how does an anode work?

[claytonr]

How does a corrosion anode prevent other parts of the motor from corroding?

 

[claytonr]

Re: how does an anode work?

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[zzzzz]

Re: how does an anode work?

 

[carmangary1]

Re: how does an anode work?

That isn't exactly correct. It has to do with electrical properties and has nothing to do with how soft the metal is. I can't remember the details but it has something to do with the anode being able to absorb or give off electrons more easily than the other metal. This causes it to corrode first. They are sometimes called "sacrificial" anodes because they are sacrifised in order to save the other metal.

 

[Paul Moir]

Re: how does an anode work?

zzzzzzz??? - lead is a terrible anode<br /><br />If you put two different metals in a conductive solution (ie, acid, salt water, bases, even 'fresh' water) and hook a voltmeter to them, you will read a voltage. If you electically connect the metals then current, or electrons, will flow. The less 'noble' metal is the one which will give up it's electrons. When it does, it reacts with oxygen in the solution to steal them back from it.<br /><br />Oxygen + metal = rust, or corrosion. This type of corrosion is called Galvanic Corrosion.<br /><br />Here's a table called the galvanic series. It lists metals from the most to least 'nobel'. The further apart metals are on the table, the more agressive the Galvanic action is going to be.<br />Say you drop your outboard in the water. The parts that touch the water are most likely going to be stainless steel and aluminum. They're not very far apart on the Galvanic series, and so Galvanic corrosion will be minimal. This, of course, is no accident.<br />Now say you were to replace your LU foot oil drain screw with a bronze one instead of stainless. The bronze is much more nobel than either stainless or aluminium, so galvanic action will be agressive. The aluminium and the stainless will corrode; the screw will not.<br /><br />So what does this have to do with anodes? Well you might notice where zinc and magnesium are on the gavanic series. They are very very un-noble metals. So if you electrically connect a piece of zinc, under the waterline, to your outboard, it will become the 'target' of galvanic corrosion.<br />Instead of your outboard's aluminum or ss.<br />The trick is to clean off the electrically insulating corrosion that forms on the anode, to help those oxygen atoms in the water attack it and not your outboard.<br /><br />Hope this helps!<br /><br />PS - the principal is the same for 'Galvanized' nails, where they're dipped in molten zinc to keep them from rusting.

 

[bhalsdorf]

Re: how does an anode work?

Exactly where is the best spot to mount an anode?

 

[DJ]

Re: how does an anode work?

Bill,<br /><br />Any place that will remain wet, if the boat is to sit in the water.

 

[claytonr]

Re: how does an anode work?

Thanks for the replies, I feel a little smarter now...........think I should call it quits for the day.

 

[SCO]

Re: how does an anode work?

There is still a piece of the puzzle missing unless I missed it in the explaination above. <br /><br />The zinc will corrode, letting go positive zinc ions to the water. When it does this it releases negative electrons that flow to the aluminum. Those surpluss electrons inhibit the aluminum from releasing positive aluminum ions(therefore no aluminum corrosion). I am pretty sure about this but not positive.

 

[DJP]

Re: how does an anode work?

WHEN IS AN ANODE NOT AN ANODE?<br /> <br /><br />Since many sacrificial aluminum anodes look the same and are often advertised as direct replacements, shouldn't they work the same, too? Not necessarily, according to Canada Metal (Pacific) Ltd, manufacturer of well-known Martyr anodes. Choosing the right products and ensuring that they meet stringent military specifications can make the difference between reliable protection against corrosion or replacing a lower unit—or worse.<br />Ineffective products and misinformation about the use of aluminum anodes have been around the marine industry for a long time, according to Canada Metal's President John Mitchell. He explained, "A good example is the myth that aluminum-indium anodes offer protection in fresh water. They simply do not."<br /><br />Mitchell further explained that the consumer has several options for proper freshwater protection. "First, use Martyr magnesium anodes," he said. "And second, use the Mercathode system for passive protection. This effectively protects Mercruiser stern drives in fresh water."<br /><br />Top-quality aluminum anodes must conform to Military Specification MIL-A-24779(SH), a 28-page document that details the general requirements and inspections required for the US Navy's aluminum alloy devices. The specification contains three critical components: certification of long-term immersion tests; the specific method of aluminum determination; and rejection of the manufacturer's entire lot of product if any deviation is found. "Basically, the consumer only needs to remember two things when selecting an aluminum anode," said Mitchell. "One, an aluminum anode is only effective in salt and brackish water. And two, the device should always carry the MIL-A-24779(SH) specification. Of course, the boat owner should never base a buying decision solely on price—saving a few dollars on an inferior-grade anode can cost thousands in engine repairs and underwater gear replacement." <br /><br />Excerpt from Boating News.com<br /><br />The Mercathode System is available for purchase aftermarket from your local Mercruiser Dealer.

 

[lakeman1999]

Re: how does an anode work?

I would think that all outboards have a sacrificial anode mounted on them, and only needs replaced when used up (deteriated/sacrificed). I know I went to the OMC parts dept. and purchased a new one to replace the one on my Johnson 40, and it was not very expensive.

 

[scubaman67]

Re: how does an anode work?

well, having some zinc problems myself. just got a slip in the local harbor here in Hawaii. My Johnny 88 outboard did not have a zinc anode. almost immediate corrosion problems. Since the motor will not tilt high enough to be completely out of the water, I Installed 2 anodes, both below the waterline. One of them was on the lower unit bolted to the cavitation plate. The other was on the transom clamp. Three days later, there was significant corrosion on those anodes. At this rate, I'll be replacing them every three weeks. Buddy said I might have a "grounding problem." He might as well been speakin japanese to me. Anyone know what kind of grounding problem I might have and How I could cure it. Again, Bayliner 19 ft capri, Johnson 88 horse outboard, saltwater.

 

[Troy_from _Oz]

Re: how does an anode work?

scubaman, Im no expert, but i think that a grounding problem is where you have current leakage through the hull - (to the water??). The leakage sort makes the boat act like a big battery (or a reverse battery??) which speeds up the corrosion process. Maybe do a search on here or on the net for current leakage and galvanic corrosion.<br /><br />this is just dredged up from the dim dark recesses of my small brain, so dont quote me..hope it helps <br /><br />cheers <br />troy

 

[Troy_from _Oz]

Re: how does an anode work?

Scubaman - theres a bit of a spiel on it here....<br /><br /> http://www.dairyland.com/marine.html <br /><br />better articles here maybe??<br /> http://www.sailnet.com/collections/articles/index.cfm?articleid=hughes0003 <br /><br /> http://www.sailnet.com/collections/articles/index.cfm?articleid=hughes0001 <br />good luck

 

[Jdeagro]

Re: how does an anode work?

Scubaman;<br /><br />If you or someone close to you has a dock power line constantly connected this can increase the corrosion problem. You may have shore power hooked up to keep your battery up. Don't do that!<br /><br />Check with the dock master and your neighbors.

 

[scubaman67]

Re: how does an anode work?

gentlemen, thank you for your input. Articles were very helpful. will check with dockside neighbors about shore power. Will take steps to properly ground my vessel. I'll get back to you guys in a few weeks to tell you if problem solved. Thanks again... you guys are the best.