Do you all coat your underwater metals with epoxy?

Atalla

Active Member
Sep 1, 2020
244
Seattle
Boat Info
2007 38 Sundancer
Engines
Twin Merc 8.1 S Horizon V-Drives
My boat goes back and forth between fresh and saltwater. No issues with corrosion in the marina. Aluminum anodes. Have the boat out getting a fresh coat of bottom paint and trying to decide whether to let them epoxy. Marine folks, of course, think it would be a great idea. Boat new to me last year, not likely that previous owner ever did it, although shafts and one prop were replaced several years back due to him failing to replace the anodes for a time.
 
I’m in the process of coating the NiBrAl pods on our boat. I had not considered doing it having spent many years of using Trilux for sterndrive coating. I was convinced to do it after a conversation with one of Volvo’s IPS product engineers in answer to the question of whether Trilux could be used on our pods.

Keep in mind epoxy will only act to prevent galvanic corrosion by performing as an electrical insulator. If you are getting growth, you will need to overcoat with a non metal reactive anti fouling like Pettit HRT. For the props you might consider Velox or prop speed that is specifically intended for props.
 
There is a school of thought that the coatings should be conductive like zinc. The thought is that if a non-conductive coating has a holiday (pin hole) or small uncoated areas it is those small areas that will be galvanically attacked and that localized area damage will be much greater than an acreage abatement or loss of sacrificial zinc. I'm kinda aligned with the school of thought.
Many of the large dock queens in our marina are coating their running gear with high zinc content paint and they report good results.
1 Gallon Galvax Cold Galvanizing Paint 95% Zinc | Fastenal
 
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I’m in the process of coating the NiBrAl pods on our boat. I had not considered doing it having spent many years of using Trilux for sterndrive coating. I was convinced to do it after a conversation with one of Volvo’s IPS product engineers in answer to the question of whether Trilux could be used on our pods.

Keep in mind epoxy will only act to prevent galvanic corrosion by performing as an electrical insulator. If you are getting growth, you will need to overcoat with a non metal reactive anti fouling like Pettit HRT. For the props you might consider Velox or prop speed that is specifically intended for props.
Growth isn't a big problem for us. I guess it's just a question of hedging on whether my anodes do the job. Enough marina hopping out in the Puget Sound, that it's impossible to know what I'm going to be parked next to.
 
There is a school of thought that the coatings should be conductive like zinc. The thought is that if a non-conductive coating has a holiday (pin hole) or small uncoated areas it is those small areas that will be galvanically attacked and that localized area damage will be much greater than an acreage abatement or loss of sacrificial zinc. I'm kinda aligned with the school of thought.
Many of the large dock queens in our marina are coating their running gear with high zinc content paint and they report good results.
1 Gallon Galvax Cold Galvanizing Paint 95% Zinc | Fastenal
That is an interesting school of thought for sure. The idea that it's better to distribute the damage across a wider surface area to reduce the impact. I'm thinking as long as I haul out consistently to get a look, I should be okay. I know I'm relatively safe in my home slip.
 
There is a school of thought that the coatings should be conductive like zinc. The thought is that if a non-conductive coating has a holiday (pin hole) or small uncoated areas it is those small areas that will be galvanically attacked and that localized area damage will be much greater than an acreage abatement or loss of sacrificial zinc. I'm kinda aligned with the school of thought.
Many of the large dock queens in our marina are coating their running gear with high zinc content paint and they report good results.
1 Gallon Galvax Cold Galvanizing Paint 95% Zinc | Fastenal

That is the underlying premise for using zinc rich epoxy primers on steel marine structures and equipment like cranes and cargo containers. The zinc rich primer is followed by a barrier top coat. In the days before VOC clean air regulations, top coats were typically epoxies, or chlorinated rubbers. But the primary mechanism for corrosion protection is the insulating top coat. The anode material is sacrificial and in a finite amount and as a result it’s useful life can be plotted on a curve. Therefor it serves as a mitigation for mechanical damage. The zinc material is not intended to be the primary corrosion preventive, just to prevent undercutting from mechanical damage.

I think your concern about a potential application defect is logical, but not very realistic when a competent painter is involved. This is true especially when talking about epoxies where dry film thicknesses of 125 to 150 microns is common. Even Pettit barrier coat using DIYer level of instruction -“ two to three coats of roller application” is pretty much guaranteed to meet spec.
 

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