anodes

TinBoats.net

Help Support TinBoats.net:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Poormans Boatright

Well-known member
Joined
May 5, 2011
Messages
270
Reaction score
0
Location
Texas City, Texas
I got to thinking about electrolysis on boats, what makes the pits and eating away at the aluminum? So I'm wondering if motors have a anode why not the hull? We all know electrolysis corrosion is a problem with aluminum hulls, right? So I thought why Don't aluminum hulls have a sacrificial anode installed on them. I could be wrong, but wouldn't an anode work on a hull just as it would on a motor? In my thinking, that they are the same. So here's what I done. I cut a block of aluminum out of some stock I had around the shop, and drilled and tapped it to mount an anode I bought off E-Bay. I then welded it to the back of my float pod and installed the anode. My thought is if electrolysis is eating away at the hull, would it eat the anode first?

What are you're thoughts? Does anybody have experience with this? do you think it wont help? I'd like to think it this would be beneficial to corrosion problems, but I am no engineer.

Anyhow, here's what I did.
 

Attachments

  • finished anode.jpg
    finished anode.jpg
    47.4 KB · Views: 1,125
  • installed.jpg
    installed.jpg
    46.5 KB · Views: 1,125
  • installed2.jpg
    installed2.jpg
    41.7 KB · Views: 1,125
  • welded.jpg
    welded.jpg
    46 KB · Views: 1,125
  • taped block2.jpg
    taped block2.jpg
    49.9 KB · Views: 1,125
  • taped block.jpg
    taped block.jpg
    58.2 KB · Views: 1,125
  • anode.jpg
    anode.jpg
    51.5 KB · Views: 1,125
Your idea makes great sense and we wonder why the manufacturers haven't provided something similar. We buy and install anodes on our aluminum engines all of the time.

I do believe that different metallurgical material anodes area recommended for freshwater vs saltwater. R
 
I think this will work for that area of your boat...Not sure but it seams like you'll keep it away from that area but its not enough for the whole boat. If I understand it right that is. I am not sure how much or how many you'd need on the whole boat actually.

I did a quick search and see they do it on large ships at several intervals around the ship. Seems to make sense to me it would work. I just dont know the ratio of size of the anode to protction coverage, ....if that make sense...
 
I think most of us here trailer, launch and retrieve every time we go out with an occasional one to two night stay in the water. Unless you are operating in salt water and keep the boat in the water, I can't see the benefit in adding anodes. However, your mod is a good one, and it can't hurt.
 
I have anodes on my jetboat, and on my 16 foot triton. It's EXTREMELY important in salt water. Remember that in salt water, you use zinc for the anodes, but in freshwater, you use magnesium for the anodes, as zinc is not reactive enough.

But instead of drilling and tapping into a block of aluminum, I used through-bolts, through my hull, sealed with 5200.

Basically, the bolt goes through from the inside, with a washer. On the outside, another washer, and a lock nut. Use a bolt long enough to allow another inch or two of threads after tightening down the lock nuts.

Then, the zinc anode goes over the protruding 'studs' and is secured with yet another set of washers and lock nuts. This way, when the anode has to be changed, you simply remove the outer set of lock nuts and washers, and you don't have to break the seal where the bolts go through the hull.

Also, it may not be a bad idea to run a bonding wire to your anode. You can make one of these with some 1/16" stainless cable, and a couple of ring terminals. Connect the bonding wire between your outboard and your aftermarket anode, or connect it directly to the negative terminal of your battery. This will allow any stray current to flow properly, and eat away at the anode, instead of your hull.

Generally speaking, a 16 foot johnboat needs between 36 and 48 square inches of anode for proper protection. On my jetboat, I have 2 anodes that are 4 inches by 6 inches, by 3/4" thick.
 
My triton is in the water at the dock right now, so, I can't get any pics of that, but my jetboat is on the trailer in the yard.

I'll get some pics of it today and post them. The difference with the jetboat is that the anodes aren't bolted through the hull like with the Triton, instead, I have them bolted to the struts that support the rear platform.
 
OK, here's a few pics of mine:


These are photos of the anode on the transom of my Triton as it sits in the water.

Sorry if they're a little blurry, these are underwater shots, and it's overcast today
100_0291.JPG

The 2 smaller bolts are the ones that go through the hull. The 2 larger bolts hold the backer plate in place. The backer plate is important, because as electrolysis begins to eat the anode, without a backer plate, once the anode is corroded where the fasteners attach it, there is nothing to keep it from falling off, much less to guarantee electrical continuity.

100_0292.JPG

You can very faintly see the bonding wire on the right hand side of the electrode (you can clearly see the blue plastic end of the ring terminal)
100_0293.JPG
This bonding wire connects to the anode on the bottom of the outboard mounting bracket, which has a factory bonding wire running to it.


OK, here's the same anode, except, these are on my jetboat.

Starboard side:

100_0295.JPG

The bolts go through the strut, then through the zinc anode, then through the backer plate. Again, the backer plate is important to keep the anode from corroding around the fastener area and falling off.
100_0296.JPG


Port side:
100_0297.JPG

100_0298.JPG
 
Poormans Boatright said:
Thanx to all for your input. My boat is strictly used in saltwater. I guess time will tell if it does any good. Kinda interesting though.


If you are leaving your boat in the water, a zinc will definitely help. You should also keep a good layer of anti-fouling paint on the bottom, as growth from fouling will accelerate corrosion. Be sure to first prime with 2 coats of "Interprotect" then follow up with a good coat of copper thiocyanate (NOT cuprous oxide) based anti-fouling paint, such as "Trilux 33"

Be sure to use the right one, or you will have SERIOUS issues with corrosion. The price will tell you which paint is formulated for use with aluminum.... as it's about 2X as expensive as fiberglass antifouling paint.
 
Not realy sure how to jump in on a thread this is my first of many post i hope.But back on subject first i would like to say i am a corrosion specalist for FDOT. the zinc anode on your boat motor is to protect all of the dissimilar metals in your motor and the fact that it is attached to your boat the anode on your motor is also protecting your boat too. An anode only works when its in solution so it only works when your motor is in the water. If you store or keep your boat in the water and lift your motor out of the water you should install a zinc anode to your hull. Yes a magnesium anode will discharge at a higher rate but will not protect any more than a zinc anode. The best way to deter corrosion is to rinse your boat and flush your motor after each use and replace your anode pucks on your boat motors when they look worn out. I hope this helps.
 
jeepnutz84 said:
Not realy sure how to jump in on a thread this is my first of many post i hope.But back on subject first i would like to say i am a corrosion specalist for FDOT. the zinc anode on your boat motor is to protect all of the dissimilar metals in your motor and the fact that it is attached to your boat the anode on your motor is also protecting your boat too. An anode only works when its in solution so it only works when your motor is in the water. If you store or keep your boat in the water and lift your motor out of the water you should install a zinc anode to your hull. Yes a magnesium anode will discharge at a higher rate but will not protect any more than a zinc anode. The best way to deter corrosion is to rinse your boat and flush your motor after each use and replace your anode pucks on your boat motors when they look worn out. I hope this helps.


Thanks for the input, good to have the opinion of an expert in this. As you said, the anode on the motor protects both the motor AND the boat. But, that's a lot of surface for just one little anode to protect. Hence, the use of anodes on the hull to supplement the galvanic protection.

A magnesium anode is more reactive than zinc, and while it's true that it won't offer any higher level of protection in saltwater, in freshwater, zinc is not reactive enough, and that's where the magnesium comes into play.

Anodes should be replaced when they reach about 75% of their original size. Keep a new replacement on hand to compare the degree of corrosion.

The more dissimilar metals that are on a boat, (such as combinations of aluminum/stainless) the more protection it will require. Also, stray electrical current in the water (common at marinas) will require more frequent inspection of the anodes.
 

Latest posts

Top