killick
New member
Advice to a recent tread indicated that only dissimilar metals should be connected to an anode.
The shaft anode makes sense but what is the hull anode doing?
The shaft anode makes sense but what is the hull anode doing?
ANODES
- Thread starter killick
- Start date
prv
Well-known member
Being connected, via an internal wire, to the shaft. Usually via a bolt on the gearbox, assuming there's no rubber components in the drivetrain which would insulate it.
If there's no such wire, then the anode isn't doing anything
Pete
pmagowan
Well-known member
Being connected, via an internal wire, to the shaft. Usually via a bolt on the gearbox, assuming there's no rubber components in the drivetrain which would insulate it.
If there's no such wire, then the anode isn't doing anything
Pete
My one is connected as above but with a wire bridging the gap where there is a plastic component
VicS
Well-known member
An anode must a have a good electrical connection to anything it to protect.
This means that flexible shaft couplings must be bridged if a hull anode intended to protect the prop and/or shaft is connected to the engine block or gearbox casing.
(A possibly poor electrical circuit via the, hopefully well oiled, bearings is usually glossed over !)
An alternative is a brush system ( eg MG Duff's "Electro Eliminator" ) making direct contact with the prop shaft immediately inboard of the stern gland.
In addition to the electrical connection an anode must also be reasonably close and within "line of sight". The latter not too literal but at least not shielded from what it is to protect.
MG Duff recommend a minimum wire gauge for anode connections.
This means that flexible shaft couplings must be bridged if a hull anode intended to protect the prop and/or shaft is connected to the engine block or gearbox casing.
(A possibly poor electrical circuit via the, hopefully well oiled, bearings is usually glossed over !)
An alternative is a brush system ( eg MG Duff's "Electro Eliminator" ) making direct contact with the prop shaft immediately inboard of the stern gland.
In addition to the electrical connection an anode must also be reasonably close and within "line of sight". The latter not too literal but at least not shielded from what it is to protect.
MG Duff recommend a minimum wire gauge for anode connections.
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l'escargot
New member
Mine is also connected to the P bracket and steering gear.
pmagowan
Well-known member
VicS, you seem to know about these things, in a non-metal boat would it not be best simply to have one anode attached to the prop and shaft, like a cone. Assuming a standard drive train (no funny saildrives etc) with perhaps a 'rubber' isolator somewhere up the line for vibration control (?an aquadrive). Why do we tend to have them sitting at the side of the hull somewhere attached by a wire? I have heard pros and cons to bonding through-hulls etc. Sometimes I think I understand it and then I glaze over again and magical galvanic currents confuse my brain.
prv
Well-known member
A number of boats in our yard have exactly that. A shaft anode or two and nothing on the hull.
We have a saildrive, which has one anode on the leg to protect it and another on the prop to protect that (the two are electrically isolated as a side-effect of some rubber shock-absorbing arrangements). No hull anode needed or fitted.
Pete
vyv_cox
Well-known member
When I first bought my boat it had a hull anode attached to the engine earth and a skin fitting for the supply to the engine. I removed it and filled in the bolt holes before I ever launched. I have a prop anode for my Bruntons, and a shaft anode because without it the prop anode corrodes one per year and it costs a bomb. That's all. I have owned my boat for 20 years, no corrosion problems. I have an Aquadrive, as you suggest.
Through hulls made from a corrosion resistant alloy such as bronze or DZR do not need any other protection. Bonding is totally unnecessary and may very well be harmful (Google Random Harvest)
RichardS
N/A
If it's a Yanmar saildrive you probably also have a third anode on the raw water inlet near the sea cock.
Richard
prv
Well-known member
pmagowan
Well-known member
So, essentially the only thing we are concerned about is the propshaft and prop. The through-hulls can take care of themselves as long as they are made from a suitable material. Then comes the other magic of the galvanic isolators. If your through-hulls are not bonded, your anode is on the prop shaft and the prop shaft is isolated from the engine, do you need one?
Tranona
Well-known member
You may well find with your boat that you have no need for an anode at all as older props are often better material than newer ones. Anodes on a wooden hull can cause more problems than they solve. Make sure the mounting studs for the anode are well insulated from the surrounding wood - I sealed the holes with epoxy after experiencing some decay of the wood around the studs on my boat. You could indeed just use an anode on the prop or shaft. However this is often impractical on boats which do not have any exposed shaft such as you get if you have a P bracket. You can get anodes mounted on a special lock nut on the end of the shaft, but they are very small and expensive.
On my boat I have an anode on the feathering prop and a hull anode connected as yours, and also to the stern tube. However they erode very slowly which suggests there is very little going on and the props, neither the original fixed one nor the fancy one have shown any signs of dezincification. For the first 20 years of its life the boat had a bronze shaft and prop and no anodes. The hull anode was only fitted when a new engine with a stainless shaft and "cheap" prop was installed. Still not convinced it was absolutely necessary.
pmagowan
Well-known member
Is there a way you can detect if one is necessary? Can you pick up the galvanic differences with a multimeter? If you were starting from scratch is there some way you could avoid the need for an anode at all, such as the bronze prop shaft Tranona mentions. I was wanting to make my own bronze fittings just for fun. I have a lot of copper as I am removing my central heating system due to installing insulation.
vyv_cox
Well-known member
It's the tin that is the expensive component, even with today's inflated copper prices. Casting bronze is quite tricky because the tin oxidises and forms a skin against the air. Phosphorus and/or zinc are added to the mix to take out some of the oxygen. When casting bronze the molten metal is poured without moving the ladle, which allows it to pour through the oxide 'tube'. You will need a pretty good heat source as copper melts at almost 1100 C.
pmagowan
Well-known member
The heat source should be easy enough with a combination of gas, old heating oil and an air line. I will probably use the lined barrel method where you pack insulation and refractory cement in the middle. Otherwise I will simply build one out of brick in the garden but portable would be better. Not sure about the tin or where I could salvage some. I am sure I could get hold of some. I have seen a number of videos of people doing it with various additives. I will obviously research the exact quantities required. I will likely start by making a few bits that have minimal importance for practice. It will be for fun rather than out of necessity. I will be getting in a metal lathe for other jobs anyway.
lpdsn
New member
Unless your boat is made of Zinc, wouldn't all other metals be dissimilar?
VicS
Well-known member
I ought to know more than I do so trying to learn as much as possible
Your questions seem to have been answered while my bb connection was down
Technically there would be no need for a GI if no underwater appendages are bonded to the shorepower earth ... I'd keep an eye on things though.
You can determine the "galvanic differences" from a galvanic series table.
Many on line .... I have this one bookmarked http://www.corrosionsource.com/FreeContent/1/Galvanic+Series.
If you are interested in monitoring the protection then you need a reference electrode ( eg silver/silver chloride) to use with a high impedance volt meter. Google Galvatest for a bit more info.
Think the reference was probably to protecting items where differnt metals are used together i the construction. eg a manganese bronze prop on a stainless steel shaft or a folding prop made of a mixture of nickel aluminium bronze and stainless steel components.
Also used to protect vulnerable structures eg steel hulls or saildrive legs as well as in the dissimilar metals scenario
pmagowan
Well-known member
Interesting. Currently I am connected to shore power via a CTEK M300 charger which simply plugs into an extension cable. I have no idea if this puts me at risk. I have no 240v system on board and any charging of phones etc is done through a cigarette lighter socket.
I looked up the Galvatest idea. It looks interesting but I would not really use a bit of kit that required set-up each time. It could be an interesting project to work out how a sensor could be permanently mounted to monitor things. There is the potential for some kind of alarm or disconnection device if there was a significant galvanic current or if the anodes were no longer working. Just an idea and probably more geeky than practical.
I looked up the Galvatest idea. It looks interesting but I would not really use a bit of kit that required set-up each time. It could be an interesting project to work out how a sensor could be permanently mounted to monitor things. There is the potential for some kind of alarm or disconnection device if there was a significant galvanic current or if the anodes were no longer working. Just an idea and probably more geeky than practical.
prv
Well-known member
I'm not sure if they measure exactly the same thing (it's all a bit of a black art to me) but I believe aluminium boats are sometimes fitted with a device that turns on a warning light if there are galvanic problems. Particularly popular in the US.
Pete
Shiver Metimbers
New member
Should the cast iron keel be connected to the hull anode?