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Thread: Anodes Eroding Fast

  1. #1

    Default Anodes Eroding Fast

    My boat has been in a slip since the beginning of May. Had to pull the boat last week because of an engine problem. Both the transom bracket and skeg/trim tab anodes were new in May. I would say they are 50% used up. I have replaced them. My question, is Whittier harbor that hot? The boat is aluminum and I am NOT hooked to shore power. Just seems like I should have gotten a little more time out of the Anodes. I do keep a battery in the on position as it sits in the slip, and everything is turned off except auto bilge pump. I have a round disc type anode attached to the boat itself and it is in good shape.

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    Member bobmikk's Avatar
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    I am not that versed in corrosion around boats or marinas... but these scenarios always peak my interest. The following is taken from an online source and seems reasonably associated with your situation... that being a boat(s) around you connected to shore power have created a galvanic cell that is impacting your boat, or you may have a current leak in your wiring system in the bilge area.

    A vessel suffering from galvanic corrosion is usually the source of it's own problem, although two vessel's linked by shore power grounds can create a galvanic cell between two very close boats.

    Stray Current corrosion : Corrosion that results from an electrical source causing a metal in contact with an electrolyte (water) to become anodic with respect to some other metal in the same electrolyte.

    In simple terms a wire touches something it shouldn't, like a faulty bilge pump float or degraded wiring lying in the bilge sending current into the water, causing one metal to give up electrons and corrode. Again any vessel suffering from this type of corrosion is likely the master of it's own disaster but the culprit could also be a neighboring vessel. This type of corrosion can can eat metals at an alarming rate.

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    Bottom paint reduced my anode wear significantly. Was once per month for replacing both hull and trim anodes: Now once every 4-5 months even during the "hotter" summer months. A once over on your electrical system could be another solution. But bottom paint pays dividends as hard as it is to shell out 2-3k every 5 years.


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    I checked out a boat last month in Whittier the slip and boat did not have a problem. One thing I found was the hold dock had a .25 AC voltage to ground. AC voltage is not a normal cause of corrosion.
    I did not have the time to track it down.

    Need more information on the round disc what does “in good shape” mean? Do you have closed up pictures of all the anodes and the hull? What type of anodes is the disc and the ones on the engines and trim tabs.

    Instead of leaving the battery switch on why don't you wire the bilge pump to the battery?

    Their not enough information at this time to say what is causing the problem. Most of the time it's the boat not the harbor or other boats.

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    As the son in-law of a marine surveyor, aluminum boats really ought to be slipped. You absolutely must use the proper primer and bottom paint designed for aluminum boats, and you really ought to hang one or two large sacrificial anodes off your boat while at the slip for extra protection. Our large family fiberglass boat gets hauled out every spring and right about mid-august our zincs need replacement (2 on the shafts, a set on the trim tabs, and a large plate zinc on the transom), it may be a hot slip.

    I also have an aluminum jet skiff that came with the regular brass or bronze boat plug, and every time I went out in the salt water when I put her back on the trailer the boat plug looked shiny from galvanic corrosion. SO MAKE SURE YOU ARE USING AN ALUMINUM BOAT PLUG for your aluminum boat!

    Sobie2

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    whitier is a HOT harbor they can't keep cleats attached to the docks so why would a little electrical problem cause any concern ??

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    I have noticed the same this year and I pull my boat out every trip. I never had to replace the anodes on my last boat that I ran for 7 years and the new boat anodes are showing signs of wear way more than the last? Either junk anodes or the sound is getting hot is my guess!
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  8. #8

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    MacGyver-- By good shape I mean that it is not eaten up and eroded away like the other anodes. This anode is attached to an unused transducer bracket at the back of the boat, it is a round disc (rudder button anode) Both bilge pumps are NOW directly to a battery.

    The boat is bottom painted and it is in excellent shape. There is no visible pitting on the hull ( even on the scum line where the bottom paint was not painted high enough is free of corrosion and pits.)

    Checked for any stray voltage today and found nothing. (Checked with meter)

    Sobie2---I am using an aluminum drain plug. Since it is basically insulated by the rubber I grounded the center twist handle with a small bracket.

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    Quote Originally Posted by AlaskaM5 View Post
    By good shape I mean that it is not eaten up and eroded away like the other anodes. NOW directly to a battery.

    Checked for any stray voltage today and found nothing. (Checked with meter)

    t.
    If a anodes does not show signs of being used when other anodes were used up in two months. The anodes is being protect by the other anodes or it is not connected to the hull or the other anodes electrically.

    What method did you use to test for stray voltage? Was the boat in the water or on the “hard”? I love using nautical terms. LOL

  10. #10

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    Trust me, the disc anode is connected to the boat, in the same fashion as the motor anodes, ss bolts and within 2 feet of the motor. Tested in my "Hard" driveway. LOL

    Explain METHOD USED, as I'm a a little under-versed when it comes to AC/DC (except the group). I just used the meter set on volts, ground to battery neg. Pos. to various parts of the hull.

    Will check it on the water once I get it back from Dewey's

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    I trust you......... what I don't trust is boats wiring and corrosion. For instance if there is corrosion between the disc anode and the hull or between the engine mount and hull they are physically connected but not electrically connected. Most people use a ohm meter to check for continuity and end up getting a false reading because of corrosion. It does not happen all the time just enough to keep a technician on his or her toes.

    That is not the way I would recommend testing for stray voltage. For one thing the battery negative and the hull if wire correctly will be a dead short. The method I use is, put the boat is in the water, vote meter positive going to the hull and the negative going to a test haft cell that is hanging in the water.

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    when i install/replace zincs i give them a whack with a hammer on the side that has the contact on the inside of the zinc them tighten them down good & tight.

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    OK dumb question : you guys aren't checking ohms in the dry are you when seeing if there's continuity?

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    The anodes have to be connected through a metal path in order for cathodic protection to take place. You can try measuring the current between the anode and Boat by using your multimeter. You can try measuring current with the anodes in different places, different times of day, etc to see if you can pin point it. Try disconnecting the battery, the reconnecting, etc.

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    From my limited 15 years experience working with anodes up to and including the 10k lb variety; anodes are very hit and miss on quality when your talking little ones (under 2-300lb)
    I've installed thousands of anodes on docks, bridges, ships, platforms, jackups, and whatever else. And it is EXTREMELY rare when one is hard mounted with bolts. If you have an

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    Quote Originally Posted by shayno View Post
    OK dumb question : you guys aren't checking ohms in the dry are you when seeing if there's continuity?
    No I'm not measuring ohm on the hard or as you prefer dry. I measure current to determine continuity.
    So I don't get a false positive.

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    Quote Originally Posted by shayno View Post
    I've installed thousands of anodes on docks, bridges, ships, platforms, jackups, and whatever else. And it is EXTREMELY rare when one is hard mounted with bolts. If you have an
    We are talking about anodes mounted on a pleasure boats. Very few are welded because of the cost of welding.

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