3 Signs You Have Galvanic Corrosion -- And How To Fix It [CHECKLIST]

Sacrificial anodes help prevent galvanic corrosion.

Signs you have a galvanic corrosion problem can indicate significant (and, if unattended, serious) damage. Understanding the proper definition of galvanic corrosion and how such damage might be affecting your boat is the first step in being proactive to prevent costly repairs.

What Is Galvanic Corrosion?

First, let's start out by getting the terminology correct. Many laymen call an electrically-oriented marine issue an "electrolysis" problem. Technically, however, that term is incorrect. The problem you can see (we'll get into the visible symptoms in a minute) is actually "galvanic corrosion", which can be summed up this way:

Galvanic corrosion... can damage or destroy underwater metal parts of boats, dock hardware and other equipment. When two different metals are touching each other or are electrically connected by a conductor, and are immersed in an electrolyte (an electrically conductive fluid, like salt water) an electro-chemical reaction can occur. One of the metals (the “least noble” metal, called the anode) will corrode faster than it normally would, and the other (the “most noble” metal, or the cathode) will dissolve more slowly.

-- West Marine

Electrolysis (in this case related to DC currents), then, is a component of galvanic corrosion but the terms are not synonymous. Here's the major difference:

• Electrolysis literally refers to what is happening in the water.

• Galvanic corrosion relates to what's happening to the metal of your boat.

So, when damage occurs you'll notice symptoms of galvanic corrosion. That is, the effects of electrolysis upon your boat's metals.

Even if you already knew all of that, is your boat protected? To avoid costly damage to your boat it's helpful for any boat owner to be proactive in monitoring electrolysis and galvanic corrosion issues.

3 Signs You Have A Galvanic Corrosion Problem

Adding the proper anode (typically zincs but can also include aluminum or magnesium) to your boat can reduce the electrical load on your equipment. The long-term outcome extends the life of your:

• engine

• prop

• hull

• rudder

• refrigeration condenser

• engine cooling system

• other metal-made components

Regularly replacing your zincs is always the first step in protecting your boat from electrical currents. However, even proper zinc maintenance doesn't always prevent galvanic corrosion. The following three signs offer a clue that something is amiss:

1 - Blistering of paint and/or gel coat -- Most people think of blistered paint and gel coat as an indication that it's time to paint, which is true. However, in addition to the age of your paint the electrical activity in your water can also produce blisters. In this case, typically you'll see a powdery, white substance forming on the exposed metal parts. If your paint is well-kept and in good condition then blistering can be a visible symptom of an invisible electrical problem.

2 - Pitting of metals -- Once the paint/gel coat are dissolved galvanic corrosion moves into the even more destructive process of pitting the metal. For example, take a look at the pictures below. This Barefoot Barnacle Cleaning client has extreme pitting on the motor mounts, something we frequently see with galvanic corrosion issues.

3 - Excessive wear on zincs -- When I'm diving even if I know it's not time to replace zincs I regularly check their status. Excessive wear of one or all zincs indicates that there is an excessive amount of electrical activity in the water.

How to Fix Galvanic Corrosion

The first key in resolving any galvanic corrosion problem lies in properly diagnosing the source. This begins with the appropriate survey.

According to Gregg Scrudders, Palm Beach Service Manager of Ward's Marine Electric, there are two approaches for conducting a professional assessment:

Corrosion survey -- – The primary tool for a corrosion survey is a silver-silver chloride reference cell. This is a cell that is put in the water and connected to a volt meter. The resulting data indicates the protection level. A marine electrician will use this process to test hull potential to discover cathodic protection levels and test for stray currents. This is done at the slip where the boat is kept. While further lab tests can detect more extensive problems usually this type of visual examination suffices.

If a problem is detected solutions for submerged metals can include:

1. Adjusting the zinc mass

2. Proving and establishing galvanic isolation (determining isolation between the dock ground and boat ground)

Localized Corrosion -- Typically, this type of corrosion occurs within the vessel’s hull. Specifically, it affects metals that are:

1. either dissimilar or not properly isolated

2. not properly maintained

3. lacking proper flow

4. experiencing erosion corrosion (for example, impellers on pumps corrode)

Additionally, this problem can arise when improper material is used during the original design of the boat (i.e. stainless steel is not corrosive but is terrible for seawater plumbing).

Specific next steps for solving the problem are determined after identifying the type of corrosion.

Being Proactive About Galvanic Corrosion

One of the reasons we take before and after photos of all our bottom cleaning jobs (and provide personalized service notes) is so that you can see what's going on beneath the waterline of your boat.

This practice becomes very useful when maintenance problems crop up. The sooner we identify issues when they are small the more quickly they can be resolved -- and for a smaller impact on your wallet.

Does this topic bring up questions? Leave them in the comments below.

And if you like science -- or just want a more detailed explanation of galvanic corrosion -- check out this detailed video: