Final word on zinc placement

[allen-deckard]

I wanted to ask if anyone had the final word on the subject?
It was brought up awhile ago about placing a zinc and I reread the thread but no definitive decision was made by the community.

I'm bringing it up again because I'm about to replace my zinc and want to do something a little different than I've done before but wanted to ask.

It was discussed that the zinc "could" be placed inside the boat and electrically connected to the winch cable or the winch so that it's electrically connected to the keel threw the cable.

In theory the electrolysis should dissolve the zinc right there inside the boat but I wanted to know if anyone has actually tried this or is it just that an untested theory? I'll be honest I think it would work but I really don't want to be the one to test the theory.

Since I don't pull my boat but once a year I'd love to be able to replace the zinc inside since this time I pulled it the zinc was just about gone.

 

[allen-deckard]

ok never mind I found this after some research and decided it will get mounted to the keel.



A friend of mine and I are arguing over the effectiveness of this anode. I contend that since it’s not actually submerged in seawater (the electrolyte), it’s basically doing nothing. My friend says that as long as it is electrically connected to the metal it serves, it will work just fine. Can you please resolve this argument once and for all? This anode has been on the boat for almost seven years now and it sure doesn’t look to me like it’s sacrificed any metal.
Answer: You win. It’s important for people to remember that all of this sacrificial anode stuff applies to what happens in a galvanic cell, where we have an anode, a cathode, an electrical connection between the anode and cathode, and all of it is sitting in the same electrolyte solution. With everything sized properly, the anode will become sacrificial and protect the cathode from corroding, at least for the expected service life of the anode, which is based on its mass and material. So in your photo, even if the bilge on the boat were flooded, the best that could happen is that the shaft section on the inside of the boat would get some cathodic protection. The propeller and the shaft section on the outside of the hull would not be protected by the anode in the photo.
Whoever installed that anode was definitely misinformed.

 

[Chief RA]

Zinc can also shrink your Prostate! Chief

 

[CloudDiver]

Before you drill a hole through your keel... I've been working on a remote anode alternative. I have the prototype ready, I have just been slacking on installing it. My version uses all bronze except the anode itself, it is a modified garboard drain plug that allows the anode to be attached to the bottom of the hull, but like your example above is electrically connected to the keel winch.

I've been slacking, too many distractions... I'll have the finished and installed product ready soon and will post pictures!

 

[$tingy Sailor]

Allen-deckard,

The post you quoted sounds like somebody thought an anode on the INSIDE of the hull would work. I cannot imagine a scenario where that would do anything, as one of the participants found out while his keel was being eaten away.

What CloudDiver is working on is a remote anode on the OUTSIDE of the hull, which should work hunky-dory.

 

[Ralph Johnstone]

Zinc can also shrink your Prostate! Chief

Chief, that's probably the most relevant statement posted here on anodes, zincs, whatever :bang:

If you want an anode on your keel that's up to you. The anode has to be IN the electrolyte (sea water) along with the object being protected (your keel). And no, you can't keep the zinc in your sock drawer.

However, don't drill a hole in your keel, it's got enough problems in life without another hole through it. Use an overboard zinc and attach its wire to a cleaned keel bolt. If it's a keel stud(s) coming through the hull into the bilge, use two nuts to compress the wire between them having first slathered the wire with a good waterproof grease.

 

[jmczzz]

Wire to a keel bolt sounds ok, but I can't figure out how to mount the anode on a C22 with swing keel.
I need to proceed and make a decision on anode replacement. As no "new" method is available I will proceed with the current method of anode mounting on the keel. Unless advised other wise in a timely manner. I must proceed so as to get my boat back in the water. This in no way is to dispute any "new" method, or denigrate its advocates.
James

 

[Ralph Johnstone]

Wire to a keel bolt sounds ok, but I can't figure out how to mount the anode on a C22 with swing keel.

My description of an overboard zinc may have been a little abbreviated.

As shown below, when the boat is not under way, the zinc is lowered overboard in the vicinity of the keel to be protected. The attached wire is lead back into the boat to the swing keel bolts, device or whatever means of attachment and permanently connected. This MUST provide good electrical contact ( 0 ohms).

Before the boat is to move, the zinc plate is brought aboard and stowed. A plug can be used as long as no (almost zero) electrical resistance is present in the wiring.

 

[jmczzz]

Oh, that makes since. So it is primarily for when boat not underway. Is the assumption being the most electrolysis happens while a boat is not underway? I guess that is generally true. Thank you for the clarification / explination on how it works.
James

 

[Charles Erwin]

Assuming the objective is to protect the swing keel metal then paint/epoxy/some other coating is the first line of defense. If that were a perfect coating then no anodes required.

Coatings are not perfect and the concern becomes avoidance of possible electo-chemical activity which will be going on when the boat is in the water because coatings are not perfect.

On the other hand - all things considered and depending on the keel metal recipe - the keel material will not degrade very fast anyway because it is not connected to more noble underwater metals. Even if so - as long as the coating is kept up then the degradation process will be very slow.

So it would seem Ralph has a good approach (zinc over the side) because most the time the boat is sitting still - unattended. Thus the keel material will be protected while the boat is sitting still and that is pretty good protection because the boat is parked most of the time.

Charles

 

[jmczzz]

Thanks, This is begiining to sink in to the rusty brain cells.
James

 

[Charles Erwin]

Forgot to ask: are you in fresh water? If so then you can probably dispense with any anodic protection but if you insist then better make it magnesium

Chalres

 

[CloudDiver]

CAN"T BELIEVE THIS NEVER OCURED TO ME, D'OH!!! LOL

My description of an overboard zinc may have been a little abbreviated.

As shown below, when the boat is not under way, the zinc is lowered overboard in the vicinity of the keel to be protected. The attached wire is lead back into the boat to the swing keel bolts, device or whatever means of attachment and permanently connected. This MUST provide good electrical contact ( 0 ohms).

Before the boat is to move, the zinc plate is brought aboard and stowed. A plug can be used as long as no (almost zero) electrical resistance is present in the wiring.

 

[CloudDiver]

This is what I have cooking, just a preview;

 

[jmczzz]

Charles, Yes I slip in Fresh water. I do plan a Gulf of Mex. cruise next fall. Based on your comment, itmust be non critical in fresh water. That is good to know. I come from the North Gulf so have always kept the zinks serviced on prior boats.
thank you, James

 

[jmczzz]

C D, looks good but how / where to connect? James

 

[allen-deckard]

I just want to pipe in on one thing. The fresh water comment that it isn't really necessary if I read that right?

Yes it is very necessary. Kept my boat in a slip for 4 years (in and out not just sitting there obviously) in fresh water before moving to the florida keys and fresh water will do a number on your keel trust me for some reason and I'm not even going to try to figure out why but I had more corrosion issues on my keel in fresh than salt here. (barnacles not that's another issue) Anyway yah in a nutshell you really need the zinc in fresh as well it really does make a difference. And for the ounce of prevention that it takes to put a zinc on no mater how you do it beats the crap out of refinishing your keel as I've done as well.

 

[CloudDiver]

C D, looks good but how / where to connect? James

The bronze fitting is called a 'garboard drain plug', it requires a 1 & 1/8" hole drilled through the hull. An additional fiberglass backing plate is epoxied where the hole will be drilled to ensure a total hull thickness of 1/2" of solid fiberglass. I will use 4200 adhesive to bed the fitting, and there are 3 #8 x 1/2" screws that secure the flange to hull. The plug that threads into the center of the fitting is screwed in from the inside of the hull, and has been drilled and blind tapped on the bottom center for a 5/16" bronze bolt. The reason I used this method is because bronze has better conductivity than stainless steel, and the entire fitting is completely serviceable and/or replaceable. The plug can also be replaced with an off the shelf zinc pencil anode because it comes with its own 1/2" NPT plug fitting.

More details and a complete write up with pics will be posted on StingySailor.com very soon.

 

[jmczzz]

Allen, lots of good intentions on this forum but sometimes that is not enough. I will get a magnesium anode and hang it over the side while my boat is in the fresh water slip connected per Mr Ralph Johnstone's post. Thank you for your input.
Better safe than sorry.
James

 

[Charles Erwin]

Depending on the content of the iron used - yours were cast in Mexico - the chemistry of the fresh water in which the keel is submerged and whether the keel is electrically connected to other dissimilar metals galvanic corrosion can be a threat. Allen's experience shows that some combinations will produce corrosion but other slightly different combinations will not. Keeping the coating intact is the best protection.

As to anodes - pancake anodes through bolted and in contact with the bare keel metal are quite effective. However, in fresh water these need to be aluminum or magnesium - zinc is not active enough. If fixed anodes are intact and active no need for an over-the-side anode. If you don't have fixed anodes then an over the side anode will do the job.

The central point is - if you fear galvanic activity or you are actually seeing galvanic corrosion - then anodes will help. But - no matter whether anodes are necessary in every case - using them will not hurt anything.

Charles