I’ve been advised to install a zinc on the prop shaft strut of my 1993 Hunter Legend 35.5. Haulout is next week for a bottom paint, so it’s time if I’m to do it. Had anyone drilled their strut to attach a zinc? Any recommendations or best practices? Our strut seems fairly slender, so I’m a bit wary of compromising it structurally by putting a hole in it, but maybe it’s the lesser of two evils.
Zinc on strut?
- Thread starter skunther
- Start date
Look around your boatyard. Do you see any boats with a zinc on the strut? Does the source who advised you have a zinc on their strut? Ask for an explanation as to "why". Lastly, does your source sell zincs?
Typically a strut is isolated from everything else so there is no electrical path that would support electrolysis which is what a zinc would prevent. The strut is bolted to the fiberglass hull and the rubber cutlass bearing isolates it from the shaft and engine. So unless you have a bonding wire to the strut, there is no electrical connection. And if you do have a bonding wire, then you should have a zinc somewhere that is connected to the bond and protects all of the bonded metals.
Typically a strut is isolated from everything else so there is no electrical path that would support electrolysis which is what a zinc would prevent. The strut is bolted to the fiberglass hull and the rubber cutlass bearing isolates it from the shaft and engine. So unless you have a bonding wire to the strut, there is no electrical connection. And if you do have a bonding wire, then you should have a zinc somewhere that is connected to the bond and protects all of the bonded metals.
It's eaten away by galvanic corrosion because it is in contact with bronze.
I would tend to go with Mr. Stidger's explanation long before any boat yard's opinion.
If your strut shows evidence of corrosion, add an anode. If it doesn't, don't. If it ain't broke, don't fix it.
Every year since we purchased our boat in 2002, I've installed two heavy zincs on our prop shaft every year, but never on our shaft strut. That has worked for us and the shaft strut, and other bright work below the waterline remains in good condition.
Mine had one when I bought it. After 5 days of ownership I replaced it this year. It has a hole, 5 bucks every 5 years seems cheap for prevention. Buy a test electrode and check the strut from the mounting bolts on the inside. I checked all of my components and found everything within specs (per the manual that came with it.).
I had to replace the shaft log because of corrosion. I connected a bonding wire internally from the new shaft log to a bolt holding the prop strut and then put a 2" zinc on the strut. I have to agree that the strut itself should not need protection.
A proper zinc on your shaft will serve to address all metals that are connected to the same ground wire in the boat. That is how your metal through hulls stay healthy. They do not have individual zincs.
If concerned, add a second zinc to the shaft.
Here is a picture of a Hunter 35.5 with 2 zincs
You can get a Corrosion Reference Electrode from Boatszincs.com and know if there is an issue for your underwater metals.
If concerned, add a second zinc to the shaft.
Here is a picture of a Hunter 35.5 with 2 zincs
You can get a Corrosion Reference Electrode from Boatszincs.com and know if there is an issue for your underwater metals.
Absolutely NO!!!!!
Anode Installation - Best Practices - Marine How To
Anode Installation I recently came from a customer’s boat after doing a winterizing and while there I noticed the anode (zinc in this case) on the $3500.00 prop was not connected to anything, other than by friction. Sadly I see this far
marinehowto.com
Boy, there is some bad information in that articleAbsolutely NO!!!!!
Anode Installation - Best Practices - Marine How To
Anode Installation I recently came from a customer’s boat after doing a winterizing and while there I noticed the anode (zinc in this case) on the $3500.00 prop was not connected to anything, other than by friction. Sadly I see this farmarinehowto.com
It would helpful if you could specify the bad information and provide references to support your claims.
Sure. For instance- the author recommends electrically isolating the anode's fasteners from both the anode and the part being protected. What the author clearly doesn't have a clue about is that the fasteners help provide electrical contact between the anode and the part being protected. And electrical contact between the anode and the part being protected is exactly what you want. Trying to extend the anode's life by reducing points of electrical contact between it and the prop (or strut or whatever) is a bad idea.
I think you are misreading his article. Rod does recommend isolating the mounting bolts from the anode so that the anode protects the important part and not the mounting screw. No where in the article does he say to isolate the anode from the metal it is intended to protect, in fact, he goes to some length to ensure the mating surfaces have good clean contact.
The one anode where your concern has a little merit is on the prop anode. However, there is more than adequate surface area between the anode and the prop hub. Any additional connectivity from the SS screws is minimal. Besides, SS is a lousy electrical conductor.
Rod is one of the most well respected Marine Electricians in the country. I'm going to go with his recommendations.
Now who is misreading? I never said he told you to isolate the anode from the part being protected. I said the metal fasteners help create the electrical connection the anode needs to protect the part in question. And this guy is telling you to eliminate that fastener/anode/part electrical connection.
"...apply a liberal coating of Tef-Gel to the entire SS bolt that passes through the anode and also to coat the anode surfaces where the bolt passes through it and where the bolt comes into direct contact with the anode. The practice of applying an insulating compound creates a spot where the stainless bolt or machine screw will be galvanically isolated, as best that it can be, from the anodic metal."
But hey, it's your dime.
Maybe I’m missing something, but I don’t follow. In a typical shaft anode the bolts pass from one half of the anode to the other. They don’t touch the metal being protected (the shaft) at all. The contact with the shaft is entirely made by the curved part of the anode itself. How is the bolt part of the circuit?Now who is misreading? I never said he told you to isolate the anode from the part being protected. I said the metal fasteners help create the electrical connection the anode needs to protect the part in question. And this guy is telling you to eliminate that fastener/anode/part electrical connection.
"...apply a liberal coating of Tef-Gel to the entire SS bolt that passes through the anode and also to coat the anode surfaces where the bolt passes through it and where the bolt comes into direct contact with the anode. The practice of applying an insulating compound creates a spot where the stainless bolt or machine screw will be galvanically isolated, as best that it can be, from the anodic metal."
But hey, it's your dime.
I love talks like this. Personally i am waiting on "this guy" to join the thread. I think I need popcorn.
@Maine Sail yer up.
Agreed. Don’t weaken the strut by drilling a hole in it for an anode that is better placed on the prop shaft. If it was designed to hold an anode, fine, but I’ve personally never seen one like that.Absolutely NO!!!!!
Anode Installation - Best Practices - Marine How To
Anode Installation I recently came from a customer’s boat after doing a winterizing and while there I noticed the anode (zinc in this case) on the $3500.00 prop was not connected to anything, other than by friction. Sadly I see this farmarinehowto.com
I’ve been following the MarineHowTo best practices on shaft anode installation for years, with one exception. I have not bothered with protecting the integrity of the anode around the bolts. The bolts are countersunk into most shaft anodes, if enough of the anode is eroding for there to be an issue, then you need to replace them more often. Perhaps also trace and remedy the cause, install a galvanic isolator, etc., but I’m digressing.
I keep two magnesium anodes on my prop shaft and replace one of them each year. My boat is on the hard almost half the year, and on shore power (with a galvanic isolator) at the dock during sailing season. It splashes in the spring with one new anode and one installed the previous year. They usually look like this at haul out.
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