I own a 1981 Hunter with a Yanmar diesel. I am working thru correcting / catching up the maintenance from the previous owner. This weekend I replaced the raw water impeller and engine cooling water zinc. When I pulled the zinc it was covered in "red iron" rust. I was expecting a bare metal or "white chaulky" zinc. In 22 years of submarines I have never seen a zinc like this. Does anyone have any ideas? Could this be a result of a poor quality zinc?
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Depending on which lake you are on in Texas, that may be the norm. Brush it off and put it back in. I am on Lake Texhoma and everything is red. Only start worrying if it is starting to go away.
Don't know what engine you have. I've got a 2QM20 on my 1980 H36. Although designed for raw water cooling, it was retro-fitted (probably at or near the boat's commissioning) to heat exchanger/antifreeze cooling. Hence salt water doesn't flow through my engine. As you did, when I bought my boat, I also checked one of the engine zincs. It was coated in a black film, which wiped off to dark metal gray of the zincs surface. The zinc was totally not sacrificed at all. Looked virtually new. You've identified yourself as "Texas Lake Sailor". If your boat has been in fresh water since the last zinc change, that could be the reason the zinc looks like it does. Coated with rust residue from the engine block. Maybe the zinc doesn't sacrifice much at all in fresh water? Probably other fresh water sailors on this forum, or in your location, can shed more light for you. And give you tips for keeping your engine's cooling system in best condition.
I don't think there is any need for zinc in fresh water. I haven't bothered with a zinc in 5 years. Maybe if you are in a marina that has power ... I am located in a marina that has no power at any of the slips and I am on a mooring. There are no boats with an electrical system anywhere around me. So, it may depend on your situation.
fresh water zinc's
This is my 5th sailboat, 2 have been in salt water and 3 in fresh. I have found that zinc's will be consumed even in fresh water, at a slower rate than in salt water. But they are still consumed. My current boat is in a slip at Lake Travis with power on the dock. I 'll keep the zinc's on it and check them at the end of the season to see how they do. I don't think it is from the water, unlike Lake Texoma the water in Travis is pretty clear, no red mud.
This is my 5th sailboat, 2 have been in salt water and 3 in fresh. I have found that zinc's will be consumed even in fresh water, at a slower rate than in salt water. But they are still consumed. My current boat is in a slip at Lake Travis with power on the dock. I 'll keep the zinc's on it and check them at the end of the season to see how they do. I don't think it is from the water, unlike Lake Texoma the water in Travis is pretty clear, no red mud.
Sacrificial anodes should be used regardless of whether you're in fresh, brackish or salt water. What kind of water you're in determines what kind of anode to use. Salt should use zinc, brackish waters require aluminum and fresh water requires magnesium anodes. Using the wrong anode will result in either insufficient protection or shortened anode life.
BTW, just cause your boat looks like it is doing fine without a sacrificial anode, you'll probably find out that isn't the case, as galvanic corrosion is cumulative, and it may take a few years to show up, but it will result in far shorter lifespan for the underwater hardware on your boat.
BTW, just cause your boat looks like it is doing fine without a sacrificial anode, you'll probably find out that isn't the case, as galvanic corrosion is cumulative, and it may take a few years to show up, but it will result in far shorter lifespan for the underwater hardware on your boat.
Sailingdog has got it right accept aluminum can be used for either salt or brackish water.
zinc in fresh water may work if their is evidence of stray current corrosion... an artificial source of current due to shore power / grounding problems in either your boat or your neighbors. Dirty or polluted fresh water lakes/rivers which have an abundance of iron can be very corrosive as well so please be careful when you say anodes is not required. I have personally seen entire Merc sterndrives wasted in stagnant-water tributaries of the Mississippi.
If there is no evidence of stray current then zinc does not have enough potential to drive the circuit. After 48hrs of installation zinc passivates and stops working altogether. Then it will just collect dirt, grime, sealife, etc. Magnesium is the most active anode material available and has the ability to drive the current required to protect in fresh water. The trouble is there is not an abundance of supply of magnesium replacements in the market. Some engine manufacturers understand this better than others but they seem to be slowly making the product available to fresh water boaters.
zinc in fresh water may work if their is evidence of stray current corrosion... an artificial source of current due to shore power / grounding problems in either your boat or your neighbors. Dirty or polluted fresh water lakes/rivers which have an abundance of iron can be very corrosive as well so please be careful when you say anodes is not required. I have personally seen entire Merc sterndrives wasted in stagnant-water tributaries of the Mississippi.
If there is no evidence of stray current then zinc does not have enough potential to drive the circuit. After 48hrs of installation zinc passivates and stops working altogether. Then it will just collect dirt, grime, sealife, etc. Magnesium is the most active anode material available and has the ability to drive the current required to protect in fresh water. The trouble is there is not an abundance of supply of magnesium replacements in the market. Some engine manufacturers understand this better than others but they seem to be slowly making the product available to fresh water boaters.
You absolutely do not want to use zinc in fresh water, it will do no harm but will do nothing to protect your boat. When used in freshwater, a zinc anode forms a coating of zinc hydroxide that insulates it and stops it from working. Chuck
IF you use aluminum in salt water, be prepared to inspect and replace the sacrificial anodes more often than normal.
Aluminum is the only anode that can be used in just about any waters, but as SD suggested aluminum does dissolve in salt water so replacement more often is needed and you won't know if you have a electrolysis problem or the material is just dissolving. Chuck
I have become quite an expert in this debate over the past 15 years so I am quite enjoying this discussion. Zinc vs. Aluminum is salt water has confused many boaters and continues to do so. The engine manufacturers such as Mercury and Yamaha offer aluminum as standard from the factory (yep aluminum anodes will protect an aluminum outdrive/outboard). The reason is the aluminum "alloy" used in anodes (a US Mil spec) has more capacity (ampere-hours per pound) 355 for zinc vs 1225 for aluminum. Understand that this is lab tests results so performance differs greatly in water type (brackish/salt) and water temperature. Anodes on your hull or your engine will last far longer in cold water. In Florida for example anodes may only last 3-6 months through natural galvanic process.
I notice myself that aluminum will corrode much differently than zinc in salt water. Aluminum anodes will pit and may even create a white film called aluminous oxide in stagnant water. This is normal. But because it looks different many boaters think that the anode is corroding faster than zinc... not true. What is true, because aluminum pits, it is fare more suceptible to errosion than zinc so in areas of high wash (ie. trim tabs, shaft anodes, etc...) aluminum can erode faster.
Here's another few bits of info I learned.
- There generally isn't enough anodes to protect most outboards/outdrives. Small anode + large cathode = high rate of corrosion. Simple fix... add more anodes if you can.
- Those Stainless Props are murder to outboards/outdrives. By adding stainless you add a metal lower on the noble scale... thus creating a higher potential between anode and cathode = higher rate of corrosion.
If you want some fun take a mag anode and attach with a wire to copper strip in the same body of salt water (ie,. fish bowl). The mag anode will immediately start to bubble (hydrogen). Because magnesium is at the top of the noble scale and copper is toward the bottom, the natural current generated is off the chart. The mag anode will be fully wasted in about a week.
Cheers
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