You’ve already learned the importance of an active anode and a few things that can cause your anodes to have a slowed rate of burn, so let us take a minute to tell you about a “normal” rate of burn. Like everything else pertaining to this subject, “normal” is relative, but we’re going to give you some good guidelines to help you find your boat’s normal!
Most manufacturer guidelines state that anodes should be changed when they corrode to 50% of their original size. This may be surprising to you (and a little frustrating if you’re thinking “I paid for the whole thing, why do I only get to use half of it?”). Here’s why those guidelines are important.
- THE HARDWARE – An anode won’t stay on your boat unless it is attached (either bolted on, clamped on, or screwed) to the metal or vessel it is protecting. That means the hardware used to attach each anode is extremely important. Anodes are produced with this importance in mind, thus the hardware is usually placed in the middle of the anode. When the anode burns to 50% of its original size, that hardware becomes exposed. Once the hardware is exposed in will no longer fix the anode to your boat effectively.
As the anode corrodes, so do the areas around the hardware (or fasteners). That area is important to keep the anode tightly fixed to your boat (and remember, metal on metal contact is the best). When the material around the fasteners erodes far enough the anode may fall off. This often happens when you take your boat out to enjoy it. The movement can cause you to “throw” an anode leaving you without protection for your boat.
- SURFACE AREA – (Quick refresh - water is an electrolytic solution that conducts the flow of ions from an anode to a cathode to protect the cathode from corrosion)
Even though your anodes are completely submerged in water, the only actual contact it makes is with the surface area of the metal alloy. Since the surface area of the anode is the point of contact, that is where the ions get pulled from to protect the cathode. Therefore, the larger the surface area, the greater the corrosion protection potential.
As the anode erodes, it gets smaller in size, also decreasing the overall surface area. In order to protect your boat efficiently, it is safest to change your anodes once they reach 50% of their original size/surface area.
If you’re in a boating environment that allows you to keep your boat in the water year-round (lucky!) we hope you have a diving service. Never be afraid to ask your service to show you the used anodes when they replace them with new anodes. If you can see bare fasteners or the anode surface area is less than 50% they should have changed them sooner. Know your boat’s “NORMAL” by looking at the anodes when they are changed and pay attention to the frequency of replacement.
Remember, there are many factors that can cause your anodes to corrode at an increased rate, so be aware of the normal rate of burn for your boat. If that timeframe suddenly changes it means some corrosive property around your boat has changed as well. Protect you boat by regularly changing your Martyr Sacrificial Anodes.
You understand the importance of an ACTIVE anode (if not, go back to week #7). Here are some common installment errors and some specific “change of environment” circumstances that can cause an anode to become inactive or less effective.
POSSIBLE INSTALLMENT ERRORS
Layer of paint – This is a big one! Especially when you haul your boat out for new bottom paint. If there is a layer of paint on the metals you are trying to protect (your trim tabs, the strut or the bolts that attach a hull plate to the hull) that will impede the flow of ions between your anode and those metal boat parts. The paint may appear to protect those parts at first, but the metal can still corrode under the layer of paint. Over time you will see the paint start to blister, but know this, once you see it, the damage will already be done. Similarly, if there is paint on the actual anode, that barrier will impede the flow of ions rendering the anode useless.
Layer of growth – If there is any marine growth, even something you can’t see, it will cause a barrier between the two metals and the circuit will be less effective since you lose the metal to metal contact. Any piece of metal on your boat should be cleaned and sanded at the anode attachment point to make sure there is direct metal to metal contact.
Layer of oxidation/corrosion – Just like marine growth, a small layer of oxidation, rust or corrosion on the anode attachment site of the metal you are protecting (trim tab, shaft, propeller) will cause a barrier that will not allow the flow of ions between the anode and the cathode to be as efficient. The anode may still work, but will be less effective and that means you’re not getting your money’s worth.
Make sure before you splash your boat after a haul out or at the start of a new boating season that the metals on your boat are sanded down at the anode attachment site so they can work effectively to protect your boat while you’re enjoying it!
CHANGES OF ENVIRONMENT
Dingy or motor storage – If you have anodes on your dingy or on an outboard motor that you take in an out of the water, you can expect those anodes to lose effectiveness or stop working all together over time. Be sure you’re keeping a close eye on the metals that go in and out of the water. If you see signs of corrosion, you know it’s time for new anodes.
Dry docking – If you haul out or store your boat in the off season, your anodes from last year will form a crust or barrier, even if you can’t see it, not allowing them to do their job when you put your boat back in the water.
Haul outs – Any time you have work done on your boat that takes it out of the water, you should plan to put all new anodes on your boat before it goes back in the water. Remember, if you have your hull painted, be sure the yard sands the paint from the anode attachment site before installing new anodes.
These tips will help to be sure your anodes are active and working to protect your boat.
Now that you know the basics of why anodes are important for your boat, theoretically how they work, and which metal alloy you should use in your boating environment, let’s talk about how to make sure your anodes are working. After all, you paid for those pieces of metal, so you want to get the most for your money.
ACTIVE vs INACTIVE – An ACTIVE anode is one that is currently in the process of corroding (or as we like to think of it, protecting the important metals on your boat). An INACTIVE anode is one that is no longer or never was corroding, or is corroding at a rate that is not protecting your boat. How can you tell? Great question!
WHAT DOES ACTIVE LOOK LIKE? – An active anode may look like it is bubbling, you may see material sluffing from it, or it will be wearing away and getting smaller over time. The bubbling may be very difficult to see, (especially if you’re not in the water) but when it happens it looks like a subtle version of the reaction between an open wound and hydrogen peroxide. This bubbling will usually be most evident when an anode is first put in the water and has become newly active.
If you get in the water to look under your boat (don’t laugh, some people do it), or you’re able to touch an anode on your boat while it is in the water, you should see a small amount of material (like a puff of dust) sluff off. This shows you that the anode is still active and there is no barrier impeding the flow of ions to the cathodic metal.
WHAT CAN I DO TO MAKE SURE MY ANODES ARE ACTIVE? – First and foremost, you should ensure that the anode has metal to metal contact with the cathode whenever possible. As we discussed before, you are creating a circuit of protection when you use an anodic metal to protect a cathodic metal. This circuit is most effective when the 2 metals are in direct contact with each other. If they are not touching, other cathodic metals nearby may pull from the anode causing it to be less effective.
Anodes can also become inactive if they are exposed to air or a different type of water environment. As discussed in week #5, an anode that is taken out of the electrolyte solution it became active in will form a crust of oxidation causing a barrier that impedes the flow of ions even if you put it back into the same electrolyte solution.
You will never see marine growth on an active anode. If you see any type of sea life attaching itself to an anode, you know that the anode as a whole, or the part where growth is occurring is no longer active. If part of the anode isn’t working properly, then the whole circuit is less effective at protecting your boat. (We’ll talk more about how to avoid this problem in a few weeks). Most importantly, you should not see corrosion on the metal parts of your boat, if you do, it’s very possible that your anodes are not active.
Come back next week to read about specific circumstances that cause anodes to become inactive or less effective and how to avoid those situations.
We understand that it is nearly impossible to check your anodes unless you get in the water and swim under your boat. If you’re in a region or boating environment that allows you to keep your boat in the water for more than a week or two at a time, be sure you have a good diving service.
Along with cleaning marine growth from your boat, you want your diving service to be knowledgeable in proper anode installment and trained in knowing when an anode is no longer active or useful. Your diving service can often show you photos if you ask in advance and should always keep you informed about the “life” of your boat’s anodes. Don’t be afraid to ask your diver questions about your anodes and the bottom of your boat!
Quick review (if you want it)…
All types of water are considered an electrolyte solution. All metals are susceptible to corrosion when placed in an electrolyte solution. Stray current leakage will increase the rate of corrosion. The relationship between dissimilar metals in this environment is relative. The metal with the lower atomic number (check out a periodic table if that is something you didn’t retain from high school) will become the anode in this relationship, and the metal with the higher atomic number will become the cathode. The anode sacrifices itself to keep the cathode intact.
You want to a Martyr sacrificial anode to sacrifice itself instead of an important metal piece of your boat! But which one is best for your boating environment, Aluminum, Zinc or Magnesium? (Check out WEEK #5 to review which anode is best in saltwater). Today we will tell you about brackish and freshwater.
Just in case you don’t know, brackish water is a combination of saltwater and fresh water. This is typically found in bays or harbors that have fresh water rivers running into them, or in tropical coastal areas where there is a lot of rainfall that runs into the ocean. So, let’s talk about brackish water first…
Aluminum responds best in brackish water, because brackish water has a lower salinity than saltwater. Since the salinity (salt content) in brackish water is lower, the metal anode can be “weaker” (have a lower atomic number) and still have the same ability to protect your boat because the water around it is also “weaker” in reference to electrical current.
Aluminum has also become very popular because it is a lighter metal, making it easier to ship, which in turn typically makes it cheaper than its zinc and magnesium counterparts. Another great thing about aluminum is that it is the most environmentally friendly anode of the 3 that can be used to protect your boat.
Magnesium has the lowest atomic number of the 3 options. Following the same thought process as above, that makes it best in fresh water, which has the lowest salinity of the 3 water types. If you were to try to use magnesium anodes on your boat in saltwater instead of zinc or aluminum you would have to change your anodes 3 times as often to protect your boat.
We want you to get the most out of your anodes and to protect your boat in the best way possible, so remember this…
SALTWATER = ZINC or ALUMINUM
BRACKISH WATER = ALUMINUM
FRESH WATER = MAGNESIUM
One of the greatest things about boating is that you can do it in so many different environments. From pristine lakes and long flowing rivers, to busy bays or the beautiful wide-open ocean. No matter where you choose to use your boat, it still needs protection from corrosion, and just like all waterways are not created equal, it is important to remember too, not all anodes are created equal. Today we are going to review the effects of SALTWATER, because it is the most common type of water when talking about boating. Come back next week to learn more about BRACKISH and FRESH WATER boating environments.
As a boater, you have 3 options when it comes to anodes; Zinc, Aluminum and Magnesium. Each one of these has a water type that it works best in to protect your boat.
We learned in week #3, corrosion happens because ions are pulled from a less noble metal (the anode) to a more noble metal (the cathode) in the presence of an electrolyte solution. As you know, saltwater, brackish water and fresh water are all electrolyte solutions, but they each have different conductive properties. Their varied conductivity is because they consist of different ratios of solute (the extra stuff that is dissolved in a water solution). This causes the ions that make up the anode to be pulled off at different rates in the different solutions. That is why there are 3 different metals for the 3 different types of water.
Saltwater has the highest salinity of the 3, which in effect makes it the most active when considering galvanic corrosion. Zinc was the first material used as a sacrificial anode, because of this, zinc has been the “go to” for boaters in saltwater. However, there is plenty of information showing that aluminum anodes can also be very effective in this environment. That’s not to take away from the effectiveness of zinc, we just want you to know that you have options. Here is some valuable information about zinc.
If an active zinc anode is taken to fresh water, the surface of that anode will become covered with the crust of oxide, because of how fresh water solution reacts with zinc. This oxide effectively creates a seal around the anode that stops the transfer of ions, causing the anode to become inactive or useless. In this case, corrosion will find the next lowest metal to eat away at, probably a piece of your boat.
Similarly, when an active zinc anode is exposed to air it stops the flow of ions (passive), again causing a seal. It may not be visible, but once a zinc anode is passive, even if it is placed back in the same water environment, it will not be as effective. This passivity may cause the next most anodic item within your anode system to start to sacrifice itself, and that will most likely be a part of your boat.
If you’ve been paying attention, now you understand why metals corrode, but wait, there’s more information that can help you take care of your boat. Anodes can and do erode at different rates. One of the most common reasons for an increased rate of erosion is caused by stray current leakage. This leakage is referred to as electrolytic corrosion. Galvanic Corrosion (see ANODE ACADEMY WEEK #3) and Electrolytic Corrosion are often confused with each other, but it is important to know the difference. Here’s how it works and how you can protect your boat.
Electrolytic Corrosion is driven by an external source of electromotive force (EMF). EMF can also be referred to as stray current leakage. This leakage can come from any external power source like your shore power connection, a battery on your boat or the wiring that controls the lights. Stray current leakage typically occurs with a damaged or worn out wiring system or poor installation of electrical equipment. This lack of grounding causes an increased amount of electrical activity which accelerates the rate of corrosion to an anodic metal.
Here are some examples…
#1- If you have twin inboard motors and the shaft anode on the left/port shaft always seems to erode at a faster rate than the one on the right/starboard, you most likely have a wiring issue internally near the left side. It could be a wire connection that has come loose, worn out, or was never grounded properly in the first place.
#2- If you move to a new marina and notice that your anodes are eroding at a faster rate than they did at the old marina, there may be wiring issues with the shore power, or a boat around you may have wiring issues that cause increased electrical activity around your boat.
The bottom line is this, there are numerous factors that can cause damage to your boat, be sure you are using Martyr sacrificial anodes to protect it.
Come back next week to learn which type of anode you should be using for your boating environment.
The definition – an electrochemical response that occurs when two dissimilar metals are in electrical contact with each other in the presence of an electrolyte.
Why does this matter? Water is an electrolyte solution. Electric current constantly flows through our waterways. Several types of metal constantly meet each other any time a boat is in water. Therefore, an electrochemical response will ALWAYS occur when metal is in water. That response is corrosion and it will eat away at the least noble metal. That means a metal with the lower atomic number will corrode sooner than a metal with a higher atomic number when side by side in the water.
That’s why you need a Martyr sacrificial anode!
Stay tuned next week for a more in-depth explanation Anodic versus Cathodic, a heavy metal war!
ANODE ACADEMY – WEEK #1 – CORROSION – What does it look like under your boat?
Corrosion occurs in all types of water, salt, brackish and fresh. As a boat owner, it’s important to be aware that any type of metal that is in contact with water is subject to corrosion.
Below on the pictures, you’ll see various types of corrosion unique to each different metal. The rate of corrosion may be affected by the type of water, the type of metal and electrical activity around your boat.
- Propeller – Bronze (most common) followed by Stainless Steel and Aluminum
- Shaft – Stainless Steel
- Rudder – Bronze or Stainless Steel
- Trim Tabs – Stainless Steel
- Hull – Fiberglass (not subject to corrosion), Steel, Aluminum, and Wood (Fasteners are highly susceptible to corrosion).
Stay tuned next week to learn more about how “GALVANIC CORROSION” and “ELECTROLYTIC CORROSION” occur.
Do you know why you use sacrificial anodes or “zincs” on your boat?
Once a week we will post information to help increase your knowledge of why you do the things you do in the name of “protecting your boat”.
In this series, we will be going over why you use anodes, how anodes work, when and where to use the correct anode alloy, proper installment and much more. We look forward to having you join us each week!