Sacrificial zincs play a vital role in making sure your boat stays above the water and you do not get saddled with expensive repairs. They protect the propeller, propeller shaft, and any other exposed metal structure below the surface of the water. Not only that, zincs help protect metals from corrosion any time they come into contact with salt water. Outboard motors have them, diesel engines also have them in the raw water circuit to protect metals from the corrosive effects of salt water.
Salt Water Environment Corrodes Metals
Galvanic corrosion is the process of one metal corroding before another metal when both metals are in electrical contact, such as salt water. Electrolysis is when stray current causes corrosion. Both processes cause corrosion and attack the metals on your boat. Stray current corrosion is the type of corrosion that divers address by putting sacrificial zincs on the prop shaft when they clean the boat bottom.
Electrolysis At Marina
When you have your boat in a marina, there is always a greater risk that your boat will be the victim of stray current corrosion. There could be faulty wiring at the marina itself, or another boat nearby could have electrical current leaking into the water through improper grounding.
Zincs need to be present and monitored to ensure your boat safety at the marina. The zincs should be checked are regular intervals to ensure that there is a good amount of zinc there to ‘sacrifice’ for the good of the other metals. If a zinc goes below 20%, it should be replaced.
Check Sacrificial Zincs Each Month
When you have a diver clean the bottom of your boat each month, one of the things they do is check the wear on your sacrificial zinc: usually located on the propeller shaft. This is a very important zinc. It protects both the propeller and drive shaft. If those were to be eaten away by electrolysis, then you could end up in some deadly conditions while out at sea or costly repairs.
Is The Metal Already Damaged?
First, it is a good idea to have your running gear inspected for corrosion. In some cases, a neglected boat will show signs of corrosion and the metal may be compromised. If this is the case, the metal you are trying to protect, may already be weaker than your sacrificial zinc. The metal then has to be replaced.
Do You Have A Problem?
If you have electrolysis problems, you will notice them quickly. You zincs will get eaten away within a matter of a couple of weeks or a month.
Fixing The Problem
If you have a problem with electrolysis, then there are some steps you can use to determine the problem.
Zinc installation is important. If not installed properly zinc will not be electrically connect and protect running gear from natural electrolysis or any improper grounding on the boat. So, the first step is to make sure the installation of your sacrificial zincs is correct.
More Than One Ground Wire
A potential source of high electrolysis is having more than one ground wire to the AC ,DC or return line, lighting , and a RF plane for the radio system.
Everyone’s first thought is to make a ground connection to anything metal, such as thru-hulls and shafts or rudder post which are underwater components. This is an absolute no no unless it is a single negative terminal or connection to a bus is a part of the connection. Better yet, never ground to a thru-hull! We recommend not grounding to anything underwater unless its a keel bolt.
All these issues will lead to serious electrolysis corrosion problems.
Grounding AC Unit
All AC units should be connected and grounded out on an isolation transformer. The Galvanic isolator would be the first chose, which is connected to the shore power cord socket of the the boat and the connection to the boats AC panel, which connects to the AC panel directly, then to the engine negative terminal or bus.
Zincs Do Not Provide Full Galvanic Protection
Zincs are intended to protect against low galvanic currents and are incapable of supplying enough galvanic protection to a DC current that flows in the water. That is why they have to be periodically replaced. Zincs are needed to any thing that has 2 different metals that are attached underwater.
Keeping up with zincs are very important to avoid all sorts of issue that are to come.