Don’T Neglect Your Anodes !

[Traveler2586]

Anodes are mounted on an outboards lower unit, and sometimes on the lower edge of the outboards mounting bracket.  referred to as Sacrificial Anodes, they are simply a disposable metal block attached to your boats underwater metal parts, that will sacrifice itself (corrode) first in order to prevent the important parts of your motor from corroding, such as your lower unit.

For Example, if two dissimilar metals are touching underwater, such as a stainless drive shaft, bronze bearings, and the aluminum housing of the lower unit, a naturally occurring transfer of electricity carries through the water from one metal to the other and causes the more active (softer) of the two metals to corrode.  A sacrificial anode secured to the aluminum housing of the lower unit is now the most active metal in the system and corrodes before the aluminum of the lower unit. When the anode reaches 40%-50% of its original size, it is replaced to continue the protection cycle.

 

Sacrificial Anodes are commonly referred to as “a zinc”; however zinc is not the only anode type that protects underwater metals, aluminum and magnesium are also used; your outboards manufacturer will specify the proper material for a given environment.

 

In order for the Anode to do its job it must be able to conduct the electrical current from the water into the metal housing it’s protecting; in our case the aluminum of the outboard’s lower unit.  As the Anode preforms its duty it will begin to “pit” and form a crust of oxidation that appears dull grey in most cases.  The pitting process is normal and indicates the anode is doing its job.  In some applications where the water is stained or muddy, the anode will form a coating of silica from the water.  These coatings (silica and/or oxidation) have an effect to insulate the anode and inhibit its ability to conduct efficiently.  Therefore anodes require periodic inspection and maintenance.  The electrical connection between the anode and the outboard can be easily checked using an Ohm Meter; there should be zero ohms between the anode and the mounting surface on the outboard.

 

When maintenance is required, the anodes should be removed from the outboard and all surfaces’ cleaned to bear metal; the outboards mounting surface should be cleaned to bear metal also.  Cleaning is accomplished by a vigorous buffing with a stiff wire brush until all oxidation or silica is removed, and bear metal is seen. (see photo’s)

 

Never paint a sacrificial anode, or the surface it mounts to. There needs to be a solid physical electrical contact between the anode and the metal requiring protection. If there is a break in this electrical continuity, the protection stops, resulting in corrosion of the important outboard parts.

 

Generally these are the rules for each body of water:

Salt Water: Use Zinc Anodes.

Brackish Water (Salt and Fresh mixed): Use Zinc Anodes.

Fresh Water: Use Magnesium Anodes.

 

Note:

The fresher the water, the less electrical current is transferred, requiring the more active anode.  Magnesium anodes are ideal for fresh waters, as they are both economical and highly effective. They have excellent properties for corrosion protection in the higher resistive fresh water environment.
 

Bottom line, Anodes need to be clean and tight to efficiently do their job, so when preforming seasonal maintenance........

 

Don’t neglect your Anodes.
 

 

Notice the mounting area is cleaner that the rest of the anode but still oxidized

 

Before & after cleaning.

 

Wire brush can be found in painting or wielding departments of hardware stores.

 

Don't forget to clean the lower units mounting points.

 

 

IMHO, annual maintenance is fine, the big thing is to clean the contact points between the anode and the housing it's mounted to; if the contact point fails the system fails and your motor is unprotected.

 

Remember, we're talking about a very slow but steady process that only takes place while the boat is in the water; it's faster in saltwater, and slowest in freshwater.

 

 

 

 

 

 

 

EDIT 04/20/2013 15:18 EST -   Added two pic's to cover items I missed above.   Thanks for the reminder Jeff. 

 

 

 

 

 

 

 

This is the Trolling Motor's anode on my MototGuide

 

 

This is the Trim-Tab anode on my Merc.

 

 

I don't have the common vertical fin, just a flat plate.  This was a real bear to get off, I don't think its ever been off for maintenance; in fact it is so heavily covered with oxidation I could not get a meter reading, and the wire brush couldn't cut through it, I had to use 100 grit sandpaper.

[00 mod]

Very good write up. And I will add that on some smaller outboards, the removable trim tab acts as the anode.

Jeff

[topwaterrob]

Great info.... I'm going to check mine this week....  How do they come out?

[Traveler2586]

Great info.... I'm going to check mine this week....  How do they come out?

 

They just bolt on.

 

 

Very good write up. And I will add that on some smaller outboards, the removable trim tab acts as the anode.

Jeff

 

Very true.  Some trolling Motors also have anodes in the form of a bolt on the motor housing.

[BassnChris]

This place is great! Always a learning experience.

 

I am new to owning a boat.............I had seen the anode, but, did not know what it was and had not gotten to the point of asking yet.

 

Thanks Traveler.

[MarkH024]

These are the posts that make this place shine! Thanks for the write up. I need to pay more attention to detail like this kind of topic right here on my boat.

[lmoore]

On a related note, i went to put on the rear lower unit anode on my 200 Johnson when I noticed it was missing, and the hole it bolts into isn't there, any ideas what that's about? The "slot" is there, but no hole in the top.

[Traveler2586]

On a related note, i went to put on the rear lower unit anode on my 200 Johnson when I noticed it was missing, and the hole it bolts into isn't there, any ideas what that's about? The "slot" is there, but no hole in the top.

 

It could be a redesign where they just abandoned the mounting site in favor of another elsewhere.

 

What year and model Johnson?  I'll look it up for you.  Any photo's would help.

 

Do you have an owners manual on the motor?

[lmoore]

1997 Johnson venom j200stleu is the model number I think. I don't have the owners manual, I've been using the seloc manual for general maintenance. I could grab a couple pictures sometime if needed.

[Traveler2586]

1997 Johnson venom j200stleu is the model number I think. I don't have the owners manual, I've been using the seloc manual for general maintenance. I could grab a couple pictures sometime if needed.

 

If I'm correct it should be part number 51 in the exploded parts view here:  http://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1997&hp=200&model=J200STLEUB&manufacturer=Johnson&section=Gearcase+-+Standard+Rotation+-+20+In.+Models

 

From my readings, your motor was made for use in saltwater and as such should have an anode or two or three......  Check the transom mounting bracket (the midsection) for part number 33 here: http://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1997&hp=200&model=J200STLEUB&manufacturer=Johnson&section=Midsection

 

 

You can get a manual in PDF format (soft copy) for $9.95 here: http://www.tradebit.com/filedetail.php/116879558--1992-2001-johnson-evinrude-65hp-

[lmoore]

51 is correct. I've got anodes and inserts for it, but the hole it bolts into just isn't there. I replaced the transom bracket One just about a week ago. Thanks for the link to the manual!

[Traveler2586]

51 is correct. I've got anodes and inserts for it, but the hole it bolts into just isn't there. I replaced the transom bracket One just about a week ago. Thanks for the link to the manual!

 

It appears the mounting bolt #50 comes up from underneath and may be covered by the trim-tab plate.  Could it be the bolt hole is plugged, maybe by a broken bolt??

 

If you can't get the anode remounted on the lower unit gear case, and the trim-tab is not a anode, you may need to run a stainless steel strap from your lower unit housing to the mounting bracket anode in order to have a good electrical connection.  The pivot pin on the transom bracket will prevent proper protection of the lower unit by the brackets anode.

If the trim-tab is a anode as I believe, then you should be OK as long as you look after its maintenance.

[lmoore]

The hole underneath the anode is there, its the hole above the anode that's missing. I may look into your strap idea.

[Traveler2586]

The hole underneath the anode is there, its the hole above the anode that's missing. I may look into your strap idea.

 

I just had a thought (and it hurt)....  This may be a dumb question but does the anode have a threaded sleeve inside?  That could account for no mounting hole above the anode.

[senile1]

Excellent post!

[BassnChris]

Clean anodes..........CHECK!

Thanks again Traveler.

Before

After

Before

After

[Traveler2586]

Clean anodes..........CHECK!

 

 

As Jeff reminded me, don't for get your trim tab as I did; my motor does not have a standard trim tab, just a flat plate just above the prop and I totally over looked it. Also, look at your trolling motor, some have a bolt on the vertical fin that is the anode; there's usually only one on a TM.

 

Your anodes are in great shape

[lmoore]

I just had a thought (and it hurt).... This may be a dumb question but does the anode have a threaded sleeve inside? That could account for no mounting hole above the anode.

Not threaded inside, although I could probably add some to it.

[BassnChris]

As Jeff reminded me, don't for get your trim tab as I did; my motor does not have a standard trim tab, just a flat plate just above the prop and I totally over looked it. Also, look at your trolling motor, some have a bolt on the vertical fin that is the anode; there's usually only one on a TM.

 

Your anodes are in great shape

I wondered what that bolt in the hole did.......huh.

Now it is pretty too......TM is new but will add that to maintenance list too.

Is this anymore than annual maintenance?

Thanks again to you and Jeff.

[Traveler2586]

I wondered what that bolt in the hole did.......huh.

Now it is pretty too......TM is new but will add that to maintenance list too.

Is this anymore than annual maintenance?

Thanks again to you and Jeff.

 

 

Looks like you got the same trim-tab anode I do; man mine was a bear to get off, I thought I would break the bolt.

 

IMHO, annual maintenance is fine, the big thing is to clean the contact points between the anode and the housing it's mounted to; if the contact point fails the system fails and your motor is unprotected.

 

Remember, we're talking about a very slow but steady process that only takes place while the boat is in the water; it faster in saltwater, and slowest in freshwater.

 

Here on the Chesapeake Bay, I've seen boats that are water kept with anode failure where the lower unit housing is eaten up from the inside out, the outside paint usually shows bubbling.  I don't think any of us will see anything like that on our bass boats though; we're usually not in saltwater, and we usually don't water-board our boats.