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Overprotection of prop (too much anode) on BENETEAU Oceanis 351

redege

.
Jun 29, 2012
18
beneteau oceanis 351 queensland
I decided to dive and take the prop off to re apply Prop Speed protection. I brought the prop to a prop specialist and he told me I should get two years protection out of Prop Speed. Other people in my marina also tell me this. I get a maximum of 6 months protection before the barnacles take over.
The prop specialist said that I might have too much anode. This has a negative effect he said. I researched and came up with this (copied):

Repels Anti-Fouling and Propeller Coatings – in the same manner as paint blasting, over protection can lead to the non-retention of anti-fouling and propeller coatings due to in compatibility of the application with sacrificial anodes. This can render the application ineffective and the increased barnacle and other marine growths lead to vessel inefficiencies and costly manual maintenance.
Lure of Marine Growths – excessive cathodic protection accelerates the formation of calcareous deposits including the calcium carbonate coral-like structure commonly encountered on a vessel’s hull, rudders and propellers.

I have a big collar anode on the shaft, never knew about the micro size for the Beneteau mentioned.
Any thoughts or experiences anyone?
 
Sep 25, 2008
6,314
Alden 50 Sarasota, Florida
Sounds like an imaginative way of blaming electrolysis for the Prop Speed failure of the “should get two years protection” claim. Over-zincing is a legit concern as you are effectively creating a bigger battery effect by excess zinc but that effect is manifested in ways other than increased marine critter growth.
 
Jan 4, 2006
3,904
Hunter 310 West Vancouver, B.C.
Sounds like an imaginative way of blaming electrolysis for the Prop Speed failure of the “should get two years protection” claim.
I'll second that.

The explanation of incompability give no explanation of the mechanism involved. Maybe hydrogen production at the cathode (prop) lifts the Prop Speed, but doubtful.

I'd need to see a lot more testing before I'd be willing to swallow the "overprotection theory"

Additionally, I didn't think any prop coating was really worth much due to the erosive action of the rotating prop.
 
Jan 11, 2014
7,827
Sabre 362 113 Fair Haven, NY
Additionally, I didn't think any prop coating was really worth much due to the erosive action of the rotating prop.
Before venturing to salt water, I painted my prop and drive shaft with several coats of Pettit Prop Paint. It is a gray high zinc content paint in a rattle can.

After 75 hours of motoring in water that was often silt laden, there was almost no wear on the prop or shaft, except for the very leading edge of the prop. There was a thin hint of bronze in the place that would be expected. In contrast, the leading edge of my keel and rudder had all the bottom paint worn off.

So, at least at this stage, I'm convinced that the paint was worth the $25 or so I paid.

What did wear was the prop anode. I typically use aluminum being fresh water and since aluminum is good for saltwater I continued the practice. After less than 2 months the prop anode (not the shaft anode) had eroded so much that in a few days it would have fallen off. I think the issue was the aluminum reacting with the zinc. I changed to zinc anodes.

Propspeed seemed to be a popular coating for the Hinckleys, Sabres, and other boats at the Hinckley Yard where Second Star was hauled.
 
Jan 4, 2006
3,904
Hunter 310 West Vancouver, B.C.
After 75 hours of motoring in water that was often silt laden, there was almost no wear on the prop or shaft, except for the very leading edge of the prop.
One case where Pettit Prop Paint stood the test of time. Gotta wonder if there's more.

What did wear was the prop anode. I typically use aluminum being fresh water and since aluminum is good for saltwater I continued the practice.
Do I understand you to say you are in fresh water now ?
 
Jan 11, 2014
7,827
Sabre 362 113 Fair Haven, NY
One case where Pettit Prop Paint stood the test of time. Gotta wonder if there's more.



Do I understand you to say you are in fresh water now ?
We were in Freshwater when we added the paint and the aluminum anodes. We are now in saltwater having transited the Erie Canal. The prop and anodes were inspected after our transmission failed and we were hauled.

Aluminum anodes have worked well in freshwater, there is always some degradation in the anodes which is a good sign, but not too much.
 
Oct 19, 2017
6,937
O'Day 19 Littleton, NH
Depending on the alloy, aluminum can actually be less noble than zinc.

If there's zinc in the paint, under protection could cause a degradation of the paint. The paint becomes the anode. I believe they actually do that with large ships on purpose to protect steel and aluminum hulls, use a high zinc paint to prevent corrosion.

-Will
 
Apr 12, 2007
133
Hunter 420 Herrington Harbor South
Though you were not supposed to mix zinc and aluminum anodes in salt water. Use one or the other but not both. Did I miss read something?
 
Jan 11, 2014
7,827
Sabre 362 113 Fair Haven, NY
Though you were not supposed to mix zinc and aluminum anodes in salt water. Use one or the other but not both. Did I miss read something?
Yes you are correct, don't mix them. When I replaced my anodes I used zinc because the aluminum failed quickly. What I had not anticipated was the interaction between the zinc in the paint and the aluminum anodes.

Of the two anodes, the prop anode was seriously degraded while the shaft anode was less degraded. I think the large amount of paint on the prop accelerated the process.

The take home message is, if you use a zinc based paint on the prop and shaft, use a zinc anode.
 

Bob S

.
Sep 27, 2007
1,687
Beneteau 393 New Bedford, MA
I've gone the season with Pettit Prop paint, when the can ran out I switched to a ZRC product with the same results. My prop has been coming out clean every fall.
 
Apr 22, 2011
735
Hunter 27 Pecan Grove, Oriental, NC
Years ago while cruising in the Caribbean, we were having excessive barnacle growth on the prop and prop shaft. I always put two zincs on the prop shaft to protect the prop from electrolysis. The bronze prop was not painted. An experienced sailor told me that I was over-zinced and it was preventing the slow release of some alloy in the bronze that the barnacles didn't like. So, what the heck, I removed one of the zincs and defiantly have fewer barnacles. After a couple of years, I didn't notice any deterioration in the prop.
 
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redege

.
Jun 29, 2012
18
beneteau oceanis 351 queensland
Thanks for all your responses. In Australia I can only get the 33mm wide 25mm shaft donut anode. In the US there seems to be a micro (17mm side) donut shaft anode. Maybe there is a difference. It is half the size after all. I'll cut one down to make it micro, have a professional Prop speed application and then.. time will tell. If this post still exists after about 6 months, I'll let you guys know what the verdict is!!
 

dLj

.
Mar 23, 2017
1,823
Belliure 41 Now on the Chesapeake
Repels Anti-Fouling and Propeller Coatings – in the same manner as paint blasting, over protection can lead to the non-retention of anti-fouling and propeller coatings due to in compatibility of the application with sacrificial anodes. This can render the application ineffective and the increased barnacle and other marine growths lead to vessel inefficiencies and costly manual maintenance.
Lure of Marine Growths – excessive cathodic protection accelerates the formation of calcareous deposits including the calcium carbonate coral-like structure commonly encountered on a vessel’s hull, rudders and propellers.
Excessive cathodic protection typically comes from impressed current cathodic protection, not from having a large zinc anode. The only thing a large zinc anode does is provide a greater quantity of zinc to be consumed giving you a longer time between changing your zinc. Over protection is when the impressed current is too high on impressed current cathodic protection systems. It has been observed mainly in pipelines where this type of system is more commonly found. I understand it's now also used on aluminum hull boats, but I don't believe you are talking about that.

The potential that is created by the use of zinc has to do with the dissimilar metals aspect and is limited by that potential difference, not the size of the zinc, that only adds longevity. The potential difference remains unchanged no matter how large your zinc is.

dj
 
Apr 14, 2009
741
Sabre 28 NH
Interesting observations.
This season I decided to try Pettit Prop Paint in lieu of coating stuff with Destin. Sprayed the prop, strut & shaft. I installed the zinc on the shaft as usual. I pulled yesterday after 14 weeks on the water. The prop, strut & shaft were covered in barnacles. This has never happened in the past. The real odd part, the zinc on the shaft looked brand new. The nail polish on the allen screws & nuts was still intact. The zinc was on a clean, unpainted part of the shaft. Apparently the zinc in Pettits product became the sacrificial product in lieu of the shaft zinc. Personally I won't do this again.