zinc

[Ralph 123]

Re: zinc

Q: Can you explain why zinc anodes are not recomended to be used in freshwater ? I have been told to use magnezium anodes in freshwater.<br /> <br />A: Sacrificial anodes protect other metals by being less noble, i.e. more susceptible to corrosion. Zinc is less noble than aluminum (and almost all other marine metals), so it corrodes first, protecting all other metals it is in electrical contact with. Magnesium is even less noble than zinc, so it provides even better protection for metals at the less-noble end of the galvanic scale, particularly aluminum. However, in saltwater magnesium is too active. Not only will it dissolve quickly, but the level of current generated can bubble the paint on the protected metal. Keep in mind that the anode and the protected metal submerged in seawater create a battery. Freshwater is much less conductive that salt water, so the damaging currents are not a concern. In this circumstance, magnesium, being less noble than zinc, offers better corrosion protection. -- Don Casey

http://63.240.201.245/?__LOGIC=888&...ey&RESTRICT=AskDonCasey&KEYWORDS=anode#QA4 <br /><br />

Don Casey Tip #39 <br /><br />Remember Your Anodes <br /><br />The rule of thumb on underwater sacrificial anodes is to check them at least once a year, but if you dry-store your boat, inspecting the anodes should be part of your wash-down routine. The anodes on outboards and stern drives can last a long time if the motor’s lower end is out of the water when not in use, but a few days or even a few hours in a “hot” marina can silently dissolve the anodes and leave your engine under protected.<br /><br />Outboards and stern drives are typically fitted with at least three anodes, often more, and every one is essential. When 50% of an anode has been lost to corrosion, replace it. If you do your boating in salt or brackish water, use zinc anodes. If you boat only in freshwater, use magnesium anodes

http://www.boatus.com/boattech/TipZincs2.htm <br />

<br />West Marine Advisor Preventing Galvanic Corrosion<br /><br />Which anode is right for you?<br /><br />Zinc or aluminum for salt water: If you are a saltwater boater, you should install zinc anodes to prevent galvanic corrosion on the engine and underwater parts of your boat. Look for aluminum anodes as a possible replacement because they last longer while providing the same level protection as zinc.<br /><br />Magnesium for fresh water: Since freshwater is much less conductive than saltwater, magnesium anodes are the best choice because they're more active (less noble) than zinc or aluminum so they will protect your engine parts much more effectively. Caution: do not use magnesium anodes in any other than a freshwater application because they corrode rapidly, exposing your boat and engine to possible damage.<br /><br />Aluminum for salt & brackish water: More active than zinc, aluminum anodes are a good compromise for a mix of fresh and saltwater, e.g. in the brackish water of river deltas. In brackish water zinc is too passive and magnesium corrodes too rapidly (because of the water's salt content), leaving your boat without adequate protection.

http://www.westmarine.com/webapp/wc...dvisor/10001/-1/10001/preventingcorrosion.htm <br /><br />What's that now, 6 independent experts all saying the same thing? But who's Don Casey or John Graviskas, West Marine, et al compared to our own experts who surely know better?

 

[Dunaruna]

Re: zinc

I'm not taking the opposite view to what you are saying, magnesium is very common (and reccommended) for freshwater. All I'm saying is, check first with the local marina.<br /><br />Aldo

 

[Pony]

Re: zinc

I appreciate all the posts guys, and i probably will go to one of the local marinas this weekend and find out what people are using around here in terms of sacraficial anodes.....Now all this being said, this may seem obvious to you guys who know more than i will know about galvanic corrosion, but being that the boat is made from aluminum...does it also need an anode of sorts??? and would i put it on the transom??

 

[umblecumbuz]

Re: zinc

Sorry if I ruffled a few feathers up there, fella’s. Didn’t mean to.<br /><br />Water varies in make-up and in corrosion potential so much that getting anodes exactly right is worth a bit of investigation. The ‘one size fits all’ approach is too general. It isn’t just a question of whether water contains sodium chloride (common sea salt) or not. As has been said, there are many other influencing factors. <br /><br />That’s why the locals who maintain their boats are the ones to ask. If you’re gonna take out insurance, get the right policy.

 

[SCO]

Re: zinc

I think I'll stick to asking questions from now on. Good info in this thread.