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There are many more project details in our SV LIMA premium area.

Born to be a sacrifice.

So called sacrificial anodes do not have a good life. The only reason why they exist is preventing other metals not getting destroyed. But how does that work?

For us boaties it is a cheap solution protecting more expensive metals that are steadily below water line of a vessel. Typical examples are metal part of rudders, shafts, props, bowthrusters and further components that are steadily below the water line of a vessel.

 

Note: This project is currently work in progress right before execution status but not yet fully done.

  • Planning -> done
  • Purchase -> done
  • Execution -> about to be done in spring 2021
  • Wrap Up -> open

In the article you already find some theory on the topic that might be valuable for you. So check it out. In the SV LIMA premium area you find even more details like e.g. planning lists, buying lists, detailed theory and more. You get more details which anodes we bought, how much they cost and what in addition to take care of (material of anode mountings, etc.) 

 

 

The theory

Why does a boat need to put sacrificial anodes to the underwater body?

It is a fair question: Why connecting some pieces of metal to an underwater body of a vessel? In the end what we know as super high sophisticated term "sacrificial anode" is in the end nothing more than a piece of metal and that's it.  

But for us skippers and boat owners it is more - by far. These small pieces of metal - mostly zink (salt water) or aluminium (fresh water) safe all components of our drive and steering that are in contact with water most of the time of their lifecycle. 

These metal components are usually:

  • Drive shafts
  • Props
  • Rudder, -bearings
  • Bowthruster

 

What is corrosion and what is the problem with it?

Metal tends to corrode in an environment that is wet. This is a specific type of corrosion: The so called chemical corrosion which is the oxidation of iron. Corrosion is an electrochemical reaction of a metal with its environment. The metal reacts in a redox-reaction with the oxygen from the environment. Electrons are being extracted from the metal and get as positive ions into salt water which acts as an electrolyte. The metal is destroyed piece by piece due to losing the electrons.

In the case of a vessel a good example is that the prop shaft would react with the oxygen in the salt water and gets corroded or better said destroyed. And we do not want that - surely. So the idea is to put a coarse metal next the metal to be protected. A coarse metal is a base metal according to the electrochemical series.

 

The magic behind: Stop corrosion of boat parts.

But another metal also corrodes doesn't it? Yes that is true. Due to that reason the idea of the galvanic cell comes into play: When you connect a base metal (= the sacrificial anode) to another metal a galvanic cell is being created. Current flows between the base metal and the metal to being protected. 

Let us stick with the example of the prop shaft: The shaft consists of steel/iron and you put a base metal which is zink next to it. With this setup a current is flowing between the shaft and the piece of zink. The shaft becomes the cathode and the zink becomes the anode in this galvanic cell.

 

Why is an anode called an anode in that case?

Again - since it is important: The zink is acting as anode in that galvanic cell we created between the shaft and the zink. The shaft to be protected is the cathode. The corrosion always happens at an anode in a galvanic cell and never at a cathode. And this is the deal. The shaft is the cathode and nothing happens there since everything happens at the piece of zink which acts as anode. The anode gets destroyed and that is also the reason why the piece of zink is called sacrificial anode.

 

How often do I have to change a sacrificial anode on a vessel?

It depends on the amount of corrosion. Usually an anode should be replaced when around 50% of the material is destroyed or gone. Typically you check your anodes once a year during maintenance period and replace when necessary.

 

What if the anodes are not destroyed even if they are connected to the vessel?

In that case you are a little in trouble since the other metals are no longer protected. 

Often reasons for anodes not being destroyed are:

  • Note: You can find all info about reasons for anodes not being destroyed / working in SV LIMA premium area. Provide us with a beer and you get access for a full year. Get more info. (If you are already premium user you can reach premium area via top level menu "SV LIMA - Premium". This is only visible if you are premium user)

 

What is the takeaway for SV LIMA?

With understanding the theory part of this article it is pretty easy to see that sacrificial anodes are a "must have" part of each and any boat and so is for SV LIMA too. So we have to check and likely replace our sacrificial anodes.

 

The project

Planning is done and the purchase as well. The project itself is ready to be executed. In the next few weeks we will go back to SV LIMA and replace the old anodes. All this is documented in detail and provided to you here shortly. Check also our SV LIMA premium area which has the same projects but with even more details and information for your own project(s). You can get access to SV LIMA premium area -> here. (If you are already premium user you can reach premium area via top level menu "SV LIMA - Premium". This is only visible if you are premium user)

 

The planning

First of course we have to check our installed anodes. Since the vessel is at the dry dock currently that is an easy thing. What we see is really interesting and makes it clear that there is a replacement necessary.

 

The anode on one side of the rudder.

 

The anode on one side of the skeg.

 

That is how it should look like:

 

 

The anode at the lower side of the rudder.

 

The anode at the end of the prop shaft.

 

The anode at the prop shaft.

 

And again how it should look like:

 

As you can see the anodes are pretty much either destroyed or vegetated with barnacles. The do not look like before at all. so it is time to change...

 

The purchase

As usual we checked the internet. Firstly we checked a website that is called opferanode24.de. 

Note: You can find all info about the purchase in SV LIMA premium area. Provide us with a beer and you get access for a full year. Get more info. (If you are already premium user you can reach premium area via top level menu "SV LIMA - Premium". This is only visible if you are premium user)

 

Dimension: We took yardstick and sliding calliper and started with the dimensions.

If you do the same please measure following values:

Note: You can find all info what to measure for purchasing anodes in SV LIMA premium area. Provide us with a beer and you get access for a full year. Get more info. (If you are already premium user you can reach premium area via top level menu "SV LIMA - Premium". This is only visible if you are premium user)

 

Our purchase was as following

 

Note: You can find all details for purchasing anodes in SV LIMA premium area. Provide us with a beer and you get access for a full year. Get more info. (If you are already premium user you can reach premium area via top level menu "SV LIMA - Premium". This is only visible if you are premium user)

 

The anode face

All our anodes we purchased for the vessel displayed in a little funny way before installing them.

 

 

What we purchased in addition and what you also should not forget thinking about

Note: There are some more things to consider for purchasing anodes. You can find all info about the right nuts, materials etc. in SV LIMA premium area. Provide us with a beer and you get access for a full year. Get more info. (If you are already premium user you can reach premium area via top level menu "SV LIMA - Premium". This is only visible if you are premium user)

 

Removing old anodes and install the new ones

In spring 2021 we are going to sandblast the entire underwater body of SV LIMA and rebuild the it completely new with epoxy primer and coppercoat. This is all going to be presented as individual project as well. Before we put on the expoxy primer and coppercoat we are going to seal the keel seam as well. 

We will let you know here and on social media (Instagram, Facebook and YouTube) when we continue with the "sealing of rusty keel seam" project. Stay tuned.

 

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