Freshwater Anode Questions

[kevintblack]

I'm fairly new to boating and am getting a little confused about the question of anodes. I have a 23 ft Thompson that was run in saltwater until this year. It is now running exclusively in fresh water and will be kept in a slip. It's located in the Great Lakes on the Erie Canal.<br /><br />My basic understanding is in freshwater, I should be using Magnesium anodes. I've also read one or two articles stating that Aluminum will work, though not as well. I've read other articles stating Aluminum will not work in fresh water. I've read other articles stating that Magnesium can be bad if used under the wrong conditions.<br /><br />The boat store I go to stocks zinc anodes even though we're hundreds of miles from the nearest ocean. They also have a small selection of aluminum anodes. They do not carry Magnesium anodes at all. This is a big chain store.<br /><br />Can someone point me in the right direction? Appreciate the help!

 

[Dunaruna]

Re: Freshwater Anode Questions

Hi Kevin, welcome to i-boats!!!<br /><br />Not all fresh water is the same, mineral content can differ greatly from one body of water to another. The type of anode you use should suit the particular type of water that the boat will be in and the type of material that needs protecting.<br /><br />Generally speaking, magnesium anodes are suggested for fresh water BUT local knowledge should be sought. Ask around the marina, listen to the old salts.<br /><br />Aldo

 

[TilliamWe]

Re: Freshwater Anode Questions

The standard anodes will work for you. You could use them & never have a problem. But magnesium might be better. Hey, it's only money, buy a set of freshwater anodes, and if they are eaten away before the end of summer, get different ones.<br />I got my freshwater anode kit at mercstuff.com.

 

[Stratocaster]

Re: Freshwater Anode Questions

Magnesium for fresh water, period. Zinc for brackish. Zinc or Aluminum for salt, but aluminum is far superior.<br /><br />Zinc or aluminum in fresh water will not protect your drive. Magnesium in salt water will burn up in a matter of weeks.

 

[kevintblack]

Re: Freshwater Anode Questions

Any sources for complete Magnesium Anode kits for an older OMC? This is a 1974 Stringer. <br /><br />I've found bits and pieces on the Internet, but I'd just as soon do a complete replacement. There seem to be a lot of Zinc parts around, but Mg is limited.<br /><br />My manuals don't even mention Anodes, so It'd be great if someone had access to part #s.

 

[umblecumbuz]

Re: Freshwater Anode Questions

You can get different anode types from places like Westmarine.<br /><br />If your water is not brackish, try magnesium. True, it erodes faster than zinc, but that's half the point. No erosion equals no protection. Zinc is a poor protector in fresh water simply because it cannot erode fast enough to protect.

 

[cuzner]

Re: Freshwater Anode Questions

If they are eroding they are doing there job. Just make sure you have enough metal to prect your boat.If you don't get a season out of them you have another problem.<br /><br /><br /> Jim

 

[lakelivin]

Re: Freshwater Anode Questions

It's amazing how often I learn something new because of these forums. <br /><br />Just curious: if there's such a big difference between freshwater protection level of zinc & magnesium, do manufacturors offer you a choice on new boats depending on where you are going to use it?

 

[kevintblack]

Re: Freshwater Anode Questions

Thanks for the input. I spoke with a Metalurgical engineer about this and he said<br /><br />I stopped by the boat store (a major chain) and spoke with the parts guy. I asked him about the anodes and why they only seemed to carry Zinc even though we're 5 miles from Lake Erie. He said that zinc will give sufficient protection in fresh water. He did admit zinc doesn't work as well as Magnesium. He also said it was because zinc was cheaper. <br /><br />After reading the previous posts I think I'll give another boat store a try.

 

[kevintblack]

Re: Freshwater Anode Questions

Oops, click too soon. Anyway the metalurgical engineer said that there are so many variables involved with water composition that it's more 'voodoo than science'. He said acidity, mineral content, etc... are hard to quantify in most cases. Trial and error and local experience are the best determinations of what type of metal to use.

 

[Dunaruna]

Re: Freshwater Anode Questions

Originally posted by Kevin Black:<br /> Anyway the metalurgical engineer said that there are so many variables involved with water composition that it's more 'voodoo than science'. He said acidity, mineral content, etc... are hard to quantify in most cases. Trial and error and local experience are the best determinations of what type of metal to use.

I hate to say I told you so, but I told you so

 

[Tacklewasher]

Re: Freshwater Anode Questions

How big an issue is this for a trailered boat that spends most of it's time in the yard? And only sees freshwater?

 

[QC]

Re: Freshwater Anode Questions

Wow!! I have never seen this mentioned or heard of it. You guys are awesome!!! How come there is no mention in the Merc manuals? <br /><br />My boat only stays in freshwater slips for 3 - 4 days max. Very little saltwater use. The manual says inspect weekly and replace when 50% corroded, that's it. I have never seen any significant corrosion so I haven't replaced any, and I have had I/Os for the last 23 years.

 

[umblecumbuz]

Re: Freshwater Anode Questions

Sometimes the anode forms a film on its surface, which actually stops the anode from degrading. Bad.<br /><br />You can tell if this is so just by looking. The surface will be dull and whitish or 'furry' looking.<br /><br />Remedy is to abrade the surface. File it or sandpaper it until it's shiny again, and it will do its job. Replace when half gone? Good advice, because the efficiency of an anode is related to its surface area. So if you have a choice of sizes - buy the bigger one every time.<br /><br />Not a huge problem in cool, clean, pure fresh water, but a bigger headache in brackish or salty water that's warm and moving.

 

[QC]

Re: Freshwater Anode Questions

Roger that Stillboy. I get the fuzz stuff and clean it off, but it sounds like I should be a little more agressive. I can't beleive Mercruiser is hoping for major parts sales by waiting for something to get eaten up other than the zincs, so I plan to stick with their plan with the additon of some sandpaper . . .

 

[lakelivin]

Re: Freshwater Anode Questions

1989 4.3L Cobra<br /><br />I have my outdrive off & noticed two things. One is that the original zincs are hardly corroded at all. Two is that I'm missing some paint on the outdrive and starting to see some corrosion on the transom/ pivot housing. <br /><br />Boat only has 450 hours, run only in warm NC lakes, and is out of the water (boathouse with lift) when not in use.<br /><br />Sanded all the annodes I could easily reach (they weren't too bad), but am thinking I'd benefit from switching to magnesium. After a quick google search, can't find many mag annodes for Cobras. I have found a magnesium horseshoe annode (I think the largest annode on the outdrive) but before replacing just that one I have the following question:<br /><br />think I read that if I do this, the magnesium annode will sacrifice itself protecting not just my boat, but also the other annodes that are zinc. Could I be creating a bigger problem if I replace only one zinc annode with magnesium, even if it is the largest one?<br /><br />Like Quietcat said, I'm surprised the issue of magnesium annodes for freshwater boats isn't better known. I learn so much from these forums! (my starting point is in the 'special ed' category, but still)

 

[umblecumbuz]

Re: Freshwater Anode Questions

Generalising a lot:<br /><br />Nice, cold, still, freshwater lakes are not seriously corrosive. Probably you could run an outboard until it dies without noticing any serious corrosion problems, even without anodes. But a lot of 'fresh' water has contaminants that will corrode boat metals<br /><br />Warm, sunlit, clear, moving, salt water is highly corrosive and even in one season can play havoc with the metals on your boat, and with your trailer.<br /><br />'Fresh' water will not attack zinc anodes agressively enough to protect other metallic parts of your boat, which is why you need an anode that will 'sacrifice' faster. This gives better protection.<br /><br />If you fit an anode rich in magnesium, for example, and also have zinc anodes elsewhere on the boat, the magnesium will 'sacrifice' first, then the zincs will 'sacrifice' once the magnesium has gone, but at a far slower rate. You can do no harm by having both.<br /><br />Local knowledge is a good guide. Talk to those who've been boating for years, and listen to their stories.

 

[ildoc]

Re: Freshwater Anode Questions

Interesting stuff. So where's a good place onlin to get Mercruiser mag. anodes?

 

[Dunaruna]

Re: Freshwater Anode Questions

Here's one site I found after a quick google..........<br /><br /> http://www.harboranodes.com/magnesium_anodes.html <br /><br />But be aware that not all magnesium anodes (or zinc) are the same. An anode is actually a concoction of half a dozen different alloys.<br /><br /> Local knowledge is by far the best indicator. Talk to local regulars. <br /><br />Aldo

 

[BillP]

Re: Freshwater Anode Questions

Use magnesium in freshwater and zinc in saltwater. You will be better off following that rule than ignoring it. Don't worry about the voodoo, etc. <br /><br />Heres a galvanic chart showing metals from least noble to most noble. <br /><br />MAGNESIUM <br />MAGNESIUM ALLOYS <br />ZINC <br />ALUMINUM 5052, 3004, 3003, 1100, 6053 <br />CADMIUM <br />ALUMINUM 2117, 2017, 2024 <br />MILD STEEL (1018), WROUGHT IRON <br />CAST IRON, LOW ALLOY HIGH STRENGTH STEEL <br />CHROME IRON (ACTIVE) <br />STAINLESS STEEL, 430 SERIES (ACTIVE) <br />302, 303, 304, 321, 347, 410,416, STAINLESS STEEL (ACTIVE) <br />NI - RESIST <br />316, 317, STAINLESS STEEL (ACTIVE) <br />CARPENTER 20 CB-3 STAINLESS (ACTIVE) <br />ALUMINUM BRONZE (CA 687) <br />HASTELLOY C (ACTIVE) INCONEL 625 (ACTIVE) TITANIUM (ACTIVE) <br />LEAD - TIN SOLDERS <br />LEAD <br />TIN <br />INCONEL 600 (ACTIVE) <br />NICKEL (ACTIVE) <br />60 NI-15 CR (ACTIVE) <br />80 NI-20 CR (ACTIVE) <br />HASTELLOY B (ACTIVE) <br />BRASSES <br />COPPER (CA102) <br />MANGANESE BRONZE (CA 675), TIN BRONZE (CA903, 905) <br />SILICON BRONZE <br />NICKEL SILVER <br />COPPER - NICKEL ALLOY 90-10 <br />COPPER - NICKEL ALLOY 80-20 <br />430 STAINLESS STEEL <br />NICKEL, ALUMINUM, BRONZE (CA 630, 632) <br />MONEL 400, K500 <br />SILVER SOLDER <br />NICKEL (PASSIVE) <br />60 NI- 15 CR (PASSIVE) <br />INCONEL 600 (PASSIVE) <br />80 NI- 20 CR (PASSIVE) <br />CHROME IRON (PASSIVE) <br />302, 303, 304, 321, 347, STAINLESS STEEL (PASSIVE) <br />316, 317, STAINLESS STEEL (PASSIVE) <br />CARPENTER 20 CB-3 STAINLESS (PASSIVE), INCOLOY 825 <br />NICKEL - MOLYBDEUM - CHROMIUM - IRON ALLOY (PASSIVE) <br />SILVER <br />TITANIUM (PASS.) HASTELLOY C & C276 (PASSIVE), INCONEL 625(PASS.) <br />GRAPHITE <br />ZIRCONIUM <br />GOLD <br />PLATINUM