Anode on thru hull

[southernman 73]

Just about to put boat in drink but noticed that one of my thru hulls is not plastic, don't have time to remove it until next year but it has had an anode mounted around the outside of it which had basically gone.  There are two bolts used to mount it.  

 

Can anyone direct me where I would find a round anode to go around the outside of the thru hull?  

 

Also where is the best place to buy an anode set for Yanmar sail drive?  

 

Cheers from the weather bomb south.  

[wheels 543]

Is it a glass hull? I assume the fitting is bronze. If yes,you don't need an Anode
Providing you have no electrical bonding to the fitting on the inside, the fitting is isolated and will be happy on it's own.
If it is a steel Hull, the Main Hull anode will protect the fitting.
The only time you need an anode, is if you have a timber Hull. And even then, the best way is to tie it to the main anode via an electrical wire on the inside. It would be very hard to fit an anode to the fitting and get it protected properly due to size. An Anode works by surface area exposed to the water and it has to be in relation electrically to the surface area exposed to the water of the skin fitting. Too much anode and the current runs backwards and can cause problems.

[southernman 73]

HI Wheels, glass hull, fitting would likely be bronze by the look of it, it's had an anode fitted in the past, a little bit of the anode remained. but had been covered with anti foul paint.  I'm not in AKL now so can't get a photo but it has two small mounting bolts to bolt an anode around the outside of it.  It's not bonded electrically, none of them are.  

 

It's in good condition by the looks, however will replace next year with plastic all round and plastic seacocks.  

[waikiore 398]

Anode set for Yanmar saildrive in Nelson - Nick at Aimex he is the dealer

[wheels 543]

it has two small mounting bolts to bolt an anode around the outside of it.

 

 

should the SS bit get some sort of protection?

No need for protection on both accounts.

For galvanic action to occur, you have to have two dissimilar metals in contact with one another and then submerged in an electrolyte (like Saltwater). This is exactly what a battery cell is. The two different metals want to play trade the electron, or for KM, the electrical bugs want to go wandering off and as they do so, they carry away an Atom of the least noble metal. So for any metal on it's own in the Water, nothing happens. It has to have an electrical connection to another metal of different Nobility. The greater the distance apart of the Noble scale, the more voltage flows in the circuit and the faster the metal depletes.

[wild violet 38]

Aimex in nelson is very expensive on yanmar parts got burnt bad last year

[southernman 73]

So wheels effectively you are saying I don't need an anode on my thru hull?  However if the valve is of a different material then I would potentially right?  

[Zozza 293]

So I think I got 5 in chemistry in school...that's 5%.

 

I have an anode on my hull, which you can see in the middle of the attached pic.

 

My boat is GRP.  I've removed the inboard engine, the prop, and all thru-hulls have been glassed over - apart from that anode.

The only metal below the waterline will be the prop of outboard motor when in use, and the lower bolts and pintles for the rudder.

The only reason I kept the anode on is I asked the boatbuilder helping me out with my boat refit if I should keep that anode on, he said "Yes".

However, my goal was always to get rid of ALL holes below the water line,  So, from what I am reading here - I don't need that anode at all, and I can remove it, glass it up, and one less thing to worry about, Right / Wrong?

[wheels 543]

 

 However if the valve is of a different material then I would potentially right? 

Yes.....technically......but not sure why you would use different metals. If you have a Bronze Through Hull, you would use a Bronze Valve. A SST Through Hull, you would use a SST Valve. Or of course you could go the Nylon or Composite Valves and then it does not matter, but then you might has well have used the same material for the Through Hull. I think it is Survey only that requires the use of Metal Through Hulls/Valves for fire purposes. Although I always thought it funny, because if a fire ever gets to the level of melting a Through Hull, then you are not really going to be concerned about the Boat anyway.

 

So, from what I am reading here - I don't need that anode at all, and I can remove it, glass it up, and one less thing to worry about, Right / Wrong?

Right.

Plus, if the Anode is just stuck on the Hull, it will be doing nothing. The anode must be connected electrically by a wire to any metal in the water, or it has no circuit. So if it is not connected to the lower bolts etc, it won't protect them anyway. If the Bolts are SST and the Pintles are SST and the SST is not connected to any other type of metal, then no you don't need the anode. In fact, the Anode will likely be gaining a white coating on it, or have gone a very dark dark grey like Anchor chain does. The white is Zinc Oxide and a sure sign it is over protecting and working in reverse, which is as bad or in some cases, worse than no anode at all. I have seen lots of damage done by over protecting. It can blow Paint right off a Hull very much like you have bad Osmosis.

 

The main reason most Glass Boats use an Anode is for the Protection of the Bronze Prop, that is mounted on a SST shaft. The Bronze is a mix of Copper and Zinc. Unprotected, the Zinc, being less noble than Copper, leaches out of the Bronze and you are left with a crumbly pink metal that is just a porous copper material. After the zinc goes, the copper then goes and you are left with nothing.

 

If you ever find pink patches on the Bronze Prop, it is a sure sign something is not connected properly or the Zinc had eroded away before you got the boat out for replacement.

For those with saildrives, the anode protects the Alluminium as well.

[Zozza 293]

 In fact, the Anode will likely be gaining a white coating on it, or have gone a very dark dark grey like Anchor chain does.

 

 

Yes! Its gone a gray / chalky white colour!

 

Thanks Wheels. Great info as per usual.\

 

And yes, pintles and bolts are stainless steel

[Dagwood 57]

A very interesting article on the issue with regards to timber boats here: https://waitematawoodys.com/2015/05/15/electrochemical-damage-to-wood-the-marine-version-of-leaky-homes/

[wheels 543]

Wooden Boats are certainly a mind field when it comes to protection. The Author in that article is correct in many respects, but I also think he made a few mistakes.
The first mistake is the test sample and the Anode. he made the comment he wanted to speed the result up. Correct, he would indeed, but that would or should not be the way it would work if the system is set up right.
He is also spot on re the older days with the metals available then. Everything was bronze. So you didn't have an issue. This is also why i have said several times that the new electrical requirements for the DC system is wrong to be included in an EWOF. Because in some situations, to be forced to bond may in fact be bad for the boat.
He is also correct that bonding can be bad. I also have always said that there are two ways to do it. Bond everything, or bond nothing. But I stress here that either way does require some very important requirements. Today we use anodes simply due to having so many dissimilar metals. Those with the Classic Wooden Boats need special attention and some expert advice. The thing is, many wooden boats do have dissimilar metals and they do need Anodes. I have seen the exact same result as the author has described take place in the timber due to no anode. It is important to have the right anode and the means of monitoring and control of the currently flowing, protecting the metals.

 

[harrytom 642]

This reminds of a yacht I had 3 yrs ago that sunk due to electrolysis,bronze thru hull with a s/s ball joint with a copper tail.little did I know that the ball joint had eaten thru,insurance co sent part off to metal tester to confirm that was the issue.The yacht had passed a survey at time of purchase.