Zinc Spray under Zincs for better contact?

[GaylesFaerie]

After wire brushing all the crud off the bronze prop nut and cone zinc bracket I can see that some small wear occurs as a result of the brushing. After years of this practice I would suspect it will eventually result in inadequate mating to the cone zinc as the surface gets worn away because the annually new cone zinc dimensions don't change. How do others handle this issue?

Would it make sense to use zinc spray to somewhat rebuild the worn surface and then fasten the new cone zinc onto it? The assumption in doing this is that a 93% zinc spray would make up for some of the lost bronze and restore the surface closer to its original dimensions making for better contact with the cone zinc. Another assumption is that the electrical properties of the spray are close enough to the cone zinc that the galvanic protection would not be compromised. Is this wishful thinking? Should I not be taking the metal down to bronze during prep? GF

 

[GaylesFaerie]

Pressed SUBMIT too soon... Could electrically conductive grease be used to promote better contact between a zinc and the surface it is protecting and keep water out of the union?

 

[knotflying]

I found that the fit between the prop nut and the zinc were rather sloppy. This resulted in always losing the zinc early and has been an issue for many tug owners. I used two pennies on two opposite sides on the nut and slipped the zinc on. Now the topic of dissimilar metals will probably initiate. However, after using my "fix" I never lost a zinc and never saw the nut dissipate in size.

 

[BB marine]

You want good contact between the anode and the surface of the item it is protecting. When I replace my anodes I clean the surfaces using a scraper, file, sand paper 80 grit, and finish it with scotch bright pad. I fit the anode to the surface so it has 80% plus contact. The better the surface contact the less corrosion buildup between services and the longer the anode works protecting. When it comes to the prop nut. I have read about, many folks loosing the anode off the nut. The biggest reason for this is exactly hat Mike stated. The anode doesn't fit the nut properly. There may only be a couple of places of contact. What I did the first time I replaced the anode was fit the anode to the nut. The base of the nut where the anode mates is rough and uneven. I cleaned this nut with a file and fit the anode to the nut. Once the nut was filed and sanded the anode was fit to make full contact to the nut. The anode should fit nicely over the nut and sit flat at the base of the mating surface. If this is done you will always have good contact between the anode and the nut and less corrosion buildup and it should never fall off. I have never lost a prop anode.

A note on my use of Aluminum alloy anodes. This is the first year that the boat transitioned from Fresh water to salt water. I have always used Aluminum alloy anodes in fresh water and have read that they will out last Zinc anodes in salt or brackish. READ never experienced. This year I installed the anodes June 2020 launched the boat in Lake Michigan used the boat for 2 months and the pulled the boat. I thought I had replaced the anodes then before launching in Grand Rivers KY. But I checked my notes and did not. I launched the boat in KY and cruised to Gulf shores Alabama where the boat stayed in the water for 4 weeks (Salt water plugged into shore power at a marina) I inspected the anodes then and they were in good condition so I didn't replace them. I then launched the boat the 3rd week of January in Punta Gorda Fl spent the winter in the water and pulled the boat out in the middle of April. The boat was plugged in at marinas 80% of the time. I just removed all the anodes Two thruster anodes have a couple of pits in them, The two 4" anodes on the trim tabs have about 90% material left. The Prop shaft anode has about 90 % material left. between fresh water and salt water the boat was in the water 7 1/2 months.I am very happy with the performance of the Aluminum. I thought maybe the prop anode was not working. I have heard many say it erodes away. I tested the continuity between the anode and the prop shaft. I got a reading of 5 to 10 ohms. It was working!!

 

[Kevin Lamont]

After wire brushing all the crud off the bronze prop nut and cone zinc bracket I can see that some small wear occurs as a result of the brushing. After years of this practice I would suspect it will eventually result in inadequate mating to the cone zinc as the surface gets worn away because the annually new cone zinc dimensions don't change. How do others handle this issue?

Would it make sense to use zinc spray to somewhat rebuild the worn surface and then fasten the new cone zinc onto it? The assumption in doing this is that a 93% zinc spray would make up for some of the lost bronze and restore the surface closer to its original dimensions making for better contact with the cone zinc. Another assumption is that the electrical properties of the spray are close enough to the cone zinc that the galvanic protection would not be compromised. Is this wishful thinking? Should I not be taking the metal down to bronze during prep? GF

Hello,

What I have found when replacing the prop zinc, I use a fender washer and lock washer for the bolt. It seems like this has helped with keeping them one till its time to replace. Hope this helps.

Thanks,