesapeake, where the boat spent the past several years).

Regarding the CS prop, they've actually taken care of the calculations for me. Several other Allmand owners have bought, and love, the props, so "all" I had to do was call them and they pulled the info. As I understand it, the CS props tend to give Allmands less prop walk and, since they push more water, they give better steering control at lower RPM's than their 2-bladed cousins.


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## Jaramaz (Aug 9, 2013)

Polishing the prop improves its performance. Well worth the time. 

If you are sure it is a bronze prop, then there is no need for a zinc anode. Without a zinc, barnacles will not grow on the prop. 

Many props are in bronze, but not all. Some are made in brass. Brass do need a zinc, outherwise the brass will de-zincify (?). 

When you are considering swapping to a 3-balde, would that be a fixed one, or a folding? It is certanly true with the advantages of a 3-blade, but but ... if it is a fixed one, it will cause much more drag. 
Folding 3-blad is good, but expensive. 
Sometimes said 3-blade is mainly for > 30 hp. Rule of thumb, doesn't mean it cannot be used at lower power. 

Note also, which may surprice, a 3-blade is not as power efficient as a 2-blade. 

Summary: Try polishing. As good as possible.

/J


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## JonEisberg (Dec 3, 2010)

Jaramaz said:


> If you are sure it is a bronze prop, then there is no need for a zinc anode. Without a zinc, barnacles will not grow on the prop.


Well, maybe not in Sweden, but they certainly will on this side of the pond


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## CalebD (Jan 11, 2008)

The prop shop I used a few years ago in NY checked the balance on my 2 blade prop for free (they were doing other paid work for me). Should not cost a lot for them to check it or "spin it" as they call it.

Good luck getting your prop off the shaft while it is that dirty. Hope you can find a prop puller rig and a whole bunch of patience.


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## jimgo (Sep 12, 2011)

Thanks Caleb! LOL


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## CalebD (Jan 11, 2008)

Start spraying PB Blaster or Kroil on your shaft/prop NOW - once you clean it up!


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## capta (Jun 27, 2011)

CalebD said:


> The prop shop I used a few years ago in NY checked the balance on my 2 blade prop for free (they were doing other paid work for me). Should not cost a lot for them to check it or "spin it" as they call it.
> 
> Good luck getting your prop off the shaft while it is that dirty. Hope you can find a prop puller rig and a whole bunch of patience.


Most props will pop right off with a puller under pressure and a bit of heat. The bronze expands much more quickly than the S/S. No banging or sprays.


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## Minnewaska (Feb 21, 2010)

As many have said, a polished prop will take on new growth much slower. I've never had it professionally polished alone, but have had them come back polished after a repair. Can't be too expensive, but I'm sure you could do it yourself. Take it off and bring it home. Easy.

Had a buddy spray his with Petit Zinc Coat Barnacle Barrier paint last spring. I just saw his prop on the hard last week. Almost no growth and the paint was only partially worn. I was surprised. 

Needless to say, if you do this, it must start totally clean.


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## capecodda (Oct 6, 2009)

The expensive solution to the growth problem is Propspeed. At our dock, past couple of hot summers, I've seen 80 degree water. Without the coating the prop was completely barnacle covered (took me 30 mins with a scraper and scuba). With Propspeed we make it through a season. YMMV, we are in a small, warm, Cape Cod bay.


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## Fstbttms (Feb 25, 2003)

Jaramaz said:


> If you are sure it is a bronze prop, then there is no need for a zinc anode.


Wow. Possibly the worst advice I've ever seen given here.


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## Jaramaz (Aug 9, 2013)

Fstbttms said:


> Wow. Possibly the worst advice I've ever seen given here.


Well, tell us more Fstbttms. Why is this the worst adivce?

Tell us, what would the purpose be with a Zinc with a bronze prop.

Eagerly waiting ...

/J


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## Jaramaz (Aug 9, 2013)

JonEisberg said:


> Well, maybe not in Sweden, but they certainly will on this side of the pond


Jon, what are you using in your anti-fouling? What is the most popular ingredient to stop barnacles?

On your side of the pond, of course.

Agree that barnacles further south is more agressive, and that the sea around Sweden is not so salt. Still, my guess is we are use the same active substances against barnacles.

/J


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## Fstbttms (Feb 25, 2003)

Jaramaz said:


> Tell us, what would the purpose be with a Zinc with a bronze prop.


Umm... ever hear of galvanic and electrolytic corrosion?


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## Fstbttms (Feb 25, 2003)

Seriously, what do you think zinc anodes are for? Keeping barnacles off the running gear? :laugher


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## Jaramaz (Aug 9, 2013)

Fstbttms said:


> Seriously, what do you think zinc anodes are for? Keeping barnacles off the running gear? :laugher


Well, Fstbttms, I am still waiting for some facts, instead of questions from you.

Tell us, what is the use of a zinc anode connected to a bronze prop?

It is clear that you have some problems with the basic physics behind this. So, a hint: Does bronze corrode? If so, in what way and in what environment?

The first picture you had in your answer was clearly not showing some pieces of bronze (now, Fstbttms, what metal could that be?).

Still waiting. This time for answers instead of more questions.

/J


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## Fstbttms (Feb 25, 2003)

Jaramaz said:


> Does bronze corrode?






























Suggest you educate yourself:

*Any time you have two different metals that are physically or electrically connected and immersed in seawater, they become a battery. Some amount of current flows between the two metals. The electrons that make up that current are supplied by one of the metals giving up bits of itself--in the form of metal ions--to the seawater. This is called galvanic corrosion and, left unchecked, it quickly destroys underwater metals.

It would be hard to overstate the importance of maintaining the anodes on your boat. When an anode is missing or largely wasted away, the metal component it was installed to protect begins to dissolve--guaranteed.*

BoatUS - BoatTech - Sacrificial Zincs by Don Casey


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## Faster (Sep 13, 2005)

Jaramaz.. you are misinformed. You should stop now....


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## Jaramaz (Aug 9, 2013)

Fstbttms said:


> Suggest you educate yourself:
> 
> *Any time you have two different metals that are physically or electrically connected and immersed in seawater, they become a battery. Some amount of current flows between the two metals. The electrons that make up that current are supplied by one of the metals giving up bits of itself--in the form of metal ions--to the seawater. This is called galvanic corrosion and, left unchecked, it quickly destroys underwater metals.
> 
> ...


Now Fstbttms, again you do not answer any questions. You put up some pics which are difficult to evaluate, as very few facts are know.

Firstly, the metal in the pic above is most likely Brass, not bronze. This can be seen from the redish color in the middle - typical for brass when zinc has gone. And brass props should most certainly have a zinc anode.

The text you are quoting is general. Doesn't mention bronze.

So instead, lets have a look on bronze. Wikipeadia will do:



> There are many different bronze alloys but modern bronze is typically 88% copper and 12% tin.[10] Alpha bronze consists of the alpha solid solution of tin in copper. Alpha bronze alloys of 4-5% tin are used to make coins, springs, turbines and blades.


and then



> Typically bronze only oxidizes superficially; once a copper oxide (eventually becoming copper carbonate) layer is formed, the underlying metal is protected from further corrosion.





> Bronze was especially suitable for use in boat and ship fittings prior to the wide employment of stainless steel owing to its combination of toughness and resistance to salt water corrosion. Bronze is still commonly used in ship propellers and submerged bearings.


Now, read this slowly. Read it again. Yes, it does say: resistance to salt water corrosion.

Fstbttms, you are confusing Bronze with Brass. They do look the same, but have quite different qualities. Both are yellow, "golden" and both are alloys based on Cu. Historically, the definition of bronze was "without zinc". 
Today, there are so many variants of bronze and brass, that many has started to call all these just "yellow metal".
Many metal parts one buys today are claimed to be bronze, but is truly brass. Real through-hulls should be in bronze, but are difficult to find (is it Mainsail who has nice pics of such on his blogg?) and much more expensive than brass. The same for valves.

Have I educated you as well now?

/J

Before stainless became affordable, many metal things on sailing boats were made in bronze


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## Fstbttms (Feb 25, 2003)

Jaramaz said:


> Firstly, the metal in the pic above is most likely Brass, not bronze. This can be seen from the redish color in the middle - typical for brass when zinc has gone. And brass props should most certainly have a zinc anode.


Props are not made of brass, they are made of bronze. And I assure you that the props in each of the pix I have posted are bronze. The one you've referred to has had much of the zinc component of the bronze leached out (due to the fact that it had not been protected by a zinc anode for a long time), making it in fact now very much closer to brass than the bronze it was originally made of. As evidenced by every single one of the pix I have provided (as well as the link to the Don Casey article), your assertion that bronze will not corrode and therefore does not need the protection of zinc anodes is simply ludicrous.

As suggested previously, you are digging yourself a deeper hole with each post you make.


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## svHyLyte (Nov 13, 2008)

Guys, you are debating what is actually a difference in vernacular based upon your locales. What is the US is often referred to as Marine Bronze is usually Manganese Bronze, copper alloyed with anywhere from 25% to 40% zinc content plus tin and lead, which makes excellent propellors. In Europe, however, Manganese Bronze is (actually properly) known as "Brass". There, "Bronze" is either Aluminum-Copper plus aluminum, nickel and iron; Silicon--copper plus silicon and manganese; or, Phosphor, copper alloyed with tin and phosphorus. A zinc is not needed on Aluminum, Silicon, or Phosphor bronze because it would serve no purpose. A zinc is needed with a Manganese Bronze prop to prevent corrosion due to de-zincafication which simply leaves a nice pink weak copper base metal.

So. You're all right...or wrong (depending upon your locale of course!)

FWIW...


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## Fstbttms (Feb 25, 2003)

I defer to your superior knowledge but it is the case that I have never seen a European boat that did not need zinc anodes on the shaft and/or prop.


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## svHyLyte (Nov 13, 2008)

Fstbttms said:


> I defer to your superior knowledge but it is the case that I have never seen a European boat that did not need zinc anodes on the shaft and/or prop.


Because most (but not all) prop's in Europe, as in the US, are made of Manganese Bronze which certainly do need zincs. But Aluminum and Silicon Bronzes are also used, albeit are more costly, in which case a zinc serves no useful purpose.

FWIW...


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## mitiempo (Sep 19, 2008)

Jaramaz said:


> Polishing the prop improves its performance. Well worth the time.
> 
> If you are sure it is a bronze prop, then there is no need for a zinc anode. Without a zinc, barnacles will not grow on the prop.
> 
> ...


This is wrong on several counts.

1. Bronze props do need a zinc. Manganese bronze has up to 39% zinc. No zinc, soon a severely dezincified prop.

2. 3 blade props are more efficient than 2 blade props. The Campbell Sailor the op is referring to has less drag than any other fixed 3 blade prop. 3 blade props are also smoother and less prone to vibration.

3. Barnacles grow on everything.

Link to the Campbell Sailor: West by North Enterprises - Campbell Sailer

3 blade vs 2 blade link: West by North Enterprises - Campbell Sailer FAQ

Other questions are answered further down the page at the link.


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## Dave_E (Aug 7, 2013)

Hi Jaramaz,

I am just another humble marine mechanic who concurs completely with the excellent dissimilar metals explanation given. Don't get wrapped up in what kind of metal. 2 different metals in salt water = some sort of corrosion... maybe fast, maybe faster. In our case (sailboaters) we are the exception to the rule of not having to have masive zinc plates bolted on to the transum and outdrives and lower units and rudders and prop shafts. Jim's boat takes 2 zincs ahead of the cutlas bearing tower and it's the best $10 a year he could spend on his boat.

Jim, I concure, get that rascal to a prop shop. Clean the bottom of the boat REALLY good. You just won't believe the performance increase you'll see. (Really) I saw 1k increase the second we were back in the water, just from a pressure wash and I had no barnicles.

Dave


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## mitiempo (Sep 19, 2008)

One other point. A spinning prop has less drag under sail than a locked prop. This has been proven multiple times. As long as your transmission/engine manufacturer allows this it is best. For example Yanmars with the Kanzaki transmission (common) are supposed to be in neutral, others possible not.


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## Fstbttms (Feb 25, 2003)

svHyLyte said:


> In Europe, however, Manganese Bronze is (actually properly) known as "Brass".


These foreigners- it's like they have a different word for everything!


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## jimgo (Sep 12, 2011)

Wow, you'd think I had asked whether I should go with a Rocna or a Mantus as my only anchor for my round-the-world trip on my MacGregor 25.


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## mitiempo (Sep 19, 2008)

jimgo said:


> Wow, you'd think I had asked whether I should go with a Rocna or a Mantus as my only anchor for my round-the-world trip on my MacGregor 25.


Just correcting some seriously wrong information from Jaramaz.

The Campbell Sailor is a good choice. For further confirmation email MaineSail for his experienced opinion.

As far as zincs, you need them, I think that is obvious. Zincs that are as covered with growth as yours are - both on the strut and on the shaft - are a lot less effective than bare zincs.


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## GeorgeB (Dec 30, 2004)

So, if "bronze" is Swedish for "brass", what is their word for "brass"? In the good o'l USA we too, have "bronze", which we call "bronze". We also have "silicon phosphor bronze" which we call "silicon phosphor bronze". As we learned in chemistry class, the silicon variety is slightly more noble than regular bronze (but not by much), it will still act as an anode if attached to a more noble metal like stainless steel. Funny, but one of the photos Fast Bottoms posted was a Scandinavian made prop which they describe on their website as "bronze".

Jimgo, I'm afraid I can't answer the anchor question untill I know what your position is regarding carrying guns on board.


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## mitiempo (Sep 19, 2008)

While manganese bronze is in the middle of the above chart it can act like it is much nearer the top. A bronze alloy can dezincify if it has over 10% zinc. Manganese has up to 39% zinc, so acts more like an impure zinc than some other bronzes. For example good seacocks are made of 85-5-5-5 bronze with zinc being one of the 5% metals. They are stable in seawater and last decades without zinc protection and often without bonding to other underwater metals. A manganese bronze prop can become pink, dull to a tap as opposed to the ring of a good prop, so porous that is has little strength and basically useless after a year or even less. 

Fastbottoms pics show the results well. He has probably seen as many props as a prop shop has, though often in more murky conditions.


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## Fstbttms (Feb 25, 2003)

mitiempo said:


> A manganese bronze prop can become pink, dull to a tap as opposed to the ring of a good prop, so porous that is has little strength and basically useless after a year or even less.


The corrosion on this Gori prop literally occurred in a matter of weeks. Although the issue was corrected, the damage was done and the prop eventually fell off.


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## mitiempo (Sep 19, 2008)

Fstbttms said:


> The corrosion on this Gori prop literally occurred in a matter of weeks. Although the issue was corrected, the damage was done and the prop eventually fell off.


I was playing it safe - I didn't want to scare anybody.


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## outbound (Dec 3, 2012)

Is there any problem putting a zinc on the shaff even if not needed?

How noble is Monel ?

Has any body used the two part prop speed on a feathering prop? What do you do with the gears?


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## mitiempo (Sep 19, 2008)

Wikipedia puts Monel 400 one below 316 stainless.






If the zinc is not needed as long as it is the least noble metal underwater I would think it is fine. When would it not be needed?


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## Fstbttms (Feb 25, 2003)

outbound said:


> Is there any problem putting a zinc on the shaff even if not needed?


No. But as mitiempo stated, under what circumstances would it not be needed?



outbound said:


> Has any body used the two part prop speed on a feathering prop? What do you do with the gears?


PropSpeed is not going to last on any parts that are in moving contact with other parts.


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## mitiempo (Sep 19, 2008)

Fstbttms said:


> PropSpeed is not going to last on any parts that are in moving contact with other parts.


So to clarify PropSpeed will work on a fixed prop but not on a folder and maybe not on a feathering prop. Correct?


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## miatapaul (Dec 15, 2006)

CalebD said:


> The prop shop I used a few years ago in NY checked the balance on my 2 blade prop for free (they were doing other paid work for me). Should not cost a lot for them to check it or "spin it" as they call it.
> 
> Good luck getting your prop off the shaft while it is that dirty. Hope you can find a prop puller rig and a whole bunch of patience.


Did you use these guys?
Welcome | precision-props.com

They seem to do a lot all up and down the east coast. They also are a local company to me and I have seem there trucks all over the place but have never stopped in. They are at all the local boat "shows" if you want to call them that and seem to be pretty stand up guys and gal (as mom still works there). I think they even do pick up and delivery, though that is not likely necessary for this one!


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## Fstbttms (Feb 25, 2003)

mitiempo said:


> So to clarify PropSpeed will work on a fixed prop but not on a folder and maybe not on a feathering prop. Correct?


No, it'll work on a feathering prop but it will not last on those parts that come into contact with other parts. So most of the prop will remain coated.


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## Dave_E (Aug 7, 2013)

I have a 12g flare gun... Does that count as a yes? 

Let's not hijack this thread.


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## Jaramaz (Aug 9, 2013)

Aaah, there are some here that want to call Wikipedia Swedish?

Using Wikipedia as it is easy to access. But other textbooks say about the same: Originally (much before US existed ...) bronse was: 


> Bronze is an alloy consisting primarily of copper, usually with tin as the main additive. It is hard and tough, and it was so significant in antiquity that the Bronze Age was named after the metal.


whereas brass consists of cuppoer and zinc.

Both are alloys. Similar and different.

Later on bronze has been developed to have tin replaced by other metals as beryllium, alu, magnesium and so on.

This is the normal names and language of these alloys. Can be found in most textbooks, as well as in Wikipedia. In the sailing world, bronze has been more and more rare, as it is expensive. As mentioned in earlier post, it is difficult to find eg through-hull in bronze, mostly one gets the brass version. Sometimes this is declared as bronze, as the dealer wants to give it a better status. Still, brass.
One of the english boat magazines (YM?) had an article about through-hulls either this year, or last year. They found that most of the standard boats (Bav, Bene, ..) had brass through-hulls, with an expected life time of some few years. 
Bronze through-hulls lasts for decades. Usually, there is no need to change.

This to illustrate the importance of correct naming. Bronze is bronze, and brass is brass.

As stated, traditionally bronze is defined as not having any zinc. This has changed, some claim now that some bronze alloys can contain someminor amounts of zinc.

Again, there are today brass which are declared as not de-zincify. This is achied with adding (heavily doping with) arsenic, which then binds the zinc. If this really works has to be seen, it is quite recent development.

In practice there are props made in brass and in bronze. Those Goris (as Fstbttms is mentioning Gori) props I have had, have all been in brass. They do need zinc anodes, eg on the prop shaft. Actually, most prop manufacturers do not declare what material they use (manufacturers home page, not the retailers; retailes state anythng they believe in). In that case one better use zinc anodes.

There are some few drawbacks in using zinc anodes on bronze equipment:
1) cost. This is a minor problem.
2) with a zinc anode attached, prop has to be painted with antifouling.

Again, is it often is difficult to determine if the prop is made of brass or bronze, in that case there is only one option: use a zinc. (that what I am doing, as the prop manufacturer doesn't declare which alloy is used).

Fsstbttms has not given any real arguments in this discussion, just putting up some pictures and random quotes, mostly without any references. It has turned out that one of the pics was of a Gori ... which is made of brass. Of course that needs a zinc anode. 
That level of discussion is a bit low, more emphatic than fact based.

Someone claimed a 3-blad prop is more power efficient than a 2-balde. Well, go to the prop text books!

/J


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## mitiempo (Sep 19, 2008)

Three blade vs 2 blade propeller?

You could have something there. Think of the wealth you could have by convincing all the world's shipping companies and all the cruise lines to switch to 2 blade propellors.

I do not know of any commercial vessel with a 2 blade propeller.

Here is an example from your part of the world - Wartsila in Finland.



And here is a link to choosing a propeller from Mercury Marine - they have done a bit of research on this in the last 50 years or so.

How to Choose Numbers of Propeller Blades | Mercury Marine


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## Minnewaska (Feb 21, 2010)

Galvanic corrosion doesn't care what the two metals are, only that they have different potentials, are in electrical contact with each other and are immersed in an electrolyte. 

Zinc will almost always have the greatest differential potential and, therefore, will protect whatever metal your prop is made from as it will take over as the anode in the event your prop may have been otherwise. Even if your prop would be the cathode, the zinc is still still necessary so corossion doesn't occur the the shaft, strut or whatever.


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## mitiempo (Sep 19, 2008)

"Bronze is bronze. Brass is brass."

Not quite that simple as there is more than one type of each. 

Red brass is a good example. "Red brass is both an American term for a copper-zinc-tin alloy known as gunmetal, and an alloy which is considered both a brass and a bronze."

Wikipedia lists 26 alloys of brass.

There are in North America 2 very different types of bronze found on most boats. There is the bronze that good through hulls are made of - 85-5-5-5 is used for through hulls and will not lose its 5% zinc in salt water. Its other 5% metals are tin and lead. These are made by Spartan, Groco, and Apollo-Conbraco. I sell both Groco and Apollo through hulls and they are good for many decades without zinc protection. 

In Europe through hulls can be inferior as far as I know - the forums in the UK have many posts about Beneteau, Bavaria, and other manufacturers stating that their through hulls only have a 5 year life span. Maybe they should buy them from the US.

While there are propellers made of different alloys the majority (except for aluminum or stainless on outboards) are made of manganese bronze. It contains up to 39% zinc. It has to be protected by a sacrificial zinc or it will not last. It also should not be painted with copper based antifouling without an epoxy barrier coat.

Gori props are made of Nibral (stated on Gori's website) an alloy of nickel, bronze, and aluminum. said to be stronger than bronze but not as strong as stainless.


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## Fstbttms (Feb 25, 2003)

Gosh, I ran into *another* prop today that must be made of brass. 'Cause if it was bronze, this wouldn't have happened  :


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## Minnewaska (Feb 21, 2010)

I wonder if this Jaramaz' thought. If you put non-zinc alloy bronze and iron/steel in an electrolyte, its the iron/steel that become the anode and corrodes, not the bronze. However, their conclusion that you don't need a zinc is still incorrect, as you still want something less noble than the iron/steel to protect it, due to the bronze prop being more noble in this scenario (ie a sacrificial zinc).

In the more common combination, a stainless steel shaft and bronze prop, the prop is going to corrode, even if the alloy has zero zinc in it. Its simply less noble than the stainless. If the bronze has zinc, it will corrode faster, but they both corrode.

Of course, iron/steel submerged in salt water is going to simply oxidize, which they may also be confusing with galvanic corrosion. 

Finally, Js comment that one needs anti-fouling paint on a bronze prop if you use a zinc is beginning to sound like a troll.

Fstbttms, you must have done something to tick J off.


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## outbound (Dec 3, 2012)

So the take home message is put a zinc on- can't hurt?right?


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## Fstbttms (Feb 25, 2003)

Minnewaska said:


> Fstbttms, you must have done something to tick J off.


Yeah, I told him he was wrong.


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## Fstbttms (Feb 25, 2003)

outbound said:


> So the take home message is put a zinc on- can't hurt?right?


Can't hurt? It's a requirement. You know, unless you don't mind replacing your prop every now and then.


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## mitiempo (Sep 19, 2008)

Minnewaska said:


> In the more common combination, a stainless steel shaft and bronze prop, the prop is going to corrode, even if the alloy has zero zinc in it. Its simply less noble than the stainless. If the bronze has zinc, it will corrode faster, but they both corrode.
> 
> Fstbttms, you must have done something to tick J off.


Actually if you have a bronze shaft and a bronze prop the prop will still corrode without a zinc. The shaft is a low zinc alloy and the prop (manganese) will lose its zinc.

J is wrong on several counts.


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## chucklesR (Sep 17, 2007)

Wow. 
Before.








After a couple hours of scrubbing and being careful (it's a 4k prop). No power at the time - it was raining cats and dogs. 









To my simple mind clean and shiny is a good start (still have to polish the prop), then some prop speed - and I think I'll be following the manufactures recommendation and putting a zinc back on (you can see I had them on in the before pic). 
I've also got a correctly wired galvanic isolator.


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## jimgo (Sep 12, 2011)

Very nice Chuck! What did you use to do the cleaning? How's the other repair project coming?


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## outbound (Dec 3, 2012)

Had a long talk with the Petit people at the Defender show after talking at length with the yard boss at the marina. What I got out of it (and from other research)
Prop speed works great especially if boat on engine fairly often and regularly. Not as well for boats that sit or engine runs rarely. Very expensive as when it get chipped or wears off ( tends to wear at edges) the whole thing needs to be entirely stripped and re applied. Can't patch it. Failures with Prop Speed are more common if not professionally applied.
Petit spray bottle product has good track record but needs to go on clean running gear. For us ( with bronze Maxprop) barrier coat first not key so not needed. 2-3 coats is max as beyond that it starts to pucker. If multi year service desired best to overcoat with a standard bottom paint but do not use one that contains zinc. Can apply two coats of that and still keep adhesion with service life of 2+yrs. Put zinc on max props.
Will see as this year spit up the anchor. Next haul hopefully will be in 2yr.


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