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on wooden boats the main area of concern is principally the stern gear, propellers, shafts, shaft brackets, stern tubes, rudders and keels.

 

Not only are these expensive to replace but they are vital to the safe boating.

 

And the 'zinc' must be in direct contact with metal it is there to protect in order to be effective.

 

So, if your propeller and shaft are of dissimilar metals, e.g. a bronze prop and stainless shaft, then you should fit a shaft anode, one for each shaft.

 

For the same reason on a metal rudder it should be bolted directly to the rudder.

 

There are plenty of wooden boat owners who are happy not to use any zincs.

 

They feel that their boats have a minimum of dissimilar metals, the water contact between them is not a problem and they are not concerned about stray current.

 

Personally I feel happier having at least one main one located on hull just below the turn of the bilge.

 

http://www.diy-wood-boat.com/Anodes.html

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This is an incredibly complex topic, particularly for wooden boat owners and there are a lot of misnomers and a range of 'theories' out there. Most of all it not a topic to be approached by google alone. Get some proper advice specific to your vessel.

 

In terms of what is available on line the following IMHO is the best resource for a wooden boat owner to consider before doing anything. its completely different for glass, alloy, steel etc but this is for wood...

 

http://waitematawoodys.com/2015/05/15/electrochemical-damage-to-wood-the-marine-version-of-leaky-homes/

 

We are 89 years old and Kauri so its a topic we take really seriously.

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This is an incredibly complex topic, particularly for wooden boat owners and there are a lot of misnomers and a range of 'theories' out there. Most of all it not a topic to be approached by google alone. Get some proper advice specific to your vessel.

 

Agree 100%. I saw this last night and was too tired to reply because I knew I would not cover something.

While Wood is free from electrolysis itself, it can still be damaged by the influence of electrolysis from metals. Timber under the waterline will go soft and fury if Anodes are not kept up on the metals. But it can be damaged just as easily with too much as well as too little.

As erice has stated, all metals (because there as dissimilar) need to be protected. This can be difficult because the Wooden hull acts as an insulator. So all metal parts need to be bonded so they are all covered by an anode. For instance, the lower bearing block(if it is metal) the Rudder shaft swings in needs to be bonded to the rest of the metal.

If you do not bond something, then it must have its own anode.

Personally I hate shaft anodes. They always erode unevenly and can cause vibration in some instances and sometimes will throw themselves off and well any silly thong really. Then others work perfectly. But to not use a shaft anode means you may need a shaft brush so as it is bonded to the rest of the metal.

You can work a ruff rule of thumb for anode size, in fact there is a calculation of surface area to be protected to anode size. Any Marine sparky should be able to do any one or more of three things. From experience, he should be able to judge a size of anode that will be about right. He should be able to throw a cell over the side and measure the exact electrical current and match and anode to suit. Or he should be able to work the sum of area to size of anode.

Remember that the anode needs to be able to protect for a year, till next haul out. Hence why no hard and fast rule, although Timber needs to be a little more accurate than many other materials, because often the Paint used was simple one pot and the timber was thus not fully insulated like say Epoxy over steel.

If you wanted something accurate, there used to be a special electrical meter with adjustment knob available, that you installed by all the other electrical panels, that maintained a specific electrical current flow for the life of the anode. Which means you could fit a large anode and then adjust the current flow as the anode erodes away. Over my life time on boats, I have only ever come across two of these installed.

I have never seen one for sale anywhere. I would love to know if they are still available.

 

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IPC systems are something I have no experience with. What little I do know is that they have both an Anode and Cathode underwater and a DC power supply. I have no clue if the Anode is Zince or not and would think probably not, but it is possible the Graphite thing was the Cathode. IPC systems are used on large scale structures/ships where large areas need protecting in which the use of anodes would mean anodes all over the place.
The unit erice has posted a link and pic to is rather a lot more simple. The Anode is physically isolated from the Hull and connected via cable to the meter and control, then via a cable to the Hull. The control knob simply adjusts the current flowing through the anode, so as the best possible current is achieved. As you see on the display, you can have too much or not enough protection. It offers greater control of anode depletion and current over the life span of the anode.

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If you think the anode placement on a wooden boat is a science akin to witchcraft, try owning an alloy yacht covered in a layer of epoxy fairing compound with a cast iron engine, lead keel, alloy sail-drive, bronze prop and stainless steel rigging.

 

I have absolutely no idea what i should be doing with anodes and neither do most people i talk to. I have one on the saildrive that appears to be doing something and I have a fish type anode on a wire that i through overboard in the marina that does nothing apart from collect slime.

 

Each time i haul out for anti-fouling I tap around the hull looking for delam that might indicate electrolysis/corrosion (or whatever its called)  and so far haven't found anything suspicious, hence I hope I'm under control and not slowly dissolving.

 

As far as i can tell, no-one really seems to understand how it should be dealt with apart from applying some common sense, vigilance and crossed fingers.

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have got a frp boat with a tiny bit of stainless drive shaft sticking out and a large vetus 3 bladed bronze prop

 

prop sm.jpg

 

no space for a shaft zinc so it has a vetus zinc screwed on the end of the prop

 

looked today and it was gone!

 

once before it had unscrewed and disappeared

 

so had replaced it with a half eroded 1 from the box of spares

 

this time the allen bolt was still there so it must have eroded too much and fallen apart

 

put another half eroded 1 on, fortunately can easily see it and reach it when the dinghy is at the stern ladder

 

 

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As far as i can tell, no-one really seems to understand how it should be dealt with apart from applying some common sense, vigilance and crossed fingers.

 

Tuffy, you don't have to worry about any metals not in the water. So engine and rigging and anything above water or inside the boat, have nothing to do with the Anode protection.

It is fairly simple to understand and the same rules apply to all Boats/metals. The metal that is the least noble will be sacrificed first. Once that has gone, or nearly gone, the next metal on the scale will be sacrificed and so on. Zinc is the least noble of all the metals used on Boats and thus the use in Salt water. In fresh water, the use of magnesium is better than Zinc. For an Aluminium Hull, the Ally is closer to Zinc than Steel is. So it is essential that the correct flow of current occurs and in the right direction. A Marine sparky "should" have a meter to be able to test the current flow with anodes in the water and select the correct size. With all Hull materials, too much anode can be as bad as not enough, but Ally is just that little more important. 

In saying all that though, it is only due to the other different metals you have in the water. So if the Hull, Saildrive and hull are all Ally, then there is actually very little protection required. Allumimium on it's own is totally fine on the water. The only part that is a different metal is likely the SST shaft sticking out the saildrive to the prop. The Nut on the end of the Prop also and that is all that is actually of concern to the rest of the Ally. So you actually have a fairly non scary situation and the "fish" anode over the side is doing nothing. In fact if anything, ot could actually cause a reverse current and the easiest way to check that is if the Anode is covered in a white material. That is Zinc Oxide and it means the anode is working the wrong way. On other material Hulls, this same result can mean too big an anode or "over protection" and that can be just as bad as not enough.

Your bigger concern will be above waterline. Galvanic corrosion, that's corrosion of the Ally between it and another metal like SST, is a concern and well, you most likely know about isolation and insulation etc etc.

I hope that helps.

 

 

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Good info thanks Wheels. Nice to know Im not slowly dissolving

 

Very familiar with the galvanic corrosion, ice cream container plastic washers and lanoline seems to take care of that although the boat does have a slightly erotic smell of sweet toothed lamb.

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with a f/glass cat with 2 motors and just the s/s shaft and bronze props in the water would it be worth removing the props if the boat was going to sit unused for say 6 months, would that mean no protection required? Assuming that the props weren,t too hard to remove that is.

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I could show you a kiwiprop totally destroyed by the lack of anode. The owners of the boat read what was posted above on the waitemata woodies site, removed the anodes altogether , went naked you could say, and the prop is now cheese.

So I just do not know, I have the greatest respect in the world for Chris McMullen, he absolutely knows what he's talking about and all that he says make sense... a real education on electrolysis and delignification.

 

And yet, the propeller is years old , was fine , anode gets left off the shaft, prop is dead in a year. They have put a new folding prop on the boat, my bet is it will be eaten too, by the time the boat is hauled in july or so.

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Sure John, you can't beat stupidity! I said a Kiwiprop has LESS metal, not none! In no way does it remove the requirement for an anode, only the blades are not metal, the hub and associated mechanisim still is!! :wtf:

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Yes , its a mess, the boss all corroded and the stops gone or about to go where they are threaded in.

I've always had a shaft anode on the boat, my current ( cough)boat has a hull anode as well. I'm not messing with it because there is no problem that I know of.

 

Once ,many years ago, I doubled the anode on my old boat. It came about because I changed props and the new one had an integrated anode on the boss. I left the shaft anode on and within a few weeks I had paint dropping off. Removed the shaft anode, problem went away. So I know about over anoding a boat.

I suppose what we could take from it is just to have minimum sacrificial anodes, something to divert those pesky little 'trolysis mites attention away from the propellor and leave it at that.

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Ha, I can show you an Ally prop totally destroyed by having Cooper antifoul applied to it and stern leg. It had more holes than Swiss cheese.
 

 

with a f/glass cat with 2 motors and just the s/s shaft and bronze props in the water would it be worth removing the props if the boat was going to sit unused for say 6 months, would that mean no protection required? Assuming that the props weren,t too hard to remove that is.

Would you not still have stern tube/bearing/what have you, all of bronze, that the SST shaft is running through, needing protection?

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