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Old 06-01-2014, 13:41   #1
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Aluminum hull anodes

What kind of anodes do you fit on your aluminum hulls? The ones I had for the last 8 years were probably zinc and they lost less than 10% in that time. What material is best? Where can I find them in Thailand? Someone stole my old ones in the boat yard during my refit.

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Old 06-01-2014, 14:29   #2
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Re: Aluminum hull anodes

Is the boat in fresh water or salt water? Fresh water use magnesium and in salt use zinc.

The reason I asked is 10% used is small for the salt in 6 years. Zincs tend to get a white coating that has to be clean brushed off as the white used zinc coating protects the unused zinc. Besides getting new anodes, might want to check if they are protecting the boat.

Here is a site of world wide zinc manufactures. China is a main supplier. Moat marine stores/supply should have them. Zinc Anodes Manufacturers, Zinc Anodes Suppliers & Exporters on Alibaba.com
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Old 06-01-2014, 15:10   #3
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Re: Aluminum hull anodes

Zinc should be ok, the fact that they havn't been reduced all that much "generally" means that you don't have any corrosion issues. (keep away from shore power if possible as most use a common earth system which can transfer someone else's issues to your boat) If you must connect to it use an isolating transformer.
You can use aluminium indium annodes instead, they are more expensive and imho don't do anything that the zincs don't. I have used both, currently have the "A I" ones fitted only because I already had them. Once they are used up (could take some years) I'll go back to zincs.
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Old 06-01-2014, 15:34   #4
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Re: Aluminum hull anodes

Zinc is for salt water, aluminium for brackish, and magnesium for fresh water. The different metals have different electrical potential, with the more reactive (mag) being prefered because of the low conductivity of fresh water relative to salt.

You can use mag (or aluminium) is salt water, but they are likely to overcompensate, and can corrode away much faster.
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Old 06-01-2014, 16:15   #5
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Re: Aluminum hull anodes

Aluminium annodes will not corrode away faster unless there are electrical issues, stray currents etc. Every electrical connection should if possible be above earth. Sometimes difficult with engines as they need have to have the starter motor, temp and oil sensors and alternator isolated from the block / hull.
On my boat although I have the alternator and sensors above earth I have been unable to get a starter motor that is. Therefore I isolate the motor whenever it is not in use. Over the last 8 years this has not shown to be a problem.
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Old 06-01-2014, 16:22   #6
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Re: Aluminum hull anodes

Any anode that last 8 years is an anode that is not working.
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Old 06-01-2014, 18:14   #7
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Question Re: Aluminum hull anodes

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Originally Posted by Steve Pope View Post
Aluminium annodes will not corrode away faster unless there are electrical issues, stray currents etc. Every electrical connection should if possible be above earth. Sometimes difficult with engines as they need have to have the starter motor, temp and oil sensors and alternator isolated from the block / hull.
On my boat although I have the alternator and sensors above earth I have been unable to get a starter motor that is. Therefore I isolate the motor whenever it is not in use. Over the last 8 years this has not shown to be a problem.
I will go with zinc based on your advice. My boat is in Phuket in only salt water. I have a new Beta marine diesel engine that is designed for aluminum hulls and it has a built in isolation switch that prevents current flow from the batteries when the engine is not used. My isolation transformer rusted away a few years ago and has been removed. I need a new one if I can find one but my boat is 110 volt and in Thailand it is 220 volt so it will not be much use here. But I really don't use any shore power since by boat is always on her mooring in Chalong and I really don't need it anyway since i have solar panels and have a enough power from the engine alternator that I have to run when I cool down the fridge for one hour per day or when I am under power.

My question now is how to attach the anodes to the hull. My boat is built in 1982 at Kanter Boat Yard in Ontario, Canada and they welded anode pads made of aluminum to the hull with threads in them and the old anodes were attached to those pads with two stainless steel bolts that hold the anodes firmly to the aluminum pads. I have read that the bolts should be galvenized steel, but worry about corrosion in those bolts. I plan to sand those pads and the surface of the new anodes and hold them firmly to the welded pads and then paint the exposed surface surrounding the anode with epoxy primer and antifouling careful not to get paint on the anodes. It was recommended to use isolation paste between the threads of the bolt where they go into the aluminum pads but I am not sure if this is the right way. Also, on other websites they talk about washers between the steel inside the zinc anode and the bolt head. Any advice about this? Or am I getting too carried away!
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Old 06-01-2014, 20:47   #8
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Re: Aluminum hull anodes

Use galvanised or plated steel bolts, they wont rust as long as the zinc is there, a little bit of lanocote on the threads or some such similar lubricant will do the trick, try to get a good metal to metal contact where the zinc strap (metal bar) comes in to contact the with the hull.
fstbttms, nowhere did I say the zinc or A I annodes had been used for 8 years
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Old 06-01-2014, 21:07   #9
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Re: Aluminum hull anodes

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Originally Posted by Steve Pope View Post
fstbttms, nowhere did I say the zinc or A I annodes had been used for 8 years
Sure sounded like it to me.

Quote:
Originally Posted by thaisail View Post
The ones I had for the last 8 years were probably zinc and they lost less than 10% in that time.
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Old 06-01-2014, 21:13   #10
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Re: Aluminum hull anodes

Ahoy, I have an ally sloop in thailand as well. Have a mixed set of anodes, some aluminium, some zinc.
The aluminium anodes dont corrode, the zinc ones from Malaysia do, I change them every year.
The anode on the prop shaft corrodes as well.
Have had corrosion in the hull, on the inside where water sat in some shallow bilge areas, never on the outside!
I have stainless bolts hold the rudder and prop shaft anodes together.
The hull anodes are aluminium bolts welded to the hull, with stainless nuts, some corrosion there, so it would be sensible to do as you were advised.
You can buy nylon bolts or aluminium bolts to prevent corrosion!
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Old 06-01-2014, 21:17   #11
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Re: Aluminum hull anodes

My anodes have the zinc bar embedded in the zinc and that bar has two holes drilled in it. The bolts go through the holes and about 1/2 inch of zinc separates the steel plate from the aluminum plate that is welded to the hull. So I am wondering if the former owner was right to use stainless bolts relying on a good metal to metal contact between the zinc and the aluminium.

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Old 06-01-2014, 21:18   #12
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Re: Aluminum hull anodes

Sorry I meant to say the steel bar embedded in the zinc.

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Old 06-01-2014, 21:24   #13
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Re: Aluminum hull anodes

Avast, the aluminium anodes are solid aluminium and have no steel inserts, maybe better to use these, they are more expensive and corrode less. But, better they corrode than the hull?

The anodes on my prop shaft corrode the quickest, and the motor has all electrics isolated from the hull.
even the starter motor is isolated, it has a huge double pole solenoid that closes the positive and negative feeds to the starter only when the motor is cranking.
Cheers from Keith.
ps.. stay out of marinas or store the yacht on the hard stand and never connect to the shore power in a marina!!!
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Old 06-01-2014, 21:28   #14
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Re: Aluminum hull anodes

Ahoy Keith, I have a different style of anode than the one in your photo. I think after seeing your photo I will stick with the stainless attaching bolts. My email address is thaisail@gmail.com . I would like to ask you some questions about antifouling and boatyard in Thailand.

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Old 06-01-2014, 21:47   #15
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Re: Aluminum hull anodes

Maaaate.. I am in Krabi boat lagoon, 50% discount off of all rates, lifts and berths.
Use international aluminium antifoul paint from eastmarine shop in boat lagoon phuket, only lasts about 6 months. Cant use the strong copper or tin based paints. Did mix 1 kilo of powdered chilli powder into 4 litres of antifoul a few years ago and that provided better protection!!!! But a rougher, pinkish colour and texture!
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